Patent Grant
10434773
This is the U.S. national stage of application No. PCT/JP2017/000622, filed on Jan. 11, 2017. Priority under 35 U.S.C. § 119(a) and 35 U.S.C. § 365(b) is claimed from Japanese Application No. 2016-015245, filed on Jan. 29, 2016, the disclosures all of which are also incorporated herein by reference.
The present invention relates to an ink jet driving apparatus which ejects ink, such as an ink jet head and an ink jet printer, and an ink jet driving method.
Conventionally, there has been known an ink jet head having a plurality of channels from which liquid ink is ejected. By controlling the ejection of ink from each channel while moving the ink jet head relative to a recording medium such as a sheet of paper or cloth, a two-dimensional image is formed on the recording medium.
The ejection of ink is performable, for example, by using a pressure actuator (such as a piezoelectric, electrostatic, or thermal deformation actuator), or by thermally forming a bubble in ink in a tube. Among such actuators, the piezoelectric actuator is advantageous over the others for its large output, modulability, high responsiveness, adaptability to any ink, etc., and has been widely used in recent years. In particular, to achieve a compact, low-cost, high-resolution (achievable with small ink droplets) printer, it is suitable to adopt an ink jet head that uses a thin-film piezoelectric element (a piezoelectric thin film). In such a piezoelectric element, a perovskite-type metal oxide, such as barium titanate (BaTiO3) or lead zirconate titanate (Pb(Zr, Ti) O3), is widely used.
Now, in an ink jet head, a non-ejection state, in which no ink is ejected, lasts long after ink is ejected from a nozzle, ink forming a meniscus (the interface between the ink and air, also referred to as an ink meniscus) in the nozzle becomes dry, and thus the viscosity of the ink increases. The increased viscosity of the ink prevents a smooth ink ejection through the nozzle, and thus degrades ink ejection properties (for example, ejection speed). Accordingly, it is necessary to take measures to moderate the degradation of the ink ejection properties.
In this regard, according to Patent Document 1 listed below, for example, during a non-ejection time, during which no ink is ejected, a non-ejection pulse, which does not cause ink droplets to be ejected from a nozzle, is applied to an actuator to thereby give oscillation to a meniscus, whereby the ink forming the meniscus is prevented from becoming dry. Further, according to Patent Document 2 listed below, for example, in a configuration where a driving pulse is applied by means of an actuator to a fluid pump chamber to cause droplets of a fluid (ink, for example) to be ejected from a nozzle, a circulation flow path part is disposed very close to the nozzle such that ink left in the nozzle without being ejected therefrom circulates via the circulation flow path part, in an attempt to prevent accumulation, in the nozzle, of substances that would hinder ink ejection. Patent Document 1 also discloses a configuration in which a circulation flow path part is disposed diverging from a flow path of ink from a pressure chamber to a nozzle such that the ink is caused to circulate via the circulation flow path part.
Patent Document 1: Japanese Patent Application Publication No. 2011-51214 (see claim 1, paragraphs [0012], [0022], and [0083] to [0092], FIG. 3, etc.)
Patent document 2: Japanese Patent Application Publication (Translation of PCT Application) No. 2011-520671 (see claim 1, paragraphs [0015] and [0046], FIG. 2, etc.)
However, Patent Document 1 does not at all mention anything about the shape of the nozzle (the size of the hole of the nozzle, for example) or the position of the circulation flow path part with respect to the nozzle (the distance between the exit of the nozzle and the circulation flow path part), or does not take into consideration the shape of the nozzle and the position of the circulation flow path part in specifying an ink withdrawal amount by which ink is withdrawn when the meniscus is caused to oscillate. Thus, when ink has failed to be prevented from becoming dry and thus has become more viscous near an exit of the nozzle, the possibility is reduced of successfully guiding the ink with the increased viscosity into the circulation flow path part to remove the ink from inside the nozzle, and thus there is a risk that the ink ejection properties (such as the ejection speed) will be degraded due to the ink.
In Patent Document 2, the meniscus is not caused to oscillate during the non-ejection time, and therefore, in the first place, it is impossible to prevent the ink near the exit of the nozzle from becoming dry and more viscous. Thus, if ink becomes dry and more viscous at the exit of the nozzle, even with a circulation flow path part disposed very close to the nozzle, it becomes difficult to guide the ink into the circulation flow path part, and, as in the case of Patent Document 1, there is a risk that the ejection properties will be degraded due to the ink.
The present invention has been made to solve the above-described problem, and aims at providing an ink jet driving apparatus and an ink jet driving method capable of avoiding the degradation of the ejection properties by appropriately setting the ink withdrawal amount by taking into consideration the shape of the nozzle and the position of the circulation flow path part to thereby increase the possibility that, even in a case where the ink has become more viscous near the exit of the nozzle, the ink with the increased viscosity will be successfully removed from inside the nozzle.
According to an aspect of the present invention, an ink jet driving apparatus includes a head substrate which includes a nozzle through which ink is ejected, a pressure chamber which communicates with the nozzle and in which the ink is stored, and a circulation flow path part which is disposed diverging from a flow path of the ink flowing toward the nozzle and which forms a flow path for circulating ink discharged from the pressure chamber, a driving element which is supported on the head substrate, and which causes ink inside the pressure chamber to be ejected through the nozzle during an ejection time and causes an ink meniscus inside the nozzle to oscillate during a non-ejection time, and a drive controller which controls the driving element. Here, when a diameter of a hole at an exit of the nozzle is represented by D (μm), the exit being a portion of the nozzle that is farthest from the pressure chamber, and a distance, in a direction perpendicular to a surface including the hole at the exit, between the exit and a position in the circulation flow path part that is nearest the exit is represented by N (μm), N≤3.47D is satisfied. The drive controller generates a driving signal for withdrawing ink from the exit of the nozzle toward the pressure chamber, to a position at a distance equal to or more than 0.16N but equal to or less than 0.555D from the exit, and for causing the ink meniscus to oscillate, and applies the driving signal to the driving element.
According to another aspect of the present invention, an ink jet driving method is one for driving an ink jet driving apparatus, the ink jet driving apparatus including a head substrate including a nozzle through which ink is ejected, a pressure chamber which communicates with the nozzle and in which the ink is stored, and a circulation flow path part which diverges from a flow path of the ink flowing toward the nozzle and which forms a flow path for circulating ink discharged from the pressure chamber, a driving element which is supported on the head substrate, and which causes ink inside the pressure chamber to be ejected through the nozzle during an ejection time and causes an ink meniscus inside the nozzle to oscillate during a non-ejection time, N≤3.47D being satisfied when a diameter of a hole at an exit of the nozzle is represented by D (μm), the exit being a portion of the nozzle that is farthest from the pressure chamber, and a distance, in a direction perpendicular to a surface including the hole at the exit, between the exit and a position in the circulation flow path part that is nearest the exit is represented by N (μm). Here, the driving method includes circulating ink via the circulation flow path part by withdrawing the ink, by means of the driving element, from the exit of the nozzle toward the pressure chamber, to a position at a distance equal to or more than 0.16N but equal to or less than 0.555D from the exit, causing the ink meniscus to oscillate, and guiding at least part of the withdrawn ink into the circulation flow path part.
As described above, by appropriately setting the ink withdrawal amount by taking into consideration the shape of the nozzle and the position of the circulation flow path part, even in a case where ink has failed to be prevented from becoming dry and thus has become more viscous near the exit of the nozzle, it is possible to increase the possibility of successfully removing the ink with the increased viscosity from inside the nozzle, even though by a small amount, and avoiding the degradation of the ejection properties attributable to the ink.
The advantages and features provided by one or more embodiments of the invention will become more fully understood from the detailed description given hereinbelow and the appended drawings which are given by way of illustration only, and thus are not intended as a definition of the limits of the present invention.
Hereinafter, one or more embodiments of the present invention will be described with reference to the drawings. However, the scope of the invention is not limited to the disclosed embodiments.
An embodiment of the present invention will be described below with reference to the accompanying drawings. Herein, when a numerical value range is indicated as A to B, the lower limit value A and the upper limit value B are both included in the numerical value range.
The following description deals with an embodiment, as an example, that employs a one-pass drawing method which draws images with a configuration using a line head (only by conveyance of a recording medium), but alternatively, another drawing method, such as a method using a scanning method or a drum method, may be adopted.
In the following description, a conveyance direction of a recording medium K is a front-back direction, a direction orthogonal to the conveyance direction on a conveying surface of the recording medium K is a left-right direction, and a direction perpendicular to the front-back direction and the left-right direction is an up-down direction.
[Overview of Ink Jet Printer]
The platen 101 supports a recording medium K on its upper surface, and conveys the recording medium K in a conveyance direction (the front-back direction) when the conveyance roller 102 is driven.
The line heads 103 to 106 are each arranged to be elongated in a width direction of the recording medium K (the left-right direction) orthogonal to the conveyance direction of the recording medium K (the front-back direction), and are arranged parallel to each other from upstream side to downstream side in the conveyance direction. The line heads 103 to 106 each have disposed inside thereof at least one later-described ink jet head 1 (see
[Schematic Configuration of Ink Jet Head]
The head chip 2 is composed of a plurality of substrates laid one on another, and in a lowermost layer of the head chip 2, there is disposed a nozzle 211 through which ink is ejected. The nozzle 211 communicates with a pressure chamber 231 in which ink is stored. On an upper surface of the head chip 2, a piezoelectric element 24 is disposed as a driving element. Details of the piezoelectric element 24 will be described later. As a result of displacement of the piezoelectric element 24, pressure is applied to the ink in the pressure chamber 231 inside the head chip 2, and the ink is ejected through the nozzle 211 as an ink droplet.
The holding plate 3 is bonded with an adhesive to the upper surface of the head chip 2 to retain strength of the head chip 2. Further, the holding plate 3 has an opening 31 in its central portion such that the piezoelectric element 24 on the upper surface of the head chip 2 is housed inside the opening 31.
The connection member 4, which is a wiring member including, for example, a flexible print circuit (FPC), is bonded close to a rear side of the upper surface of the holding plate 3 such that a width direction of the connection member 4 is along the left-right direction of the holding plate 3. The connection member 4 is electrically connected by a bonding wire 41 to the piezoelectric element 24. The bonding wire 41 is disposed to pass through the opening 31 which is disposed in the center portion of the holding plate 3. The connection member 4 is also connected to a drive circuit 60 (see
The ink flow path members 5 are bonded one to each of opposing end portions of the upper surface of the holding plate 3 in the left-right direction. One of the ink flow path members 5 includes an ink supply flow path 501 for supplying ink into the head chip 2 and an ink circulation flow path 504 for discharging ink from inside the head chip 2. The other one of the ink flow path members 5 includes an ink supply flow path 502 for supplying ink into the head chip 2 and an ink circulation flow path 503 for discharging ink from inside the head chip 2.
Hereinafter, detailed descriptions will be given of the head chip 2, the holding plate 3, and the ink flow path members 5.
[Head Chip]
The head chip 2 includes a plurality of piezoelectric elements 24 aligned on the upper surface thereof in the left-right direction, ink supply ports 201 and 202 for supplying ink into the head chip 2 from the ink flow path members 5, ink circulation ports 203 and 204 for discharging ink from inside the head chip 2 into the ink flow path members 5, and so on.
(Nozzle Plate)
The nozzle plate 21 is a substrate disposed in the lowermost layer of the head chip 2, and includes, for example, a silicon-on-insulator (SOI) wafer composed of three layers including a nozzle layer 21a, a bonding layer 21b, and a nozzle support layer 21c.
The nozzle layer 21a is a layer in which the nozzle 211 for ejecting ink droplets is formed, and includes an Si substrate having a thickness of, for example, 10 to 20 μm. A nozzle surface 214, which is a lower surface of the nozzle layer 21a, has formed thereon an ink-repellent film (unillustrated). The bonding layer 21b includes an SiO2 substrate having a thickness of, for example, 0.3 to 1.0 μm. The nozzle support layer 21c includes an Si substrate having a thickness of, for example 100 to 300 μm. The nozzle support layer 21c has formed therein the following parts: a large-diameter part 212 which communicates with the nozzle 211 and has a diameter larger than that of the nozzle 211; and a circulation flow path part 213 which communicates with the large-diameter part 212. The circulation flow path part 213 diverges, via the large-diameter part 212, from a flow path of ink flowing from the pressure chamber 231 to the nozzle 211, and forms a flow path for circulating ink discharged from the pressure chamber 231.
In the present embodiment, the nozzle 211 has a circular shape as a sectional shape taken in a direction perpendicular to an ink ejection direction, but this is not meant as a limitation, and the sectional shape may be any shape as long as the shape allows ink to be ejected. For example, the sectional shape of the nozzle 211 may be the shape of a polygon, such as a quadrangle and a hexagon. In this case, a later-described diameter D of the nozzle 211 may be defined as a diameter of a circumscribed circle of the polygon. When a center of the circumscribed circle is on a diagonal line of the polygon, the diameter D may be defined as having a length of the diagonal line.
Since the nozzle layer 21a and the nozzle support layer 21c each include an Si substrate, it is possible to process the nozzle layer 21a and the nozzle support layer 21c easily by dry etching or wet etching.
The circulation flow path part 213 is formed in the nozzle support layer 21c with a space facing the bonding layer 21b, and thus is produced by processing with fine accuracy. Here, alternatively, the circulation flow path part 213 may be formed with a space facing the nozzle layer 21a by removing the bonding layer 21b by a wet etching process using a buffered hydrofluoric acid (BHF), etc., after forming the space facing the bonding layer 21b.
(Intermediate Plate)
The intermediate plate 22 includes a glass substrate having a thickness of, for example, about 100 to 300 μm, and has a communication hole 221 formed therein at a position corresponding to the large-diameter part 212 of the nozzle plate 21. The communication hole 221 is formed to penetrate the intermediate plate 22 in its thickness direction to achieve communication between the pressure chamber 231 and the large-diameter part 212, and functions as an ink flow path when ink is ejected. By adjusting a shape of the ink flow path in the communication hole 221 by reducing a diameter of the communication hole 221 somewhere along the ink flow path, for example, it is possible to adjust kinetic energy applied to the ink when the ink is ejected.
Used preferably as the glass substrate of the intermediate plate 22 is a borosilicate glass (for example, Tempax glass).
(Body Plate)
The body plate 23 includes a pressure chamber layer 23a and an oscillation layer 23b. The pressure chamber layer 23a includes, for example, an Si substrate having a thickness of, for example, about 100 to 300 μm. The pressure chamber layer 23a has formed therein a plurality of pressure chambers 231 which communicate with communication holes 221 of the intermediate plate 22 and have a substantially circular shape in plan view, a common supply flow path 25 for supplying ink commonly to the plurality of pressure chambers 231, and inlets 232 via which the plurality of pressure chambers 231 individually communicate with the common supply flow path 25 so as to supply ink inside the common supply flow path 25 into the pressure chambers 231. Each inlet 232 includes a narrow portion which is a flow path narrower than the pressure chamber 231, such that it is difficult for pressure applied to the pressure chamber 231 to escape via the inlet-232 side. The narrow portion may have any shape that makes it a flow path narrower than the pressure chamber 231, and the shape may be suitably changed.
The oscillation layer 23b is a thin elastically deformable Si substrate having a thickness of, for example, about 20 to 30 μm, and the oscillation layer 23b is laid on an upper surface of the pressure chamber layer 23a. In the oscillation layer 23b, an upper surface of the pressure chamber 231 functions as a diaphragm 233. The diaphragm 233 oscillates in accordance with the operation of the piezoelectric element 24 provided on an upper surface of the diaphragm 233, and thereby, it is possible to apply pressure to the ink in the pressure chamber 231.
Further, in the intermediate plate 22 and the pressure chamber layer 23a, there is formed a common circulation flow path 26 where flows of ink from a plurality of circulation flow path parts 213 formed in the nozzle support layer 21c join together.
The oscillation layer 23b includes a damper 234 formed on an upper surface of the common supply flow path 25, and a damper 235 formed on an upper surface of the common circulation flow path 26. The dampers 234 and 235 are slightly elastically deformable when, for example, pressure is applied all at once to the pressure chamber 231 such that the ink flows from the pressure chamber 231 into the common circulation flow path 26 all at once, and the dampers 234 and 235 are provided for the purpose of preventing abrupt change of pressure in the ink flow path.
In the configuration discussed above, ink flows in the following manner. First, ink is supplied from the ink supply ports 201 and 202 into the common supply flow path 25, all illustrated in
The above description has dealt with an example where the circulation flow path part 213 is formed in the nozzle plate 21, but the circulation flow path part 213, which needs to be disposed closer to the nozzle than the body plate 23 which has the pressure chamber 231 formed therein, may alternatively be formed in the intermediate plate 22, for example. However, in order to securely guide and remove from inside the nozzle 211, by the oscillation of a later-described ink meniscus, the ink that has failed to be prevented from becoming dry and thus has become more viscous near an exit of the nozzle 211, it is desirable that the circulation flow path part 213 be disposed close to the nozzle 211, and in this regard, it is preferable that the circulation flow path part 213 be disposed in the nozzle plate 21.
[Holding Plate]
As illustrated in
The holding plate 3 is formed in a shape, in plan view, that is larger than the head chip 2 both in the front-back and left-right directions. In particular, both end portions of the holding plate 3 in the left-right direction are disposed more outward than the head chip 2 by a large amount. In a center portion of the holding plate 3, an opening 31 is formed through the holding plate 3 to be large enough to surround all piezoelectric elements 24 aligned on the upper surface of the head chip 2 when the holding plate 3 is bonded with the head chip 2.
The opening 31 is formed in a rectangular shape extending along the left-right direction and sized large enough to surround all the piezoelectric elements 24 but not large enough to reach positions of the ink supply ports 201 and 202 and the ink circulation ports 203 and 204 provided on both end portions of the upper surface of the head chip 2. When viewed from above the holding plate 3, each nozzle 211 formed in the nozzle plate 21 is located inside the opening 31.
A lower half portion of the opening 31 of the holding plate 3 is formed to have a larger space than an upper half portion of the opening 31. The lower half portion of the opening 31 has an outer shape sized such that, when the holding plate 3 and the head chip 2 are bonded together, the piezoelectric elements 24 and the common supply flow path 25 and the common circulation flow path 26 disposed in the front-back direction of the piezoelectric elements 24 are all located inside the lower half portion of the opening 31.
As illustrated in
[Ink Flow Path Member]
The ink flow path members 5 are formed of a synthesized resin such as a poly phenylene sulfide resin (PPS), each in a shape of a box with an open bottom, and are disposed one on each end portion of an upper surface of the holding plate 3 in the left-right direction.
The left and right ink flow path members 5 have similar structures, and thus, hereinafter, the configuration of only the right ink flow path member 5 will be described, and the description of the left ink flow path member 5 will be omitted.
[Circulation Mechanism]
Next, a description will be given of the circulation mechanism 107 for ink.
The ink supply flow path 501 of the ink flow path member 5 is connected via the ink flow path 72 to the supply subtank 62. Thereby, it is possible to supply ink from the supply subtank 62 into the ink flow path member 5, and to supply the ink via the through hole 301 (see
The ink circulation flow path 504 of the ink flow path member 5 is connected via the ink flow path 73 to the circulation subtank 63. Thereby, it is possible to discharge, into the circulation subtank 63, ink that has been discharged via the ink supply port 204 (see
The supply subtank 62 and the circulation subtank 63 are disposed at different positions in the up-down direction (the gravity direction) with respect to a position reference surface where the common supply flow path 25 and the common circulation flow path 26 inside the head chip 2 are disposed. And, with pressure P1 and pressure P2, respectively resulting from positional differences between the positional reference surface and water heads of the supply subtank 62 and the circulation subtank 63, it is possible to circulate the ink inside the head chip 2.
The supply subtank 62 is connected via the ink flow path 74 to the circulation subtank 63, and it is possible to return ink from the circulation subtank 63 to the supply subtank 62 by means of the pump 82.
The supply subtank 62 is connected via the ink flow path 71 to a main tank 61, and it is possible to supply ink from the main tank 61 to the supply subtank 62 by means of the pump 81.
Accordingly, by appropriately adjusting a difference between the water heads of the supply subtank 62 and the circulation subtank 63 and the positions of the subtanks in the up-down direction (the gravity direction), it is possible to adjust the pressure P1 and the pressure P2, and thus to circulate the ink inside the head chip 2 at an appropriate circulation flow rate.
[Details of Piezoelectric Element]
There is no particular limitation on the piezoelectric element to be used in the present embodiment so long as it is capable of causing ink to be ejected from a nozzle and is also capable of oscillating an ink meniscus. Hereinafter, a description will be given of the details of the piezoelectric element 24 as an example of piezoelectric elements.
The lower electrode 241 is a common electrode which is shared by the plurality of pressure chambers 231, and includes a layer of platinum (Pt) having a thickness of, for example, about 0.1 μm. Here, the lower electrode 241 may have an adhesion layer of titanium (Ti) or a titanium oxide (TiOx) to be disposed between the Pt layer and the head chip 2.
The piezoelectric thin film 242 includes a ferroelectric thin film made of lead zirconate titanate (PZT) or the like, and one piezoelectric thin film 242 is disposed corresponding to each pressure chamber 231. The piezoelectric thin film 242 has a thickness of, for example, equal to or more than 1 μm but equal to or less than 10 μm. Usable as a method for forming the piezoelectric thin film 242 are various methods including chemical film forming methods such as the chemical-vapor deposition (CVD) method, physical methods such as the sputtering method and the ion plating method, liquid phase growth methods such as the sol-gel method, and printing methods.
The upper electrode 243 is an individual electrode disposed corresponding to each pressure chamber 231, and is formed with a platinum (Pt) layer having a thickness of, for example, about 0.1 μm. Here, the upper electrode 243 may have an adhesion layer to be disposed between the Pt layer and the piezoelectric thin film 242. Alternatively, the upper electrode 243 may be formed by using gold (Au) instead of Pt.
The piezoelectric element 24 is connected to the drive circuit 60 via the connection member 4 (see
In the ink jet driving apparatus, the piezoelectric element 24 is driven based on the driving signal fed from the drive circuit 60. Specifically, when the driving signal (a driving voltage) is applied from the drive circuit 60 to the lower electrode 241 and the upper electrode 243, the piezoelectric thin film 242 expands or contracts in a direction perpendicular to its thickness direction in accordance with a difference in potential between the lower electrode 241 and the upper electrode 243. Then, a difference in length between the piezoelectric thin film 242 and the diaphragm 233 causes curvature in the diaphragm 233, and the diaphragm 233 is displaced (curved, oscillated) in its thickness direction.
Accordingly, with ink stored in the pressure chamber 231, during an ejection time, during which ink is ejected, the oscillation of the diaphragm 233 described above causes a pressure wave to be transmitted to the ink stored in the pressure chamber 231, and thereby, the ink is caused to be ejected through the nozzle 211 as an ink droplet. On the other hand, during a non-ejection time, during which ink is not ejected, a driving signal having an amplitude smaller than during the ejection time is generated by the drive circuit 60 and fed to the piezoelectric element 24, and the piezoelectric element 24 is driven based on the driving signal to cause an ink meniscus (an interface between the ink and air) inside the nozzle 211 to oscillate, details of which will be described later.
[Position of Circulation Flow Path Portion]
Next, a description will be given of the details of a position of the circulation flow path part 213 described above.
N≤3.47D (1)
That is, the circulation flow path part 213 is formed at such a position in the nozzle plate 21 that satisfies conditional formula (1). Here, 3.47D means 3.47×D. When conditional formula (1) is satisfied, the circulation flow path part 213 is arranged near the exit 211a of the nozzle 211 in the thickness direction of the nozzle plate 21. Thereby, it becomes easy to withdraw the ink from inside the nozzle 211 and circulate the ink via the circulation flow path part 213.
Further, by satisfying conditional formula (1), it is possible, as illustrated in
Conditional formula (1) defines a condition for later-described conditional formula (2) to hold. That is, whenever a later-described lower limit value (0.16N) of conditional formula (2) is equal to or lower than a later-described upper limit value (0.555D) of conditional formula (2), conditional formula (2) holds. When 0.16N≤0.555D holds, then N≤0.555D/0.16=3.47D holds, and conditional formula (1) is obtained. Accordingly, when conditional formula (1) is not satisfied as in a case where, for example, D=10 μm and N=40 μm, conditional formula (2) no longer holds (that is, such a withdrawal amount H as satisfies conditional formula (2) does not exist), and thus it becomes impossible to obtain a decapping effect (an effect of preventing reduction of ejection speed) from circulation and later-described oscillation of an ink meniscus.
Here, from the perspective of facilitating control of such a withdrawal amount H that satisfies formula (2), which will be described later, with respect to N and D, it is more preferable to satisfy the following conditional formula (1a), and it is still more preferable to satisfy the following conditional formula (1b). That is,
N≤3.00D (1a)
N≤2.00D (1b)
Here, in a case where the circulation flow path part 213 faces the bonding layer 21b of the nozzle plate 21, that is, in a case where the circulation flow path part 213 is formed in the nozzle support layer 21c of the nozzle plate 21, and a surface of the bonding layer 21b forms a bottom surface (a surface on the nozzle-211 side) of the circulation flow path part 213, the distance N described above is equal to a sum of a thickness of the nozzle layer 21a and a thickness of the bonding layer 21b of the nozzle plate 21. In a case where the circulation flow path part 213 faces the nozzle layer 21a of the nozzle plate 21, that is, in a case where the circulation flow path part 213 is formed in the nozzle support layer 21c and the bonding layer 21b of the nozzle plate 21, and a surface of the nozzle layer 21a forms the bottom surface of the circulation flow path part 213, the distance N mentioned above is equal to the thickness of the nozzle layer 21a. The nozzle 211, which has been described above, has a shape such that a nozzle diameter is constant in the ink-ejection direction, but alternatively, the nozzle diameter may change continuously or in stages in the ink-ejection direction. For example, the nozzle 211 may be formed with a two-diameter hole where the nozzle diameter changes in the ink-ejection direction in two stages.
[Oscillation of Ink Meniscus during Non-Ejection Time]
The inventor of the present invention has discovered the following: in a case where, from the perspective of partly withdrawing ink from near the nozzle into the circulation flow path part, when a diameter of a hole at an exit of a nozzle is represented by D (μm), the exit being a portion of the nozzle that is farthest from a pressure chamber, and a distance between the exit and a position in a circulation flow path part that is nearest the exit is represented by N (μm), N≤3.47D is satisfied, then, by oscillating an ink meniscus under predetermined conditions determined by taking into consideration the ink withdrawal amount, details of the conditions being described later, even when ink near the exit of the nozzle has failed to be prevented from becoming dry and thus has become more viscous, it is possible to increase the possibility of successfully removing the ink from inside the nozzle, whereby it is possible to avoid the degradation of the ejection properties attributable to the ink. Hereinafter, a detailed description will be given of oscillation of the ink meniscus.
In the present embodiment, during the non-ejection time, during which ink is not ejected, the drive circuit 60 generates a driving signal for withdrawing ink from the exit 211a of the nozzle 211 to the pressure chamber 231 side, to a position that is away from the exit 211a by a distance that is equal to or more than 0.16N but equal to or less than 0.555D and for causing an ink meniscus to oscillate, and the drive circuit 60 applies the driving signal to the piezoelectric element 24 functioning as a driving element. Here, 0.16N means 0.16×N, and 0.555D means 0.555×D. The distance D may have a value that is, for example, equal to or more than 10 μm but equal to or less than 30 μm, and the distance N may have a value that is, for example, equal to or more than 10 μm but equal to or less than 20 μm, but the distances are not limited to these ranges. The details of the ink withdrawal amount will be described later.
When the driving signal illustrated in
From
Accordingly, in a case where the diameter D of the nozzle 211 is 20 μm, from the perspective of removing ink from inside the nozzle 211 to avoid the degradation of the ejection properties caused by the ink even in a case where the ink has failed to be prevented from becoming dry and more viscous near the exit 211a of the nozzle 211 despite the withdrawal of the ink performed while stabilizing the ink meniscus, it is necessary for the shaking driving potential to be equal to or more than 0.1(×31V) but equal to or less than 0.7(×31V). In this range of the shaking driving potential, the ink meniscus withdrawal amount is, from
Here, the ink meniscus withdrawal amount 1.6 μm corresponds to the ink meniscus protrusion amount 1.3 μm as mentioned above, and the value 1.3 μm of the ink meniscus protrusion amount is equal to 0.065 times the diameter D of the nozzle 211. Also, from
Next, appropriate ink withdrawal amounts will be discussed with respect to various amounts of the diameter D and the distance N (the nozzle length). As illustrated in
When the shaking driving potential during the non-ejection time is too low (below 0.1(×31V)), ink becomes dry and more viscous, which results in reduction of the ink ejection speed from a reference range (for example, ±5% of a reference speed). On the other hand, when the shaking driving potential during the non-ejection time is too high (above 0.7(×31V)), the ink meniscus becomes unstable to cause the ink ejection direction to become unstable as well, which results in poor ink ejection. In contrast to these cases, when the shaking driving potential is within the above-mentioned reference range, ink is ejected in a preferable manner.
0.16N≤H≤0.555D (2)
Here, for the purpose of making Hmin common to all the cases where the diameter D is respectively 10 μm, 20 μm, 24 μm, and 30 μm, for the sake of convenience, Hmin is plotted, in all the cases except the case of D=20 μm, based on a consideration that a border between preferable ink ejection and poor ink ejection exists between one circle and one cross which are adjacent to each other on a line of the same value of the distance N (N=20 μm, for example).
Based on the above examination, in the present embodiment, as has been previously described, the drive circuit 60 is configured to generate a driving signal for withdrawing ink from the exit 211a of the nozzle 211 to the pressure chamber 231 side, to a position at a distance of 0.16N or more but 0.555D or less from the exit 211a, and for causing the ink meniscus to oscillate, during the non-ejection time, during which ink is not ejected, such that the driving element (the piezoelectric element 24) is driven based on this driving signal.
Thus, during the non-ejection time, during which ink is not ejected, by taking into consideration the relationship between the diameter D of the nozzle and the distance N, in other words, by taking into consideration the size of the hole at the exit 211a of the nozzle 211 and the position of the circulation flow path part 213, in withdrawing ink by a predetermined amount (equal to or more than 0.16N but equal to or less than 0.555D), it is possible to avoid the degradation of the ink ejection properties (the ink ejection speed). From this, it is possible to say that even in a case where, during the non-ejection time, the ink has failed to be prevented from becoming dry and thus has become more viscous near the exit 211a of the nozzle 211, there is a strong possibility that the ink with the increased viscosity has been successfully withdrawn to circulate to be removed from inside the nozzle 211. Furthermore, by circulating ink having increased viscosity, it is made possible to reuse such ink by adjusting its viscosity, and this eliminates the need of a maintenance operation of discharging ink with increased viscosity, such that the amount of waste ink greatly decreases as well.
From behavior of the piezoelectric element 24 based on the driving signal described above, it is possible to say that the ink jet driving method of the present embodiment includes circulating ink via the circulation flow path part 213 during the non-ejection time by withdrawing the ink from the exit 211a of the nozzle 211 toward the pressure chamber 231 side, to a position at a distance of 0.16N or more but 0.555D or less from the exit 211a, causing an ink meniscus to oscillate, and guiding at least part of the withdrawn ink into the circulation flow path part 213, by means of the piezoelectric element 24.
Here, as illustrated in
Alternatively, the drive circuit 60 may generate a driving signal that causes the ink meniscus to oscillate immediately before ink is ejected as illustrated in
[Relationship Between Presence/Absence of Circulation and Oscillation and Ejection Speed]
Next, results of an examination conducted on the relationship between presence/absence of circulation and oscillation (shaking) and ejection speed will be given below.
Accordingly, from
Further,
From
It has also become clear that when the circulation amount exceeds 0.01 times the ejection amount, the ejection speed increases (see graphs c1 and c2). It is conceivable that the reason for this increase of the ejection speed is that when the circulation amount during the non-ejection time increases, it becomes easier for air bubbles and the ink with increased viscosity both existing near the nozzle to enter the circulation flow path. On the other hand, it is possible to say that, from the perspective of preventing degradation of ejection efficiency caused when the circulation flow path is enlarged in order to achieve a larger head and a larger circulation amount, it is desirable for the circulation amount to be equal to or less than one time the ejection amount.
It is also clear that, when the circulation amount is equal to 0.025 times the ejection amount, it is possible to restrict the amount of increase of the ejection speed to 5% (see graph c2), but when the circulation amount exceeds 0.025 times the ejection amount, the amount of increase of the ejection speed exceeds 5%, and the ejection properties are significantly degraded (see graph c1). Accordingly, it is possible to say that, from the perspective of securely avoiding significant degradation of the ejection properties (significant increase of the ejection speed), it is desirable for the circulation amount to be equal to or less than 0.025 times the ejection amount.
The above description has dealt with cases where the present embodiment uses the piezoelectric element 24 as a driving element, but there may be used another type of driving element such as a heater element which generates air bubbles inside a pressure chamber, an electrostatic actuator which uses electrostatic force to change the capacity of a pressure chamber, or the like.
[Supplementary Description]
In
Further,
[Others]
With the ink jet driving apparatus and the ink jet driving method of the present embodiment described above, which are also describable as follows, it is possible to achieve the following operational effects.
According to the present embodiment, an ink jet driving apparatus includes a head substrate having a nozzle through which ink is ejects, a pressure chamber which communicates with the nozzle and in which the ink is stored, and a circulation flow path part which diverges from a flow path of the ink flowing toward the nozzle and forms a flow path for circulating ink discharged from the pressure chamber, a driving element which is supported on the head substrate, causes ink in the pressure chamber to be ejected through the nozzle during an ejection time, and causes an ink meniscus in the nozzle to oscillate during a non-ejection time, and a drive controller which controls the driving element. Here, when a diameter of a hole at an exit of the nozzle is represented by D (μm), the exit being a portion of the nozzle that is farthest from the pressure chamber, and a distance, in a direction perpendicular to a surface including the hole at the exit, between the exit and a position in the circulation flow path part that is nearest the exit is represented by N (μm), N≤3.47D is satisfied. During the non-ejection time, the drive controller generates a driving signal for withdrawing ink from the exit of the nozzle toward the pressure chamber side, to a position at a distance of 0.16N or more but 0.555D or less from the exit, and for causing the ink meniscus to oscillate, and the drive controller applies the driving signal to the driving element.
As described above, by taking into consideration the relationship between the distance N and the diameter D, in other words, the relationship between the size of the hole at the exit of the nozzle and the position of the circulation flow path part, in withdrawing ink by a predetermined amount (distance) to cause the ink meniscus to oscillate, it is possible, even in a case where ink near the nozzle exit has failed to be prevented from becoming dry and thus has become more viscous, to increase the possibility of successfully guiding the ink with the increased viscosity into the circulation flow path part to remove the ink from inside the nozzle, even though by a small amount. As a result, it is possible to avoid the degradation of the ejection properties attributable to the ink. Furthermore, when N≤3.47D is satisfied, the position of the circulation flow path part is near the exit of the nozzle, and thus, it becomes easy to withdraw the ink from inside the nozzle and circulate the ink via the circulation flow path part.
According to the present embodiment, an ink jet driving method is a method for driving an ink jet driving apparatus having the following configuration. The ink jet driving apparatus includes a head substrate having a nozzle through which ink is ejected, a pressure chamber which communicates with the nozzle and in which the ink is stored, and a circulation flow path part which diverges from a flow path of the ink flowing toward the nozzle and forms a flow path for circulating ink discharged from the pressure chamber, and a driving element which is supported on the head substrate, causes ink in the pressure chamber to be ejected through the nozzle during an ejection time, and causes an ink meniscus in the nozzle to oscillate during a non-ejection time. When a diameter of a hole at an exit of the nozzle is represented by D (μm), the exit being a portion of the nozzle that is farthest from the pressure chamber, and a distance, in a direction perpendicular to a surface including the hole at the exit, between the exit and a position in the circulation flow path part that is nearest the exit is represented by N (μm), N≤3.47D is satisfied. The driving method includes circulating ink via the circulation flow path part by withdrawing the ink, by means of the driving element, from the exit of the nozzle toward the pressure chamber, to a position at a distance equal to or more than 0.16N but equal to or less than 0.555D from the exit, causing the ink meniscus to oscillate, and guiding at least part of the withdrawn ink into the circulation flow path part.
As described above, by taking into consideration the relationship between the distance N and the diameter D, ink is withdrawn by a predetermined amount (distance), and the ink meniscus is caused to oscillate. Then, by at least partly guiding the withdrawn ink into the circulation flow path part, the ink is circulated via the circulation flow path part. Thereby, even in a case where the ink has failed to be prevented from becoming dry and thus has become more viscous near the exit of the nozzle, it is possible to increase the possibility of successfully guiding the ink with the increased viscosity into the circulation flow path part to remove the ink from inside the nozzle, even though by a small amount. As a result, it is possible to avoid the degradation of the ejection properties attributable to the ink. Furthermore, when N≤3.47D is satisfied, the position of the circulation flow path part is near the nozzle exit, and thus, it becomes easy to withdraw the ink existing inside the nozzle and circulate the ink via the circulation flow path part.
In the driving apparatus and the driving method described above, it is desirable that the amount of ink that flows in the circulation flow path part per second during the non-ejection time be equal to or more than 0.0025 times the amount of ink that is ejected through the nozzle per second during the ejection time.
When the circulation amount during the non-ejection time is equal to or more than 0.0025 times the ejection amount during the ejection time, by guiding the ink, which has become more viscous near the exit of the nozzle, into the circulation flow path part to circulate therein, it is possible to almost completely remove the ink from inside the nozzle. Thereby, it is possible to securely avoid significant degradation of the ejection properties. For example, it is possible to restrict the amount of reduction of the ejection speed to 5% of the reference speed at the maximum.
In the driving apparatus and the driving method described above, it is desirable that the amount of ink that flows in the circulation flow path part per second during the non-ejection time be equal to or less than one time the amount of ink ejected through the nozzle per second during the ejection time.
In order to achieve a circulation amount during the non-ejection time that exceeds one time the ejection amount during the ejection time, it is necessary to enlarge the circulation flow path part, which will make it difficult to arrange nozzles highly densely. With the circulation amount that is equal to or less than one time the ejection amount, it is possible to avoid significant degradation of the ejection properties while simultaneously achieving a high-density arrangement of nozzles easily.
In the driving apparatus and the driving method described above, it is desirable that the amount of ink that flows in the circulation flow path part per second during the non-ejection time be equal to or less than 0.025 times the amount of ink ejected through the nozzle per second during the ejection time.
With the circulation amount during the non-ejection time that is equal to or less than 0.025 times the ejection amount during the ejection time, it is possible to restrict the variation of the ejection properties caused by the circulation as much as possible, and securely avoid the degradation of the ejection properties.
In the driving apparatus described above, it is desirable that, during the non-ejection time, the drive controller generate a driving signal for oscillating the ink meniscus a plurality of times, and feed the driving signal to the driving element. In the driving method described above, it is desirable that, during the circulating of the ink, during the non-ejection time, the ink meniscus be caused to oscillate a plurality of times.
By the driving element causing an ink meniscus to oscillate a plurality of times during the non-ejection time based on the driving signal described above, it is possible to securely prevent ink near the exit of the nozzle from becoming dry and prevent increase in viscosity of the ink itself during the non-ejection time, and thus to securely avoid significant degradation of the ejection properties.
In the driving apparatus described above, it is desirable that the drive controller generate a driving signal for oscillating the ink meniscus immediately before ink is ejected, and feed the driving signal to the driving element. In the driving method described above, it is desirable that, during the circulating of the ink, the ink meniscus be caused to oscillate immediately before ink is ejected.
By the driving element causing an ink meniscus to oscillate based on the driving signal immediately before ink is ejected, it is possible, immediately before ink is ejected, to guide the ink with increased viscosity near the exit of the nozzle into the circulation flow path part to remove the ink from inside the nozzle, while supplying fresh ink (with a predetermined viscosity) from the pressure chamber into the nozzle, and have the ink ejected during the ejection time. Thereby, it is possible to securely avoid the degradation of the ejection properties.
In the driving apparatus and the driving method, the circulation flow path part may be disposed to diverge from a flow path of the ink flowing from the pressure chamber toward the nozzle. In this case, it is possible to form the circulation flow path part by making use of a space in an ink flow direction from the pressure chamber to the nozzle (that is, for example, the thickness direction of the head substrate), and thus it becomes easy to increase the capacity of the circulation flow path part (a circulation flow path).
In the driving apparatus and the driving method, it is preferable that N≤3.00D is satisfied. In this case, the position of the circulation flow path part is even closer to the exit of the nozzle, and this makes it easy to control the ink withdrawal amount such that the ink withdrawal amount is equal to or more than 0.16N but equal to or less than 0.555D.
In the driving apparatus and the driving method described above, it is desirable that N≤2.00D be satisfied. In this case, the position of the circulation flow path part is much closer to the exit of the nozzle, and this makes it easier to control the ink withdrawal amount such that the ink withdrawal amount is equal to or more than 0.16N but equal to or less than 0.555D.
In the driving apparatus and the driving method described above, it is desirable that, during the non-ejection time, ink circulation (caused by the pump) and ink meniscus oscillation (withdrawal of ink from the nozzle) (caused by the driving element) be performed simultaneously (see graphs a1 to a3 of
Although embodiments of the present invention have been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and not limitation, the scope of the present invention should be interpreted by terms of the appended claims.
The ink jet driving apparatus and driving method of the present invention are usable in ink jet heads and ink jet printers.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2016-015245 | Jan 2016 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2017/000622 | 1/11/2017 | WO | 00 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2017/130695 | 8/3/2017 | WO | A |
| Number | Name | Date | Kind |
|---|---|---|---|
| 20030058307 | Eguchi et al. | Mar 2003 | A1 |
| 20050248627 | Ito | Nov 2005 | A1 |
| 20140098160 | Hong et al. | Apr 2014 | A1 |
| 20150115202 | Kagata | Apr 2015 | A1 |
| Number | Date | Country |
|---|---|---|
| 2006111 | Dec 2008 | EP |
| 2004262237 | Sep 2004 | JP |
| 2011051214 | Mar 2011 | JP |
| 2011520671 | Jul 2011 | JP |
| 2013129089 | Jul 2013 | JP |
| 2014054844 | Mar 2014 | JP |
| 2010044775 | Apr 2010 | WO |
| Entry |
|---|
| Extended European Search Report corresponding to Application No. 17743926.2-1019/3409474 PCT/JP2017000622; dated Jan. 8, 2019. |
| International Search Report corresponding to Application No. PCT/JP2017/000622; dated Mar. 14, 2017. |
| IPRP and Written Opinion of corresponding Application No. PCT/JP2017/000622; dated Jul. 31, 2018. |
| Number | Date | Country | |
|---|---|---|---|
| 20190030893 A1 | Jan 2019 | US |
