JP6201527B2 - Inkjet head - Google Patents

Description

  The present invention relates to an inkjet head and an inkjet head driving method, and more particularly to an inkjet head and an inkjet head driving method capable of reducing the influence between rows of pressure chambers due to crosstalk.

  In the industrial inkjet technology, the number of nozzles and the number of rows are increasing. Along with this, it has become more difficult to arrange the injection performance for each nozzle than before.

  For example, injection performance may become non-uniform due to pressure waves and temperature distribution generated by driving. In the case of an ink jet head having a structure in which the pressure chambers are constituted by a plurality of rows and the ink inlets of the pressure chambers between the rows communicate with each other by a common ink chamber, Causes a problem of so-called crosstalk that propagates to the pressure chambers in the other rows through the common ink chamber and causes fluctuations in the ejection characteristics of the pressure chambers through which the pressure waves propagate.

  On the other hand, the unit price of nozzles is decreasing with the practical application of inkjet technology, and there is a demand for inkjet heads that are simple in structure, inexpensive, and highly productive.

  Conventionally, as a technique for reducing the influence between pressure chambers due to crosstalk, a wall member that intersects a straight extension line connecting an ink inlet and an ink outlet of a pressure chamber is made of a material having a bulk modulus of 40 GPa or less. A formed damper (Patent Document 1), a damper wall that is elastically deformed facing the common ink chamber (Patent Document 2), or a damper member having a damper chamber filled with air in the common ink chamber is disposed. (Patent Document 3) and the like have been proposed.

JP 2007-168185 A JP 2012-106513 A JP 2007-111831 A

  In the ink jet head, the variation in ejection characteristics increases as the number of pressure chambers increases. Especially when there are more than three rows, the pressure wave generated in the pressure chamber in the middle row affects each pressure chamber in the two rows adjacent to each other, so that the influence of crosstalk between rows cannot be ignored. As a result, the variation in injection characteristics increases.

  Although Patent Documents 1 and 2 have a simple structure because one wall surface of a common ink chamber has a pressure wave attenuation function, the effect of pressure wave attenuation may become insufficient as the number of rows of pressure chambers increases. This is because as the number of pressure chambers increases, the amount of ink supplied to the pressure chambers increases and the common ink chamber increases in volume, and as the volume of the common ink chamber increases, the pressure inlet ink inlet and the pressure wave are increased. This is because the distance from the wall surface having the attenuation function increases.

  Japanese Patent Application Laid-Open No. 2004-228561 has a structure in which a damper member is arranged as a separate member in a common ink chamber, and thus does not have the above-described problem, but discloses that it solves the problem of crosstalk between rows of pressure chambers. There is no.

  Regarding crosstalk between rows of pressure chambers, in Patent Document 2, a narrowing portion that narrows a cross-sectional area of a flow path in a common ink chamber is formed by providing a partition wall in the common ink chamber, and the crosstalk between rows is formed by this narrowing portion. Is disclosed. However, in this case, in addition to providing a damper member in the common ink chamber, it is necessary to form a constricted portion, and there is a problem that the structure becomes complicated and the cost increases.

  Therefore, an object of the present invention is to provide an ink jet head that can reduce the influence of crosstalk between rows of pressure chambers arranged in two or more rows with a simple configuration and can realize stable ejection characteristics.

  Further, when an inkjet head provided with a damper member in a common ink chamber is driven at a high frequency of 15 kHz or more, a pressure wave generated by the driving may be attenuated and reflected continuously, thereby generating regular pressure unevenness. Although such pressure unevenness is slight, in some cases, it may be visually recognized as a change in liquid amount or uneven concentration.

  Accordingly, another object of the present invention is to provide a driving method of an ink jet head that can reduce density unevenness by suppressing the occurrence of pressure wave unevenness during high frequency driving in an ink jet head provided with a damper member in a common ink chamber. There is to do.

  Other problems of the present invention will become apparent from the following description.

  The above problems are solved by the following inventions.

1.
There are two or more rows of pressure chambers and a common ink chamber communicating with all the pressure chambers, and each of the pressure chambers is separated from the common ink chamber via an ink inlet facing the common ink chamber. In an inkjet head that is supplied with ink in common and ejects ink from a nozzle that communicates with an ink outlet of the pressure chamber by a pressure change generated in the pressure chamber.
A damper member is provided inside the common ink chamber,
The shortest distance connecting the damper member and the ink inlet, rather smaller than the distance between the ink inlet in adjacent rows,
The damper member has a damper chamber filled with gas,
The inkjet head according to claim 1 , wherein a pressure inside the damper member when the ink in the common ink chamber reaches a use temperature is equal to or lower than an atmospheric pressure .

2.
2. The inkjet head according to claim 1, wherein the shortest distance connecting the damper member and the ink inlet is the same for all the ink inlets.

3.
3. The ink jet head according to 2, wherein the common ink chamber has only one damper member , and the damper member is disposed so as to straddle all the rows of the pressure chambers.

4).
4. The inkjet head according to item 3, wherein the damper member includes all of the ink inlets when the damper member is projected from a direction perpendicular to a plane on which the ink inlets exist.

5.
5. The ink jet head according to any one of 1 to 4, wherein the ink inlet, the ink outlet, and the nozzle are arranged in a straight line, and the straight line and the damper member intersect each other.

6).
6. The inkjet according to claim 5, wherein a partition between adjacent pressure chambers includes a piezoelectric element, and pressure is applied to the ink in the pressure chamber by deformation of the partition and the ink is ejected from the nozzle. head.

7).
7. The ink jet head according to any one of 1 to 6, wherein a member having a bulk modulus of 40 GPa or more is disposed in parallel with the damper member around the ink inlet.

8 .
The damper member is formed such that at least one surface of the housing is formed of a flexible film, the damper chamber is defined by the housing and the film, and the film faces the ink inlet. 2. The inkjet head as described in 1 above, wherein

9 .
9. The ink jet head according to 8, wherein the casing contains a metal.

1 0 .
One wall surface of the pressure chamber is formed by a vibration plate in which piezoelectric elements are stacked, and is configured to apply pressure to the ink in the pressure chamber by the vibration of the vibration plate and eject the ink from the nozzle. 2. The inkjet head according to 1 above.

  According to the present invention, it is possible to provide an ink jet head capable of reducing the influence of crosstalk between rows of pressure chambers arranged in two or more rows with a simple configuration and realizing stable ejection characteristics.

  In addition, according to the present invention, it is possible to provide a method for driving an ink jet head that can suppress uneven density during high frequency driving in an ink jet head provided with a damper member in a common ink chamber, thereby reducing density unevenness. it can.

1 is an exploded perspective view showing a first embodiment of an inkjet head according to the present invention. Sectional view of the ink jet head shown in FIG. Cross section of damper member The figure explaining the distance between the ink inlets in the row | line | column of an adjacent pressure chamber The perspective view which shows the one aspect | mode of the damper member which protruded the leg part Sectional drawing which shows 2nd Embodiment of the inkjet head which concerns on this invention. The figure which shows an example of the timing chart at the time of applying a drive signal with respect to the drive electrode of each drive group divided | segmented into two groups Diagram showing an example of drive waveform

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(First Embodiment of Inkjet Head)
1 is an exploded perspective view showing a first embodiment of an inkjet head according to the present invention, FIG. 2 is a sectional view of the inkjet head, and FIG. 3 is a sectional view of a damper member.

  In the inkjet head 1, a nozzle plate 11, a head chip 12, a substrate 13, and an ink manifold 14 are joined in order from the bottom in the figure, and a damper member 15 is disposed inside the ink manifold 14.

  The head chip 12 has a hexahedral shape, and a plurality of channels 121 functioning as pressure chambers in the present invention are arranged. Each channel 121 is formed so as to penetrate straight through the surface on the nozzle plate 11 side of the head chip 12 and the surface on the substrate 13 side, and a plurality of the channels 121 are arranged in parallel along the X direction in FIG. Thus, one channel row is formed. A plurality of channel rows are arranged in parallel along the Y direction intersecting with the X direction, thereby forming a plurality of channel rows.

  Here, one channel row extending in the X direction is formed by seven channels 121, and four channel rows are arranged side by side in the Y direction. However, in the present invention, Any number. Further, the number of channel rows may be two or more, and preferably three or more. In the case of having three or more channel rows, the pressure wave generated in one channel row affects the two adjacent channel rows, so that the influence of crosstalk becomes remarkable and the effect of the present invention is remarkable. It is because it is obtained.

  In the head chip 12, partition walls 122 that partition between adjacent channels 121 and 121 in each channel row include piezoelectric elements, and drive electrodes (not shown) are formed on both surfaces of each partition wall 122. The partition wall 122 is shear-deformed when a drive signal of a predetermined voltage is applied to the drive electrodes on both sides, and the volume in the channel 121 sandwiched between the pair of partition walls 122 and 122 is changed. As a result, a pressure change for ejection is applied to the ink supplied into the channel 121, and ink droplets are ejected from the nozzle 111 that is formed in the nozzle plate 11 so as to communicate with the ink outlet 121 a of the channel 121. It is like that. The ink outlet 121a is a lower opening in the channel 121 in FIG.

  The substrate 13 is a flat thin plate having a larger area than the head chip 12. The substrate 13 is provided with electrodes (not shown) that are electrically connected to the drive electrodes of the head chip 12 on the surface on the head chip 12 side. It also functions as a connection part with an external wiring member such as an FPC (not shown). Through holes 131 are individually formed in the region of the substrate 13 where the head chip 12 is bonded so as to correspond to each channel 121 of the head chip 12 on a one-to-one basis. Therefore, the inside of each channel 121 communicates with the corresponding through hole 131. The opening on the head chip 12 side of the through hole 131 has an area substantially the same as the opening of the channel 121 and is formed to have the same shape as the opening of the channel 121.

  The ink manifold 14 is formed in a box shape having an opening on one surface, and is joined to the substrate 13 so as to close the opening, whereby a common ink chamber 141 that supplies ink to all the channels 121 in the ink manifold 14 in common. Is forming. In the common ink chamber 141, ink supplied from an ink inlet (not shown) is stored.

  All the through holes 131 of the substrate 13 are opened so as to face the common ink chamber 141. Therefore, each through-hole 131 constitutes an individual ink flow path that supplies the ink in the common ink chamber 141 into the channel 121 between the common ink chamber 141 and the channel 121. The opening portion of each through hole 131 facing the common ink chamber 141 is an ink inlet 131 a through which ink flows individually into each channel 121. That is, in the present invention, the ink inlet is an opening that communicates with the pressure chamber and opens individually for each pressure chamber on the surface facing the common ink chamber.

  The damper member 15 shown in the present embodiment is formed in a thin box shape, and only one damper member 15 is disposed in the common ink chamber 141 so as to be close to the substrate 13 and straddle all the channel rows. As shown in FIG. 3, the damper member 15 has a damper chamber 152 therein. At least one surface of the casing 151 is a damper wall 153 formed by a thin-walled flexible film, and an internal space defined by the damper wall 153 and the casing 151 is a damper chamber 152. A gas is sealed in the damper chamber 152. The type of gas is not particularly limited. The damper member 15 is arranged so that the damper wall 153 faces the substrate 13. A synthetic resin film can be used as the flexible film constituting the damper wall 153. The synthetic resin film is preferably a polyimide film.

  The damper member 15 is formed in a size that can cover the ink inlets 131 a of all the through holes 131 formed in the substrate 13 by the damper wall 153. That is, as shown in FIG. 1, when the damper member 15 is projected onto the plane from a direction perpendicular to the plane of the substrate 13 where the ink inlet 131a exists, the damper member 15 includes all of the ink inlet 131a. Yes. In the present embodiment, it is formed in a rectangular shape in plan view, but may be any shape such as a circular shape or an elliptical shape as long as it includes all of the ink inlets 131a. However, the damper member 15 is formed smaller than the opening area of the ink manifold 14. Therefore, as shown in FIG. 2, an ink flow path 141a to the ink inlet 131a is secured between the periphery of the damper member 15 and the inner wall surface of the common ink chamber 141.

  The separation distance of the damper member 15 from the substrate 13 is defined by the shortest distance between the surface of the damper member 15 facing the ink inlet 131 a of the substrate 13 and the ink inlet 131 a of the through hole 131 corresponding to the channel 121. Accordingly, the damper member 15 is defined by the shortest distance connecting the damper wall 153 and the ink inlet 131a. When the shortest distance is D (see FIG. 2) and the distances between the ink inlets 131a in the adjacent channel rows are d1, d2, and d3 (see FIG. 4), respectively, D <d1, and D <d2, In addition, D <d3. That is, the damper member 15 is disposed such that the shortest distance D is smaller than the distances d1, d2, and d3 between the ink inlets 131a and 131a of adjacent channel rows. Accordingly, when viewed from each ink inlet 131a, the distance to the damper wall 153 of the damper member 15 is closer than the distance to the ink inlet 131a of the adjacent channel row.

  Since the damper member 15 is arranged in the vicinity of the substrate 13 as described above, a large space is secured between the damper member 15 and the rear inner wall surface 142 of the common ink chamber 141. The rear inner wall surface 142 is an inner wall surface facing the substrate 13 in the common ink chamber 141. Therefore, even if the damper member 15 is disposed inside the common ink chamber 141, sufficient ink can be stored using the space secured between the rear inner wall surface 142 and the common ink chamber 141.

  Here, the shortest distance D is a distance defined by a straight line drawn from each ink inlet 131a so as to be orthogonal to the damper wall 153 of the damper member 15. The damper member 15 is arranged so that the damper wall 153 is parallel to the plane of the substrate 13 where the ink inlet 131a opens so that the shortest distance D is equal for all the ink inlets 131a.

  The distances d1, d2, and d3 are the ink inlets in one channel row (referred to as ink inlet A) and the ink inlets closest to the ink inlet A in the adjacent channel row (this is referred to as “ink inlet A”). The shortest distance from the ink inlet B). This distance is generally the width of the inter-column gap formed between the ink inlets 131a and 131a of adjacent channel columns as shown in FIG. The distances d1, d2, and d3 may not be the same value.

  Next, the operation of the inkjet head 1 will be described.

  When the partition 122 is deformed by applying a drive signal having a predetermined voltage to the drive electrode based on predetermined print data, the inkjet head 1 applies an ejection pressure to the ink in the channel 121 sandwiched between the pair of partitions 122. Ink droplets are ejected from the nozzle 111. The pressure wave generated in the channel 121 at this time has not only a component toward the nozzle 111 but also a component toward the through hole 131 side of the substrate 13. A part of the component toward the through hole 131 propagates into the common ink chamber 141 through the through hole 131 of the substrate 13. At this time, since the damper member 15 is closer to the damper member 15 than the ink inlet 131a of the adjacent channel row, the distance from the ink inlet 131a reaches the damper member 15 out of the pressure waves propagated from the ink inlet 131a into the common ink chamber 141. The component that goes straight to the surface immediately collides with the damper member 15 and is absorbed by the deformation of the damper wall 153 due to the flexibility of the damper wall 153 and the compressibility of the gas sealed inside.

  As a result, the pressure wave propagated in the common ink chamber 141 is reduced before reaching the ink inlet 131a of the adjacent channel row, and is applied to the channel 121 of the adjacent channel row communicating with the common ink chamber 141. The influence of the given crosstalk can be reduced. In addition, the pressure wave remaining in the channel 121 can be reduced. This is because the pressure wave can be reduced at an earlier timing as the distance for absorbing the pressure wave generated in the channel 121 is shorter. As a result, fluctuations in the injection characteristics can be suppressed and stable injection characteristics can be realized. In order to obtain such an effect, it is only necessary to define the arrangement of the damper member 15 in the common ink chamber 141. Therefore, there is no need to provide a member different from the damper member, such as forming a constricted portion by a partition wall as in the prior art, and the configuration of the crosstalk between the pressure chambers arranged in two or more rows is simplified. Can be reduced.

  In particular, as shown in the present embodiment, the damper member 15 is disposed so that the damper wall 153 faces each ink inlet 131a. Therefore, the pressure wave that travels straight from the ink inlet 131a toward the damper member 15 is the damper wall 153. Will collide directly with. For this reason, the pressure wave absorption effect is high, and the effect of reducing the influence of crosstalk is high.

  Further, the ink in the common ink chamber 141 has a predetermined temperature due to heat generated by the heat generated by the head chip 12 during driving, or when heating means such as a heater (not shown) is provided. . In this case, if a large amount of ink is stored in the common ink chamber 141, temperature distribution is likely to occur in the ink, and the viscosity of the ink varies, so that the ejection characteristics vary for each channel row or each channel 121. There is a fear. If the ejection characteristics vary, the ejection speed of the ink droplets becomes uneven and the landing position is disturbed. However, since the damper member 15 is disposed so as to be close to the substrate 13, the amount of ink existing between the damper member 15 and the ink inlet 131a can be reduced, thereby reducing the influence of the temperature distribution. be able to.

  Since only one damper member 15 shown in this embodiment is provided in the common ink chamber 141, it can be configured at low cost. Further, for example, one damper member may be arranged for each channel row, or two damper members may be arranged so as to correspond to two channel rows, respectively. In the case where the members are arranged, if a variation in the separation distance from the substrate 13 occurs for each damper member, the pressure wave absorption performance varies, and the influence of crosstalk and the influence of the temperature distribution between channel arrays corresponding to different damper members. It is assumed that the reduction effect is not uniform and the injection characteristics vary. However, as shown in the present embodiment, if one damper member 15 is provided so as to straddle all the channel rows, this is not the case. Therefore, the effect of reducing the effects of crosstalk and temperature distribution can be reduced. Uniformity can be achieved between channel columns.

  Further, in the present embodiment, since one damper member 15 is disposed so as to include all of the ink inlets 131a, it is possible to reduce variation in pressure wave absorption performance for each channel 121. For this reason, the effect of reducing the influence of crosstalk and the influence of temperature distribution can be made uniform among the channels 121.

  Furthermore, in this embodiment, since each ink inlet 131a facing the common ink chamber 141 has the same distance to the damper wall 153 of the damper member 15, there is a variation in pressure wave absorption performance for each channel 121. It can be further reduced. In addition, since the flow resistance of the ink when supplied from the common ink chamber 141 to each ink inlet 131a can be made uniform, variations in ejection characteristics due to variations in the flow resistance are reduced.

  The damper member 15 is preferably such that the casing 151 contains a metal. The metal may be used for a part of the wall surface of the casing 151 or may form all the wall surfaces. In general, since metal has a higher thermal conductivity than ink (liquid), the temperature distribution of ink in the common ink chamber 141 can be made uniform quickly. For this reason, coupled with the fact that the damper member 15 is close to the ink inlet 131a, the temperature distribution as a whole can be made uniform while suppressing a rapid temperature change in the vicinity of the channel 121.

  As the metal, a metal having good thermal conductivity can be preferably used, and examples thereof include aluminum, copper, and stainless steel. Such metal is preferably exposed on the surface of the casing 151 so that it can be in direct contact with the ink in the common ink chamber 141.

  In the inkjet head 1 shown in the present embodiment, the ink inlet 131a, the ink outlet 121a, and the nozzle 111 are arranged on a straight line as shown by a straight line L shown by a broken line in FIG. 2, and the straight line L intersects the damper member 15. ing. According to this configuration, since the component of the pressure wave generated in the channel 121 and directed to the ink inlet 131a can be directly absorbed by the damper member 15, the absorption effect of the pressure wave is the highest and the effect of reducing the influence of crosstalk is achieved. It is preferable because it is remarkably obtained.

  Since the ink inlet 131a is open to the substrate 13, the substrate 13 is disposed around each ink inlet 131a so as to face the damper member 15 in parallel. Therefore, some components of the pressure wave that collided with the damper member 15 may be reflected from the damper member 15 toward the substrate 13 and remain in the common ink chamber 141. Therefore, in order to prevent the residual due to the pressure wave reflected toward the substrate 13 in this way, a member having a volume modulus of elasticity of 40 GPa or more is arranged in parallel with the damper member 15 around the ink inlet 131a. Preferably it is. According to this, the pressure wave reflected by the damper member 15 can be reflected again toward the damper member 15 around the ink inlet 131a, and the pressure wave remaining in the common ink chamber 141 can be reduced. .

  The material of such a member is not particularly limited as long as the bulk modulus is 40 GPa or more, and glass, silicon, metal, synthetic resin, or the like can be used. Among them, glass is preferable because it is easy to process and inexpensive, and is not easily deformed by pressure waves. Such a member can be disposed between the substrate 13 and the damper member 15 so as to be disposed around the ink inlet 131a. However, if the substrate 13 itself is made of glass, it is necessary to separately provide the member. This is particularly preferable because the structure can be simplified and the cost is low.

  The pressure (atmospheric pressure) inside the damper member 15 is preferably equal to or lower than atmospheric pressure when the ink in the common ink chamber 141 reaches the use temperature. Since the damper member 15 can be prevented from expanding during use, it does not cause a situation such as an increase in ink flow path resistance or a decrease in the amount of ink that can be stored. The ink use temperature is the temperature at which the ink is heated by a heating means such as a heater, such as UV ink or ceramic ink. In the case where heating is not performed, the temperature is generally room temperature (25 ° C.).

  Such a damper member 15 forms a damper chamber 152 in which a gas such as air is sealed by attaching a damper wall 153 to one surface of the casing 151 in an atmosphere higher than the ink use temperature, for example, 60 ° C. It can produce by doing. By disposing the damper member 15 in the common ink chamber 141 such that the ink use temperature is 60 ° C. or less, the damper chamber 152 during use is at atmospheric pressure or less and does not expand.

  The means for arranging the damper member 15 at a predetermined distance from the substrate 13 is not particularly limited. For example, as shown in FIG. 5, an appropriate number of leg portions 154 may be provided so as to project on the damper wall 153 side facing the substrate 13. If this leg portion 154 is bonded to the substrate 13, the damper wall 153 of the damper member 15 can be easily arranged so as to have a predetermined separation distance defined by the protruding height of the leg portion 154 from the substrate 13. be able to.

  Further, such a leg portion 154 may be provided so as to protrude not on the damper member 15 side but on the substrate 13 side.

  In addition, although not shown, a support may be bridged between the damper member 15 and the inner wall surface of the common ink chamber 141 to support the damper member 15 at a predetermined distance from the substrate 13.

(Second Embodiment of Inkjet Head)
FIG. 6 is a sectional view showing a second embodiment of the inkjet head according to the present invention.

  In the inkjet head 2, a head substrate 21 and a wiring substrate 22 are laminated and integrated by an adhesive resin layer 23. A box-shaped ink manifold 24 is joined to the upper surface of the wiring board 22, and a common ink chamber 241 in which ink is stored is formed between the box and the wiring board 22. A damper member 25 is disposed in the common ink chamber 241.

The head substrate 21 includes, from the lower side in the figure, a nozzle plate 211 formed of a Si (silicon) substrate, an intermediate plate 212 formed of a glass substrate, a pressure chamber plate 213 formed of a Si (silicon) substrate, and SiO _2. It has a diaphragm 214 formed of a thin film. A nozzle 211 a is opened on the lower surface of the nozzle plate 211.

  The pressure chamber plate 213 is formed with a pressure chamber 213 a for containing ink, and an upper wall thereof is constituted by a vibration plate 214 and a lower wall is constituted by an intermediate plate 212. The intermediate plate 212 is formed with a communication passage 212a through which the inside of the pressure chamber 213a communicates with the nozzle 211a.

  On the upper surface of the diaphragm 214, actuators 215 are stacked in a one-to-one correspondence with the pressure chambers 213a. The actuator 215 has a structure in which an actuator body made of a piezoelectric element such as a thin film PZT is sandwiched between an upper electrode and a lower electrode as drive electrodes, and the lower electrode side is disposed on the upper surface of the diaphragm 214. .

  The wiring board 22 is a board on which wiring for applying a drive signal of a predetermined voltage to each actuator 215 is formed, and an external wiring member 26 such as an FPC is provided at an end portion of the wiring board 22 with an ACF (anisotropic conductive film). Are electrically connected.

  The adhesive resin layer 23 is formed of, for example, a thermosetting photosensitive adhesive resin sheet, and is interposed between the head substrate 21 and the wiring substrate 22 so that the substrates 21 and 22 are laminated and integrated. The adhesive resin layer 23 provides an interval corresponding to the thickness of the adhesive resin layer 23 between the substrates 21 and 22. In the adhesive resin layer 23, the actuator 215 and the area corresponding to the periphery thereof are removed by exposure and development. Each actuator 215 is accommodated in the space from which the adhesive resin layer 23 is removed.

  In the adhesive resin layer 23, through holes 231 penetrating vertically are formed corresponding to the number of the pressure chambers 213a. One end (upper end) of each through-hole 231 communicates with the ink supply path 221 formed in the wiring substrate 22, and the other end (lower end) passes through the opening 214 a formed in the vibration plate 214 and is inside the pressure chamber 213 a. Communicated with. The ink supply path 221 opens on the upper surface of the wiring board 22. The opening faces the common ink chamber 241 and functions as an ink inlet 221a for supplying ink in the common ink chamber 241 into each pressure chamber 213a.

  In the inkjet head 2, ink is supplied from the common ink chamber 241 to the pressure chamber 213a through the ink inlet 221a. When a driving signal is applied from the external wiring member 26 to the actuator 215, the vibration plate 214 is vibrated by the deformation operation of the actuator 215, and a pressure change for discharge is applied to the pressure chamber 213a. The ink inside is ejected from the nozzle 211a through the communication path 212a.

  Although not shown, the inkjet head 2 forms a row of pressure chambers 213a by arranging a plurality of pressure chambers 213a, and a plurality of rows, preferably 3 by arranging a plurality of rows of the pressure chambers 213a. The pressure chambers 213a are provided above the rows. Therefore, the ink inlets 221 a corresponding to the pressure chambers 213 a in each row face the common ink chamber 241. In the damper member 25, the shortest distance connecting the ink inlet 221a is smaller than the distance between the ink inlets 221a and 221a in the row of adjacent pressure chambers 213a, similarly to the damper member 15 in the first embodiment. Are arranged as follows. The damper member 25 has a damper chamber 251 in which gas is sealed.

  Also in the inkjet head 2, when the actuator 215 is operated, a pressure wave is generated in the pressure chamber 213a. A part of the pressure wave is slightly attenuated by narrowing the flow path in the process from the pressure chamber 213a to the through hole 231 and the ink supply path 221, but is propagated from the ink inlet 221a into the common ink chamber 241. Become. However, since the pressure wave propagated in the common ink chamber 241 can be absorbed by the damper member 25 before reaching the ink inlet 221a in the adjacent row, the pressure wave is absorbed in the pressure chamber 213a in the adjacent row. It is possible to reduce the influence of the crosstalk that has an influence, and it is possible to achieve the same effect as in the first embodiment.

  The configuration related to the arrangement and structure of the damper member 25 can be the same as the configuration of the damper member 15 described in the first embodiment, and the details thereof will be described below. Is omitted here.

(Other Embodiments of Inkjet Head)
In the embodiment described above, a preferred embodiment in which the wall surface of the casing 151 is formed by the damper wall 153 made of a flexible film as the damper members 15 and 25 is exemplified, but the present invention is not limited to this, and two possible sheets are possible. It is good also as a bag-shaped damper member which sealed the circumference | surroundings of a flexible film | membrane and enclosed gas inside.

  Further, the damper members 15 and 25 encapsulated with gas have the highest effect of absorbing the pressure wave and can be preferably used in the present invention. However, the damper member only needs to have an effect of absorbing the pressure wave, and is not necessarily limited. It can use not only the thing with which gas was enclosed inside. For example, although not shown, a damper member made of a plate-like member formed of a material having a volume elastic modulus of 40 GPa or less may be used as a wall surface facing at least the ink inlet. Such a damper member has a solid interior and is not filled with gas. Even with such a damper member, when the pressure wave propagated into the common ink chamber collides with the wall surface facing the ink inlet of the damper member, the reflection of the pressure wave can be dulled and a part thereof can be absorbed. Therefore, as with the damper members 15 and 25, the effect of reducing the influence of crosstalk between rows can be obtained.

  As a material having a bulk modulus of 40 GPa or less, a soft synthetic resin can be preferably used. Examples of the soft synthetic resin that can be used in such applications include polyetherimide, liquid crystal polymer, polyphenylene ether, polyamide, polyphenylene sulfide, polyimide, and unsaturated polyester.

(Driving method of inkjet head)
Next, a preferable driving method of the ink jet head according to the present invention will be described.

  The present inventor has examined regular pressure unevenness that occurs when an inkjet head provided with a damper member in a common ink chamber is driven at high speed, and has a constant period corresponding to the acoustic resonance period of the pressure chamber. I understood. The pressure in the pressure chamber changes from positive to negative and from negative to positive according to the acoustic resonance period. Therefore, depending on the period in which this pressure unevenness occurs, there is a gap between one drive timing and the following drive timing. By giving a predetermined phase difference to each other and changing the timing so that the pressure between these drive groups is a combination of a positive pressure and a negative pressure, the pressure unevenness can be offset.

  Therefore, the inkjet head driving method according to the present invention divides all pressure chambers into N drive groups, and shifts the drive timing by (2n-1) AL for each drive group. Here, N is an integer of 2 or more. n is a number satisfying 0.8 <n <1.2. AL (Acoustic Length) is 1/2 of the acoustic resonance period of the pressure chamber. As a result, the timing between the different drive groups is shifted by almost an odd number AL, so that the pressure for each drive group can be a combination of positive pressure and negative pressure, and pressure unevenness can be substantially offset. Thereby, generation | occurrence | production of density | concentration unevenness can be suppressed and it can make it difficult to visually recognize density | concentration unevenness. Further, by shifting the drive timing in the drive group, it is possible to reduce the load on the drive circuit, particularly under high-speed drive. For this reason, there is an effect of reducing waveform dullness due to heat generation and load.

  The AL measures the velocity of the ink droplet ejected when a rectangular wave drive signal is applied to the drive electrode of the pressure chamber (channel 121, pressure chamber 213a), and makes the rectangular wave voltage value constant. When the pulse width of the rectangular wave is changed, it is obtained as a pulse width that maximizes the flying speed of the ink droplet. The pulse is a rectangular wave having a constant voltage peak value. When 0V is 0% and the peak voltage is 100%, the pulse width is 10% of the rise from 0V and 10% of the fall from the peak voltage. It is defined as the time between%. A rectangular wave refers to a waveform in which both the rise time and fall time between 10% and 90% of the voltage are within 1/2, preferably within 1/4 of AL.

  FIG. 7 shows an example of a timing chart when a drive signal is applied to the drive electrodes of each drive group when the drive group is divided into two groups AB. A phase difference of (2n−1) AL is given between the drive group A and the drive group B thus divided. Here, an example in which one drive signal P is applied to each drive period T of the drive group A and the drive group A is driven before the drive group B is shown. The specific waveform shape of each drive signal P is not particularly limited. The pulse width PW is not particularly limited. For example, the pulse width PW can be in the vicinity of 1AL where the pressure in the pressure chamber changes from negative to positive, and specifically, a range of 0.8AL to 1.2AL. It can be.

  The drive group is a group of pressure chambers to which drive signals are applied at the same timing within the drive cycle of the inkjet head. This drive group is preferably divided in units of pressure chamber columns. According to this, the pressure wave which propagates between the rows of pressure chambers can be canceled efficiently. In this case, the pressure chambers in the same row are included in the same drive group. All pressure chambers in the same drive group are driven simultaneously. The same drive group may include a plurality of columns.

  When there are three or more pressure chamber columns, it is preferable that the adjacent pressure chamber columns are divided so as to belong to different drive groups. According to this, at least one row of pressure chambers belonging to different drive groups is arranged between the rows of pressure chambers belonging to the same drive group, so that the same drive groups driven at the same timing are separated from each other. The distance increases accordingly, and the influence of crosstalk between the same drive groups can be further reduced.

  In addition, when there are three or more drive groups to be divided, it is preferable that all the values of n of the phase differences (2n−1) AL between the drive groups are 1 from the viewpoint of avoiding a decrease in landing accuracy.

  The drive frequency in such an ink jet head is preferably 15 kHz or more. As high-frequency driving of 15 kHz or higher occurs, the above-described problem of pressure unevenness occurs more remarkably, and the effect of reducing the occurrence of pressure unevenness becomes significant.

Example 1
A shear mode type ink jet head similar to that shown in FIGS. 1 and 2 was configured using a head chip in which four channel rows in which partition walls including piezoelectric elements and straight channels were alternately arranged were arranged in four rows. The number of channels constituting one channel row is 256, and the ink inlet distances d1 to d3 (see FIG. 4) between the channel rows are d1 = 0.85 mm, d2 = 1.13 mm, d3 = 0.85 mm. It was.

  In the common ink chamber, a damper member in which air is sealed in the damper chamber is disposed so as to be close to the ink inlet. The damper member sealed air inside by sticking a damper wall made of a polyimide film on one surface of an aluminum casing in an atmosphere of 60 ° C. The damper member has a size covering all the ink inlets, and is parallel to the substrate so that the shortest distance D connecting the damper wall and the ink inlet is 0.3 mm at all the ink inlets. Arranged.

When the influence of crosstalk occurs between the measurement channel trains of AL fluctuation, the emission characteristics of the channel fluctuate. The channel AL (1/2 of the acoustic resonance period) of the obtained inkjet head is originally uniquely determined for each channel. However, when the influence of crosstalk is large, the AL fluctuates due to the influence of adjacent channel driving. Therefore, it is possible to examine the occurrence of the influence of crosstalk by measuring the AL fluctuation.

  Therefore, the AL fluctuation of the channel was measured as follows, and the degree of occurrence of the crosstalk between the channel strings was evaluated.

  First, any 10 channels are selected from the center, end, etc. of the head, and when the inkjet head is driven by the following drive patterns (1) to (6), the selected 10 channel AL is selected. Were measured, and the AL fluctuation by each driving pattern was compared. Note that AL was measured by measuring a pulse width at which the ejection speed is maximum when a pulse by a rectangular wave is applied to the head and an ink droplet is ejected from the nozzle.

(1) When driving only one channel (2) When driving all the channels in one row (256 channels) (3) When driving two rows (512 channels) together with adjacent rows (4) Three rows (768 (5) When driving 4 rows (1024 channels) (6) When driving all 4 rows every other nozzle (512 channels)

  The AL fluctuation is obtained when the average value of AL is obtained for each driving pattern from the AL values measured for the above driving patterns with 10 channels, and the smallest average value of the AL is Xmin and the largest value is Xmax. , (| Xmin−Xmax | / Xmin) × 100 (%).

The evaluation criteria are as follows.
○: AL variation due to drive pattern is less than 2% △: AL variation due to drive pattern is 2% or more and less than 5% ×: AL variation due to drive pattern is 5% or more

  If the AL fluctuation is less than 2%, the influence of crosstalk is negligible, the ejection speed of ink droplets ejected from the nozzles is stable at each nozzle, and no noticeable disturbance occurs in the obtained image. If it is 2% or more, there will be a problem in recording a high-definition image by causing variations in the ejection speed of ink droplets due to crosstalk and starting density unevenness in the image. On the other hand, if it is 5% or more, the variation in the ejection speed of ink droplets due to crosstalk becomes large, and the resulting image is greatly disturbed.

  The results are shown in Table 1.

(Example 2)
In Example 1, the AL fluctuation was measured and evaluated in the same manner as in Example 1 except that the shortest distance D connecting the damper wall and the ink inlet was 0.5 mm. The results are shown in Table 1.

(Comparative Example 1)
In Example 1, the AL variation was measured and evaluated in the same manner as in Example 1 except that the shortest distance D connecting the damper wall and the ink inlet was 1.0 mm. The results are shown in Table 1.

(Comparative Example 2)
The AL fluctuation was measured and evaluated in the same manner as in Example 1 except that the damper member was not provided in the common ink chamber. The results are shown in Table 1.

  As described above, in Embodiments 1 and 2 in which the shortest distance D between the damper member and the ink inlet is smaller than any of the distances d1 to d3 between the ink inlets between the four channel rows, the AL fluctuation is reduced. The influence of crosstalk between channel strings was reduced.

Drawing Test <Drawing Test 1>
For Examples 1 and 2 and Comparative Examples 1 and 2, in the process of scanning the inkjet head in the direction orthogonal to the length direction of the channel row, drawing is performed by driving all channels at drive frequencies of 14 kHz, 10 kHz, and 60 Hz, respectively. A solid image drawing test was performed.

  The reason for using the solid image is that the number of channels that are driven simultaneously is large, so that the influence of crosstalk is large and the density unevenness after landing is easily visible.

  The driving waveform used was the DRR waveform shown in FIG. This drive waveform includes a pulse P1 that expands the volume of the channel by deforming a pair of partition walls on both sides of the channel outward, a pulse P2 that maintains the pulse P1 for a certain period of time, and a pulse P2 after this pulse P2. , A pulse P3 for restoring the deformation of the expanded partition wall, and a pulse that, after this pulse P3, deforms the pair of partition walls inwardly to contract the volume of the channel and pushes ink in the channel from the nozzle. P4, a pulse P5 for maintaining the pulse P4 for a certain period of time, and a pulse P6 for restoring the deformation of the contracted partition after the pulse P5. The sustain period PW1 of the pulse P2 is 5.1 μs (= 1AL), and the sustain period PW2 of the pulse P5 is 10.2 μs (= 2AL).

  As a result of visual observation of the obtained image, in Examples 1 and 2, a uniform solid image having no density unevenness could be obtained at any driving frequency. This means that the droplet amount for each channel row is made uniform.

  However, in Comparative Example 1, the density unevenness was slightly noticeable at 14 kHz. Further, in Comparative Example 2, band-like density unevenness was conspicuous at frequencies other than 60 Hz.

<Drawing test 2>
Next, in the first and second embodiments, when all the channels were driven at the driving frequency of 15 kHz using the same driving signal as described above, solid images were recorded, which seems to be caused by pressure unevenness generated by the high frequency driving. Slight density unevenness was observed.

  Therefore, the four channel columns were divided into two driving groups AB, and the driving timing between each driving group was shifted by 5.1 μs (= 1 AL), and all channels were driven at the same driving frequency of 15 kHz. The drive group is divided into drive groups A, A, B, and B in order from the end channel row in units of channel rows.

  As a result, in all of Examples 1 and 2, the density unevenness did not become conspicuous, and the influence of the pressure unevenness generated during high frequency driving was reduced.

1: Inkjet head 11: Nozzle plate 111: Nozzle 12: Head chip 121: Channel (pressure chamber)
121a: Ink outlet 122: Partition wall 13: Substrate 131: Through hole 131a: Ink inlet 14: Ink manifold 141: Common ink chamber 141a: Ink flow path 142: Rear inner wall surface 15: Damper member 151: Housing 152: Damper chamber 153 : Damper wall 154: leg 2: inkjet head 21: head substrate 211: nozzle plate 211 a: nozzle 212: intermediate plate 212 a: communication path 213: pressure chamber plate 213 a: pressure chamber 214: diaphragm 214 a: opening 215: actuator 22: Wiring board 221: Ink supply path 221a: Ink inlet 23: Adhesive resin layer 231: Through hole 24: Ink manifold 241: Common ink chamber 25: Damper member 251: Damper chamber 26: External wiring member P: Drive signal PW: pulse width

Claims (10)

There are two or more rows of pressure chambers and a common ink chamber communicating with all the pressure chambers, and each of the pressure chambers is separated from the common ink chamber via an ink inlet facing the common ink chamber. In an inkjet head that is supplied with ink in common and ejects ink from a nozzle that communicates with an ink outlet of the pressure chamber by a pressure change generated in the pressure chamber.
A damper member is provided inside the common ink chamber,
The shortest distance connecting the damper member and the ink inlet, rather smaller than the distance between the ink inlet in adjacent rows,
The damper member has a damper chamber filled with gas,
The inkjet head according to claim 1 , wherein a pressure inside the damper member when the ink in the common ink chamber reaches a use temperature is equal to or lower than an atmospheric pressure .   2. The ink jet head according to claim 1, wherein the shortest distance connecting the damper member and the ink inlet is the same for all the ink inlets. 3. The ink jet head according to claim 2, wherein the common ink chamber has only one damper member , and the damper member is arranged so as to straddle all the rows of the pressure chambers.   4. The inkjet head according to claim 3, wherein the damper member includes all of the ink inlets when the damper member is projected from a direction perpendicular to a plane on which the ink inlets exist.   The inkjet head according to claim 1, wherein the ink inlet, the ink outlet, and the nozzle are arranged in a straight line, and the straight line and the damper member intersect each other.   The partition between the pressure chambers adjacent to each other includes a piezoelectric element, and a pressure is applied to the ink in the pressure chamber by the deformation of the partition and the ink is ejected from the nozzle. Inkjet head.   The ink jet head according to claim 1, wherein a member having a bulk modulus of 40 GPa or more is disposed in parallel with the damper member around the ink inlet. The damper member is formed such that at least one surface of the housing is formed of a flexible film, the damper chamber is defined by the housing and the film, and the film faces the ink inlet. The inkjet head according to claim 1 , wherein the inkjet head is formed. The inkjet head according to claim 8, wherein the casing contains a metal.   One wall surface of the pressure chamber is formed by a vibration plate in which piezoelectric elements are stacked, and is configured to apply pressure to the ink in the pressure chamber by the vibration of the vibration plate and eject the ink from the nozzle. The inkjet head according to claim 1.

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