JP4900589B2 - Droplet discharge device - Google Patents

Description

  The present invention relates to a droplet discharge device that discharges droplets from a cavity unit by displacement of an active portion in a piezoelectric actuator.

  Examples of the droplet discharge device include an inkjet head. In Japanese Patent Application Laid-Open No. 2004-291543, etc., the present applicant discloses an ink jet head that discharges ink droplets from the nozzle by applying discharge pressure from a piezoelectric actuator to a cavity unit including the nozzle. ing. In Patent Document 1, an ink flow path extending from a plurality of pressure chambers formed on one surface of a cavity unit to a plurality of nozzles formed on the other surface is provided for each nozzle inside the substantially flat cavity unit. Is formed.

  The piezoelectric actuator has a plurality of piezoelectric layers, a plurality of individual electrodes respectively corresponding to the pressure chambers, and a common electrode, and a region of the piezoelectric layer sandwiched between the individual electrodes and the common electrode is an individual electrode. An active portion that is displaced by a driving voltage applied between the common electrode and the common electrode is formed. A piezoelectric actuator is stacked on the one surface of the cavity unit so as to straddle a plurality of pressure chambers, and is fixed to the cavity unit. Here, the piezoelectric actuator is disposed on the one surface of the cavity unit so that the active portions respectively correspond to the pressure chambers.

In the ink jet head formed in this way, the volume of the pressure chamber changes due to the displacement of the active portion, and the ink filled in the pressure chamber is ejected from the nozzle. In order to eject a predetermined amount of ink droplets at a predetermined speed, it is necessary to change the volume of the pressure chamber by a predetermined amount.
JP 2004-291543 A (see FIGS. 5 and 7)

  In a droplet discharge device, it is desired to change the discharge amount and / or discharge speed depending on the nozzle. For example, in an inkjet head having a plurality of colors of ink for color recording, it may be desired to change the ejection amount in accordance with the color of the ejected ink. Specifically, in the case of black ink mainly used for text recording, there is a desire to increase the discharge speed per droplet to increase the recording speed, while yellow used mainly for image recording. In the case of color inks such as magenta and cyan, there is a demand for recording with high definition by reducing the discharge amount per droplet.

  In order to change the ejection amount according to the color of ink, there is also a method of changing the volume change given to the pressure chamber by the active part by changing the value of the drive voltage applied to the active part corresponding to the ink color. However, in this method, it is necessary to set a plurality of drive voltage values in advance in a control device (drive IC or the like) that controls the drive voltage, and there is a problem that the cost of the control device increases.

  An object of the present invention is to make drive voltages applied to active portions belonging to all discharge groups substantially the same in a droplet discharge apparatus in which active portions divided into a plurality of discharge groups are formed.

Means for Solving the Problems and Effects of the Invention

  According to a first aspect of the present invention, there is provided a liquid droplet ejection apparatus that ejects liquid droplets onto an object, comprising a plurality of nozzles and a plurality of pressure chambers corresponding to the nozzles and extending in a first direction. A cavity unit having a plurality of pressure chambers and stacked on the cavity unit, the piezoelectric actuators being disposed corresponding to the pressure chambers, and applying a predetermined drive voltage to the pressure chambers. A piezoelectric actuator having a plurality of active portions that change in volume and that are long in the first direction, wherein the plurality of active portions, the nozzles, and the pressure chambers include a first discharge group and a second discharge group. And the length of the active part included in the first discharge group in the first direction is longer than the length of the active part included in the second discharge group in the first direction. Discharge group The length of the active part included in the loop in the second direction orthogonal to the first direction is longer than the length of the active part included in the second ejection group in the second direction. A droplet discharge device is provided in which the drive voltage applied to the active portion included in the discharge group is the same as the drive voltage applied to the active portion included in the second discharge group.

  According to the first aspect of the present invention, the length (length in the first direction) and the width (length in the second direction) of the active portion are different between the first discharge group and the second discharge group. Thus, the drive voltage of the active part is made substantially the same in these ejection groups. For this reason, in a control device (drive IC or the like) that controls the drive voltage, it is not necessary to individually set the drive voltage value for each ejection group, and the cost of the control device can be reduced. Note that the width of the active portion of the first discharge group is desirably about 3% or more larger than the width of the active portion of the second discharge group.

  In the droplet discharge device of the present invention, the physical properties of the liquid discharged from the first discharge group may be different from the physical properties of the liquid discharged from the second discharge group. The discharge conditions may be different in the discharge groups.

  According to the droplet discharge device of the present invention, in the first discharge group and the second discharge group, for example, the physical properties of liquid (viscosity, surface tension, color, etc.) and / or discharge conditions (nozzle diameter, discharge amount) Even if the discharge speed is different, the drive voltage of these discharge groups can be made substantially the same by adjusting the length and width of the active portion, and the cost of the control device can be reduced. .

  In the droplet discharge device of the present invention, the velocity of the liquid discharged from the nozzle at the drive voltage may be substantially the same in the first discharge group and the second discharge group.

  In this case as well, the cost of the control device can be reduced. Furthermore, since the speed of the liquid ejected from the nozzles is substantially the same, for example, when the droplet ejection device is an inkjet head, the recording state (landing position) of the ink droplets ejected from the nozzles is between ejection groups. Therefore, the recording image quality can be improved.

  In the droplet discharge device of the present invention, the first discharge group and the second discharge group are set to have different discharge amounts, and the discharge having a large discharge amount among the first discharge group and the second discharge group. The length in the first direction and the length in the second direction of the active portion of the group are respectively the length in the first direction and the length in the second direction of the active portion in the discharge group with a small discharge amount. It may be larger than that.

  In this case, the length of the active portion (length in the first direction) and the width (length in the second direction) of the discharge group having a large discharge amount are larger than those of the discharge group having a small discharge amount. As a result, since the area of the active portion is increased, the total amount of displacement of the active portion can be increased even with the same driving voltage, and the discharge amount can be increased.

  In the droplet discharge device of the present invention, the nozzle diameter of the discharge group having a large discharge amount may be larger than the diameter of the nozzle of the discharge group having a small discharge amount.

  In this case, by changing the size of the nozzle diameter according to the ejection group, the liquid ejection amount according to the ejection group can be made different. For example, when the liquid is ink, recording is performed. The image quality can be improved.

  In the liquid droplet ejection apparatus of the present invention, the liquid ejected from the nozzle of the ejection group having a large ejection amount may be a pigment ink, and the liquid ejected from the nozzle of the ejection group having a small ejection amount is a dye Ink may be used.

  In this case, a discharge group having a large discharge amount is a group that discharges pigment ink, and a discharge group having a small discharge amount is a group that discharges dye ink. In other words, since the discharge amount of the pigment ink is larger than the discharge amount of the dye ink, even when the pigment ink is less likely to bleed than the dye ink, The balance of the spread (area) of the dye ink can be improved.

  In the droplet discharge device of the present invention, the pigment ink may be a black ink, and the dye ink may be a color ink.

  In this case, since the pigment ink is black ink and the dye ink is other color ink, the balance of the spread per drop of the black ink and other color ink on the recording medium is improved, and the recording quality is improved. Can be good.

  In the droplet discharge device of the present invention, the piezoelectric actuator may have a plurality of stacked piezoelectric layers. In this case, the deformation of the piezoelectric actuator can be increased, and the drive voltage applied to the active part can be kept low.

  In the droplet discharge device of the present invention, the length of the pressure chambers included in the first discharge group in the first direction is longer than the length of the pressure chambers included in the second discharge group in the first direction. Also good. In this case, a pressure chamber having a large capacity can be used for a liquid used in a large amount such as black ink.

  In the liquid droplet ejection apparatus of the present invention, the liquid droplet ejection apparatus may be an inkjet head that ejects ink droplets. In this case, since it is not necessary to set a driving voltage according to each ejection group, it is possible to simplify the power source and the control unit that controls the power source.

  Below, basic embodiment of this invention is described using FIGS. 1-8.

  FIG. 1 is an exploded perspective view of an inkjet head 100 which is an embodiment of a droplet discharge device. A plate-like piezoelectric actuator 2 is joined to a cavity unit 1 having a plurality of plates, and a flexible flat cable 3 for connection to an external device is joined to the upper surface of the piezoelectric actuator 2. Ink is ejected downward from a nozzle 4 (see FIG. 3) that opens on the lower surface of the cavity unit 1.

  As shown in FIG. 2, the cavity unit 1 is composed of eight thin plates including a nozzle plate 11, a spacer plate 12, a damper plate 13, two manifold plates 14 a and 14 b, a supply plate 15, a base plate 16, and a cavity plate 17. A flat plate is provided, and these flat plates are laminated and joined with an adhesive.

  In this embodiment, the thickness of each plate 11-17 is about 40-150 micrometers. The nozzle plate 11 is made of synthetic resin such as polyimide, and the other plates 12 to 17 are made of 42% nickel alloy steel plate. The nozzle plate 11 is formed with a plurality of nozzles 4 arranged at minute intervals. The diameter of each nozzle 4 is about 17 to 21 μm. The nozzles 4 are arranged in five rows along the long side direction (X direction) of the nozzle plate 11.

  The ink jet head 100 can eject four color inks of black ink (Bk), yellow ink (Y), magenta ink (M), and cyan ink (C) for color recording. In the ink jet head 100, five nozzle rows are formed. The same color ink is ejected from the nozzles belonging to each nozzle row. Two nozzle rows are used for discharging black ink, and one nozzle row is used for each of the other color inks (yellow, magenta, cyan).

  As shown in FIG. 3, the nozzle 4 is formed in the cavity plate 17 via a through passage 38 formed in the spacer plate 12, the damper plate 13, the two manifold plates 14 a and 14 b, the supply plate 15, and the base plate 16. The pressure chamber 36 communicates with the pressure chamber 36.

  As shown in FIG. 2, the cavity plate 17 has a plurality of pressure chambers 36 arranged in five rows along the long sides (X direction, second direction) of the cavity plate 17. Each pressure chamber 36 is formed in an elongated shape, and the length of the pressure chamber 36 parallel to the ink flow direction is larger than the width perpendicular to the pressure chamber 36. The longitudinal direction of the pressure chamber 30 is along the short side direction (Y direction, first direction) of the cavity plate 17. The pressure chamber 30 is formed as a through hole that penetrates the cavity plate 17. As shown in FIG. 3, one end 36 a in the longitudinal direction of each pressure chamber 36 communicates with the common ink chamber 7 via a communication hole 37 and a connection channel 40 which will be described later. The other end 36 b in the longitudinal direction of each pressure chamber 36 communicates with the through passage 38. Corresponding to the allocation of four color inks to the nozzle rows, in the pressure chambers 36 arranged in five rows, two pressure chamber rows are used for black ink, and the other three color inks (yellow, magenta, One pressure chamber row is used for each of cyan.

  A communication hole 37 connected to one end 36 a of the pressure chamber 36 is formed in the base plate 16 disposed below the cavity plate 17. A plurality of connection flow paths 40 for supplying ink from the common ink chamber 7 to the pressure chamber 36 are formed in the supply plate 15 disposed below the base plate 16. As shown in FIG. 3, the connection channel 40 has an inlet hole (inflow hole) 40 a through which ink flows from the common ink chamber 7, an outlet hole 40 b that opens facing the communication hole 37, an inlet hole, and an outlet. A constricted portion 40c formed between the holes and having a small cross-sectional area so as to have the largest flow path resistance in the connection flow path 40 is provided. This restricting portion prevents ink from flowing backward to the common ink chamber 7 side when the discharge pressure is applied to the pressure chamber 36, and allows the ink to efficiently flow to the nozzle 4 side, thereby causing ink to flow from the nozzle 4. It is formed for discharging.

  Two common ink chambers (manifold chambers) 7 that are long in the long side direction (X direction) are formed in the two manifold plates 14a and 14b. The common ink chamber 7 is formed as a through hole extending along the row of nozzles 4. As shown in FIG. 3, two common ink chambers 7 are formed by stacking two manifold plates 14a and 14b and covering the upper and lower surfaces with a supply plate 15 and a damper plate 13, respectively. Each common ink chamber 7 overlaps with a part of the pressure chamber 36 in plan view (viewed from the stacking direction of each plate), and extends in the row direction of the pressure chambers 36 (row direction of the nozzles 4). It is extended.

  2 and 3, a damper chamber 41 isolated from the common ink chamber 7 is formed as a groove (concave portion) on the lower surface side of the damper plate 13 disposed below the manifold plate 14a. As shown in FIG. 2, the position and shape of the damper chamber 41 in plan view coincide with the common ink chamber 7. Since the damper plate 13 is formed of an elastically deformable metal material, the thin plate-like ceiling portion on the upper side of the damper chamber 41 can freely vibrate toward the common ink chamber 7 side and the damper chamber 41 side. . Even when the pressure fluctuation generated in the pressure chamber 36 propagates to the common ink chamber 7 during ink ejection, the ceiling portion functions as a damper that absorbs and attenuates the pressure fluctuation by elastically deforming and vibrating. Yes (damper effect). Therefore, the phenomenon (crosstalk) in which the pressure fluctuation propagates to the other pressure chambers 36 can be suppressed.

  As shown in FIG. 2, four ink supply ports 42 are formed at one short side end of the cavity plate 17 as ink inlets to the cavity unit 1. Connection ports 43 are respectively formed at positions where the base plate 16 and the supply plate 15 overlap with the ink supply ports 42. The ink supplied from the ink source is supplied to one end portion in the longitudinal direction of the common ink chamber 7 through the ink supply port 42 and the connection port 43. A filter body 20 having a filtering part 20a corresponding to four ink supply ports 42 is attached to the cavity plate 17 with an adhesive or the like so as to cover the ink supply ports 42.

  In this embodiment, four ink supply ports 42 and four connection ports 43 are provided. In contrast, five common ink chambers 7 are provided. The ink supply port 42 located at the left end in FIG. 2 supplies ink to the two common ink chambers 7. In the present embodiment, black ink is supplied to the ink supply ports 42 that supply ink to the two common ink chambers 7 in consideration that black ink is used more frequently than other color inks. The other ink supply ports 42 are supplied with yellow, magenta, and cyan inks, respectively.

  The piezoelectric actuator 2 has a flat plate-like shape that can cover all the pressure chambers, similar to the known one disclosed in JP-A-2002-254634, etc. A plurality of ceramic layers stacked in a direction orthogonal to the thickness (thickness direction) and a plurality of electrodes (electrode layers) disposed on the surfaces of the plurality of ceramic layers are provided. Here, the piezoelectric actuator 2 is formed as follows. First, a mixture of ceramic powder, a binder, and a solvent is formed into a sheet having a thickness of about 15 to 40 μm to form a plurality of piezoelectric ceramic material sheets (green sheets). On the surface of the green sheet, an electrode is formed with a conductive paste by a printing method or the like. The piezoelectric actuator 2 is formed by laminating and firing a plurality of green sheets on which electrodes are formed.

  The electrodes include drive electrodes (individual electrodes 46 formed corresponding to the pressure chambers 36 and common electrodes 47 formed across the plurality of pressure chambers 24), and surface electrodes 48. The individual electrodes 46 and the common electrodes 47 are alternately arranged with the ceramic layers sandwiched in the stacking direction of the ceramic layers. The surface electrode 48 is disposed on the uppermost surface of the piezoelectric actuator 2 (surface opposite to the cavity unit side). The surface electrode 48 is connected to the individual electrode 46 and the common electrode 47 through electrical through holes (see FIG. 1), and each surface electrode 48 is electrically connected to the flexible flat cable 3.

  In the piezoelectric actuator 2 in which the electrodes are arranged in a layer like this, a portion of the ceramic layer sandwiched between both electrodes is polarized by applying a high voltage between the individual electrode 46 and the common electrode 47 as is well known. Is done. The part of the polarized ceramic layer becomes an active part 54 having piezoelectric characteristics. In this embodiment, as will be described later, active portions 54 are formed in a plurality of ceramic layers (hereinafter referred to as a base piezoelectric layer 51), and these active portions 54 overlap in the stacking direction of the piezoelectric layers. As shown in FIG. 5, the individual electrode 46 is formed in an elongated shape corresponding to the shape of the pressure chamber 36, and the common electrode 47 is formed in a wide shape covering the plurality of pressure chambers 36. The shape of the active portion 54 is equal to the shape of the overlapping portion between the individual electrode 46 and the common electrode 47. In FIG. 5, the active part 54 is shown by hatching.

  The ceramic layer includes a base piezoelectric layer 51 in which an active portion 54 sandwiched between the individual electrode 46 and the common electrode 47 is formed, and a bottom that is disposed between the base piezoelectric layer 51 and the cavity unit 1 and does not include the active portion 54. It includes a layer 52 and a top layer 53 that is disposed on the opposite side of the base piezoelectric layer 51 from the cavity unit 1 and does not include the active portion 54.

  The top layer 53 suppresses the active portion 54 so that the active portion 54 does not deform so as to protrude toward the side opposite to the pressure chamber 36 (on the top layer 53 side), and the displacement (deformation) of the active portion 54 is reduced. It is provided for efficient transmission to the chamber 36 side. The bottom layer 52 is provided to prevent the ink in the pressure chamber 36 from penetrating into the piezoelectric actuator 2 covering the opening of the pressure chamber 36 and short-circuiting between the electrodes. In the piezoelectric actuator 2 of this embodiment, a single-layer bottom layer 52, a multilayer base piezoelectric layer 51, and a top layer 53 are formed. FIG. 4 illustrates the piezoelectric actuator 2 formed by four base piezoelectric layers 51, one bottom layer 52, and two top layers 53. In the present application, one layer refers to a ceramic layer formed from one green sheet. For example, it is assumed that two layers are formed even if the two green sheets are integrated with each other without being sandwiched between the two electrode sheets and are fired.

  The plate-type piezoelectric actuator 2 is stacked on the cavity unit 1 and fixed with an adhesive or the like so that the stacking direction of the piezoelectric layers and the stacking direction of the piezoelectric actuator 2 and the cavity unit 1 coincide. At this time, the individual electrodes 46 of the piezoelectric actuator 2 and the pressure chambers 36 formed in the cavity unit 1 are arranged so as to overlap each other. The flexible flat cable 3 (see FIG. 3) is joined to the upper surface of the piezoelectric actuator 2, and the pattern wiring (not shown) of the flexible flat cable 3 is electrically joined to the surface electrode 48.

  In the inkjet head 100 of the embodiment, the nozzle pitch (resolution in the X direction) is set to 75 dot per inch (dpi) in order to arrange the nozzles with high density. The pressure chambers 36 are formed in the cavity plate 17 at a pitch corresponding to the nozzle pitch 75 dpi. In order to ensure manufacturing stability when forming the pressure chamber 36 in the cavity plate 17, the width W (see FIG. 5) in the direction perpendicular to the ink flow in the pressure chamber 36 is 260 ± 20 μm. It is desirable to be. In this case, in the pressure chamber row, the interval W0 between the adjacent pressure chambers 36 is about 80 μm. The nozzles may be arranged at a higher density so that the nozzle pitch is 75 dpi or more.

  In the inkjet head 100, color ink (yellow, magenta, cyan) is mainly used for image recording, and black ink is mainly used for text recording. There has been a demand to increase the recording speed by increasing the discharge amount of one drop of black ink compared to color ink. Further, in order to increase the sharpness of black in character recording and to make the color vivid, pigment ink may be used as black ink and dye ink may be used as the other three colors of ink. In this case, since the pigment ink has the property of hardly bleeding, even if the same volume of the pigment ink and the dye ink are ejected onto the recording medium to form the dots, the dots of the pigment ink are the same as those of the dye ink. It is formed smaller than a dot. Therefore, in order to improve the dot balance (recording quality) between the black ink as the pigment ink and the color ink as the dye ink, there has been a demand for increasing the discharge amount per drop of the black ink.

  Therefore, in this embodiment, the diameter of the nozzle 4 for black ink is made larger than the diameter of the nozzle 4 for color ink, and the volume of the pressure chamber 36 for black ink is set to the pressure chamber 36 for color ink. Larger than the volume. Here, the diameter of the nozzle for black ink is 20.5 μm, and the diameter of the nozzle for color ink is 17.0 μm.

  The width of the pressure chamber 36 is defined so as to maintain the above-mentioned 75 dpi nozzle pitch, and the depth of the pressure chamber 36 is defined by the uniform thickness of the cavity plate 17. However, since the length of the pressure chamber 36 for black ink is longer than the length of the pressure chamber 36 for color ink, the volume of the pressure chamber 36 for black ink is It is larger than the volume with the pressure chamber 36 for ink. Specifically, the length Lb of the pressure chamber 36 for black ink is 1.4 ± 0.1 mm to 1.5 ± 0.1 mm (hereinafter referred to as 1.4 mm), and other color inks (yellow, magenta The length Lc of the pressure chamber 36 for cyan) is 1.1 ± 0.1 mm to 1.2 ± 0.1 mm (hereinafter referred to as 1.1 mm).

  In order to efficiently transmit the deformation (displacement) of the active portion 54 to the pressure chamber 36, the active portion 54 is formed in a shape slightly smaller than the pressure chamber 36 (see FIG. 5). Corresponding to the difference between the length of the pressure chamber 36 for black ink and the length of the pressure chamber 36 for color ink, the active portion 54 for black ink is formed longer than the active portion 54 for color ink. Yes. Here, the length Pb of the active portion 54 for black ink is 1.2 mm, and the length Pc of the active portion 54 for other color inks (yellow, magenta, cyan) is 0.9 mm ( Pb> Pc).

  In determining the width of the active portion 54, the applicant of the present application first sets the width wb of the active portion 54 for black ink and the width wc of the active portion 54 for color ink to 160 μm (wb = wc = 160 μm). A discharge experiment was performed using ink jet heads having only different active portion lengths. FIG. 6 shows the result of the discharge experiment.

  In the discharge experiment, for 16 (No. 1 to No. 16) ink jet heads 100, black ink (shown as “Bk”), which is necessary to discharge ink droplets at a predetermined discharge speed (9 m / s), is illustrated. ) Driving voltage of the active portion 54 and the driving voltage of the active portion 54 for color ink (shown as “CL”) necessary for discharging ink droplets at a predetermined discharge speed (9 m / s). It was. The item “voltage difference” in FIG. 6 shows the difference between the driving voltage of the active portion 54 for black ink and the driving voltage of the active portion 54 for color ink. The average of 16 ink jet heads 100 was found to be 0.6V. In this way, when the width of the active portion 54 for black ink is the same as the width of the active portion 54 for color ink, the voltage difference becomes 0.6 V, so that the control device (drive for controlling the drive voltage) In an IC or the like (not shown), it is necessary to set the driving voltage value for black ink and the driving voltage value for color ink separately, which increases the cost of the control device.

  Therefore, the applicant of the present application repeatedly performed the same discharge experiment as described above, with the active portion 54 for black ink and the active portion 54 for color ink being different not only in length but also in width. As a result, it is confirmed that the drive voltage applied to the active portion 54 is almost the same by setting the width wb of the active portion 54 for black ink to 160 μm and the width wc of the active portion 54 for color ink to 154 μm. did. The result of this discharge experiment is shown in FIG. The length of the active portion 54 is the same as the length of the active portion 54 in the experiment shown in FIG. FIG. 7 shows the results of measurements performed on 26 inkjet heads 100. The average “voltage difference” between the driving voltage for black ink and the driving voltage for color ink when ejecting ink droplets at a predetermined speed (9 m / s) was 0.1V. With such a small voltage difference, ink droplets can be ejected at the same ejection speed even if the drive voltage value set in the control device is set to the same value for black ink and color ink in advance.

  That is, even when the discharge amount per drop of black ink is larger than the discharge amount per drop of other color inks, the width of the long active portion 54 (for black ink) is widened and short. By narrowing the width of the active portion 54 (for other color inks), all the active portions 54 can be driven with the same drive voltage, and the discharge speed of the discharged droplets can be made the same.

  By the way, when the cavity unit 1 and the piezoelectric actuator 2 are joined (assembled), the pressure chamber 36 and the active portion 54 may be misaligned. If the displacement is large, the displacement of the active portion 54 is not efficiently transmitted to the pressure chamber 36, and as a result, ink droplets can be ejected only at a speed lower than a predetermined speed.

  According to the experiment by the applicant of the present application, when the active portion 54 for black ink is longer than the active portion 54 for color ink and has the same width, as shown in FIG. It has been found that the decrease in the ejection speed with respect to the displacement amount is more sensitive in the active portion for color ink than in the active portion for black ink. This is because the area of the active portion 54 for color ink is smaller than the area of the active portion 54 for black ink, and the energy of displacement is small, so even if the amount of displacement is the same, the ejected droplets This is thought to be due to the greater impact.

  When the width of the active portion 54 for color ink is made narrower than the width of the active portion 54 for black ink, that is, the width of the short active portion 54 is made narrower than the width of the long active portion, the drive as described above is performed. In addition to the effect of making the voltage the same, there is also an effect that the sensitivity of the discharge decrease with respect to the positional deviation in the width direction can be made dull. As a result, even if a positional deviation occurs when the cavity unit 1 and the piezoelectric actuator 2 are joined, it is possible to suppress the occurrence of variations in ejection characteristics between the black ink and other color inks.

  In the above embodiment, an ink jet head that discharges ink is exemplified as the droplet discharge device. However, the present invention can be applied to a device that applies a colored liquid to a medium, a device that forms a thin film on a medium, or one or more The present invention can also be applied to an apparatus that quantitatively discharges liquid.

  In the above embodiment, the active portion (and the pressure chamber and nozzle corresponding to the active portion) are divided into two discharge groups (first discharge group and second discharge) according to the color of the liquid to be discharged (difference in discharge amount). The length and width of the active portion 54 are determined so that all the discharge groups have the same drive voltage and the same discharge speed. However, the method of dividing the discharge group is not limited to the color of the liquid, and depending on the purpose, it may be divided according to other physical properties of the liquid (for example, surface tension, viscosity, etc.). Alternatively, it may be divided according to a difference in discharge conditions such as a discharge amount. For example, different discharge speeds may be set for each discharge group, or the discharge groups may be divided according to the difference in physical properties, and the discharge amount may be set to be the same.

It is a disassembled perspective view of the inkjet head as a droplet discharge device. It is a disassembled perspective view of a cavity unit. FIG. 3 is a cross-sectional view taken along line III-III in FIG. 1. FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. 3. It is explanatory drawing which shows the positional relationship of a pressure chamber and an active part. It is a figure which shows the result of a discharge experiment. It is a figure which shows the result of another discharge experiment. It is a figure which shows the fall of the discharge speed with respect to positional offset amount.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Cavity unit 2 Piezoelectric actuator 3 Flexible flat cable 4 Nozzle 36 Pressure chamber 46 Individual electrode 47 Common electrode 48 Surface electrode 54 Active part 100 Inkjet head

Claims (11)

A liquid droplet ejection device that ejects liquid droplets onto an object,
A plurality of nozzles, and cavity units each having a plurality of pressure chambers corresponding to the nozzles and extending in the first direction;
Piezoelectric actuators that are stacked on the cavity unit so as to cover a plurality of the pressure chambers, are arranged corresponding to the pressure chambers respectively, and the volume of the pressure chambers is changed by applying a predetermined driving voltage, And a piezoelectric actuator having a plurality of active portions long in the first direction,
The plurality of active portions, the nozzles, and the pressure chambers form a first discharge group and a second discharge group,
The length in the first direction of the active part included in the first discharge group is longer than the length in the first direction of the active part included in the second discharge group,
The length of the active part included in the first discharge group in the second direction orthogonal to the first direction is longer than the length of the active part included in the second discharge group in the second direction. ,
A droplet discharge apparatus in which a drive voltage applied to an active portion included in a first discharge group is the same as a drive voltage applied to an active portion included in a second discharge group.   The liquid droplet ejection apparatus according to claim 1, wherein the physical properties of the liquid ejected from the first ejection group are different from the physical properties of the liquid ejected from the second ejection group.   The droplet discharge device according to claim 1, wherein discharge conditions are different between the first discharge group and the second discharge group.   2. The droplet discharge device according to claim 1, wherein the first discharge group and the second discharge group have substantially the same speed of liquid discharged from the nozzle at the drive voltage.   The first discharge group and the second discharge group are set to have different discharge amounts, and the first of the active portions of the discharge group having a large discharge amount among the first discharge group and the second discharge group. The length in the direction and the length in the second direction are respectively larger than the length in the first direction and the length in the second direction of the active portion of the discharge group with a small discharge amount. The liquid droplet ejection apparatus described.   The droplet discharge device according to claim 5, wherein the diameter of the nozzle of the discharge group having a large discharge amount is larger than the diameter of the nozzle of the discharge group having a small discharge amount.   The liquid droplet ejection according to claim 5, wherein the liquid ejected from the nozzle of the ejection group having a large ejection amount is pigment ink, and the liquid ejected from the nozzle of the ejection group having a small ejection amount is a dye ink. apparatus.   The liquid droplet ejection apparatus according to claim 7, wherein the pigment ink is a black ink, and the dye ink is a color ink.   The droplet discharge device according to claim 1, wherein the piezoelectric actuator has a plurality of stacked piezoelectric layers.   2. The droplet discharge device according to claim 1, wherein the length of the pressure chamber included in the first discharge group in the first direction is longer than the length of the pressure chamber included in the second discharge group in the first direction. .   The droplet discharge device according to claim 1, wherein the droplet discharge device is an inkjet head that discharges ink droplets.

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