JP4457818B2 - Inkjet head - Google Patents

Description

  The present invention relates to an inkjet head that performs printing by discharging ink onto a recording medium.

  In an ink jet printer, an ink jet head distributes ink supplied from an ink tank to a plurality of pressure chambers, and discharges ink from nozzles by selectively applying pressure to each pressure chamber. As one means for selectively applying pressure to the pressure chamber, a plurality of laminated piezoelectric sheets made of ceramic may be used.

  As an example of such an inkjet head, a plurality of continuous flat plate-like piezoelectric sheets straddling a plurality of pressure chambers arranged two-dimensionally in a matrix are stacked, and at least one piezoelectric sheet is shared by a number of pressure chambers. There is known one having one actuator unit sandwiched between a common electrode held at a ground potential and a large number of individual electrodes disposed at positions facing each pressure chamber (Patent Document 1). reference). In this inkjet head, a plurality of individual electrodes and a plurality of grounding electrodes arranged so as to surround the individual electrodes are formed on the upper surface of the actuator unit, and each grounding electrode and the common electrode are through holes. It is electrically connected through a conductive material filled therein. The plurality of grounding electrodes and the plurality of individual electrodes are respectively connected to a plurality of power supply pads of a flexible printed circuit (FPC) on which a driver IC is mounted. In this configuration, when a driving voltage is supplied from the driver IC to the individual electrode and the individual electrode is set to a different potential from the common electrode, the portion of the piezoelectric sheet sandwiched between the individual electrode and the common electrode and polarized in the stacking direction is activated. The layer expands and contracts in the stacking direction due to the so-called piezoelectric longitudinal effect. As a result, the volume in the pressure chamber fluctuates, and ink can be ejected from the nozzle communicating with the pressure chamber toward the print medium.

JP 2003-305852 A

  However, in the ink jet head described in Patent Document 1 described above, the individual electrodes are disposed only in the region facing the plurality of pressure chambers in the piezoelectric sheet, and therefore only the region between the plurality of individual electrodes and the common electrode. Is polarized. This polarization is usually performed by supplying a voltage to each of the individual electrodes and the common electrode so as to cause a high potential difference when the inkjet head is manufactured. Due to this polarization, an internal stress difference is generated in the piezoelectric sheet due to polarization and non-polarization locations. In such an ink-jet head, in order to meet the demand for higher density and higher resolution, polarization portions have been arranged close to each other. The internal stress possessed by this polarization location induces strain in the surrounding piezoelectric sheet. Therefore, when a plurality of pressure chambers are densely arranged adjacent to each other, the piezoelectric sheet corresponding to the pressure chamber is also affected by the internal stress from the side of the piezoelectric sheet corresponding to the neighboring pressure chamber, and distortion is induced. . This distortion may cause variations in ink ejection characteristics. That is, if the pressure chamber related to ink ejection is a pressure chamber other than the pressure chamber located on the outermost side in the arrangement direction, the distortion of the piezoelectric sheet region facing the pressure chamber from one side in the arrangement direction and the pressure The strain induced from the other side of the chamber is the same. On the other hand, when the pressure chamber for ink ejection is the outermost pressure chamber with respect to the arrangement direction, there is a polarized region of the piezoelectric sheet only on the inner side in the arrangement direction with respect to the pressure chamber. The sheet region is affected by internal stress from the inside in the arrangement direction, but is hardly affected by internal stress from the outside in the arrangement direction. For this reason, the ink ejection characteristics are significantly different between the nozzles related to the outermost pressure chambers in the arrangement direction and the nozzles related to the other pressure chambers.

  Accordingly, an object of the present invention is to provide an ink jet head capable of suppressing variations in ink ejection characteristics.

Means for Solving the Problems and Effects of the Invention

  The inkjet head according to the present invention includes a flow path unit formed with a plurality of pressure chambers each communicating with a nozzle, a plurality of individual electrodes each facing the pressure chamber, and an arrangement direction of the plurality of individual electrodes. A peripheral electrode spaced outward from the outermost individual electrode in the arrangement direction, the plurality of individual electrodes and a common electrode formed across the peripheral electrode, the plurality of individual electrodes and the peripheral electrode, and the common And an actuator unit having a piezoelectric sheet sandwiched between electrodes. In the piezoelectric sheet, a region sandwiched between the peripheral electrode and the common electrode and a region sandwiched between the individual electrode and the common electrode are polarized to substantially the same extent, The peripheral electrodes are electrically connected to each other via a conductive member disposed on the actuator unit.

  As a result, the region sandwiched between the peripheral electrode and the common electrode in the piezoelectric sheet and the region sandwiched between the individual electrode and the common electrode in the piezoelectric sheet are both polarized to substantially the same degree. The variation in ink ejection characteristics between the nozzles related to the outermost pressure chamber and the nozzles related to other pressure chambers can be suppressed. In addition, since the plurality of peripheral electrodes are electrically connected to each other via the conductive member disposed on the actuator unit, it is necessary to join the wiring necessary for performing the polarization treatment to each of the plurality of peripheral electrodes. The wiring structure is simplified.

  In the present invention, it is preferable that the plurality of pressure chambers are two-dimensionally arranged in a matrix, and the plurality of peripheral electrodes surround the plurality of individual electrodes. As a result, even when a large number of pressure chambers are two-dimensionally arranged in a matrix, variation in ink ejection characteristics between the nozzles related to the outermost pressure chamber and the nozzles related to other pressure chambers in the arrangement direction can be reduced. Can be suppressed.

  Further, at this time, the flow path unit is formed with a plurality of common ink chambers in which ink is stored, and the plurality of pressure chambers communicates with any one of the common ink chambers. The electrodes may be electrically connected to each other via one conductive member. Thereby, since all the peripheral electrodes are electrically connected by one conductive member, the wiring structure necessary for performing polarization is further simplified.

  Further, at this time, the flow path unit is formed with a plurality of common ink chambers for storing ink corresponding to a plurality of ink colors, and the plurality of pressure chambers are provided in any one of the common ink chambers. The plurality of peripheral electrodes are connected to each other, and at least a plurality of chromatic color peripheral electrodes associated with the common ink chamber for storing chromatic ink, and a plurality of peripheral electrodes for the common ink chamber for storing achromatic ink. A peripheral electrode for achromatic color. The plurality of chromatic color peripheral electrodes are electrically connected to each other through one conductive member, and the plurality of achromatic color peripheral electrodes electrically connect the plurality of chromatic color peripheral electrodes. They may be electrically connected to each other via one other conductive member other than the one conductive member connected to the. As a result, it is possible to supply a voltage by distinguishing between the plurality of chromatic color peripheral electrodes and the plurality of achromatic color peripheral electrodes. Therefore, power consumption can be reduced.

  Further, at this time, the plurality of peripheral electrodes store the common ink chamber for storing chromatic color ink and achromatic color ink separately from the plurality of chromatic color peripheral electrodes and the plurality of achromatic color peripheral electrodes. A boundary edge electrode with the common ink chamber is further included. Then, the plurality of boundary peripheral electrodes distinguish one of the plurality of chromatic color peripheral electrodes and the plurality of achromatic color peripheral electrodes from each other and electrically connect the other one of the conductive members. It may be electrically connected via a member. Thus, the plurality of boundary peripheral electrodes can be supplied with voltages separately from the plurality of chromatic color peripheral electrodes and the plurality of achromatic color peripheral electrodes. Therefore, power consumption can be further reduced.

  Also, at this time, the flow path unit is formed with a plurality of common ink chambers for storing ink, and the plurality of pressure chambers communicate with any one of the common ink chambers, and the same common A plurality of peripheral electrodes related to the ink chambers are electrically connected to each other via the one conductive member, and a plurality of peripheral electrodes related to different common ink chambers are connected via the one conductive member. Are not necessarily electrically connected to each other. Thereby, power consumption can be reduced.

  At this time, the conductive member may connect regions of the peripheral electrode farthest from the individual electrode. Accordingly, it is possible to minimize the adverse effect of the region facing the pressure chamber located on the outermost side in the arrangement direction in the piezoelectric sheet due to the deformation of the region facing the conductive member in the piezoelectric sheet.

  Also, at this time, the plurality of individual electrodes and the plurality of peripheral electrodes are both arranged in an elongated shape so that the longitudinal direction thereof faces the same direction, and the conductive member is arranged in the longitudinal direction of the peripheral electrodes. The end vicinity regions may be connected to each other. As a result, even if both the individual electrode and the peripheral electrode are elongated, the region facing the outermost pressure chamber in the piezoelectric sheet is adversely affected by the deformation of the region facing the conductive member in the piezoelectric sheet. Can be minimized.

  Further, at this time, the individual electrode has a lead-out region extending along the longitudinal direction at the longitudinal end portion, and the peripheral electrode extends along the longitudinal direction at the longitudinal end portion. The connection region of the peripheral electrode may be formed at the end on the same side as the lead region of the individual electrode adjacent to the peripheral electrode. Thereby, it is possible to further suppress variations in ink ejection characteristics between the nozzles related to the pressure chambers on the outermost side in the arrangement direction and the nozzles related to the other pressure chambers.

  At this time, the flow path unit is formed with a plurality of common ink chambers extending in one direction in which ink is stored, and the plurality of pressure chambers communicate with any one of the common ink chambers. The longitudinal directions of the plurality of individual electrodes and the plurality of peripheral electrodes may be orthogonal to the one direction. Thereby, it becomes possible to arrange a plurality of individual electrodes and peripheral electrodes.

  Further, at this time, on the surface of the actuator unit opposite to the surface in contact with the flow path unit, a surface electrode electrically connected to the common electrode further outside the individual electrode and the peripheral electrode May be formed. Thereby, since the peripheral electrode is formed between the individual electrode and the surface electrode on the same plane, it is possible to prevent the individual electrode and the surface electrode from being electrically connected due to migration.

  Moreover, in this invention, it is preferable that the said peripheral electrode has the same planar size and planar shape as the said individual electrode. In the present invention, it is preferable that a peripheral gap facing the peripheral electrode is formed in the flow path unit. Moreover, in this invention, it is preferable that the said peripheral space | gap has the same planar size and planar shape as the said pressure chamber. Moreover, in this invention, it is preferable that the distance between the said peripheral space | gap and the outermost pressure chamber is equal to the distance between the said adjacent pressure chambers regarding the said arrangement direction. Thereby, it is possible to further suppress variations in ink ejection characteristics between the nozzles related to the pressure chambers on the outermost side in the arrangement direction and the nozzles related to the other pressure chambers.

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

  FIG. 1 is a schematic perspective view illustrating the internal configuration of a color inkjet printer to which an inkjet head according to an embodiment of the present invention is applied. In FIG. 1, a head unit 2 is disposed in the color inkjet printer 1. To the holder 3 of the head unit 2, an ink tank 4 for storing inks of four colors, magenta, yellow, cyan, and black, and an ink jet head 5 (see FIG. 3) for discharging the inks of four colors are fixed. The holder 3 is fixed to a carriage 11 that reciprocates in a linear direction by a drive mechanism 10. The platen roller 18 serving as a conveying unit that conveys the paper P as a recording medium is disposed so that its axis is along the reciprocating direction of the carriage 11, and faces the inkjet head 5.

  The carriage 11 is slidably supported by a guide shaft 12 and a guide plate 13 that are arranged in parallel with the support shaft of the platen roller 18. Pulleys 14 and 15 are supported in the vicinity of both ends of the guide shaft 12, and an endless belt 16 is bridged between the pulleys 14 and 15. The carriage 11 is fixed at an appropriate position of the endless belt 16.

  In such a configuration of the driving mechanism 10, when one pulley 14 rotates forward and backward by driving the motor 17, the carriage 11 reciprocates in the linear direction (main scanning direction) along the guide shaft 12 and the guide plate 13. Accordingly, the head unit 2 also reciprocates.

  The paper P is fed from a paper feed cassette (not shown) provided on the side of the ink jet printer 1, guided to the space between the ink jet head 5 and the platen roller 18, and discharged from the ink jet head 5. The paper is ejected after printing is performed. In FIG. 1, the paper feed mechanism and paper discharge mechanism for paper P are not shown.

  Further, a purge mechanism 20 shown at the lower left in FIG. 1 is provided in the inkjet printer 1. The purge mechanism 20 covers a part of the lower surface of the inkjet head 5 with a purge cap 21 and forcibly sucks and removes defective ink containing bubbles and dust accumulated in the inkjet head 5. .

  That is, the inkjet head 5 is restored by being sucked by the pump 23 by the drive of the cam 22 and discarded in the waste ink reservoir 24. Note that the four caps 25 shown in FIG. 1 cover all the nozzles 53 of the inkjet head 5 on the carriage 11 returned to the reset position (position facing the purge mechanism 20) after printing is completed, thereby drying the ink. It is for preventing.

  FIG. 2 is a perspective view of the head unit 2 shown in FIG. FIG. 3 is a cross-sectional view taken along the line II-II in FIG. 2 and shows a state where the ink tank 4 and the inkjet head 5 are assembled to the holder 3 constituting the head unit 2. 4 is a perspective view showing a state in which a frame is bonded to the inkjet head 5 shown in FIG. As shown in FIG. 2, the head unit 2 includes a holder 3 having a substantially rectangular parallelepiped shape, an ink tank 4 disposed in the holder 3, and an inkjet head 5 disposed below the ink tank 4 (see FIG. 3). And.

  The ink tank 4 is formed with four ink chambers 6 in which magenta, yellow, cyan, and black inks are respectively stored in order from the left in FIG. The ink chamber 6 is connected to a corresponding tube 29 (see FIG. 2), and ink of each color is supplied. The ink tank 4 is assembled to a frame 30 having a planar rectangular shape. The frame 30 is fixed to the holder 3 with an ultraviolet curable adhesive 31. The ink jet head 5 is fixed to the frame 30 such that the actuator unit 42 is disposed in the window 32.

  The inkjet head 5 includes a flow path unit 41 in which a plurality of ink flow paths are formed for each color, and an actuator unit 42 that is bonded to the upper surface of the flow path unit 41 with an epoxy-based thermosetting adhesive. The head main body 40 and a flexible printed wiring board (FPC) 50 joined to the upper side of the head main body 40 are included. As shown in FIG. 4, both the flow path unit 41 and the actuator unit 42 are configured by laminating a plurality of thin plates having a rectangular planar shape, and are disposed below the ink tank 4. On the upper surface of the flow path unit 41, four ink supply ports 41a (see FIG. 5) having an elliptical planar shape are formed so as to avoid the actuator unit. The flow path unit 41 is bonded to the frame 30 so that the through holes 33 formed in the frame 30 and the ink supply ports 41 a formed in the flow path unit 41 are connected to each other. With this configuration, the ink in the ink tank 4 passes through the ink outlet 7 of the ink tank 4 and the through hole 33 of the frame 30 to the channel unit 41 from the corresponding ink supply port 41 a of the channel unit 41. Supplied.

  As shown in FIG. 3, the head main body 40 is disposed in the stepped window 8a of the holder 3 so that the ink discharge surface 40a is exposed to the outside. A sealant 35 is disposed in the gap between the holder 3 and the flow path unit 41. The bottom surface of the head body 40 is an ink ejection surface 40a on which a large number of nozzles 53 having a minute diameter are arranged.

  The FPC 50 bonded to the upper surface of the actuator unit 42 is pulled out to one side in the main scanning direction as shown in FIG. 3, and is pulled upward while being bent. An aluminum plate 34 is disposed on the upper surface of the FPC 50. The aluminum plate 34 dissipates the heat generated by the actuator unit 42 and makes it uniform so that a temperature difference does not partially occur in the actuator unit 42.

  The FPC 50 joined to the actuator unit 42 is pulled out along the side surface of the ink tank 4 through an elastic member 27 such as a sponge, and a driver IC 51 is installed on the FPC 50. On the other hand, the FPC 50 is electrically joined to the actuator unit 42 by soldering so as to transmit the ejection signal, the standby signal, and the reference signal output from the driver IC 51 to the actuator unit 42.

  The base end of the FPC 50 is connected to a control unit 101 (see FIG. 11) provided in the inkjet printer 1. As will be described later, the control unit 101 sequentially instructs the ink discharge amount from each nozzle 53 and also sequentially specifies the potential of the peripheral electrode 65, and three waveform patterns corresponding to three different ink discharge amounts. A signal, a high potential signal held at a positive potential called a standby potential (for example, 20V), a low potential signal held at a positive potential (for example, 3.3V) lower than the high potential signal, and a ground potential The held reference signal is supplied to the driver IC 51. Based on these signals, the driver IC 51 generates an ejection signal for each individual electrode that alternately repeats the standby potential and the ground potential. Further, a standby signal is generated for each peripheral electrode 65 based on the low potential signal.

  In FIG. 3, a window 8b for dissipating heat of the driver IC 51 to the outside is formed on the side wall of the holder 3 facing the driver IC 51. A heat sink 28 made of an aluminum plate is disposed between the driver IC 51 and the window 8b. The driver IC 51 is pressed against the heat sink 28 by the elastic member 27 with the FPC 50 interposed therebetween. The heat generated by the driver IC 51 can be efficiently dissipated by the heat sink 28 and the window 8b. Further, a sealing agent 36 for filling a gap between the side wall of the holder 3 and the heat sink 28 is disposed in the window 8b, and dust and ink are prevented from entering the head unit 2 from the outside.

  FIG. 5 is a plan view of the inkjet head 5. As shown in FIG. 5, the head body 40 of the inkjet head 5 has a rectangular planar shape extending in the longitudinal direction (sub-scanning direction) of the flow path unit 41. In FIG. 5, four manifolds (common ink chambers) 45 extending in parallel with each other along the longitudinal direction of the flow path unit 41 are formed in the flow path unit 41. Ink is supplied from the ink chamber 6 of the ink tank 4 to the manifolds 45 through the four ink supply ports 41 a of the flow path unit 41. In the present embodiment, the four manifolds 45 in FIG. 5 are the manifolds 45M, 45Y, 45C, and 45K corresponding to magenta, yellow, shear, and black in order from the top to the bottom. Of these four manifolds 45M, 45Y, 45C, and 45K, the three manifolds 45M, 45Y, and 45C are arranged at equal intervals in the width direction (main scanning direction) of the flow path unit 41, and the manifold 45K includes three manifolds 45K. It is formed at a position (a position below the flow path unit 41 in FIG. 5) that is separated from the manifold 45C at an interval larger than the arrangement interval of the manifolds 45M, 45Y, 45C. Further, a filter 44 is disposed at a position on the upper surface of the flow path unit 41 and covering the four ink supply ports 41a. The filter 44 has a plurality of micro holes formed at positions overlapping the ink supply ports 41a. As a result, dust in the ink supplied from the ink tank 4 into the flow path unit 41 is captured by the filter 44.

  On the upper surface of the flow path unit 41, an actuator unit 42 having a rectangular planar shape is bonded to a substantially central portion avoiding the ink supply port 41a. A large number of pressure chambers 46 (see FIG. 7) and voids 55 (see FIG. 6) arranged in a matrix are formed in the adhesion region of the flow path unit 41 facing the actuator unit 42. In other words, the actuator unit 42 has dimensions over all the pressure chambers 46 and the gaps (peripheral gaps) 55.

  FIG. 6 is an enlarged view of a region surrounded by a one-dot chain line drawn in FIG. In the flow path unit 41, 16 pressure chamber rows 47 in which a plurality of pressure chambers 46 are arranged in parallel with the extending direction of the manifold 45 (arrangement direction A), and a large number of gaps 55 are in parallel with the pressure chamber rows 47. 6 gap rows 56 and four gap rows 57 in which a large number of gaps 55 are arranged in a direction perpendicular to the extending direction of the manifold 45 (arrangement direction C) are formed. As shown in FIG. 6, two gap rows 57 are arranged at one end in the sub-scanning direction in the adhesion region of the flow path unit 41 facing the actuator unit 42. Actually, two gap rows 57 are formed at both ends of the adhesion region, and a total of four gap rows 57 extending in the arrangement direction C (main scanning direction) are formed in the flow path unit 41. Yes. The sixteen pressure chamber rows 47 are separated into twelve groups and four groups by a group of four gap rows 56 formed adjacent to each other. As a result, the 12 groups and the 4 groups of the pressure chamber row 47 are surrounded by the six gap rows 56 and the four gap rows 57, respectively. As shown in FIG. 6, the pressure chamber 46 and the gap 55 have the same planar shape and planar size. The plurality of pressure chambers 46 and the gaps 55 are regularly arranged so that one arrangement pattern is formed in the flow path unit 41 when the two are considered indistinguishable.

  The pressure chamber 46 formed in the flow path unit 41 has a substantially rhombic planar shape with rounded corners, and the longer diagonal line is the width direction of the flow path unit 41 (main scanning direction). Parallel to One end of each pressure chamber 46 communicates with the nozzle 53, and the other end communicates with the manifold 45 via the aperture 54. As a result, each manifold 45 is connected to a number of individual ink flow paths 9 (see FIG. 7) that communicate with the nozzles 53 and are formed for each pressure chamber 46. In FIG. 6, the pressure chamber 46, the gap 55, the aperture 54, the nozzle 53, and the like that are to be drawn with broken lines in the flow path unit 41 are drawn with solid lines for easy understanding of the drawing.

7 is a cross-sectional view showing the individual ink flow path, and is a cross-sectional view taken along the line VII-VII shown in FIG. As can be seen from FIG. 7, each nozzle 53 communicates with the manifold 45 through a pressure chamber 46 and an aperture (that is, a throttle) 54. That is, one flow path is formed from the outlet of the manifold 45 to the nozzle 53 through the aperture 54 and the pressure chamber 46. In this way, the individual ink channels 9 are formed in the head body 40 for each pressure chamber 46.

  The head body 40 includes a flow path unit 41 and an actuator unit 42. Among these, the flow path unit 41 has a laminated structure in which a total of nine sheet materials of a cavity plate 81, a base plate 82, an aperture plate 83, a supply plate 84, manifold plates 85 to 88, and a nozzle plate 89 are laminated from the top. It has become.

  As will be described in detail later, the actuator unit 42 is a laminated body of four piezoelectric sheets 91 to 94 (see FIG. 8). Of the four piezoelectric sheets 91 to 94, only the uppermost layer is a layer having a portion that becomes an active portion when an electric field is applied (hereinafter simply referred to as “layer having an active portion”), and the remaining three layers are This is a non-active layer having no active part. Note that the total number of layers having active portions is appropriately determined according to the required amount of displacement of the actuator unit 42, and is not limited to one layer as in the present embodiment. That is, a plurality of layers can be stacked.

  The cavity plate 81 is a metal plate in which a large number of substantially rhombic holes constituting the pressure chamber 46 and the gap 55 are provided in the pasting range (adhesion region) of the actuator unit 42. The base plate 82 is a metal plate provided with a communication hole between the pressure chamber 46 and the aperture 54 and a communication hole from the pressure chamber 46 to the nozzle 53 with respect to one pressure chamber 46 of the cavity plate 81.

  The aperture plate 83 is a metal plate in which a communication hole from the pressure chamber 46 to the nozzle 53 is provided in addition to the hole serving as the aperture 54 for one pressure chamber 46 of the cavity plate 81. The supply plate 84 is a metal plate provided with a communication hole between the aperture 54 and the manifold 45 and a communication hole from the pressure chamber 46 to the nozzle 53 with respect to one pressure chamber 46 of the cavity plate 81. The manifold plates 85 to 88 are metal plates each provided with a communication hole from the pressure chamber 46 to the nozzle 53 for one pressure chamber 46 of the cavity plate 81 in addition to the manifold 45. The nozzle plate 89 is a metal plate in which the nozzles 53 are provided for one pressure chamber 46 of the cavity plate 81.

  These nine sheets 81 to 89 and the actuator unit 42 are stacked in alignment with each other so that the individual ink flow paths 9 as shown in FIG. 7 are formed. The individual ink flow path 9 first extends upward from the manifold 45, extends horizontally in the aperture 54, then further upwards, extends horizontally again in the pressure chamber 46, and then moves away from the aperture 54 for a while. Heading diagonally downward and then vertically downward toward nozzle 53.

  As is clear from FIG. 7, the pressure chamber 46 and the aperture 54 are provided at different levels in the stacking direction of the plates. As a result, as shown in FIG. 6, in the flow path unit 41 facing the actuator unit 42, the aperture 54 communicated with one pressure chamber 46 is seen in plan view with another pressure chamber 46 adjacent to the pressure chamber 46. Can be arranged at the same position. As a result, the pressure chambers 46 are in close contact with each other and are arranged at high density, so that high-resolution image printing is realized by the inkjet head 5 having a relatively small occupation area.

  Returning to FIG. 6, each pressure chamber 46 communicates with the nozzle 53 at one end of the long diagonal line, and communicates with the manifold 45 through the aperture 54 at the other end of the long diagonal line. As will be described later, on the actuator unit 42, individual electrodes 60 (see FIG. 8) whose planar shape is almost diamond-shaped and slightly smaller than the pressure chamber 46 are arranged in a matrix so as to face the pressure chamber 46. Yes. Furthermore, a peripheral electrode 65 having the same planar shape and planar size as the individual electrode 60 is arranged on the actuator unit 42 so as to face each gap 55. Since the plurality of pressure chambers 46 are surrounded by a plurality of gaps 55, the plurality of individual electrodes 60 are also surrounded by a plurality of peripheral electrodes 65. In FIG. 6, only some of the plurality of individual electrodes 60 and the peripheral electrode 65 are drawn and only the individual electrodes 60 are hatched in order to simplify the drawing.

  The plurality of gaps 55 formed in the cavity plate 81 are defined by being closed by the actuator unit 42 and the base plate 82. Therefore, no ink flow path is connected to the gap 55, and the plurality of gaps 55 are not filled with ink. Among the six gap rows 56, the plurality of gaps 55 constituting the four adjacent gap rows 56 are arranged in a matrix with a staggered arrangement pattern in two directions of arrangement direction A (sub-scanning direction) and arrangement direction B. Adjacent to each other. Further, the plurality of gaps 55 constituting the other two gap rows 56 are adjacently arranged along the arrangement direction A, respectively. The two gap rows 57 positioned outside the both end portions of the pressure chamber row 47 include one gap 55 located at the end portion of each gap row 56 and the arrangement direction A outside the end portion of each pressure chamber row 47. A pressure chamber 46 and a single gap 55 arranged continuously are included. That is, the plurality of gaps 55 constituting these gap rows 57 are adjacently arranged in two rows in a staggered arrangement pattern in two directions of the arrangement direction C (main scanning direction) and the arrangement direction B.

  In the present embodiment, both the pressure chamber 46 and the gap 55 are formed without distinction in shape, size, and arrangement state. In other words, the adjacent pressure chambers 46, the gaps 55, and the separation distances between the pressure chambers 46 and the gaps 55 are all the same distance. Adjacently arranged in a matrix in a staggered arrangement pattern in two directions of arrangement direction B. The arrangement direction A is the longitudinal direction of the flow path unit 41 and is parallel to the shorter diagonal line of the pressure chamber 46. The arrangement direction B is an oblique side direction of the pressure chamber 46 that forms an obtuse angle θ with the arrangement direction A. With such a configuration, the gap 55 can be deformed in substantially the same manner as the pressure chamber 46. This is because the surrounding structure viewed from each pressure chamber 46 is the same regardless of the installation position, so that the influence on the discharge characteristics from the structural surface received by each pressure chamber 46 is made uniform. That is, it contributes to uniform ink ejection characteristics.

  The pressure chambers 46 adjacently arranged in a matrix in two directions of the arrangement direction A and the arrangement direction B are arranged along the arrangement direction A in a gap corresponding to the resolution. In the present embodiment, the nozzles 53 communicating with the pressure chambers 46 belonging to each pressure chamber row 47 are separated by a distance corresponding to 37.5 dpi with respect to the arrangement direction A. Projection points with respect to a straight line extending in the arrangement direction A of the nozzles 53 are separated by an interval corresponding to a print resolution of 150 dpi. This is because the four nozzles 53 having the same relative positional relationship in the four pressure chamber row groups described later are projected at the same position on a straight line extending in the arrangement direction A. Note that if the positions of the projected points of all the nozzles 53 do not overlap, the distance between the projected points of the nozzles 53 can be separated by an interval corresponding to 600 dpi, but in this embodiment, for each color (pressure A plurality of nozzles 53 are divided into four groups for each chamber row group, and the interval between projection points of the nozzles 53 is set to an interval corresponding to a resolution (150 dpi) of 1/4 of 600 dpi. Corresponding to such resolution, the adjacent pressure chambers 46 are separated along the arrangement direction A by a distance corresponding to 37.5 dpi. Further, 16 pressure chambers 46 are arranged in the bonding region of the flow path unit 41 so as to sandwich the four gaps 55 along the arrangement direction B, and are viewed from a direction perpendicular to the paper surface of FIG. Thus, eight pieces are arranged along the arrangement direction C so as to sandwich the two gaps 55.

  A large number of pressure chambers 46 arranged in a matrix form a plurality of pressure chamber rows 47 along the arrangement direction A shown in FIG. The plurality of pressure chamber rows 47 are viewed from the direction perpendicular to the paper surface of FIG. 6 according to the relative positions with respect to the manifolds 45, the first pressure chamber row 47a, the second pressure chamber row 47b, 3 pressure chamber rows 47c and a fourth pressure chamber row 47d. These first to fourth pressure chamber rows 47a to 47d are 47c → 47a → 47d → 47b from one side in the width direction (main scanning direction) of the flow path unit 41 to the other (from the bottom to the top in FIG. 6). Four pieces are arranged periodically in the order of → 47c → 47a →... 47b. The first to fourth pressure chamber rows 47 arranged periodically and adjacent to each other form one pressure chamber row group 48. Therefore, four pressure chamber row groups 48 are formed in the adhesion region of the flow path unit 41.

  All the pressure chambers 46 belonging to each pressure chamber row group 48 are communicated with the same manifold 45 through the respective apertures 54. That is, since each pressure chamber row group 48 is formed for each manifold 45, the four pressure chamber row groups 48 are pressure chamber row groups 48M, 48Y, 48C, and 48K corresponding to four colors of ink. The pressure chambers 46 belonging to each of the four pressure chamber row groups 48M, 48Y, 48C, and 48K are changed in volume by the actuator unit 42, whereby the four color inks communicate with the pressure chambers 46 belonging to the respective pressure chamber row groups 48. It becomes possible to discharge from the nozzle 53.

  As shown in FIG. 6, the pressure chambers 46a constituting the first pressure chamber row 47a and the pressure chambers 46c constituting the third pressure chamber row 47c of the pressure chamber row group 48 are perpendicular to the paper surface of FIG. When viewed from the right direction, the nozzle 53 is unevenly distributed on the lower side of the drawing in FIG. The nozzles 53 are adjacent to the vicinity of the left side of the lower end portion of the corresponding pressure chamber 46. On the other hand, in the pressure chambers 46b constituting the second pressure chamber row 47b and the pressure chambers 46d constituting the fourth pressure chamber row 47d, the nozzles 53 are unevenly distributed on the upper side of the drawing in FIG. . The nozzles 53 are adjacent to the vicinity of the right side of the upper end portion of the corresponding pressure chamber 46. In the first and fourth pressure chamber rows 47a and 47d, when viewed from the direction perpendicular to the plane of FIG. 6, more than half of the pressure chambers 46a and 46d overlap the manifold 45. In the second and third pressure chamber rows 47 b and 47 c, almost all the regions of the pressure chambers 46 b and 46 c do not overlap the manifold 45 when viewed from the direction perpendicular to the paper surface of FIG. Therefore, for the pressure chambers 46 belonging to any pressure chamber row 47, the nozzle 53 communicating therewith does not overlap the manifold 45, and the manifold 45 is widened as much as possible to smoothly supply ink to each pressure chamber 46. It is possible to supply to.

  Further, since the nozzles 53 are not formed at positions facing the gaps 55 belonging to the four adjacent gap rows 56 on the ink discharge face 40a of the flow path unit 41, black ink is applied to the ink discharge face 40a. This is divided into a black area (achromatic area) constituted by a plurality of nozzles 53 to be ejected and a chromatic color area constituted by a plurality of nozzles 53 that eject magenta, yellow and cyan inks.

  In this way, the ink discharge surface 40a is divided into the chromatic color region and the black region across the region facing the four adjacent gap rows 56, and the plurality of nozzles 53 from which black ink is discharged and the chromatic color A plurality of nozzles 53 from which ink is ejected are isolated. Therefore, during the maintenance of the ink discharge surface 40a of the flow path unit 41, the color mixture of the black ink and the chromatic color ink can be suppressed. That is, in the maintenance of the ink discharge surface 40a, each color ink attached to the ink discharge surface 40a is wiped off with a blade (not shown) made of a plate-like elastic member. When the black area and the chromatic color area are close to each other, the black ink moves along the blade to the chromatic color area, and the black ink remains near the outlet of the nozzle 53 that discharges the chromatic color ink. Color ink causes color mixing. However, as in the present embodiment, the black area and the chromatic color area are separated from each other, so that it is difficult to reach the chromatic color area even if the black ink moves along the blade during maintenance during ink ejection. Further, the color mixture of the black ink and the chromatic color ink hardly occurs.

  Next, the configuration of the actuator unit 42 and the FPC 50 will be described. On the actuator unit 42, the individual electrodes 60 and the peripheral electrodes 65 are arranged in the same arrangement pattern as the pressure chambers 46 and the gaps 55 formed in the flow path unit 41, respectively. Each of the electrodes 60 and 65 is formed in an elongated shape, and has a longitudinal direction in a direction orthogonal to the extending direction of the manifold 45. Each individual electrode 60 is disposed at a position facing the pressure chamber 46 in plan view. Each peripheral electrode 65 is disposed at a position facing the gap 55 in plan view.

  8A and 8B show the actuator unit 42, where FIG. 8A is an enlarged view of a portion surrounded by a chain line in FIG. 7, and FIG. 8B is a plan view of an individual electrode. FIG. 9 is a partially enlarged plan view of the actuator unit 46. FIG. 10 is a partially enlarged plan view of the inkjet head 5 shown in FIG. In FIG. 9, only the individual electrode 60 is hatched so that it can be easily distinguished from the peripheral electrode 65. Further, in FIG. 10, the wiring pattern 112 and the terminal 113 to be drawn with broken lines are drawn with solid lines for easy understanding of the drawing. As shown in FIGS. 8A and 8B, the individual electrode 60 has a main electrode region 61a formed in a plane region of the pressure chamber 46 in plan view, and is connected to the main electrode region 61a and is a pressure chamber. 46 and an auxiliary electrode region 61b formed outside the planar region.

  As shown in FIG. 8A, the actuator unit 46 includes four piezoelectric sheets 91, 92, 93, and 94 formed to have the same thickness of about 15 μm. These piezoelectric sheets 91 to 94 are formed into a continuous layered flat plate (continuous flat plate layer) so as to be disposed across the plurality of pressure chambers 46 and the gap 55. Since the piezoelectric sheets 91 to 94 are arranged as a continuous flat plate layer across the plurality of pressure chambers 46 and the gaps 55, the individual electrodes 60 and the peripheral electrodes 65 are densely formed on the piezoelectric sheet 91 by using, for example, a screen printing technique. It is possible to arrange in. Therefore, the pressure chambers 46 and the gaps 55 formed at positions corresponding to the individual electrodes 46 and the peripheral electrodes 65 can be arranged at high density, and high-resolution images can be printed. The piezoelectric sheets 91 to 94 are made of a lead zirconate titanate (PZT) ceramic material having ferroelectricity.

  As shown in FIG. 8B, the main electrode region 61a of the individual electrode 60 formed on the uppermost piezoelectric sheet 91 has a substantially rhombic planar shape that is substantially similar to the pressure chamber 46. The auxiliary electrode region 61b extends from one acute angle portion of the main electrode region 61a in a direction parallel to the longer diagonal line of the pressure chamber 46 (that is, the arrangement direction C). A circular land 62 is provided at the tip of the auxiliary electrode region 61b. As shown in FIG. 8B, the land 62 faces a region where the pressure chamber 46 is not formed in the cavity plate 81. The land 62 is made of gold containing glass frit, for example, and is formed on the tip surface of the auxiliary electrode region 61b as shown in FIG. The peripheral electrode 65 has the same configuration as the individual electrode 60 as shown in FIG. In other words, the peripheral electrode 65 has a main electrode region 66 a formed in the plane region of the gap 55 and an auxiliary electrode region 66 b connected to the main electrode region 66 a and formed outside the plane region of the gap 55. A land 67 is provided on the tip of the auxiliary electrode region 66b.

  As shown in FIG. 9, a plurality of individual electrodes 60 are arranged in parallel with each other along the arrangement direction A (sub-scanning direction) in accordance with the arrangement mode of the pressure chambers 46 of the cavity plate 81. 63 is formed. The plurality of individual electrode rows 63 are divided into individual electrode rows 63a to 63d so as to correspond to the pressure chamber rows 47a to 47d, respectively. Further, with these individual electrode rows 63a to 63d as one group, four individual electrode row groups 64M, 64Y, 64C and 64K corresponding to the four pressure chamber row groups 48 are formed. In the present embodiment, among the four individual electrode row groups 64, the auxiliary electrode regions 61b of the individual electrodes 60 belonging to the two individual electrode row groups 64M and 64Y located above in FIG. 9 are arranged on the upper side. The auxiliary electrode region 61b of the individual electrode 60 belonging to the other two individual electrode row groups 64C and 64K is disposed on the lower side.

  In addition, the plurality of peripheral electrodes 65 include a plurality of peripheral electrode rows 68 and 69 arranged in parallel along the arrangement direction A and the arrangement direction C (main scanning direction) corresponding to the arrangement of the gaps 55 of the cavity plate 81. Forming. That is, the plurality of peripheral electrodes 65 include four adjacent peripheral electrode arrays 68 between the individual electrode array group 64C and the individual electrode array group 64K, and the four adjacent peripheral electrode arrays 68. Two peripheral electrode rows 68 arranged at positions sandwiching three individual electrode row groups 64M, 64Y, 64C and one individual electrode row group 64K, respectively, and both ends of each individual electrode row 63 in the arrangement direction A They are arranged so as to constitute two rows of peripheral electrode rows 69 located on the outside of the part.

  In the present embodiment, as described above, the individual electrode array groups 64M, 64Y, and 64C related to the chromatic ink ejection and the individual electrode array group 64K related to the achromatic ink ejection include the peripheral electrode array 68 and the peripheral electrode array 68, respectively. 69. For this reason, the pressure chambers 46 belonging to the respective regions have almost the same influence (internal stress) of the deformation of the piezoelectric sheet received from the surroundings regardless of the arrangement position, and the ink discharge characteristics are further uniform. Further, the plurality of peripheral electrodes 65 include an achromatic peripheral electrode group 97 surrounding the periphery of one individual electrode array group 64K, and a chromatic peripheral electrode group surrounding the periphery of the three individual electrode array groups 64M, 64Y, 64C. 98 and a boundary peripheral electrode group 99 formed by two inner rows of the peripheral electrode rows 68 disposed between the electrode groups 97 and 98. The boundary peripheral electrode group 99 is disposed so as to face the boundary portion 38 (see FIG. 6) between the manifold 45K and the manifold 45C. That is, the peripheral electrode group 97 for achromatic color is the peripheral electrode 65 belonging to the lowermost peripheral electrode row 68 in FIG. 9 and the peripheral electrode belonging to the lower peripheral electrode row 68 of the four adjacent rows. 65 and the peripheral electrode 65 belonging to the peripheral electrode array 69 existing between the two peripheral electrode arrays 68. In FIG. 9, the chromatic color peripheral electrode group 98 includes a peripheral electrode 65 belonging to the uppermost peripheral electrode array 68, and a peripheral electrode 65 belonging to the upper peripheral electrode array 68 among the four adjacent lines. , And the peripheral electrode 65 belonging to the peripheral electrode array 69 existing between the two peripheral electrode arrays 68.

  The auxiliary electrode regions 66b of the plurality of peripheral electrodes 65 are formed so as to face the same direction as the auxiliary electrode regions 61b of the adjacent individual electrodes 60. For example, as shown in FIG. 9, in the peripheral electrode row 68 located at the uppermost position, the auxiliary electrode region 66 b of the peripheral electrode 65 belonging to the uppermost peripheral electrode row 68 is arranged in the upper part in FIG. Yes. On the contrary, in the peripheral electrode 68 located at the lowermost position, the auxiliary electrode region 66b is disposed at the lower side in FIG. Further, in the peripheral electrode 65 located on the extension line in the arrangement direction A of each individual electrode row 63, each auxiliary electrode region 66b is arranged similarly to the individual electrode 60 adjacent thereto. Therefore, the peripheral electrode row 69 includes two types of peripheral electrodes 68 having auxiliary electrode regions 66b arranged in opposite directions corresponding to the adjacent individual electrodes 60.

  As shown in FIG. 9, the plurality of peripheral electrodes 65 are connected by conductive members 75 and 76 formed on the upper surface of the actuator unit 42, respectively. Among these, the conductive member 75 is disposed so as to surround the individual electrode array group 64K. The conductive member 75 connects the peripheral electrodes 65 belonging to the achromatic peripheral electrode group 97 as a whole. Further, the conductive member 75 is also connected to the peripheral electrode 65 arranged below the boundary peripheral electrode group 99. The conductive member 75 is formed so as to connect the regions farthest from the individual electrode 60 adjacent to the peripheral electrode 65 belonging to the achromatic peripheral electrode group 97.

  Similarly to the conductive member 75, the conductive member 76 electrically connects the peripheral electrode 65 constituting the chromatic color peripheral electrode group 98, and is also connected to the peripheral electrode 65 arranged above the boundary peripheral electrode group 99. ing. Further, the conductive member 76 is formed so as to connect the regions farthest from the individual electrode 60 adjacent to the peripheral electrode 65 belonging to the chromatic color peripheral electrode group 98. In FIG. 9, the conductive member 75 is divided at a peripheral electrode 65 portion located at the lower left. However, the peripheral electrode 65 belonging to the achromatic peripheral electrode group 97 and the peripheral electrode 65 arranged below the boundary peripheral electrode group 99 are electrically connected by one conductive member 75. The conductive member 76 is also divided at the peripheral electrode 65 located at the upper left. However, the peripheral electrode 65 belonging to the chromatic color peripheral electrode group 98 and the peripheral electrode 65 arranged above the boundary peripheral electrode group 99 are electrically connected by one conductive member 76.

  On the upper surface of the actuator unit 42, as shown in FIG. 9, surface electrodes 70 formed intermittently along the arrangement direction C are formed in the vicinity of the outside of the peripheral electrode row 69. The surface electrode 70 is electrically connected to a later-described common electrode 72 through a conductor filled in a through hole (not shown) penetrating in the thickness direction of the actuator unit 42. Further, among the plurality of surface electrodes 70, the surface electrode 70 located at the lowest position in FIG. 9 is formed with lands 71 that are electrically connected to the FPC 50. The land 71 is also made of the same material as the lands 62 and 67 described above.

  Returning to FIG. 8A, a common electrode 72 having the same outer shape as the piezoelectric sheet 91 and a thickness of about 2 μm is interposed between the uppermost piezoelectric sheet 91 and the lower piezoelectric sheet 92. . The individual electrode 60, the peripheral electrode 65, and the common electrode 72 are all made of, for example, a metal material such as Ag—Pd.

  In the piezoelectric sheet 91, regions facing the plurality of individual electrodes 60 and the plurality of peripheral electrodes 65 are polarized in the same direction in the same direction. In other words, when the inkjet head 5 is manufactured, the common electrode 72 is held at the ground potential, and the polarization process is performed by applying the same high positive potential (for example, a potential of about 40 V) to the individual electrode 60 and the peripheral electrode 65. And Thus, the polarization direction of the polarized region in the piezoelectric sheet 91 is parallel to the thickness direction of the piezoelectric sheet 91 and is directed from the individual electrode 60 and the peripheral electrode 65 toward the common electrode 72. When the polarization direction is reversed, the individual electrode 60 and the peripheral electrode 65 may be set to the ground potential and a high positive potential may be applied to the common electrode 72.

  As shown in FIG. 8A, the FPC 50 includes a base film 111, a wiring pattern 112 formed on the lower surface thereof, and a cover film 115 that covers almost the entire lower surface of the base film 111. As shown in FIG. 10, the wiring pattern 112 is electrically connected to each of the plurality of individual wirings 117 electrically connected to each of the plurality of individual electrodes 60, the plurality of peripheral electrodes 65, and the conductive members 75 and 76. A plurality of peripheral wirings 118 to be connected and a common wiring 119 electrically connected to the surface electrode 70 are provided. The individual wiring 117, the peripheral wiring 118, and the common wiring 119 all extend along the extending direction of the FPC 50, and their base ends are electrically connected to the driver IC 51.

  Through holes 116 are formed in the cover film 115 at positions facing the tips of the wires 117 to 119, respectively. In the base film 111, each wiring 117-119, and the cover film 115, the center of each through-hole 116 and the center line of each wiring 117-119 correspond, and the front-end | tip outer periphery part of each wiring 117-119 is a cover film. 115 so as to be covered with each other and stacked. The plurality of terminals 113 of the FPC 50 are connected to the wirings 117 to 119 through the respective through holes 116.

  The base film 111 and the cover film 115 are both sheet members having insulating properties. In the present embodiment, the base film 111 is made of a polyimide resin, and the cover film 115 is made of a photosensitive material. Thus, by forming the cover film 115 from a photosensitive material, it is easy to form a large number of through holes 116.

  Moreover, each wiring 117-119 of the wiring pattern 112 is formed with the copper foil. The terminal 113 is made of a conductive material such as nickel. The terminal 113 closes the through hole 116, covers the outer periphery of the through hole 116, and is formed to protrude slightly from the lower surface of the cover film 115.

  As shown in FIG. 10, the plurality of terminals 113 are arranged at positions facing the lands 62 of the individual electrodes 60, the lands 67 of the peripheral electrode 65, and the lands 71 of the surface electrode 70, respectively. These terminals 113 are joined to the lands 62, 67, 71 by the solder 114, so that the individual wiring 117 is common to the individual electrode 60, the peripheral wiring 118 is the peripheral electrode 65, and the common wiring 119 is common via the surface electrode 70. It is electrically connected to the electrode 72. With this configuration, the ejection signal, the standby signal, and the reference signal are supplied from the driver IC 51 to the corresponding individual electrode 60, the peripheral electrode 65, and the common electrode 72 via the wirings 117 to 119.

  Next, a method for driving the actuator unit 42 will be described. The polarization direction of the piezoelectric sheet 91 in the actuator unit 42 is the thickness direction as described above. That is, the actuator unit 42 has a so-called unimorph type configuration in which the upper one piezoelectric sheet 91 is an active layer and the lower three piezoelectric sheets 92 to 94 are inactive layers. Yes. Accordingly, when the individual electrode 60 is set to a reference potential, for example, a predetermined potential that is positive or negative with respect to the ground potential, for example, if the electric field and the polarization direction are the same direction, the individual electrode 60 and the common electrode 72 in the piezoelectric sheet 91. The electric field application portion sandwiched between the two functions as an active layer and contracts in a direction perpendicular to the polarization direction due to the piezoelectric transverse effect. On the other hand, since the piezoelectric sheets 92 to 94 are not affected by the electric field and do not spontaneously shrink, the piezoelectric sheets 92 to 94 are deformed in a direction perpendicular to the polarization direction between the upper piezoelectric sheet 91 and the lower piezoelectric sheets 92 to 94. Try to (unimorph deformation). At this time, since the lower surfaces of the piezoelectric sheets 91 to 94 are fixed to the upper surface of the cavity plate 81 that partitions the pressure chamber 46, the piezoelectric sheets 91 to 94 are deformed so as to protrude toward the pressure chamber 46 as a result. . For this reason, the volume of the pressure chamber 10 is reduced, the pressure of the ink is increased, and ink droplets are ejected from the nozzle 53. Thereafter, when the individual electrode 60 is returned to the same potential as that of the common electrode 72, the piezoelectric sheets 91 to 94 have the original shape, and the volume of the pressure chamber 46 returns to the original volume, so that ink is sucked from the manifold 45 side.

  In the present embodiment, in the actual driving procedure, the individual electrode 60 and the peripheral electrode 65 are previously held at a standby potential different from the ground potential, and the volume of the pressure chamber 46 is reduced. Each time there is a discharge request, only the individual electrode 60 is set to the ground potential. At this time, the piezoelectric sheets 91 to 94 return to their original shapes, and the volume of the pressure chamber 46 increases as compared with the initial state, so that a negative pressure is generated in the pressure chamber 46. Further, a negative pressure wave propagates through the individual ink flow path 9 and ink is sucked into the pressure chamber 46 from the manifold 45 side. Thereafter, the individual electrode 60 is set to the standby potential again at the timing when the pressure wave that has become positive pressure returns to the center of the pressure chamber 46. As a result, the piezoelectric sheets 91 to 94 are deformed so as to protrude toward the pressure chamber 46, the pressure in the pressure chamber 46 increases due to a decrease in the volume of the pressure chamber 46, and ink droplets are ejected. In other words, in order to eject ink droplets, an ejection signal of standby potential → ground potential → standby potential is supplied to the individual electrode 60. Correspondingly, when the individual electrode 60 is at the standby potential, the volume of the pressure chamber 46 is smaller than the basic volume when the individual electrode 60 is at the ground potential.

  In gradation printing, gradation expression is performed by the number of ink droplets that are continuously ejected from the nozzle 53 and form substantially one dot on the paper, that is, the ink amount (volume). For this reason, the number of ink ejections corresponding to the designated gradation is performed once or continuously several times from the nozzle 53 corresponding to the designated dot area. In general, when ink is ejected continuously, it is preferable that the interval between pulses supplied to eject ink droplets be AL (Acoustic Length). As a result, the period of the residual pressure wave of the pressure generated when ejecting the previously ejected ink droplets coincides with the period of the pressure wave of the pressure generated when ejecting the ink droplets ejected later, and these are superimposed. Then, the pressure is amplified to eject the ink droplets. In the present embodiment, as will be described later, the number of continuous ejections of ink droplets from the nozzle 53 can be set to an arbitrary number of 3 or less, thereby realizing gradation expression.

  Next, control of the ink jet printer 1 will be described below. FIG. 11 is a block diagram illustrating a control configuration of the inkjet printer 1. FIG. 12 is a diagram depicting a waveform pattern corresponding to each signal applied to the inkjet head 5. As shown in FIG. 11, a control unit 101 is provided inside the inkjet printer 1. The control unit 101 is a central processing unit (CPU) that is an arithmetic processing unit, a ROM (Read Only Memory) that stores a program executed by the CPU and data used in the program, and temporarily stores data when the program is executed. RAM (Random Access Memory) for this purpose, and the functional units described below are constructed by these.

  The control unit 101 operates based on print data from the PC 100, and includes a communication unit 102, an operation control unit 103, and a print control unit 104 as shown in FIG. Among these, the communication part 102 communicates with PC100. The print data transmitted from the PC 100 includes image data and operation data. The communication unit 102 outputs operation data to the operation control unit 103 and outputs image data to the print control unit 104. The operation control unit 103 drives and controls the motor 17 that drives the pulley 14, the motor that drives the platen roller 18, the cam 22, and the like based on instructions from the PC 100 and the print control unit 104.

  A power source 108 is connected to the control unit 101. The power supply 108 commercializes voltages necessary for three signals: a high potential signal held at a standby potential, a reference signal held at a ground potential, and a low potential signal held at a positive potential lower than the high potential signal. It is generated from an AC power supply and supplied to the control unit 101. In the present embodiment, the power supply 108 generates 20 V for the high potential signal 134, 3.3 V for the low potential signal, and the ground potential. Note that one reference signal line may be provided for each of the high potential signal and the low potential signal.

  The print control unit 104 includes an image data storage unit 105 for storing image data, a waveform pattern storage unit 106, and a print signal generation unit 107. The image data storage unit 101 stores bitmap data of gradation values (8 bits (256 gradations)) of each pixel constituting the image data for each color of magenta, yellow, cyan, and black. The waveform pattern storage unit 106 stores three types of waveform pattern signals 131 to 133 that indicate waveform patterns of ejection signals supplied only to the individual electrodes 60 in order to eject ink droplets from the nozzles 53 and form dots on the paper. I remember it.

  The print signal generation unit 107 generates a print signal that sequentially indicates the ink discharge amount (number of continuous ink discharges) from each nozzle 53 based on the data for each color stored in the image data storage unit 105. This print signal includes a signal that indicates which level the potential applied to the peripheral electrode 65 during ink ejection is to be set. The instruction of the potential to be maintained can be performed for each of the achromatic color peripheral electrode group 97 and the chromatic color peripheral electrode group 98. In the present embodiment, the print signal generation unit 107 When the color ink is ejected, all the peripheral electrodes 65 are set to the standby potential. Further, when only black ink is discharged, only the peripheral electrode 65 belonging to the achromatic color peripheral electrode group 97 is set to the standby potential, and the peripheral electrode 65 belonging to the chromatic color peripheral electrode group 98 is set to the ground potential. Generate a signal. The print signal is a 2-bit serial signal.

  12A to 12C show waveform pattern signals 131 to 133 of three types of ejection signals for gradation control, and FIG. 12D shows a high potential signal 134 (described later). The reference signal 135 is shown in FIG. 12 (e). Note that the vertical axis represents potential and the horizontal axis represents time.

  A waveform pattern signal 131 shown in FIG. 12A is used to form a dot for one ink droplet on the printing paper. The waveform pattern signal 132 shown in FIG. 12B is used to form dots for two ink droplets on the printing paper. A waveform pattern signal 133 shown in FIG. 12C is used to form dots for three ink droplets on the printing paper. In the waveform pattern signals 131 to 133 shown in FIGS. 12A to 12C, the high level potential is, for example, 3.3V. As will be described later, the waveform pattern signals 131 to 133 are amplified by the driver IC 51 so that the high level potential becomes 20V.

  As shown in FIGS. 12A to 12C, the waveform pattern signals 131 to 133 both have a pulse width and a pulse interval that are substantially AL, and the final pulse is an individual ink channel after ink ejection. This is a cancel pulse for removing the pressure remaining in 9. The cancel pulse generates a new pressure in which the residual pressure and the positive / negative are reversed in the individual ink channel 9. Thereby, the residual pressure is offset.

  As shown in FIG. 11, the print control unit 104 is connected to a driver IC 51 on the FPC 50. The print control unit 104 includes a low potential signal and a high potential signal generated by the power source 108 together with the print signal generated by the print signal generation unit 107 and the three waveform pattern signals 131 to 133 stored in the waveform pattern storage unit 106. 134 and the reference signal 135 are supplied to the driver IC 51. The driver IC 51 always supplies the reference signal 135 (ground potential) to the common electrode 72 via the common wiring 119. The driver IC 51 includes a waveform selection unit 141 and an ejection signal generation unit 142. The waveform selection unit 141 sequentially selects a waveform pattern to be supplied to each individual electrode 60 from the four signals of the three waveform pattern signals 131 to 133 and the high potential signal 134 on the basis of the print signal, and achromatic color. A waveform pattern to be supplied to the peripheral electrode group 97 for chromatic color and the peripheral electrode group 98 for chromatic color is sequentially selected from two signals of a low potential signal and a reference signal 135.

  The ejection signal generation unit 142 uses the signal selected by the waveform selection unit 141 from the above four signals based on the print signal for each individual electrode 60, and uses the high potential signal 134 so that the high level potential is 20V. Modulation and amplification. The driver IC 51 supplies the ejection signal generated in this way to each corresponding individual electrode 60 via the individual wiring 117 of the FPC 50. Further, the ejection signal generation unit 142 selects a low potential signal among the signals selected by the waveform selection unit 141 from the two signals based on the print signal for the achromatic peripheral electrode group 97 and the chromatic peripheral electrode group 98. Is amplified using the high potential signal 134 so that the potential becomes 20 V, thereby generating a standby signal (the same signal as the high potential signal 134 shown in FIG. 12D). The driver IC 51 supplies a standby signal or reference signal 135 (ground potential) to the achromatic color peripheral electrode group 97 and the chromatic color peripheral electrode group 98 via the peripheral wiring 118 of the FPC 50. As a result, during color printing in which all color inks are ejected, standby signals are given to all the peripheral electrodes 65. On the other hand, during monochrome printing in which only black ink is ejected, a standby signal is applied to the achromatic peripheral electrode group 97, while a reference signal 135 is applied to the chromatic peripheral electrode group 98. Become. Therefore, it is not necessary to supply a standby signal to all the peripheral electrodes 65, so that power consumption is reduced.

  Further, in a standby period until the ejection signal is supplied to the individual electrodes 60, the ejection signal generation unit 142 supplies standby signals to all the individual electrodes 60 and all the peripheral electrodes 65. Among these, for the individual electrode 60, the high potential signal 134 is supplied as a standby signal. On the other hand, the ejection signal generator 142 generates and supplies a standby signal having a potential of 20 V from the high potential signal 134 to the peripheral electrode 65 based on the low potential signal. That is, in order to wait for the supply of the discharge signal, the standby signal is supplied to the peripheral electrode 65 as well as the individual electrode 60 in the present embodiment. After the discharge signal is supplied, the standby signal is selectively supplied to the achromatic color peripheral electrode group 97 and the chromatic color peripheral electrode group 98 as described above.

  As described above, according to the inkjet head 5 of the present embodiment, in the piezoelectric sheet 91, the region sandwiched between the peripheral electrode 65 and the common electrode 72 and the region sandwiched between the individual electrode 60 and the common electrode 72. Are both polarized to substantially the same degree. Therefore, even if the individual electrode 60 is on the outermost side in the arrangement direction, the portions of the piezoelectric sheet 91 adjacent in the arrangement direction, in this case, the adjacent peripheral electrode 65 side and the individual electrode 60 adjacent on the opposite side are adjacent. The same degree of distortion is induced from each side. This strain is almost the same as the strain induced at the site where the other individual electrode 60 is disposed. In other words, the strain distribution from the adjacent portion to each individual electrode 60 is in a uniform state. Further, even when ink is ejected, regardless of the installation position of the individual electrodes 60, it can be said that the influence of this distortion received from both sides in the arrangement direction is almost the same. Accordingly, it is possible to suppress variations in ink ejection characteristics between the nozzle 53 communicating with the pressure chamber 46 located on the outermost side in the arrangement direction and the nozzle 53 communicating with the other pressure chamber 46. In addition, since the plurality of peripheral electrodes 65 are electrically connected to each other via the conductive members 75 and 76 disposed on the actuator unit 42, the peripheral wiring 118 necessary for performing polarization is connected to the plurality of peripheral electrodes 65. Therefore, it is not necessary to join each of them, and the wiring structure is simplified. That is, the peripheral wiring 118 only needs to be formed in a number corresponding to the conductive members 75 and 76, and thus the wiring structure of the FPC 50 is simplified.

  Furthermore, when ink is ejected, when a voltage (by the ejection signal) is applied between the individual electrode 60 and the common electrode 72, the piezoelectric sheets 91 to 94 in this portion are deformed. This deformation causes unnecessary distortion of the piezoelectric sheets 91 to 94 in the adjacent pressure chamber 46 and deformation accompanying the unnecessary distortion. However, since the standby signal held at a high potential is supplied to the peripheral electrode 65, in the piezoelectric sheets 91 to 94, the region facing the plurality of individual electrodes 60 and the region facing the peripheral electrode 65 are the same. Then, it deforms convexly toward the pressure chamber 46. Thereby, when ink is ejected from the nozzles 53, regardless of the installation position of the individual electrodes 60, the regions of the piezoelectric sheets 91 to 94 facing the individual electrodes 60 are subjected to distortions and deformations caused by both sides in the arrangement direction. Are comparable. Accordingly, it is possible to suppress variations in ink ejection characteristics between the nozzles 53 related to the individual electrodes 60 located on the outermost side in the arrangement direction and the nozzles 53 related to the other individual electrodes 60. In addition, since the standby signal is continuously supplied to the peripheral electrode 65 even when ink is ejected, the peripheral electrode 65 is unlikely to become a floating potential. If a potential is applied to the individual electrode 60 adjacent to the peripheral electrode 65 without applying a potential to the peripheral electrode 65, the peripheral electrode 65, the peripheral wiring 118 connected to the peripheral electrode 65, etc. Under the influence of the electric field, the peripheral electrode 65 may become an unstable floating potential. As a result, unintended piezoelectric sheets 91 to 94 are sometimes deformed, which adversely affects ink ejection. However, in the present embodiment, since the standby signal is supplied to the peripheral electrode 65, it is difficult for adverse effects on ejection to occur due to the peripheral electrode 65 becoming a floating potential. As a result, the discharge performance becomes stable.

  Even when a large number of pressure chambers 46 are two-dimensionally arranged in a matrix, as described above, the nozzle 53 related to the outermost individual electrode 60 in the arrangement direction and the nozzle 53 related to the other individual electrodes 60 as described above. Variation in ink ejection characteristics can be suppressed.

  Further, since the individual electrode 60 and the peripheral electrode 65 have the same planar shape and planar size, in the piezoelectric sheet 91, the respective polarization regions facing the individual electrode 60 and the peripheral electrode 65 have the same planar shape and the same planar size. It becomes. Therefore, with respect to the arrangement direction, in the region of the piezoelectric sheet 91 corresponding to the outermost individual electrode 60, the strain induced from the adjacent peripheral electrode 65 side is almost the same as the strain induced from the adjacent individual electrode 60 side. become. In addition, even when ink is ejected from the nozzles 53, the distortion that the piezoelectric sheet 91 receives from the regions on both sides in the arrangement direction and the deformations associated therewith are almost the same regardless of the position of the individual electrodes 60. Further, since the auxiliary electrode region 66b of the peripheral electrode 65 is formed at the end on the same side as the auxiliary electrode region 61b of the adjacent individual electrode 60, the piezoelectric sheet 91 is formed on both sides in the arrangement direction as described above. The difference in distortion and deformation caused by this is further reduced. Accordingly, it is possible to further suppress variations in ink ejection characteristics between the nozzle 53 communicating with the pressure chamber 46 located on the outermost side in the arrangement direction and the nozzle 53 communicating with the other pressure chamber 46.

  Further, since the gap 55 is formed at a position facing the peripheral electrode 65, in the piezoelectric sheets 91 to 94, the region facing the peripheral electrode 65 is convexly deformed to the pressure chamber 46 side. In the same manner as described above, the convex deformation toward the gap 55 side is possible. Further, since the gap 55 and the pressure chamber 46 have the same planar shape and plane size, for example, when a standby signal is supplied to each electrode, the corresponding pressure chamber 46 and the gap 55 are respectively the same. Convex deformation. As a result, even when the individual electrode 60 is located on the outermost side in the arrangement direction when ink is ejected from the nozzles 53, the distortion and deformation generated in the region of the piezoelectric sheets 91 to 94 facing the individual electrode 60 are not changed in the arrangement direction. It is almost the same as that in the part inside. Accordingly, it is possible to further suppress variations in ink ejection characteristics between the nozzle 53 related to the outermost individual electrode 60 in the arrangement direction and the other nozzles 53.

  Further, since the separation distance between the peripheral electrode 65 and the outermost individual electrode 60 in the arrangement direction is the same as the separation distance between the individual electrodes 60, in the piezoelectric sheets 91 to 94, the individual electrode 60 and the peripheral electrode are arranged. Each of the regions facing 65 has the same separation distance in the arrangement direction. Therefore, there is no distortion due to the difference in the separation distance between these regions and the difference in deformation accompanying the distortion. Accordingly, it is possible to further suppress variations in ink ejection characteristics between the nozzle 53 related to the outermost individual electrode 60 in the arrangement direction and the other nozzles 53.

  A surface electrode 70 is formed on the upper surface of the actuator unit 21 (on the piezoelectric sheet 91) on one end side in the arrangement direction A so as to sandwich the peripheral electrode 65 with the individual electrode 60. That is, the peripheral electrode 65 is formed between the individual electrode 60 and the surface electrode 70 on the same plane. Therefore, it is possible to prevent the individual electrode 60 and the surface electrode 70 from being electrically connected due to migration. This is because when the reference signal is supplied to the common electrode 72 to obtain the ground potential, the surface electrode 70 also becomes the ground potential. In this state, even if a standby signal or an ejection signal is supplied to the individual electrode 60, the peripheral electrode 65 exists between the individual electrode 60 and the surface electrode 70. There will be no direct migration in between. Thereby, the individual electrode 60 and the surface electrode 70 are not directly electrically connected.

  In addition, the conductive members 75 and 76 connect the regions farthest from the adjacent individual electrodes 60 in the peripheral electrode 65. Therefore, the region of the piezoelectric sheets 91 to 94 facing the outermost individual electrodes 60 in the arrangement direction minimizes unnecessary distortion and deformation induced by polarization and deformation of the regions facing the conductive members 75 and 76. It can be suppressed to the limit. That is, in the piezoelectric sheets 91 to 94, the degree of influence of internal stress and deformation generated at a specific part is determined by the separation distance from this part. As in this embodiment, the conductive members 75 and 76 are disposed at a position away from the individual electrodes 60 located on the outermost side in the arrangement direction. Even if it is done, its influence on the adjacent individual electrode 60 is weakened. In the peripheral electrode array 68, the ends of the plurality of peripheral electrodes 65 having an elongated shape as in the individual electrode 60 are connected by conductive members 75 and 76. Therefore, the conductive members 75 and 76 are positioned away from the individual electrode 60 adjacent to the peripheral electrode 65. Thereby, the effect mentioned above can be acquired.

  Further, since the longitudinal direction of the individual electrode 60 and the peripheral electrode 65 is a direction orthogonal to the extending direction of the manifold 45, a plurality of the individual electrodes 60 and the peripheral electrodes 65 can be arranged.

  Further, since the conductive member 75 connects the peripheral electrode 65 belonging to the achromatic peripheral electrode group 97 and the conductive member 76 connects the peripheral electrode 65 belonging to the chromatic peripheral electrode group 98, the standby signal is distinguished. It becomes possible to supply. Therefore, power consumption can be reduced. In addition, since it is not necessary to form the peripheral wiring corresponding to all the peripheral electrodes 65, the number of peripheral wirings of the FPC 50 is reduced, and the configuration of the FPC 50 is further simplified.

  In the present embodiment, the peripheral electrode 65 belonging to the boundary peripheral electrode group 99 is electrically connected to each peripheral electrode array 68 by the conductive members 75 and 76, but the achromatic peripheral electrode group 97, The peripheral electrodes 65 belonging to the coloring peripheral electrode group 98 and the boundary peripheral electrode group 99 may be electrically connected to each peripheral electrode group by three conductive members 77 to 79. FIG. 13 is an enlarged plan view showing a modification of the actuator unit of the inkjet head according to the embodiment of the present invention. The same components as those described above are denoted by the same reference numerals and description thereof is omitted.

  The actuator unit 80 of the ink jet head in the present modification has the same configuration as the actuator unit 42 described above except that only three conductive members 77 to 79 are provided. As shown in FIG. 13, the conductive member 77 electrically connects only the peripheral electrodes 65 belonging to the achromatic peripheral electrode group 97. Compared with the conductive member 75 described above, a part of the conductive member 77 extending along the arrangement direction A at the top in FIG. 13 is located slightly on the lower side, and the peripheral electrode belonging to the boundary peripheral electrode group 99 65 is not electrically connected. A part of the conductive member 77 in the region facing the boundary portion 38 is connected to the peripheral electrode 65 belonging to the achromatic peripheral electrode group 97 at a part as far as possible from the adjacent individual electrode 60. .

  The conductive member 78 electrically connects only the peripheral electrodes 65 belonging to the chromatic color peripheral electrode group 98. Compared with the conductive member 76 described above, a part of the conductive member 78 extending along the arrangement direction A at the lower side in FIG. 13 is located slightly above the peripheral electrode belonging to the boundary peripheral electrode group 99. 65 is not electrically connected. Of course, a part of the conductive member 78 in the region facing the boundary portion 38 is also connected to the peripheral electrode 65 belonging to the chromatic color peripheral electrode group 98 at a part as far as possible from the adjacent individual electrode 60. . The conductive member 79 extends substantially in the center of the two peripheral electrode rows 68 constituting the boundary peripheral electrode group 99 along the arrangement direction A, and the peripheral electrode 65 belonging to the boundary peripheral electrode group 99. Are only electrically connected to each other.

  By forming these three conductive members 77 to 79, the plurality of peripheral electrodes 65 belong to any one of the achromatic peripheral electrode group 97, the chromatic peripheral electrode group 98, and the boundary peripheral electrode group 99. It becomes possible to supply a standby signal only to the peripheral electrode 65. Therefore, if the selected nozzle 53 is in the black region, the standby signal can be selected and supplied to the peripheral electrode 65 belonging to the achromatic peripheral electrode group 97 and the individual electrode 60 belonging to the individual electrode group 64K. It becomes possible. In the actuator unit 42 described above, when a standby signal is supplied to the peripheral electrode 65 belonging to the achromatic peripheral electrode group 97 via the conductive member 75, the standby signal is also supplied to some peripheral electrodes 65 belonging to the boundary peripheral electrode group 99. However, in this modification, by forming the three conductive members 77 to 79 as described above, the plurality of peripheral electrodes 65 are distinguished into the respective peripheral electrode groups, and standby signals are supplied. It becomes possible. Therefore, power consumption for driving the peripheral electrode 65 is reduced.

  In this modification, the standby signal may be supplied to the boundary peripheral electrode group 99 as necessary. From the viewpoint of reducing power consumption, it is necessary to supply the standby signal to the boundary peripheral electrode group 99. Absent. However, from the viewpoint of preventing unnecessary deformation accompanying the generation of the floating potential, it may be maintained at a predetermined potential. In this case, a standby signal may be supplied or held at the ground potential.

  In addition, as can be said with any embodiment or modification, from the viewpoint of reducing the power consumed by the peripheral electrode 65, a peripheral electrode group corresponding to each manifold 45 may be configured. For example, it has a manifold 45K to which black ink as achromatic ink is supplied, and three manifolds 45M, 45Y and 45C to which magenta, yellow and cyan are supplied as chromatic ink. In each of the above embodiments, the plurality of peripheral electrodes 65 are roughly divided into two for achromatic and chromatic colors, but the peripheral electrodes 65 arranged for chromatic colors are further divided for each color. Also good.

  In this modification, as in the other embodiments, among the chromatic color individual electrode row groups 64, the yellow ink individual electrode row group 64Y is sandwiched between the other two color individual electrode row groups 64M and 64C. ing. Furthermore, the arrangement state of each individual electrode 60 is two-dimensionally arranged in a matrix form regardless of the ink color. Therefore, the structural difference in the periphery as viewed from the individual electrode 60 is only at both ends in the arrangement direction A of the individual electrode row group 64Y. Therefore, the peripheral electrode 65 (a part of the peripheral electrode array 69) adjacent to both ends of each individual electrode array 63 a to 63 d is connected by a conductive member independent of the conductive members for other colors. One yellow conductive member is arranged on each side of the individual electrode array group 64Y. As a result, a dedicated conductive member is provided for each color. With this configuration, for example, even when color printing is in progress, when a specific color is not printed, it is not always necessary to supply a standby signal to the conductive member corresponding to that color. This may be held at the ground potential. Alternatively, the standby signal may be applied to the corresponding conductive member in accordance with the timing at which the individual electrode 60 positioned at the end in the array is driven, regardless of the color. In any case, the degree of freedom of the drive mode of the peripheral electrode 65 can be increased in accordance with the printing state, and the power consumption can be reduced.

  As another modification, from the viewpoint of reducing power consumption, only the conductive member 77 or the conductive member 78 may be formed in the actuator unit. When only the conductive member 77 is formed, the peripheral wiring connected to the conductive member 77 and the peripheral wiring corresponding to the number of the plurality of peripheral electrodes 65 connected to the conductive members 78 and 79 are formed in the FPC. These peripheral wirings are independently connected to the conductive member 77, the peripheral electrode 65 belonging to the chromatic peripheral electrode group 98, and the peripheral electrode 65 belonging to the boundary peripheral electrode group 99. By doing this, when the nozzle 53 related to ink discharge is in the chromatic color region and is at the outermost side in the arrangement direction at the time of ink discharge, the individual electrode 60 related to the nozzle 53 related to ink discharge and the individual electrode 60 are connected. A standby signal can be supplied only to the adjacent peripheral electrode 65. On the other hand, when only the conductive member 78 is formed, the peripheral wiring connected to the conductive member 78 and the peripheral wiring corresponding to the number of the plurality of peripheral electrodes 65 connected to the conductive members 77 and 79 are FPCs. The peripheral wirings are independently connected to the conductive member 78, the peripheral electrode 65 belonging to the achromatic peripheral electrode group 97, and the peripheral electrode 65 belonging to the boundary peripheral electrode group 99. By doing this, when the nozzle 53 related to ink discharge is in the achromatic region and is located on the outermost side in the arrangement direction during ink discharge, the individual electrode 60 related to the nozzle 53 related to ink discharge and the individual electrode 60 are connected. A standby signal can be supplied only to the adjacent peripheral electrode 65. Therefore, it is possible to further reduce the power consumption for driving the individual electrode 60 and the peripheral electrode 65.

  On the other hand, from the viewpoint of simplifying the FPC wiring configuration, if one conductive member is formed in the actuator unit and all the peripheral electrodes 65 formed in the actuator unit are electrically connected to each other by the conductive member, Good. By doing so, the number of peripheral wirings formed in the FPC is only one connected to the conductive member, so that the wiring configuration of the FPC can be simplified.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the above-described embodiments, and various modifications can be made as long as they are described in the claims. For example, in the actuator unit 42 of the inkjet head 5 described above, the peripheral electrode 65 may be formed on the outer side in the arrangement direction of the outermost individual electrode 60 with respect to the arrangement direction of the plurality of individual electrodes 60. It is not necessary to form the peripheral electrode 65 belonging to the peripheral electrode group 99 for use. In addition, the plurality of pressure chambers 46 may not be formed in a matrix, and the plurality of gaps 55 may not surround the plurality of pressure chambers 46. Accordingly, the plurality of peripheral electrodes 65 may not surround the plurality of individual electrodes 60. Further, the present invention can be applied to a head in which pressure chambers are arranged only in one direction. The above-described ink jet printer is a serial printer in which the head reciprocates, but may be a line printer in which the head is fixed. Further, a standby signal may be supplied to all the peripheral electrodes 65 during printing without distinguishing between the achromatic peripheral electrode group 97 and the chromatic peripheral electrode group 98.

  Moreover, the pressure chamber 46 and the space | gap 55 by this Embodiment mentioned above do not need to be formed in the same plane shape and plane size. Further, the individual electrode 60 and the peripheral electrode 65 may not be formed in the same planar shape and planar size. Further, the conductive members 75 and 76 may not connect the regions farthest from the individual electrode 60 in the peripheral electrode 65. Further, the plurality of manifolds 45 may not be formed in the flow path unit 41, and the plurality of pressure chambers 46 may not constitute the pressure chamber row group 48. Further, in the flow path unit 42, the gap 55 may not be formed at a position facing the peripheral electrode 65. Further, the auxiliary electrode region 66b of the peripheral electrode 65 may not be formed at the end on the same side where the auxiliary electrode region 61b of the adjacent individual electrode 60 is formed. Further, the longitudinal direction of the individual electrode 60 and the peripheral electrode 65 may not be orthogonal to the extending direction of the manifold 45. In the inkjet head 5 according to this embodiment described above, the standby signal is held at the same potential as the high potential of the ejection signal, but may be held at a potential other than the high potential of the ejection signal. The reference signal may also be held at a potential other than the low potential of the ejection signal.

1 is a schematic perspective view illustrating an internal configuration of a color inkjet printer to which an inkjet head according to an embodiment of the present invention is applied. FIG. 2 is a perspective view of the head unit shown in FIG. 1. It is sectional drawing in the II-II line of FIG. FIG. 4 is a perspective view showing a state where a frame is bonded to the inkjet head shown in FIG. 3. It is a top view of an inkjet head. FIG. 6 is an enlarged view of a region surrounded by an alternate long and short dash line drawn in FIG. 5. It is sectional drawing along the VII-VII line shown in FIG. The actuator unit is shown, (a) is an enlarged view of a portion surrounded by a one-dot chain line in FIG. 7, (b) is a plan view of an individual electrode. It is an enlarged plan view of an actuator unit. FIG. 6 is an enlarged plan view of the inkjet head shown in FIG. 5. It is a block diagram which shows the control structure of the inkjet printer with which the inkjet head by one Embodiment of this invention was applied. It is the figure on which the waveform pattern corresponding to each signal given to the ink jet head by one embodiment of the present invention was drawn. It is an enlarged plan view which shows the modification of the actuator unit of the inkjet head by one Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Inkjet printer 5 Inkjet head 41 Flow path unit 42,80 Actuator unit 45 Manifold (common ink chamber)
46 Pressure chamber 50 FPC (flexible printed wiring board)
51 Driver IC
53 nozzle 55 gap (peripheral gap)
60 Individual Electrode 65 Peripheral Electrode 70 Front Electrode 72 Common Electrode 75 to 79 Conductive Member 97 Achromatic Peripheral Electrode Group 98 Chromatic Peripheral Electrode Group 99 Boundary Peripheral Electrode Group

Claims (15)

A flow path unit formed with a plurality of pressure chambers each communicating with a nozzle;
A plurality of individual electrodes each facing the pressure chamber, a peripheral electrode spaced outward from the individual electrode located on the outermost side in each arrangement direction of the plurality of individual electrodes, the plurality of individual electrodes, and An actuator unit having a common electrode formed across a peripheral electrode, and a plurality of individual electrodes and a piezoelectric sheet sandwiched between the peripheral electrode and the common electrode;
In the piezoelectric sheet, a region sandwiched between the peripheral electrode and the common electrode, and a region sandwiched between the individual electrode and the common electrode are polarized to substantially the same degree,
A plurality of the peripheral electrodes are electrically connected to each other through a conductive member disposed on the actuator unit. The plurality of pressure chambers are two-dimensionally arranged in a matrix,
The inkjet head according to claim 1, wherein the plurality of peripheral electrodes surround the plurality of individual electrodes. A plurality of common ink chambers for storing ink are formed in the flow path unit, and the plurality of pressure chambers communicate with any one of the common ink chambers,
The inkjet head according to claim 2, wherein all the peripheral electrodes are electrically connected to each other through the one conductive member. In the flow path unit, a plurality of common ink chambers for storing ink are formed corresponding to a plurality of ink colors, and the plurality of pressure chambers communicate with any one of the common ink chambers,
A plurality of peripheral electrodes for chromatic color associated with the common ink chamber for storing at least chromatic ink, and a plurality of peripheral electrodes for achromatic color associated with the common ink chamber for storing achromatic ink. And
The plurality of chromatic color peripheral electrodes are electrically connected to each other via one conductive member,
The plurality of achromatic peripheral electrodes are electrically connected to each other via one other conductive member other than the one conductive member electrically connected to the plurality of chromatic peripheral electrodes. The inkjet head according to claim 2. The plurality of peripheral electrodes are separate from the plurality of chromatic color peripheral electrodes and the plurality of achromatic color peripheral electrodes, the common ink chamber for storing chromatic color ink, and the common ink chamber for storing achromatic color ink. A plurality of boundary peripheral electrodes at the boundary portion of
The plurality of boundary peripheral electrodes are connected to one of the conductive members other than the two conductive members, wherein the plurality of chromatic color peripheral electrodes and the plurality of achromatic color peripheral electrodes are distinguished and electrically connected to each other. The ink jet head according to claim 4, wherein the ink jet head is electrically connected to the ink jet head. A plurality of common ink chambers for storing ink are formed in the flow path unit, and the plurality of pressure chambers communicate with any one of the common ink chambers,
A plurality of peripheral electrodes related to the same common ink chamber are electrically connected to each other via one conductive member, and a plurality of peripheral electrodes related to different common ink chambers are connected to one conductive material. The inkjet head according to claim 2, wherein the inkjet head is not electrically connected to each other through a member.   The inkjet head according to any one of claims 2 to 6, wherein the conductive member connects regions farthest from the individual electrodes in the peripheral electrode. A plurality of the individual electrodes and a plurality of the peripheral electrodes are arranged so that the longitudinal direction thereof faces the same direction while having an elongated shape.
The inkjet head according to claim 7, wherein the conductive member connects regions in the vicinity of end portions in the longitudinal direction of the peripheral electrode. The individual electrode has a lead-out region extending along the longitudinal direction at a longitudinal end;
The peripheral electrode has a connection region extending along the longitudinal direction at a longitudinal end;
9. The ink jet head according to claim 8, wherein the connection area of the peripheral electrode is formed at an end portion on the same side as the lead area of the individual electrode adjacent to the peripheral electrode. A plurality of common ink chambers extending in one direction in which ink is stored are formed in the flow path unit, and the plurality of pressure chambers communicate with any one of the common ink chambers,
The inkjet head according to claim 8 or 9, wherein longitudinal directions of the plurality of individual electrodes and the plurality of peripheral electrodes are orthogonal to the one direction.   In the actuator unit, a surface electrode electrically connected to the common electrode is formed on the surface opposite to the surface in contact with the flow path unit on the outer side of the individual electrode and the peripheral electrode. The inkjet recording apparatus according to claim 2.   The inkjet head according to any one of claims 1 to 11, wherein the peripheral electrode has the same planar size and planar shape as the individual electrode.   The inkjet head according to any one of claims 1 to 12, wherein the flow path unit is formed with a peripheral gap facing the peripheral electrode.   The inkjet head according to claim 13, wherein the peripheral gap has the same planar size and planar shape as the pressure chamber.   15. The distance between the peripheral gap and the outermost pressure chamber with respect to the arrangement direction is equal to the distance between the adjacent pressure chambers. Inkjet head.

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