# Patent

## Title
Channel member for liquid ejecting head, liquid ejecting head including the same, and recording device including the same

## Abstract

A channel member 4 for a liquid ejecting head according to the present invention includes plates 4a to 4m that are stacked together. The plates include a first plate 4c including a first hole 7c, a second plate 4d including a second hole 7d, and a third plate 4e including a third hole 7e. In plan view, an opening 7cb at the bottom side of the first hole 7c and an opening 7ea at the top side of the third hole 7e have a region in which the openings 7cb and 7ea overlap and a region in which the openings 7cb and 7ea do not overlap, and the opening at the bottom side of the first hole 7c and the opening 7ea at the top side of the third hole 7e are inside the second hole 7d.

## Background
TECHNICAL FIELD
The present invention relates to a channel member for a liquid ejecting head, a liquid ejecting head including the channel member, and a recording device including the channel member.
BACKGROUND ART
A known example of a liquid ejecting head is an inkjet head that performs various types of printing by ejecting liquid toward a recording medium. A liquid ejecting head includes a channel member, which includes a plurality of ejection holes and a plurality of compression chambers, and a piezoelectric actuator substrate, which includes displacement elements that compress liquid in the compression chambers. The channel member includes a plurality of plates that are stacked together, the plates including holes that constitute channels. The ejection holes are provided on one principal surface of the channel member, and the compression chambers are provided on the other principal surface of the channel member. The channel member includes channels that connect the ejection holes to the compression chambers (see, for example, PTL 1).
CITATION LIST
Patent Literature
PTL 1: Japanese Unexamined Patent Application Publication No. 2003-311955
SUMMARY OF INVENTION
Technical Problem
In the liquid ejecting head described in PTL 1, the channels connecting the ejection holes to the compression chambers may be slightly inclined relative to a stacking direction in which the plates are stacked. In such a case, when the holes in the plates are displaced due to, for example, variations in the manufacturing process, the channel characteristics, such as the channel resistance, are changed in different ways depending on the directions of the displacements. Accordingly, the ejection characteristics, such as the ejection speed and the amount of ejection of the liquid, may greatly vary depending on the directions of the displacements.
Accordingly, an object of the present invention is to provide a channel member for a liquid ejecting head, a liquid ejecting head including the channel member, and a recording device including the channel member with which variations in ejection characteristics caused when holes in plates that constitute channels are displaced are small.
Solution to Problem
A channel member for a liquid ejecting head according to an embodiment of the present invention is a channel member for a liquid ejecting head including a channel that includes a partial channel. The channel member includes a plurality of plates that are stacked together, the plurality of plates including a first plate, a second plate, and a third plate that are successively stacked together. The first plate includes a first hole that extends through the first plate and constitutes a portion of the partial channel. The second plate includes a second hole that extends through the second plate and constitutes a portion of the partial channel. The third plate includes a third hole that extends through the third plate and constitutes a portion of the partial channel. In plan view of the channel member, an opening of the first hole at a side adjacent to the second plate and an opening of the third hole at a side adjacent to the second plate include a region in which the opening of the first hole at the side adjacent to the second plate and the opening of the third hole at the side adjacent to the second plate overlap and a region in which the opening of the first hole at the side adjacent to the second plate and the opening of the third hole at the side adjacent to the second plate do not overlap, and the opening of the first hole at the side adjacent to the second plate and the opening of the third hole at the side adjacent to the second plate are inside the second hole.
A liquid ejecting head according to an embodiment of the present invention includes the channel member for a liquid ejecting head, and a compressing portion that compresses liquid in the channel.
A recording device according to an embodiment of the present invention includes the liquid ejecting head, a conveying unit that conveys a recording medium relative to the liquid ejecting head, and a control unit that controls the liquid ejecting head.
Advantageous Effects of Invention
With a liquid ejecting head including a channel member for a liquid ejecting head according to an aspect of the present invention, even when holes constituting partial channels are displaced, variations in liquid ejection characteristics can be reduced.



BRIEF DESCRIPTION OF DRAWINGS
FIGS. 1(a) and 1(b) are a side view and a plan view, respectively, of a recording device including liquid ejecting heads according to an embodiment of the present invention.
FIG. 2 is a plan view of a head body, which is a main portion of each liquid ejecting head in FIG. 1.
FIG. 3 is an enlarged view of the region enclosed by the dotted-chain line in FIG. 2, where some channels are omitted to simplify the description.
FIG. 4 is another enlarged view of the region enclosed by the dotted-chain line in FIG. 2, where some channels are omitted to simplify the description.
FIG. 5(a) is a longitudinal sectional view taken along line V-V in FIG. 3, FIG. 5(b) is an enlarged sectional view of a portion of FIG. 5(a), and FIG. 5(c) is a plan view of a channel illustrated in FIG. 5(b).
FIG. 6 is a schematic enlarged plan view of a portion of a head body.



DESCRIPTION OF EMBODIMENTS
FIGS. 1(a) and 1(b) are a schematic side view and a schematic plan view, respectively, of a color inkjet printer 1 (hereinafter sometimes referred to simply as a printer), which is a recording device including liquid ejecting heads 2 according to an embodiment of the present invention. The printer 1 moves a print sheet P, which is a recording medium, relative to the liquid ejecting heads 2 by conveying the print sheet P from guide rollers 82A to conveying rollers 82B. A control unit 88 controls the liquid ejecting heads 2 on the basis of image and character data so that the liquid ejecting heads 2 eject liquid toward the recording medium P. Recording, such as printing, is performed on the print sheet P by applying liquid droplets to the print sheet P.
In the present embodiment, the liquid ejecting heads 2 are fixed to the printer 1. The printer 1 is a line printer. A recording device according to another embodiment of the present invention may be a serial printer in which an operation of moving the liquid ejecting heads 2 in a direction that crosses a conveying direction of the print sheet P, for example, in a direction substantially perpendicular to the conveying direction, and an operation of conveying the print sheet P are alternately performed.
A flat plate-shaped head mounting frame 70 (hereinafter sometimes referred to simply as a frame) is fixed to the printer 1 such that the frame 70 is substantially parallel to the print sheet P. The frame 70 has twenty holes (not shown), and twenty liquid ejecting heads 2 are placed in the holes in such a manner that portions of the liquid ejecting heads 2 from which the liquid is ejected face the print sheet P. The distance from the liquid ejecting heads 2 to the print sheet P is, for example, about 0.5 to 20 mm. Every five liquid ejecting heads 2 form a single head groups 72; accordingly, the printer 1 includes four head groups 72.
The liquid ejecting heads 2 have a long and narrow shape that extends in a direction from the near side toward the far side in FIG. 1(a), which is a vertical direction in FIG. 1(b). The direction in which the liquid ejecting heads 2 extend may be referred to as a long-side direction. In each head group 72, three liquid ejecting heads 2 are arranged in a direction that crosses the conveying direction of the print sheet P, for example, in a direction substantially perpendicular to the conveying direction. The remaining two liquid ejecting heads 2 are arranged at locations shifted from the three liquid ejecting heads 2 in the conveying direction, and each of the two liquid ejecting heads 2 is disposed between the three liquid ejecting heads 2. The liquid ejecting heads 2 are arranged such that printable areas thereof are connected to each other, or overlap at the ends, in the width direction of the print sheet P (direction that crosses the conveying direction of the print sheet P). Thus, an image that is continuous in the width direction of the print sheet P can be printed.
The four head groups 72 are arranged in the conveying direction of the recording sheet P. Each liquid ejecting head 2 receives liquid, for example, ink, from a liquid tank (not shown). The liquid ejecting heads 2 belonging to each head group 72 receive ink of the same color, so that the four head groups 72 are capable of performing printing by using inks of four colors. The colors of inks ejected from the head groups 72 are, for example, magenta (M), yellow (Y), cyan (C), and black (K). Color image printing can be performed by using these inks under the control of the control unit 88.
If monochrome printing is to be performed over an area within a printable area of a single liquid ejecting head 2, the number of liquid ejecting heads 2 to be mounted on the printer 1 may be one. The number of liquid ejecting heads 2 belonging to each head group 72 and the number of head groups 72 may be changed as appropriate depending on the printing subject and printing conditions. For example, the number of head groups 72 may be increased to increase the number of colors that can be printed. When a plurality of head groups 72 that perform printing in the same color are provided and caused to perform printing alternately in the conveying direction, the conveying speed can be increased without changing the performance of the liquid ejecting heads 2. In this case, the print area per unit time can be increased. Alternatively, a plurality of head groups 72 that perform printing in the same color may be arranged at locations shifted from each other in a direction that crosses the conveying direction to increase the resolution in the width direction of the print sheet P.
Instead of performing printing by using colored ink, surface treatment for the print sheet P may be performed by applying liquid such as a coating agent to the print sheet P.
The printer 1 prints on the print sheet P, which is a recording medium. The print sheet P is wound around a feed roller 80a. The print sheet P passes through the space between the two guide rollers 82A, the space below the liquid ejecting heads 2 mounted on the frame 70, and the space between the two conveying rollers 82B, and is finally wound around a take-up roller 80b. In a printing operation, the conveying rollers 82B are rotated so that the print sheet P is conveyed at a constant speed, and the liquid ejecting heads 2 performs printing. The print sheet P conveyed by the conveying rollers 82B is wound around the take-up roller 80b. The conveying speed is, for example, 75 m/min. Each roller may be controlled either by the control unit 88 or manually by a user.
The recording medium may be a roll of cloth instead of the print sheet P. The printer 1 may convey the recording medium by placing the recording medium on a conveying belt and directly moving the conveying belt instead of directly conveying the print sheet P. In this case, a cut sheet, a cut piece of cloth, a wood piece, a tile, etc., may be used as the recording medium. The liquid ejecting heads 2 may eject liquid containing conductive powder to print, for example, a wiring pattern of an electronic device. Alternatively, the liquid ejecting heads 2 may eject a predetermined amount of liquid chemical agent or liquid containing a chemical agent toward a reaction chamber to create a reaction for producing a chemical.
Position sensors, speed sensors, temperature sensors, etc., may be attached to the printer 1. The control unit 88 may control each part of the printer 1 in accordance with the states of the parts of the printer 1 that can be determined from information obtained by the sensors. For example, when the temperature of the liquid ejecting heads 2, the temperature of the liquid in the liquid tank, and the pressure applied to the liquid ejecting heads 2 by the liquid in the liquid tank affect the ejection characteristics (such as the amount of liquid that is ejected and the ejection speed), driving signals used to eject the liquid may be changed in accordance with these pieces of information.
The liquid ejecting heads 2 according to the embodiment of the present invention will now be described. FIG. 2 is a plan view of a head body 2a, which is the main portion of each liquid ejecting head 2 illustrated in FIG. 1. FIG. 3 is an enlarged plan view of a portion of the head body 2a in the region enclosed by the dotted-chain line in FIG. 2. In FIG. 3, some channels are omitted to simplify the description. FIG. 4 is an enlarged plan view of the same portion as that in FIG. 3, where channels other than those omitted in FIG. 3 are omitted. FIG. 5(a) is a longitudinal sectional view taken along line V-V in FIG. 3. FIG. 5(b) is an enlarged sectional view of a portion of FIG. 5(a), and FIG. 5(c) is a plan view of a channel illustrated in FIG. 5(b). In FIGS. 3 and 4, compression chambers 10, restricting portions 6, ejection holes 8, etc., which are arranged below a piezoelectric actuator substrate 21 and therefore are to be drawn with broken lines, are drawn with solid lines to facilitate understanding of the drawing.
Each liquid ejecting head 2 may include a reservoir, which supplies the liquid to the head body 2a, and a housing in addition to the head body 2a. The head body 2a includes a channel member 4 and the piezoelectric actuator substrate 21 having displacement elements 30, which are compressing portions, formed therein.
The channel member 4 of the head body 2a includes manifolds 5 that serve as common channels, the compression chambers 10 connected to the manifolds 5, and the ejection holes 8 connected to the compression chambers 10. The compression chambers 10 open at the top surface of the channel member 4, and the top surface of the channel member 4 serves as a compression chamber surface 4-2. The top surface of the channel member 4 has openings 5a connected to the manifolds 5, and liquid is supplied to the manifolds 5 through the openings 5a. 
The piezoelectric actuator substrate 21 including the displacement elements 30 is bonded to the top surface of the channel member 4 such that each displacement element 30 is arranged above the corresponding compression chamber 10. Signal transmission units 60 that supply signals to the displacement elements 30 are connected to the piezoelectric actuator substrate 21. In FIG. 2, to clearly illustrate the state in which two signal transmission units 60 are connected to the piezoelectric actuator substrate 21, the contours of the signal transmission units 60 in the regions around the portions that are connected to the piezoelectric actuator substrate 21 are shown by the dotted lines. Electrodes formed on the signal transmission units 60 and electrically connected to the piezoelectric actuator substrate 21 are arranged in a rectangular pattern at the ends of the signal transmission units 60. The two signal transmission units 60 are connected to the piezoelectric actuator substrate 21 such that the ends there of are in a central region of the piezoelectric actuator substrate 21 in the short-side direction.
The head body 2a includes the flat plate-shaped channel member 4 and a single piezoelectric actuator substrate 21 that is bonded to the channel member 4 and that includes the displacement elements 30. The piezoelectric actuator substrate 21 has a rectangular shape in plan view, and is arranged on the top surface of the channel member 4 such that the long sides of the rectangular shape extend in the long-side direction of the channel member 4.
Two manifolds 5 are formed in the channel member 4. The manifolds 5 have a long and narrow shape that extends from one end of the channel member 4 in the long-side direction toward the other end. Each manifold 5 has openings 5a that open at the top surface of the channel member 4 at both ends of the manifold 5.
Each manifold 5 is partitioned into sections by partition walls 15 at least in a central region thereof in the long-side direction, that is, a region in which the manifold 5 is connected to the compression chambers 10. The partition walls 15 are spaced from each other in the short-side direction. In the central region in the long-side direction, which is the region in which the manifold 5 is connected to the compression chambers 10, the partition walls 15 have the same height as that of the manifold 5 so that the manifold 5 is completely partitioned into a plurality of sub-manifolds 5b. Accordingly, the ejection holes 8 and channels extending from the ejection holes 8 to the compression chambers 10 can be formed so as to overlap the partition walls 15 in plan view.
The sections into which each manifold 5 is partitioned may be referred to as the sub-manifolds 5b. In the present embodiment, two independent manifolds 5 are provided, and each manifold 5 has the openings 5a at both ends thereof. Each manifold 5 is partitioned into eight sub-manifolds 5b by seven partition walls 15. The width of the sub-manifolds 5b is greater than that of the partition walls 15, so that the sub-manifolds 5b allow a large amount of liquid to flow therethrough.
The compression chambers 10 are arranged two dimensionally in the channel member 4. The compression chambers 10 are hollow spaces having a diamond shape with rounded corners or an elliptical shape in plan view.
Each compression chamber 10 is connected to one of the sub-manifolds 5b through the corresponding individual supply channel 14. Two compression chamber rows 11 are arranged one on each side of each sub-manifold 5b so as to extend along the sub-manifold 5b, each compression chamber row 11 including compression chambers 10 that are connected to the sub-manifold 5b. Accordingly, 16 compression chamber rows 11 are provided for each manifold 5, and 32 compression chamber rows 11 are provided in total in the head body 2a. In each compression chamber row 11, the compression chambers 10 are arranged with constant intervals therebetween in the long-side direction, the intervals corresponding to, for example, 37.5 dpi.
The compression chamber rows 11 have dummy compression chambers 16 at both ends thereof so that the dummy compression chambers 16 form two dummy compression chamber lines. The dummy compression chambers 16 belonging to the dummy compression chamber lines are connected to the manifolds 5, but are not connected to the ejection holes 8. Also, a dummy compression chamber row in which the dummy compression chambers 16 are linearly arranged is provided at each outer side of the 32 compression chamber rows 11 (each of the sides adjacent to the 1st compression chamber row 11 and the 32nd compression chamber row 11). The dummy compression chambers 16 belonging to the dummy compression chamber rows are not connected to the manifolds 5 or the ejection holes 8. Owing to the dummy compression chambers 16, the compression chambers 10 disposed at the periphery have surrounding structures (rigidities) similar to the surrounding structures (rigidities) of the other compression chambers 10, so that differences in the liquid ejecting characteristics between the compression chambers 10 at the periphery and the other compression chambers 10 can be reduced. The influence of the differences between the surrounding structures is large for the compression chambers 10 that are arranged next to each other in the longitudinal direction of the channel member 4 and that are close to each other, and the influence is relatively small for the compression chambers 10 arranged next to each other in the width direction of the channel member 4. For this reason, although the compression chamber rows that are adjacent to each other in a central region of the head body 2a in the width direction have a large gap therebetween, no dummy compression chamber lines are provided in this region. Accordingly, the width of the head body 2a can be reduced.
The compression chambers 10 connected to each manifold 5 are arranged in a grid pattern having rows and columns along the outer sides of the rectangular piezoelectric actuator substrate 21. Accordingly, individual electrodes 25, which are arranged above the compression chambers 10, are evenly spaced from the outer sides of the piezoelectric actuator substrate 21. Therefore, the piezoelectric actuator substrate 21 is not easily deformed when the individual electrodes 25 are formed. If the piezoelectric actuator substrate 21 is largely deformed when the piezoelectric actuator substrate 21 and the channel member 4 are bonded together, there is a risk that the displacement elements 30 near the outer sides will receive a stress and the displacement characteristics thereof will vary. The variation in the displacement characteristics can be reduced by reducing the deformation. The influence of the deformation is further reduced since the dummy compression chamber rows including the dummy compression chambers 16 are provided on the outer side of the compression chamber rows 11 that are closest to the outer sides of the piezoelectric actuator substrate 21. The compression chambers 10 belonging to each compression chamber row 11 are arranged with constant intervals therebetween, and the individual electrodes 25 that correspond to the compression chamber rows 11 are also arranged with constant intervals therebetween. The compression chamber rows 11 are arranged with constant intervals therebetween in the short-side direction, and the rows of the individual electrodes 25 corresponding to the compression chamber rows 11 are also arranged with constant intervals therebetween in the short-side direction. Accordingly, regions in which the influence of crosstalk, in particular, is significant may be eliminated.
Although the compression chambers 10 are arranged in a grid pattern in the present embodiment, they may instead be arranged in a staggered pattern in which the compression chambers 10 of each compression chamber row 11 are disposed between the compression chambers 10 of the adjacent compression chamber row 11. In this case, the distance between the compression chambers 10 belonging to the adjacent compression chamber rows 11 can be increased, so that crosstalk can be further reduced.
Irrespective of how the compression chamber rows 11 are arranged, crosstalk can be reduced by arranging the compression chambers 10 such that, in plan view of the channel member 4, the compression chambers 10 of each compression chamber row 11 do not overlap the compression chambers 10 of the adjacent compression chamber row 11 in the long-side direction of the liquid ejecting head 2. If the distances between the compression chamber rows 11 are increased, the width of the liquid ejecting head 2 is increased accordingly. As a result, the accuracy of the angle at which the liquid ejecting head 2 is attached to the printer 1 greatly affects the printing result. When multiple liquid ejecting heads 2 are used, the accuracy of the relative positions between the liquid ejecting heads 2 also greatly affects the printing result. The influence of these accuracies on the printing result can be reduced by setting the width of the partition walls 15 smaller than that of the sub-manifolds 5b. 
The compression chambers 10 connected to each sub-manifold 5b form two compression chamber rows 11, and the ejection holes 8 connected to the compression chambers 10 belonging to each compression chamber row 11 form a single ejection hole row 9. The ejection holes 8 connected to the compression chambers 10 belonging to the two compression chamber rows 11 open at different sides of the sub-manifold 5b. Although two ejection hole rows 9 are provided on each partition wall 15 in FIG. 4, the ejection holes 8 belonging to each ejection hole row 9 are connected to the sub-manifold 5b adjacent to the ejection holes 8 through the compression chambers 10. When the ejection holes 8 connected to the adjacent sub-manifolds 5b through the compression chamber rows 11 are arranged so as not to overlap in the long-side direction of the liquid ejecting head 2, crosstalk between the channels that connect the compression chambers 10 to the ejection holes 8 can be suppressed. Thus, crosstalk can be further reduced. When the entireties of the channels that connect the compression chambers 10 to the ejection holes 8 do not overlap in the long-side direction of the liquid ejecting head 2, crosstalk can be further reduced.
The compression chambers 10 connected to each manifold 5 form a compression chamber group. Since there are two manifolds 5, two compression chamber groups are provided. The compression chambers 10 that contribute to ejection in the compression chamber groups are arranged in the same way at positions translated from one another in the short-side direction. The compression chambers 10 are arranged along the top surface of the channel member 4 over almost the entirety of the region that faces the piezoelectric actuator substrate 21, although there are regions in which the intervals between the compression chambers 10 are somewhat large, such as the region between the compression chamber groups. In other words, the compression chamber groups including the compression chambers 10 occupy a region having substantially the same shape as that of the piezoelectric actuator substrate 21. The open side of each compression chamber 10 is covered with the piezoelectric actuator substrate 21 that is bonded to the top surface of the channel member 4.
Each compression chamber 10 has a channel extending therefrom at a corner that opposes the corner at which the individual supply channel 14 is connected to the compression chamber 10, the channel extending to the corresponding ejection hole 8 which opens in an ejection-hole surface 4-1 at the bottom of the channel member 4. The channel extends in a direction away from the compression chamber 10 in plan view. More specifically, the channel extends away from the compression chamber 10 in the diagonal direction of the compression chamber 10 while being shifted leftward or rightward relative to the diagonal direction. Accordingly, although the compression chambers 10 are arranged in a grid pattern such that the intervals therebetween in each compression chamber row 11 correspond to 37.5 dpi, the ejection holes 8 may be arranged with intervals corresponding to 1200 dpi over the entire region.
In other words, if the ejection holes 8 are projected onto a plane perpendicular to an imaginary straight line that is parallel to the long-side direction of the channel member 4, the 16 ejection holes 8 connected to each of the manifolds 5 in the region R enclosed by the imaginary straight lines in FIG. 4, that is, 32 ejection holes 8 in total, are arranged at constant intervals that correspond to 1200 dpi. This means that, when ink of the same color is supplied to both of the manifolds 5, an image can be formed at a resolution of 1200 dpi in the long-side direction. The 16 ejection holes 8 connected to each manifold 5 are arranged at constant intervals corresponding to 600 dpi in the region R enclosed by the imaginary straight lines in FIG. 4. Accordingly, when inks of different colors are supplied to the manifolds 5, a two-color image can be formed at a resolution of 600 dpi in the long-side direction. When two liquid ejecting heads 2 are used, a four-color image can be formed at a resolution of 600 dpi. In this case, the printing accuracy is higher than that achieved when four liquid ejecting heads capable of performing printing at 600 dpi are used, and print settings can be facilitated. The ejection holes 8 connected to the compression chambers 10 belonging to a single compression chamber line that extends in the short-side direction of the head body 2a cover the region R enclosed by the imaginary straight lines.
The individual electrodes 25 are formed on the top surface of the piezoelectric actuator substrate 21 at positions where the individual electrodes 25 face the corresponding compression chambers 10. Each individual electrode 25 is somewhat smaller than the corresponding compression chamber 10, and includes an individual electrode body 25a having a shape that is substantially similar to that of the compression chamber 10 and a lead electrode 25b that extends from the individual electrode body 25a. Similar to the compression chambers 10, the individual electrodes 25 also form individual electrode rows and individual electrode groups. Common-electrode surface electrodes 28 are also formed on the top surface of the piezoelectric actuator substrate 21. The common-electrode surface electrodes 28 are electrically connected to a common electrode 24 by through conductors (not illustrated) formed in a piezoelectric ceramic layer 21b. 
The ejection holes 8 are located outside the regions that face the manifolds 5 arranged at the bottom side of the channel member 4. Also, the ejection holes 8 are arranged in a region facing the piezoelectric actuator substrate 21 at the bottom side of the channel member 4. The ejection holes 8 occupy a region having substantially the same shape as that of the piezoelectric actuator substrate 21 as a single group. Liquid droplets are ejected from the ejection holes 8 when the corresponding displacement elements 30 of the piezoelectric actuator substrate 21 are displaced.
The channel member 4 included in the head body 2a has a multilayer structure in which multiple plates are stacked together. The plates include a cavity plate 4a, a base plate 4b, an aperture (restricting portion) plate 4c, a supply plate 4d, manifold plates 4e to 4j, a cover plate 4k, and a nozzle plate 4m in that order from the top of the channel member 4. Multiple holes are formed in these plates. Each plate has a thickness of about 10 to 300 μm, so that high-precision holes can be formed. The channel member 4 has a thickness of about 500 μm to 2 mm. The plates are positioned relative to each other and stacked together so that the holes formed therein communicate with each other so as to form individual channels 12 and the manifolds 5. The head body 2a is configured such that the compression chambers 10 are formed in the top surface of the channel member 4, the manifolds 5 are formed in the channel member 4 at the bottom side of the channel member 4, and the ejection holes 8 are formed in the bottom surface of the channel member 4. Portions that form the individual channels 12 are arranged near each other at different locations so that the manifolds 5 are connected to the ejection holes 8 through the compression chambers 10.
The holes formed in the plates will now be described. The holes include the following first to fourth holes. The first holes are the compression chambers 10 formed in the cavity plate 4a. The second holes are communication holes that constitute the individual supply channels 14, each of which connects one end of the corresponding compression chamber 10 to the corresponding manifold 5. These communication holes are formed in each of the plates from the base plate 4b (specifically, inlets of the compression chambers 10) to the supply plate 4d (specifically, outlets of the manifolds 5). The individual supply channels 14 include the restricting portions 6, which are channel portions having a small cross-sectional area, in the aperture plate 4c. 
The third holes are descenders 7 that extend from the ends of the compression chambers 10 opposite the ends connected to the individual supply channels 14 to the ejection holes 8. The descenders 7 are formed in each of the plates from the base plate 4b to the cover plate 4k. 
The fourth holes are communication holes that constitute the sub-manifolds 5b. These communication holes are formed in the manifold plates 4e to 4j. The holes are formed in the manifold plates 4e to 4j so that partitioning portions that form the partition walls 15 remain so as to define the sub-manifolds 5b. The partitioning portions of the manifold plates 4e to 4j are connected to the manifold plates 4e to 4j by half-etched support portions (not illustrated).
The first to fourth communication holes are connected to each other to form the individual channels 12 extending from the inlets through which the liquid is supplied form the manifolds 5 (outlets of the manifolds 5) to the ejection holes 8. The liquid supplied to the manifolds 5 is ejected from each ejection hole 8 along the following path. First, the liquid flows upward from the corresponding manifold 5 through the individual supply channel 14 to one end of the corresponding restricting portion 6. Next, the liquid flows horizontally in the extending direction of the restricting portion 6 to the other end of the restricting portion 6. Then, the liquid flows upward toward one end of the corresponding compression chamber 10. Then, the liquid flows horizontally in the extending direction of the compression chamber 10 to the other end of the compression chamber 10. The liquid enters the corresponding descender 7 from the compression chamber 10 and flows mainly downward while moving also in the horizontal direction. Then, the liquid reaches the ejection hole 8 that opens in the bottom surface, and is ejected outward.
The piezoelectric actuator substrate 21 has a multilayer structure including two piezoelectric ceramic layers 21a and 21b composed of piezoelectric materials. Each of the piezoelectric ceramic layers 21a and 21b has a thickness of about 20 μm. The thickness of the piezoelectric actuator substrate 21 from the bottom surface of the piezoelectric ceramic layer 21a to the top surface of the piezoelectric ceramic layer 21b is about 40 μm. Each of the piezoelectric ceramic layers 21a and 21b extends over the compression chambers 10. The piezoelectric ceramic layers 21a and 21b are made of a ferroelectric ceramic material, such as a lead zirconate titanate (PZT) based, NaNbO3 based, BaTiO3 based, (BiNa)NbO3 based, or BiNaNb5O15 based ceramic material. The piezoelectric ceramic layer 21a serves as a vibration substrate, and is not necessarily composed of a piezoelectric material. The piezoelectric ceramic layer 21a may be replaced by, for example, a ceramic layer that is not composed of a piezoelectric material or a metal plate.
The piezoelectric actuator substrate 21 includes the common electrode 24 made of a metal material such as a Ag—Pd-based material, and the individual electrodes 25 made of a metallic material such as a Au-based material. The common electrode 24 has a thickness of about 2 μm, and the individual electrodes 25 have a thickness of about 1 μm.
The individual electrodes 25 are formed on the top surface of the piezoelectric actuator substrate 21 at positions where the individual electrodes 25 face their respective compression chambers 10. Each individual electrode 25 is somewhat smaller than a compression chamber 10 in plan view, and includes an individual electrode body 25a having a shape that is substantially similar to that of the compression chamber 10 and a lead electrode 25b that extends from the individual electrode body 25a. A connecting electrode 26 is provided on an end portion of the lead electrode 25b that extends away from the region facing the compression chamber 10. The connecting electrode 26 is formed of a conductive resin containing conductive powder, such as silver powder, and has a thickness of about 5 to 200 μm. The connecting electrode 26 is electrically bonded to a corresponding one of the electrodes provided on the signal transmission units 60.
Drive signals are supplied to the individual electrodes 25 from the control unit 88 through the signal transmission units 60. This will be described in detail below. The drive signals are supplied at a constant period in synchronization with the conveyance speed of the print medium P.
The common electrode 24 is arranged between the piezoelectric ceramic layer 21b and the piezoelectric ceramic layer 21a so as to extend over almost the entire surfaces thereof in the planar direction. In other words, the common electrode 24 extends so as to cover all of the compression chambers 10 within the region that faces the piezoelectric actuator substrate 21. The common electrode 24 is connected to the common-electrode surface electrodes 38 by the through conductors that extend through the piezoelectric ceramic layer 21b. The common-electrode surface electrodes 38 are formed on the piezoelectric ceramic layer 21b at locations separated from the electrode groups of the individual electrodes 25. The common electrode 24 is grounded by the common-electrode surface electrodes 38, and is maintained at the ground potential. Similar to the individual electrodes 25, the common-electrode surface electrodes 38 are directly or indirectly connected to the control unit 88.
Portions of the piezoelectric ceramic layer 21b that are interposed between the individual electrodes 25 and the common electrode 24 are polarized in the thickness direction, and serve as displacement elements 30 having a unimorph structure that are displaced when a voltage is applied to the individual electrodes 25. More specifically, when the individual electrodes 25 and the common electrode 24 are set to different potentials to apply an electric field to the piezoelectric ceramic layer 21b in the direction of polarization thereof, the portions to which the electric field is applied function as active portions that are deformed due to the piezoelectric effect. When the control unit 88 sets the individual electrodes 25 to a predetermined positive or negative potential relative to the potential of the common electrode 24 so that the direction of the electric field is the same as the direction of polarization, the portions of the piezoelectric ceramic layer 21b interposed between the electrodes (active portions) contract in the planar direction. Conversely, the piezoelectric ceramic layer 21a, which is an inactive layer, is not affected by the electric field, and therefore does not contract by itself but tries to restrict the deformation of the active portions. As a result, the piezoelectric ceramic layer 21a and the piezoelectric ceramic layer 21b are deformed by different amounts in the direction of polarization, so that the piezoelectric ceramic layer 21a is deformed so as to be convex toward the compression chambers 10 (unimorph deformation).
The liquid ejection operation will now be described. The displacement elements 30 are driven (displaced) in response to drive signals supplied to the individual electrodes 25 through, for example, a driver IC under the control of the control unit 88. The liquid ejection operation can be performed by using various types of drive signals in the present embodiment; here, a so-called pulling driving method will be described.
The individual electrodes 25 are initially set to a potential higher than that of the common electrode 24 (hereafter referred to as a high potential). The potential of each individual electrode 25 is temporarily reduced to that of the common electrode 24 (hereafter referred to as a low potential) every time an ejection request is issued, and is then returned to the high potential at a predetermined timing. Accordingly, the piezoelectric ceramic layers 21a and 21b return (start to return) to their original (flat) shape at the time when the individual electrode 25 is set to the low potential, and the volume of the corresponding compression chamber 10 increases from that in the initial state (state in which the individual and common electrodes are set to different potentials). Therefore, a negative pressure is applied to the liquid in the compression chamber 10. As a result, the liquid in the compression chamber 10 starts to vibrate at its natural vibration period. More specifically, first, the volume of the compression chamber 10 starts to increase, and the negative pressure gradually decreases. Then, the volume of the compression chamber 10 reaches a maximum volume, and the pressure decreases to approximately zero. Then, the volume of the compression chamber 10 starts to decrease, and the pressure starts to increase. The individual electrode 25 is set to the high potential substantially when the pressure reaches a maximum pressure. Accordingly, the vibration applied first and the vibration applied next are combined so that a larger pressure is applied to the liquid. The pressure is transmitted through the corresponding descender 7, so that the liquid is ejected from the corresponding ejection hole 8.
Thus, a liquid droplet can be ejected by applying a pulse driving signal to the individual electrode 25, the driving signal being set basically to the high potential and to the low potential for a predetermined period. In principle, the liquid ejection speed and the amount of ejection can be maximized by setting the pulse width to an acoustic length (AL), which is half the natural vibration period of the liquid in the compression chamber 10. The natural vibration period of the liquid in the compression chamber 10 depends greatly on the properties of the liquid and the shape of the compression chamber 10, but it depends also on the properties of the piezoelectric actuator substrate 21 and the properties of the channels connected to the compression chamber 10.
The pulse width is set to a value that is about 0.5 AL to 1.5 AL in practice because of other factors to be taken into consideration, for example, to eject the liquid in the form of a single droplet. Since the amount of ejection can be reduced by setting the pulse width to a value different from AL, the pulse width may be set to a value different from AL for the purpose of reducing the amount of ejection.
Each descender 7 is a channel that connects the corresponding compression chamber 10 to the corresponding ejection hole 8, and serves as a partial channel that constitutes a portion of a channel through which the liquid flows. The descender 7 extends through the plates 4b to 4k. The descender 7 allows the liquid to flow therethrough in the stacking direction. The liquid mainly flows from the compression chamber surface 4-2 to the ejection-hole surface 4-1. However, since the end portion of the compression chamber 10 to which the descender 7 is connected is displaced from the ejection hole 8 in a planar direction, the liquid flows while being gradually shifted in a planar direction. In other words, the descender 7 is inclined relative to the stacking direction.
Descender holes 7b to 7k, which constitute the descender 7, are somewhat displaced due to variations in the manufacturing process. When the descender 7 is inclined relative to the stacking direction, in particular, the way in which the channel characteristics are changed greatly varies depending on the relationship between the inclination direction of the descender 7 and the direction of the displacement. Unlike the case in which the inclination direction and the direction of the displacement differ by 90 degrees, when the inclination direction is the same as the direction of the displacement, the inclination and the displacement are combined such that the descender 7 includes a portion having a small cross-sectional area at an intermediate position thereof. Accordingly, the channel characteristics change significantly, and the ejection characteristics are greatly influenced.
The displacement occurs when the positions of the individual descender holes formed in the plates are displaced or when the plates are displaced when they are stacked so that the entireties of the descender holes formed in the plates are displaced. The descenders 7 included in the head body 2a according to the present embodiment are inclined in various directions. When the plates are displaced when they are stacked together, for example, the volume of liquid droplets may increase in the descenders 7 inclined in a certain direction and decrease in the descenders 7 inclined in another direction. Thus, there is a risk that variations in the entire head body 2a will be increased and the print accuracy will be reduced.
Accordingly, each descender 7, which is formed by stacking three or more plates together, is formed so as to have the following configuration. FIG. 5(b) illustrates an embodiment of the configuration. FIG. 5(b) is an enlarged longitudinal cross-sectional view of a portion of the descender 7 illustrated in FIG. 5(a). In FIG. 5(a), detailed shapes of the descender 7 formed by etching are not illustrated. FIG. 5(c) is a plan view illustrating the arrangement of openings of the holes that constitute the descender 7. In FIG. 5(c), the inner region of an opening 7cb at a bottom side of a first hole 7c (side adjacent to a second plate 4d) is hatched with slanted lines that extend in a direction from the upper right toward the lower left. Also, the inner region of an opening 7ea at a top side of a third hole 7e (side adjacent to the second plate 4d) is hatched with slanted lines that extend in a direction from the upper left toward the lower right.
Three plates that are successively stacked together are defined as a first plate 4c, a second plate 4d, and a third plate 4e in that order from the top. Each of the first plate 4c, the second plate 4d, and the third plate 4e may be a compound body obtained by bonding a plurality of elements together. Here, the first plate 4c is the above-described aperture (restricting portion) plate 4c, the second plate 4d is the above-described supply plate 4d, and the third plate 4e is the above-described manifold plate 4e. The first hole 7c, which constitutes a portion of the descender 7, is formed in the first plate 4c. A second hole 7d, which also constitutes a portion of the descender 7, is formed in the second plate 4d. The third hole 7e, which also constitutes a portion of the descender 7, is formed in the third plate 4e. 
In plan view, a region included in both the opening 7cb at the bottom side of the first hole 7c (side adjacent to the second plate 4d) and the opening 7ea at the top side of the third hole 7e (side adjacent to the second plate 4d) exists. In addition, a region included in the opening 7cb at the bottom side of the first hole 7c but not included in the opening 7ea at the top side of the third hole 7e also exists. In addition, a region included in the opening 7ea at the top side of the third hole 7e but not included in the opening at the bottom side 7cb of the first hole 7c exists. The opening 7cb at the bottom side of the first hole 7c and the opening 7ea at the top side of the third hole 7e are inside the second hole 7d. In other words, in plan view, the opening 7cb of the first hole 7c at the side adjacent to the second plate 4d and the opening 7ea of the third hole 7e at the side adjacent to the second plate 4d have a region in which they overlap and regions in which they do not overlap. In addition, in plan view, the opening 7cb of the first hole 7c at the side adjacent to the second plate 4d and the opening 7ea of the third hole 7e at the side adjacent to the second plate 4d are inside the second hole 7d. 
The state in which the opening 7cb at the bottom side of the first hole 7c and the opening 7ea at the top side of the third hole 7e are inside the second hole 7d will now be described. This state means that, as illustrated in FIG. 5(c), in plan view, the opening 7cb at the bottom side of the first hole 7c is inside an opening 7da at the top side of the second hole 7d (side adjacent to the first plate 4c), and the opening 7ea at the top side of the third hole 7e is inside an opening 7db at the bottom side of the second hole 7d (side adjacent to the third plate 4e). In this specification, when it simply mentions “in plan view”, it means that the configuration is viewed in the stacking direction of the plates 4a to 4m. 
It is difficult to observe the channel member 4 that has been manufactured in practice in plan view and confirm that the opening 7cb at the bottom side of the first hole 7c is inside the opening 7da at the top side of the second hole 7d and that the opening 7ea at the top side of the third hole 7e is inside the opening 7db at the bottom side of the second hole 7d. Accordingly, to examine the channel member 4 manufactured in practice, a single longitudinal cross section of a single descender 7 may be observed, as illustrated in FIG. 5(b). In this cross section, it can be confirmed that the opening 7cb at the bottom side of the first hole 7c is inside the opening 7da at the top side of the second hole 7d and that the opening 7ea at the top side of the third hole 7e is inside the opening 7db at the bottom side of the second hole 7d. 
This method may also be used to confirm that, in plan view, a region included in both the opening 7cb at the bottom side of the first hole 7c and the opening 7ea at the top side of the third hole 7e exists, a region included in the opening 7cb at the bottom side of the first hole 7c but not included in the opening 7ea at the top side of the third hole 7e exists, and a region included in the opening 7ea at the top side of the third hole 7e but not included in the opening at the bottom side 7cb of the first hole 7c exists. To examine the channel member 4 manufactured in practice, a single longitudinal cross section of a single descender 7 may be observed. In this cross section, it can be confirmed that a region included in both the opening 7cb at the bottom side of the first hole 7c and the opening 7ea at the top side of the third hole 7e exists, that a region included in the opening 7cb at the bottom side of the first hole 7c but not included in the opening 7ea at the top side of the third hole 7e exists, and that a region included in the opening 7ea at the top side of the third hole 7e but not included in the opening at the bottom side 7cb of the first hole 7c exists.
When the region included in both the opening 7cb at the bottom side of the first hole 7c and the opening 7ea at the top side of the third hole 7e exists, the liquid smoothly flows from the first hole 7c to the third hole 7e. When the region included in the opening 7cb at the bottom side of the first hole 7c but not included in the opening 7ea at the top side of the third hole 7e exists, and when the region included in the opening 7ea at the top side of the third hole 7e but not included in the opening 7cb of the first hole 7c at the bottom side also exists, the first hole 7c and the third hole 7e are displaced from each other. Accordingly, when the liquid flows from the compression chamber surface 4-2 toward the ejection-hole surface 4-1, the liquid moves in the planar direction. In addition, when the opening 7cb at the bottom side of the first hole 7c and the opening lea at the top side of the third hole 7e are inside the second hole 7d, the influence caused when the holes are displaced from each other can be reduced.
The above-described arrangement is also effective for channels other than the descenders 7 through which the liquid flows in the stacking direction. In the descenders 7, variations in the pressure transmitted therethrough directly affect the ejection characteristics. Therefore, the descenders 7 have a particularly high need for the above-described arrangement. Moreover, not only does the magnitude of the pressure in the descenders 7 affect the ejection speed and the amount of ejection, but also the way in which the pressure is transmitted through the descenders 7 also affect the ejection characteristics because the direction in which the liquid is ejected from the ejection holes 8 slightly changes. Therefore, the descenders 7 have a high need for the above-described arrangement.
In plan view, the opening 7da at the top side of the second hole 7d and the opening 7db at the bottom side of the second hole 7d may be displaced from each other. In this case, compared to the case in which the opening 7da at the top side and the opening 7db at the bottom side are at the same position, the area of the opening 7da at the top side of the second hole 7d and the area of the opening 7db at the bottom side of the second hole 7d may be reduced while enabling the opening 7cb at the bottom side of the first hole 7c and the opening 7ea at the top side of the third hole 7e to be inside the second hole 7d. When the descender 7 includes an intermediate portion at which the cross-sectional area thereof changes, it may become difficult for the descender 7 to transmit pressure waves because, for example, the pressure waves are partially reflected at the boundary. However, when the opening 7da at the top side of the second hole 7d and the opening 7db at the bottom side of the second hole 7d are displaced from each other, the ratio of the area of the opening 7da at the top side of the second hole 7d to the area of the opening 7cb at the bottom side of the first hole 7c can be reduced. Also, the ratio of the area of the opening 7ea at the top side of the third hole 7e to the area of the opening 7db at the bottom side of the second hole 7d can be reduced. As a result, the pressure-wave transmission efficiency can be increased.
The direction from the area centroid of the opening 7da at the top side of the second hole 7d to the area centroid of the opening 7db at the bottom side of the second hole 7d may be the same as the direction from the area centroid of the opening 7cb at the bottom side of the first hole 7c to the area centroid of the opening 7ea at the top side of the third hole 7e. In such a case, the pressure transmission efficiency can be increased, as described above, while enabling the liquid to flow through the descender 7 while being moved in the planar direction. Here, the state in which the directions are the same means that the angle between the above-described two directions is smaller than 90 degrees. The angle between the two directions is preferably 60 degrees or less, and more preferably, 30 degrees or less.
When the opening 7da at the top side of the second hole 7d and the opening 7db at the bottom side of the second hole 7d are displaced from each other, the opening 7cb at the bottom side of the first hole 7c may be arranged so as to be inside the opening 7da at the top side of the second hole 7d and so as to include a region that is not included in the opening 7db at the bottom side of the second hole 7d. Also, the opening 7ea at the top side of the third hole 7e may be arranged so as to be inside opening 7db at the bottom side of the second hole 7d and so as to include a region that is not included in the opening 7da at the top side of the second hole 7d. This arrangement allows the liquid to smoothly move in the planar direction while preventing a reduction in the pressure transmission efficiency.
It is difficult to observe the channel member 4 that has been manufactured in practice in plan view and confirm that the opening 7cb at the bottom side of the first hole 7c is inside the opening 7da at the top side of the second hole 7d and includes a region that is not included in the opening 7db at the bottom side of the second hole 7d, and that the opening 7ea at the top side of the third hole 7e is inside the opening 7db at the bottom side of the second hole 7d and includes a region that is not included in the opening 7da at the top side of the second hole 7d. Accordingly, to examine that the channel member 4 manufactured in practice, a single longitudinal cross section of a single descender 7 may be observed. In this cross section, it can be confirmed that the opening 7cb at the bottom side of the first hole 7c is inside the opening 7da at the top side of the second hole 7d and includes a region that is not included in the opening 7db at the bottom side of the second hole 7d, and that the opening 7ea at the top side of the third hole 7e is inside the opening 7db at the bottom side of the second hole 7d and includes a region that is not included in the opening 7da at the top side of the second hole 7d. 
It is preferable that the second plate 4d is the thickest among the first plate 4c, the second plate 4d, and the third plate 4e. The second hole 7d in the second plate 4d is larger than the opening 7cb at the bottom side of the first hole 7c and the opening 7ea at the top side of the third hole 7e. Therefore, a region in which the liquid does not easily flow exists at the peripheral edge of the second hole 7d. When the second plate 4d is thin, the region in which the liquid does not easily flow at the outer periphery of the second hole 7d expands over a large area relative to the length of the second plate 4d in the direction in which the liquid flows, and accordingly the liquid easily stagnates. Therefore, the second plate 4d is preferably thick. In other words, preferably, a hole having a large cross-sectional area is formed in a thick plate as the second hole 7d. Moreover, the second plate 4d is preferably the thickest among the plates 4b to 4k in which the descender holes 7b to 7k are formed.
The descender 7 extends at an angle relative to the stacking direction. However, the descender 7 is formed by connecting the descender holes 7b to 7k to each other along a substantially straight line. The displacements between the plates 4b to 4k are considered to occur irrespective of the thicknesses of the plates 4b to 4k. However, the influence of the displacements differs depending on the thicknesses of the plates 4b to 4k. 
In the present embodiment, the second hole 7d has a large cross-sectional area. However, to simplify the description, a channel member in which the second hole has the same cross-sectional area as those of the first and third holes is considered. Since the descender holes are connected to each other along a straight line, if the plates are displaced when they are stacked together, a portion of the descender is displaced from the original straight line. Since the portion of the descender is displaced from the straight line, the displacement causes a slight increase in the length of the descender. (To be more precise, the length of the descender along the center thereof increases. The center is the same as the center of the liquid flow, and therefore extends along an inclined straight line.) More specifically, as a result of the displacement, the inclination of the liquid flow increases in some of the plates, and accordingly the length by which the liquid flows (hereinafter sometimes referred to as a channel length) increases. Assume that a thin plate or a plate stacked above or below the thin plate is displaced so that the inclination of the liquid flow through the thin plate is increased. Even when the amount of displacement is constant, when the plate is thinner than the other plates, the inclination of the liquid flow through a hole formed in that plate is increased by a larger amount, and accordingly the channel length is also increased by a larger amount. In other words, the displacement has a large influence on the thin plate. To reduce the influence, a large hole is preferably formed in a plate adjacent to the thin plate as the second hole.
Accordingly, in the present embodiment, a hole is formed in the second plate 4d that is stacked immediately below the first plate 4c, which is thin, as the second hole 7d having a large cross-sectional area. When the reduction in the influence of the displacement is the only factor to be considered, the cross-sectional area of the first hole 7c in the thin first plate 4c is preferably increased. However, in such a case, the influence of the above-described stagnation of the liquid increases. Therefore, the cross-sectional area of the second hole 7d in the second plate 4d, which is arranged below the thin first plate 4c, is preferably increased.
From the above-described viewpoint, it is not preferable to provide a plate that is extremely thinner than the other plates. However, in the present embodiment, the first plate 4c having a small thickness is provided to form channels having a high channel resistance with small variations as parts of the restricting portions 6 that connect the compression chambers 10 to the manifolds 5. The liquid ejecting head 2 according to the present embodiment ejects the liquid by the pulling driving method. Therefore, to partially reflect the pressure waves transmitted from the compression chambers 10 toward the manifolds 5, the restricting portions 6 are required to have a high channel resistance. Since the way in which the pressure waves are reflected varies depending on the channel resistance, variations in the channel resistance are preferably small. When channels through which the liquid flows in the stacking direction are to be structured such that the channels have a high channel resistance, the opening area is reduced. Therefore, it is difficult to reduce the variations since the influence of variations in the opening area caused when the channels are formed and the displacements cased in the stacking process is large. When channels through which the liquid flows in a horizontal direction are to be structured such that the channels have a high channel resistance, the width of the channels (to be more precise, the width of the openings in the plate) may be reduced. In such a case, variations in the opening width caused when the channels are formed are increased, and it is therefore difficult to form channels having an extremely small width. However, unless the cross-sectional area of the restricting portions 6 in the direction in which the liquid flows is reduced, the length of the restricting portions 6 required to obtain the necessary channel resistance increases and the size of the channel member 4 increases accordingly. For the above-described reason, preferably, parts of the restricting portions 6 having a high channel resistance are formed of channels that extend in a horizontal direction in a single plate, and the thickness of the plate is reduced. Accordingly, in the channel member 4 according to the present embodiment, the thickness of the first plate 4c is set to be as small as 25 μm, and, to reduce the influence of the small thickness, the large second hole 7d is formed in the second plate 4d, and the thickness of the second plate 4d is set to be as large as 150 μm. The thickness of the other plates 4b and 4e to 4k is 100 μm. To sum up, the second hole 7d having a large cross-sectional area is preferably formed in the second plate 4d stacked between the first plate 4c and the third plate 4e having different thicknesses. Accordingly, the influence of the displacement of the thinner one of the first plate 4c and the third plate 4e can be reduced.
The above-described configuration is particularly advantageous when, in plan view, the descender hole 7b formed in the plate 4b stacked above the first plate 4c is at a side of the first hole 7c opposite to the side at which the second hole 7d is disposed. In addition, the above-described configuration is particularly advantageous when, in plan view, the descender hole 7f formed in the plate 4f stacked below the third plate 4e is at a side of the third hole 7e opposite to the side at which the second hole 7d is disposed.
In the present embodiment, the second hole 7d has a circular shape in cross section perpendicular to the stacking direction. However, the second hole 7d may instead have an oval shape. The oval shape is not limited to an elliptical shape in a mathematical sense, but also includes a shape obtained by elongating a circle in a certain direction. When the opening 7cb at the bottom side of the first hole 7c and the opening 7ea at the top side of the third hole 7e are separated from each other in plan view, the shape of the second hole 7d in cross section perpendicular to the stacking direction may be an oval shape that is long in a direction connecting the area centroid of the opening 7cb at the bottom side of the first hole 7c and the area centroid of the opening 7ea at the top side of the third hole 7e. In such a case, the opening 7cb at the bottom side of the first hole 7c and the opening 7ea at the top side of the third hole 7e may be connected by the second hole 7d without increasing the width in a direction perpendicular to the direction connecting the area centroid of the opening 7cb at the bottom side of the first hole 7c and the area centroid of the opening 7ea at the top side of the third hole 7e. In other words, preferably, the second hole 7d has an oval shape in cross section perpendicular to the stacking direction, and, in plan view of the channel member 4, the second hole 7d is long in the direction connecting the area centroid of the opening 7cb of the first hole 7c at the side adjacent to the second plate 4d and the area centroid of the opening lea of the third hole 7e at the side adjacent to the second plate 4d. 
The inclination of the direction in which the holes from the first hole 7c to the third hole 7e are arranged will be further described. FIG. 6 is a schematic plan view illustrating the relationship between the compression chambers 10 and the ejection holes 8. FIG. 6 illustrates two compression chambers 10 that are connected to different sub-manifolds 5b and that are adjacent to each other, and the ejection holes 8 that are connected to the respective compression chambers 10. The two compression chambers 10 belong to the same compression chamber line, and are arranged along an imaginary straight line L that extends in the short-side direction of the head body 2a. 
The ejection holes 8 connected to the compression chambers 10 belonging to the compression chamber line that extends along the imaginary straight line L are in a region indicated by R in FIG. 6 in the longitudinal direction of the channel member 4. The positions of the 32 ejection holes 8 connected to the 32 compression chambers 10 belonging to the compression chamber line that extends along the imaginary straight line L in the longitudinal direction of the channel member 4 are indicated by the dashed circles. The positions of the two ejection holes 8 connected to the two compression chambers illustrated in FIG. 6 are indicated by the filled circles. The intervals between the ejection holes 8 are constant (d [μm] in FIG. 6).
The descender holes 7b to 7k that constitute each descender 7 are arranged along the straight line that connects the opening at the top side of the descender hole 7b to the corresponding ejection hole 8. For simplicity, the descender holes 7c to 7k are not illustrated in FIG. 6, and only the openings at the top sides of the descender holes 7b, the ejection holes 8, and the straight lines that connect the openings at the top sides of the descender holes 7b to the ejection holes 8 are illustrated.
In FIG. 6, C1 indicates the area centroid of the opening at the top side of the descender hole 7b of the descender 7 connected to the compression chamber 10 drawn in the upper part, and C2 indicates the position of the ejection hole 8 connected to the compression chamber 10. The direction from C1 to C2 is the same as the direction from the area centroid of the opening 7cb at the bottom side of the first hole 7c to the area centroid of the opening lea at the top side of the third hole 7e in this descender 7. In FIG. 6, C3 indicates the area centroid of the opening at the top side of the descender hole 7b of the descender 7 connected to the compression chamber 10 drawn in the lower part, and C4 indicates the position of the ejection hole 8 connected to the compression chamber 10. The direction from C3 to C4 is the same as the direction from the area centroid of the opening 7cb at the bottom side of the first hole 7c to the area centroid of the opening 7ea at the top side of the third hole 7e in this descender 7.
The angle between a first direction D1, which is the direction from C1 to C2, and a second direction D2, which is the direction from C3 to C4, is the sum of the angle θ1 between the imaginary straight line L and the first direction D1 and the angle θ2 between the imaginary straight line L and the second direction D2, and is only slightly smaller than 180 degrees. This shows that the directions of the inclinations of the two descenders 7 are substantially opposite. In other words, the position of the opening 7ea at the top side of the third hole 7e relative to the opening 7cb at the bottom side of the first hole 7c in one of the two descenders 7 is substantially opposite to that in the other descender 7.
In this arrangement, when the displacements between the first plate 4c, the second plate 4d, and the third plate 4e occur in the direction from C1 to C2 or in the direction opposite thereto, the amount of ejection and the ejection speed differ between the two descenders 7. For example, the amount of ejection may increase in one descender 7 and decrease in the other descender 7.
When the maximum angle between the first direction D1 and the second direction D2 in the head body 2a is greater than 90 degrees, the ejection characteristics greatly differ between the descenders 7. Therefore, in such a head body 2a, the above-described configuration of the first hole 7c, the second hole 7d, and the first hole 7e is effective. The configuration is particularly effective when the maximum angle between the first direction D1 and the second direction D2 is 135 degrees or more.
REFERENCE SIGNS LIST
1 color inkjet printer
2 liquid ejecting head
2a head body
4 channel member
4a to 4m plates (of channel member)
4c first plate
4d second plate
4e third plate
4-1 ejection-hole surface
4-2 compression chamber surface
5 manifold
5a opening (of manifold)
5b sub-manifold
6 restricting portion
7 descender
7c first hole (descender hole)
7cb opening at bottom side (side adjacent to second plate) of first hole
7d second hole (descender hole)
7da opening at top side (side adjacent to first plate) of first hole
7db opening at bottom side (side adjacent to third plate) of second hole
7e third hole (descender hole)
7ea opening at top side (side adjacent to second plate) of third hole
7b, 7g descender hole
8 ejection hole
9 ejection hole row
10 compression chamber
11 compression chamber row
12 individual channel
14 individual supply channel
15 partition
16 dummy compression chamber
21 piezoelectric actuator substrate
21a piezoelectric ceramic layer (vibration substrate)
21b piezoelectric ceramic layer
24 common electrode
25 individual electrode
25a individual electrode body
25b lead electrode
26 connecting electrode
28 common-electrode surface electrode
30 displacement element
60 signal transmission unit
70 head mounting frame
72 head group
80a feed roller
80b take-up roller
82A guide roller
82B conveying roller
88 control unit
P print sheet

## Claims

1. A channel member for a liquid ejecting head including a channel that includes a partial channel, the channel member comprising:
a plurality of plates that are stacked together, the plurality of plates including a first plate, a second plate, and a third plate that are successively stacked together,
wherein the first plate includes a first hole that extends through the first plate and constitutes a first portion of the partial channel,
wherein the second plate includes a second hole that extends through the second plate and constitutes a second portion of the partial channel,
wherein the third plate includes a third hole that extends through the third plate and constitutes a third portion of the partial channel, and
wherein, in a plan view of the channel member,
an opening of the first hole having a first region and a second region, at an interface between the first plate and the second plate, the first region overlapping an opening of the third hole at an interface between the second plate and the third plate, the second region not overlapping the opening of the third hole at the interface between the second plate and the third plate, and
the opening of the third hole having a third region and a fourth region, at the interface between the second plate and the third plate, the third region overlapping the opening of the first hole at the interface between the first plate and the second plate, the fourth region not overlapping the opening of the first hole at the interface between the first plate and the second plate,
the opening of the first hole is smaller than an opening of the second hole at the interface between the first plate and the second plate, and the opening of the first hole is completely overlapped by the opening of the second hole at the interface between the first plate and the second plate, and
the opening of the third hole is smaller than an opening of the second hole at the interface between the second plate and the third plate, and the opening of the third hole is completely overlapped by the opening of the second hole at the interface between the second plate and the third plate.

2. The channel member for a liquid ejecting head according to claim 1,
wherein the channel member includes an ejection hole and a compression chamber, and the partial channel is connected to the compression chamber and the ejection hole.

3. The channel member for a liquid ejecting head according to claim 1,
wherein, in the plan view of the channel member,
a direction from an area centroid of the opening of the second hole, at the interface between the first plate and the second plate, to an area centroid of the opening of the second hole at the interface between the second plate and the third plate is the same as a direction from an area centroid of the opening of the first hole, at the interface between the first plate and the second plate, to an area centroid of the opening of the third hole at the interface between the second plate and the third plate.

4. The channel member for a liquid ejecting head according to claim 1,
wherein, in the plan view of the channel member,
the opening of the first hole at the interface between the first plate and the second plate is completely overlapped by the opening of the second hole at the interface between the first plate and the second plate, and includes a region that is not overlapped by the opening of the second hole at the interface between the second plate and the third plate.

5. The channel member for a liquid ejecting head according to claim 1,
wherein, in the plan view of the channel member,
the opening of the third hole at the interface between the second plate and the third plate is completely overlapped by the opening of the second hole at the interface between the second plate and the third plate, and includes a region that is not overlapped by the opening of the second hole at the interface between the first plate and the second plate.

6. The channel member for a liquid ejecting head according to claim 1,
wherein the second plate is thickest among the first plate, the second plate, and the third plate.

7. The channel member for a liquid ejecting head according to claim 1,
wherein a thickness of first plate differs from a thickness of the third plate.

8. The channel member for a liquid ejecting head according to claim 1,
wherein the second hole has an oval shape in a cross section perpendicular to a stacking direction, and
wherein, in the plan view of the channel member,
the second hole is long in a direction connecting an area centroid of the opening of the first hole at the interface between the first plate and the second plate and an area centroid of the opening of the third hole at the the interface between the second plate and the third plate.

9. The channel member for a liquid ejecting head according to claim 1,
wherein the channel member includes a plurality of partial channels having a structure identical to a structure of the partial channel, a plurality of ejection holes, and a plurality of compression chambers,
wherein the plurality of partial channels connect the plurality of ejection holes to the plurality of compression chambers, and
wherein, in the plan view of the channel member,
an angle between a first direction, which is a direction from an area centroid of the opening of the first hole at the interface between the first plate and the second plate to an area centroid of the opening of the third hole at the interface between the second plate and the third plate in one of the partial channels, and a second direction, which is a direction from the area centroid of the opening of the first hole at the interface between the first plate and the second plate to the area centroid of the opening of the third hole at the interface between the second plate and the third plate in another one of the partial channels, is greater than 90 degrees.

10. A liquid ejecting head comprising:
the channel member for a liquid ejecting head according to claim 1; and
a compressing portion that compresses liquid in the channel.

11. A recording device comprising:
the liquid ejecting head according to claim 10;
a conveying unit that conveys a recording medium relative to the liquid ejecting head; and
a control unit that controls the liquid ejecting head.