JP3132916B2 - Inkjet print head - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the shape of a head of an ink jet printing apparatus.

[0002]

2. Description of the Related Art Japanese Patent Application Laid-Open No.
No. 252750. This structure and operation principle will be described with reference to FIGS. 7 , 8 , and 10. FIG . FIG. 10 is an exploded perspective view of an inkjet print head using a shear mode, and is PZT (lead zirconate titanate).
A large number of elongated grooves are formed in parallel on the piezoelectric body 28 as described above. Then, the upper surface of the partition walls 48ab and 48bc remaining between the grooves and the lid 1 made of glass, ceramic, plastic or the like are flexibly bonded by the elastic member 2. As a result, the grooves become the ink chambers 38a, 38b, 38c.
One end of each of the ink chambers 38a, 38b, 38c is adapted to supply ink from a common ink reservoir (not shown), and the other end is bonded to a nozzle plate 5 having a small nozzle 3. . Here, the piezoelectric body 28 is a partition 48
Polarization is performed in one direction as indicated by the arrow 4 (or in the opposite direction) including ab and 48bc. Further, electrodes 18a, 18b, 18c and the like are formed on the inner surface of the groove.

FIG . 7 is a sectional view of the non-driving state of the ink jet print head using the share mode.
Here, if a sufficiently large positive potential is applied to the electrode 18a in FIG. 7 with respect to the electrode 18b, the partition wall 48ab as shown in FIG.
Causes a shear mode deformation when the electric lines of force 58ab in the partition wall are orthogonal to the polarization direction of the piezoelectric body. If the same operation is performed for the partition wall 48bc, the ink chamber 38
The sectional area of b decreases as shown in FIGS. 7 and 8 in the initial state. That is, if the ink is filled in the ink chamber 38b, the pressure of the ink is instantaneously increased due to the volume reduction of the groove, and the ink droplet is ejected from the nozzle.

[0004]

The conventional ink jet print head using the share mode has an ink chamber 3
The cross-sectional shapes of the bottom surfaces, such as 8a, 38b, and 38c, were straight. In order to cause the transformation of pure share mode,
It is most preferable that the electric field between the electrodes 18a and 18b on both sides of the partition wall 48ab be concentrated only in the partition wall 48ab. However, actually, the partition wall 48ab and the ink chamber 38a
b, the electric field lines 68
ab results. Similarly, the partition wall 48bc and the ink chamber 38bc
The electric field lines 68
bc occurs. In the vicinity of the bottom of the ink chamber 38b, the lines of electric force 68ab and 68bc are substantially parallel to and in the same direction as the polarization direction of the piezoelectric body below the ink chamber 38b. Deformation occurs, and the bottom of the ink chamber 38b is lifted as shown by the dashed line. On the other hand, near the bottom of the ink chamber 38a, the line of electric force 68ab and the polarization direction of the piezoelectric body are substantially parallel and opposite to each other, and contraction deformation occurs in this direction. It becomes a deformed deformation. Such deformation is called rotation.

Referring to FIG . 9 , this rotation will be briefly described. When only the partition 78a is driven, the piezoelectric body 28 is driven.
Is deformed as shown by the two-dot chain line, and it can be seen that the other partition walls 78b, 78c, etc., which are different from the partition wall 78a, are also deformed.

[0006] Such rotation acts in such a direction as to cancel the deformation of the partition 48ab and the partition 48bc in the shear mode, so that the ejection force of the ink jet print head is reduced. However, on the other hand, by raising the bottom of the ink chamber 38b, the effect of reducing the sectional area of the ink chamber and increasing the ejection force can be expected. In order to clarify this balance, the present inventors measured the displacement of the partition wall 78a by laser measurement. In the experiment, a small mirror was adhered to the upper surface of the partition, and the amount of mirror movement was measured from the laser beam applied to the mirror while changing the voltage applied to the electrodes on both sides of the partition, and converted to the deformation of the partition. It is.
And this experiment showed that the effect of canceling out the deformation was superior. According to this result, the amount of change in the volume of the ink chamber 38b in FIG. 8 was considerably small, about 2/3, compared to the case of only the virtual share mode. As a result, there is a problem that the ejection force of the ink is greatly reduced and the ejection speed of the ink droplet is reduced. This drop in ejection speed not only causes instability in the ejection direction of the ink droplets, causing misalignment of the printed dots, but also makes it impossible to eject highly viscous ink near the nozzles, causing fatalities such as missing print dots. It can also lead to mechanical defects.

[0007] In order to solve this problem, an object of the present invention is to provide an ink jet print head capable of reducing the rotating action of the piezoelectric body when the head is driven and providing high-reliability and high-quality printing. .

[0008]

Means for Solving the Problems In order to achieve the above object, while the cross-sectional shape of the bottom surface of the ink chamber is conventionally perpendicular to the polarization direction, the present invention is directed to the cross-sectional shape of the bottom surface of the groove serving as the ink chamber. The shape is formed by line segments that include certain slopes that are not perpendicular to the polarization direction. That is, the bottom of the ink chamber is characterized by a concave portion, the concave shape of the concave portion is formed, at least in one, by a line segment connected by at least two lines, It is formed by a line segment connected by one inclined straight line.
Has been established . In this case, the shape of the bottom of the ink chamber does not necessarily have to be symmetric.

[0009]

The rotation of the piezoelectric body due to the leakage electric field at the bottom of the ink chamber in the conventional example is an undesirable effect.
This can be suppressed by forming the cross-sectional shape of the bottom surface of the groove serving as the ink chamber by a line segment including a certain slope that is not perpendicular to the polarization direction. To be precise, it is characterized in that the bottom of the ink chamber is concave, and the concave shape of the bottom is, in part, a line segment connected by at least two lines.
It is configured. When the bottom of the ink chamber is formed in such a shape, the direction of electric lines of force at the bottom faces a direction perpendicular to the slope and has a certain angle with respect to the polarization direction of the piezoelectric body. At this time,
The lines of electric force are divided into a component perpendicular to the polarization direction and a component parallel to the polarization direction, and the component in the perpendicular direction acts to cause a pure shear mode deformation, and the component in the parallel direction induces rotation. In the conventional example, since all the electric lines of force at the bottom of the ink chamber are parallel to the polarization direction, all the leaked electric fields acted as components that induce rotation, but in the present invention, the leaked electric field at the bottom of the ink chamber has a shear mode. It also works as a waking component,
The effect of rotation is also reduced. By this action, the amount of deformation of the partition is ensured, so that an ink jet print head having good ink ejection performance can be obtained.

[0010]

Embodiment 1 Hereinafter, a first embodiment of an ink jet print head according to the present invention will be described with reference to the drawings. FIG. 1 is a diagram of a conventional example .
FIG. 7 is a diagram corresponding to FIG. 7 and shows an example of the configuration of an inkjet print head according to the present invention. Here, the ink chambers 30a, 30b, 30
c are the ink chambers 38a, 38b, 38c in FIG.
Those corresponding to, is the same as FIG. 7 of the nozzle 3 at the end of each ink chamber is provided. In the first embodiment of the present invention, the most different point from the conventional example is the ink chamber 30a,
The point is that a concave portion 70 is provided at the bottom of 30b, 30c. FIG. 1 shows an embodiment in which the cross-sectional shape of the concave portion 70 at the bottom of the ink chamber is formed by connecting at least two lines, and particularly, the two line segments are both straight lines, and the left and right sides are substantially symmetrical. one of. Here, electrodes 10a, 10b, 10c, etc. are formed on the inner surface of the ink chamber, respectively.

FIG. 2 is a view for explaining the operation of the first embodiment of the present invention and corresponds to FIG . 8 of a conventional example. Here, a sufficiently large positive potential with respect to the electrode 10b is applied to the electrode 10b.
a, the electric lines of force 50a in the partition 40ab
b is formed so as to be orthogonal to the polarization direction of the piezoelectric body,
As in the case of FIG. 8 , the partition 40ab causes a deformation in the shear mode. Similarly, if a sufficiently large positive potential is applied to the electrode 10b with respect to the electrode 10b, the lines of electric force 50bc in the partition wall 40bc are formed so as to be orthogonal to the polarization direction of the piezoelectric body, similar to the case of FIG. In addition, the partition 40bc causes a shear mode deformation. These partition walls 40ab, 40
The shear mode deformation of bc, reduced cross-sectional area of the ink chamber 30b according to the ink discharge (flow path volume of the ink chamber 30b) is, the ink pops from the nozzle 3 is the same as described in FIG.

Now, the effect of the present invention of suppressing the rotation of the piezoelectric body at the bottom of the ink chamber will be described. The rotation that acts to cancel the deformation of the partition wall due to the shear mode is caused by the leakage electric field to the bottom of the piezoelectric body 20.
This is described above with reference to FIG . Referring again to FIG. 2, the first embodiment of the present invention will be described with respect to the leakage electric field.
In the first embodiment, the electric lines of force generated by the leakage electric field are, as in the electric lines of force 60ab, 60bc, etc., inclined on the right side of the bottom of the ink chamber 30a (in a direction that is not perpendicular to the polarization direction of the piezoelectric body). From the holding surface) to the left slope at the bottom of the ink chamber 30b.

[0013] Here, the effect of the present invention, to explain with reference to FIG. 3 is an enlarged view of the ink chamber bottom. The direction of the end point of the electric force line 60ab shown in FIG. 2 is represented by a direction vector A (FIG. 3). This direction vector A is composed of a vector X and a vector Y
And two-way components. Vector X is
This is a vector component in a direction orthogonal to the polarization direction of the piezoelectric body. Thus, the vector X works in a direction that purely assists the share mode. On the other hand, the vector Y is a vector component parallel to the polarization direction of the piezoelectric body. Therefore, the vector Y works in a direction to induce rotation.

When the cross-sectional shape of the bottom surface of the groove is formed by a single straight line (see FIGS . 7 and 8 ), the direction vector at the end point of the line of electric force is only the component in the direction of the vector Y. And there is no component corresponding to the vector X.

As described above, comparing the first embodiment of the present invention with the conventional example, when the sectional shape of the bottom of the groove is formed by a line segment connected by at least two lines, a voltage is applied. The force exerted on the bottom of the groove by the line of electric force that occurs sometimes is dispersed in two directions, and the component of the component Y that induces rotation more than when the cross-sectional shape of the bottom of the groove is constituted by a line connected by a single straight line. The value becomes smaller as a whole. On the other hand, here, the electric lines of force 60
Although described at the end point of ab, the same applies to the start point.

When the bottom of the ink chamber in the piezoelectric body 20 is substantially symmetrical, rotation, which is one of the effects of the leakage electric field between the electrodes 10a and 10b, is caused by the rotation of the electrode 10a attached to the ink chamber 30a. This is due to the leakage field affected by the right half. This is because the element as the leakage electric field affected by the left half of the electrode 10a is the electrode 1
This is because the length of the electric line of force formed by the left half of Oa and the electrode 10b becomes very long and becomes negligible compared to the effect of the right half of the electrode 10a. For this reason, the range affected by the leakage electric field is about 2/3 smaller in the case of the present invention than in the case where the bottom of the ink chamber is straight in the related art.

(Embodiment 2) FIG. 4 is a view corresponding to FIG . 7 of a conventional example, and shows a second embodiment of the ink jet print head according to the present invention. Here, the ink chambers 32a, 32b, and 32c related to the ink ejection are the ink chambers 3 in FIG.
8a, 38b, which corresponds to 38c, is the same as FIG. 7 of the nozzle 3 at the end of each ink chamber is provided. The most different point of the second embodiment of the present invention from the conventional example is that the concave portions 72 are provided at the bottoms of the ink chambers 32a, 32b and 32c.
Is provided. FIG. 4 shows that the cross-sectional shape of the concave portion 72 at the bottom of the ink chamber is constituted by one inclined straight line,
Therefore, this is one of the embodiments in which the left and right are asymmetrical.

FIG. 5 is a view for explaining the operation of the second embodiment of the present invention and corresponds to FIG . 8 of the conventional example. Similar to the first embodiment, the effect of the present invention of suppressing the rotation of the bottom of the ink chamber of the piezoelectric body will be described. First, the rotation that acts to cancel the deformation of the partition wall in the shear mode will be described with reference to FIG. 5 in the second embodiment. The electric lines of force generated by the leakage electric field are electric lines of electric force 6
A curve such as 2ab, 62bc, etc., is directed from a plane substantially perpendicular to the polarization direction of the piezoelectric body to a plane having a certain angle (or vice versa). Here, the operation of the present invention will be described with reference to FIG. 6 which is an enlarged view of the bottom of the ink chamber. A vector at the end point in the electric force lines 62ab shown in FIG. 5 is represented by a direction vector B (FIG. 6). The direction vector B can be divided into two components, a vector U and a vector V.
The vector U is a vector component in a direction orthogonal to the polarization direction of the piezoelectric body. Thus, the vector U works in a direction that purely assists the share mode. On the other hand, the vector V is a vector component in a direction parallel to the polarization direction of the piezoelectric body. Thus, the vector V acts in a direction that induces rotation.

When the cross-sectional shape of the bottom surface of the groove is constituted by a line connected by one straight line having no inclination ( FIGS .
8 ) The direction vector at the end point of the line of electric force is only a component in the direction of the vector V, and there is no component corresponding to the vector U.

As described above, when the second embodiment of the present invention is compared with the conventional example, when the sectional shape of the bottom of the groove is constituted by a line connected by one inclined straight line, a voltage is applied. The force exerted on the bottom of the groove by the line of electric force that is sometimes generated is dispersed in two directions, and the component of the component Y that induces rotation is more than when the cross-sectional shape of the bottom of the groove is formed by one straight line without inclination. The value becomes smaller as a whole. That is, even in the second embodiment of the present invention, the same effects as in the first embodiment can be obtained.
Since the vector component at the start point is a component substantially perpendicular to the polarization direction, the shear mode is purely deformed.

Next, the asymmetry of the bottom of the ink chamber in the piezoelectric body 22 will be described. As shown in FIG. 5, when the ink chamber has a bottom formed by one inclined straight line,
Since the right side of the ink chamber 32a is a straight line, a component that causes a pure shear mode deformation is very large. Therefore, the rotation component is mostly on the left side only, and the rotation component can be kept small when considered as a whole. From the above, the shape of the bottom of the ink chamber is not necessarily symmetric.

[0022]

As described above, in the ink jet print head according to the present invention, the cross-sectional shape of the bottom surface of the groove serving as the ink chamber is constituted by a line segment including a certain slope that is not perpendicular to the polarization direction. To be precise, the bottom of the ink chamber has a concave portion, and the concave shape of the concave portion at the bottom is formed, at least in one, by at least two lines,
For one, it is formed by a single inclined straight line . For this reason, the direction of the electric field lines at the bottom is normal to the slope and has an angle to the polarization direction of the piezoelectric body. For this reason, the electric flux lines are divided into a component perpendicular to the polarization direction and a component parallel to the polarization direction. The vertical component causes a pure shear mode deformation, and the parallel component induces rotation. However, in contrast to the related art in which the cross-sectional shapes of the bottom surfaces of the ink chambers are connected by one straight line, the present invention can reduce the effect of rotation, and can obtain the effect of the share mode more. This solves the problem that the drop in ink ejection force is reduced and the ejection speed of ink droplets is reduced, and it is also possible to eject highly viscous ink near the nozzles.

[Brief description of the drawings]

FIG. 1 is a sectional view of a first embodiment of an ink jet print head according to the present invention when it is not driven.

FIG. 2 is a sectional view of the first embodiment of the ink jet print head according to the present invention when it is driven.

FIG. 3 is a first embodiment of the ink jet print head according to the present invention, in which a part of the wall in FIG. 1 is enlarged.

FIG. 4 is a sectional view of a second embodiment of the ink jet print head according to the present invention when it is not driven.

FIG. 5 is a sectional view of the second embodiment of the ink jet print head according to the present invention when it is driven.

FIG. 6 is a second embodiment of the ink jet print head according to the present invention, in which a part of the wall in FIG. 4 is enlarged.

FIG. 7 is an explanatory view of a conventional technique, and is a cross-sectional view when the apparatus is not driven.
It is.

FIG. 8 is an explanatory view of a conventional technique, and is a cross-sectional view at the time of driving.
is there.

FIG. 9 is an explanatory diagram of a conventional technique, in which a wall of a piezoelectric body is driven.
Diagram showing how the wall is deformed and the surrounding wall
It is.

FIG. 10 shows a conventional ink jet print head.
It is an exploded perspective view.

[Explanation of symbols]

 3 nozzle 10a electrode 10b electrode 10c electrode 20 piezoelectric body 30a ink chamber 30b ink chamber 30c ink chamber 40ab partition 40bc partition 70 recess

Claims (2)

(57) [Claims] 1. A plurality of elongated grooves are formed in parallel on the upper surface of a flat piezoelectric body, electrodes are provided on side and bottom surfaces of the grooves, and a space formed by covering the grooves is defined as an ink chamber. hand,
A voltage is applied to the electrode to drive the walls on both sides of the groove, and an ink jet print head that discharges ink from a nozzle is provided with a concave portion on the bottom surface of the groove.
And the cross-sectional shape of the recess is at least two lines
An ink jet print head comprising a connected line segment . 2. An elongated groove is formed in parallel on the upper surface of a flat piezoelectric body.
A plurality of electrodes are provided on the side and bottom surfaces of the groove,
The space formed by covering the groove with the lid is used as the ink chamber,
A voltage is applied to the electrode to drive the walls on both sides of the groove.
Ink and eject ink from nozzles
In the print head, a concave portion is provided on the bottom surface of the groove.
And the cross-sectional shape of the recess is connected by one inclined straight line.
An ink jet print head, comprising: