JPH04115951A - Ink jet head - Google Patents

Abstract

PURPOSE:To obtain a large displacement of a vibration board by a method wherein the vibration board is provided with an expansion member which expands or contracts by an electric field, a voltage to be applied to a first area of the expansion member is set reverse to a voltage to be applied to a second area surrounding the first area. CONSTITUTION:A voltage is applied between electrodes 7, 8, and a voltage reverse to said voltage in electric potential is applied between ring electrodes 8, 9. Polarizing directions P1 and P2 of a piezoelectric element are vertical to the direction of an electrical axis. Thus, the transverse effect of the piezoelectric element allows a part between the electrodes 6, 7 to contract vertically to the direction of an electric field on the side of the electrode 6 and expand vertically to the direction of the electric field on the side of the electrode 7, furthermore allowing the expansion vertically to the direction of the electric field on the side of the ring electrode 8 and the contraction vertically to the direction of the electric field on the side of the ring electrode 9. In this manner, by the action of the force, the part between the electrodes 6, 7 of the vibration board is recessed and the part between the ring electrodes 8, 9 is projected. In this manner, a part of the vibration board 1 forming an inner wall of a pressure chamber 4 is deflected in an arrow direction G1, the inside of the pressure chamber 4 is pressurized, and ink is jetted out of a nozzle 5.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an inkjet head that ejects ink from a nozzle using the strain effect of a piezoelectric element.

2. Description of the Related Art In recent years, printers using inkjet heads are superior to other printers in terms of high print quality, high resolution, quietness, and ease of color printing, and have rapidly become popular.

A conventional inkjet head will be explained below.

Figure 3 (a) is a top view of a conventional inkjet head;
FIG. 3(b) is a cross-sectional view of the ink nozzle head taken along line BB in FIG. 3(a).

In FIGS. 3(A) and 3(0), 31 is a diaphragm made of glass or the like, 32 is a channel substrate with a concave portion on the top surface, and the diaphragm 31 is bonded to the top surface, so that the concave portion and the diaphragm 3
1, an ink reservoir 33 including a pressure chamber 34 and a nozzle 35
A space is formed consisting of. Reference numeral 36 denotes a driving portion of the diaphragm 3, which is formed of a piezoelectric element whose polarization direction is oriented in the direction of arrow P2, and has electrodes 36a and 36b connected to the upper and lower surfaces, respectively.
1 and the portion facing the pressure chamber 34.

The operation of the inkjet head constructed as described above will be explained with reference to FIGS.

FIG. 4(a) shows a state in which no voltage is applied to the drive unit 36, and the ink reservoir 33 is filled with ink and the nozzle 3
5, a meniscus 41 is formed near the tip. When a voltage is applied between the electrodes 36a and 36b in this state, the polarization direction P2 of the piezoelectric element forming the drive section 36 is perpendicular to the electric axis, so the drive section 36 contracts due to the transverse effect of the piezoelectric element. do. However, since the diaphragm 31 does not contract, due to the difference in contraction between the drive unit 36 and the diaphragm 31, the area around the pressure chamber 34 of the diaphragm 31 is displaced in the direction of arrow G1 as shown in FIG. Chamber 34 is pressurized, pressure chamber 3
The ink at 4 is pushed out in the direction of the nozzle 35, and the ink is ejected from the nozzle 35. When the application of voltage between the electrodes 36a and 36b is stopped, the driving portion 36 expands and the contact surface with the diaphragm 31 becomes flat as shown in FIG. 4(c).
The vicinity of the first pressure chamber 34 is displaced in the direction of arrow G2. This displacement creates a negative pressure inside the pressure chamber 34, and the ink near the nozzle 35 moves in the direction of arrow G3, separating the ejected ink from the ink near the nozzle 35. Thereafter, the ejected ink adheres to the paper 39 to form ink droplets 40 as shown in FIG. 4(d). Further, the pressure chamber 34 is replenished with ink from the direction B, and the meniscus 41 gradually returns to its original position as shown in FIG. Become.

However, in the conventional configuration described above, when the diaphragm 31 or the pressure chamber 34 is pressurized, the drive section 36 contracts, and the difference in contraction between the drive section 36 and the diaphragm 31 causes the diaphragm 31 to shrink. Since the diaphragm tends to become concave, the displacement of the diaphragm is small and the pressing force is insufficient.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention provides a diaphragm having an elastic member that expands and contracts by an electric field, and a first region of the elastic member.
The second region surrounding the first region is configured to apply voltages opposite to each other.

Effects With the above-described configuration, the present invention can make the diaphragm concave by changing the elastic member under the electric field of one electrode, and make the diaphragm convex by changing the elastic member under the electric field of the other electrode.

Embodiment FIG. 1(A) is a top view of an inkjet head in an embodiment of the present invention, and FIG. 1(0) is a cross-sectional view of the inkjet head taken along line A-A in FIG. 1(A). .

In Figures 1 (a) and (b), 1 is a diaphragm made by gluing together two piezoelectric elements with polarization directions in the directions of arrows P1 and P2, and 2 is a flow path substrate with a recess on the top surface. Since a diaphragm is bonded to the upper surface of the diaphragm 1, a space is formed between the recess and the diaphragm 1 and the ink flow path 3 including the cylindrical pressure chamber 4 and the nozzle 5. 7 is a circular electrode formed on the pressure chamber 4 side of the diaphragm 1 near the center of the pressure chamber 4; 6 is a circular electrode formed on the upper surface of the diaphragm 1 at a position opposite to the electrode 7; 9; is an annular electrode formed around electrode 7, 8
is a ring-shaped electrode formed around the electrode 6 at a position facing the ring-shaped electrode 9. The diameters of the electrodes 6 and 7 are 85% of the diameter of the pressure chamber, and their proportion to the square area of the pressure chamber 4 is 720 mm.

The operation of the inkjet head configured as described above will be explained using the operation explanatory diagrams shown in FIGS. 2(a) to 2(d). Initially, the ink forms a meniscus 10 near the tip of the nozzle 5, as shown in FIG. 2(A). In this state, when a voltage is applied between the electrodes 6 and 7, and a voltage opposite in positive and negative to that between the annular electrodes 8 and 9 is applied between the electrodes 6 and 7, the polarization direction P of the piezoelectric element forming the diaphragm l is applied.
1 and P2 are perpendicular to the electric axis, so due to the transverse effect of the piezoelectric element, the electrode 6 side of the part sandwiched between electrodes 6 and 7 shrinks in the direction perpendicular to the direction of the electric field, and the electrode 7 side shrinks in the direction perpendicular to the direction of the electric field. It extends in a direction perpendicular to the direction of the electric field. Furthermore, the portion sandwiched between the ring electrodes 8 and 9 on the ring electrode 8 side extends in a direction perpendicular to the direction of the electric field, and the ring electrode 9 side contracts in a direction perpendicular to the direction of the electric field. Therefore, a force acts on the portion of the diaphragm sandwiched between the electrodes 6-7 to make it concave, and a force acts on the portion sandwiched between the annular electrodes 8-9 to make it convex. The peripheral part of the diaphragm forming the inner wall of the pressure chamber 4 is convex and the central part is concave, so that the part of the diaphragm 1 forming the inner wall of the pressure chamber 4 is shown in FIG. 2 (0). As shown, the inside of the pressure chamber 4 is pressurized by bending in the direction of the arrow G1, and ink is ejected from the nozzle 5. When the voltage application between the electrodes 6 and 7 and between the annular electrodes 8 and 9 is stopped, as shown in FIG. 8
The part that was sandwiched between -9 tries to return to its original position, and arrow G2
displacement in the direction. Due to this displacement, the inside of the pressure chamber 4 becomes negative pressure, and the ink near the nozzle 5 moves in the direction of arrow G3.
The ejected ink and the ink near the nozzle 5 are separated. Thereafter, the ejected ink forms ink droplets 12 on the paper 11 as shown in FIG. 2(d). Further, the pressure chamber 4 is replenished with ink from the direction of arrow B, and the meniscus 10 gradually becomes the second
It returns to the original position shown in Figure (a) and enters the standby state.

FIG. 6 shows experimental values when the proportions of the electrodes 6 and 7 in the upper tank of the pressure chamber 4 were varied.

The piezoelectric element used in the experiment had a manufacturer name: Tokin ■, a model number: N-10, and a Young's modulus: 5. Ox l
O”N/am 2, Poisson's ratio: 0.34, density: 7
．． 82XlO-3g/fiIm3, piezoelectric constant d31...
・-287 m/v.

The electric field strength between electrodes 6 and 7 and between ring electrodes 8 and 9 is 290V.
/mm. The pressure chamber has a cylindrical shape with a diameter of 3 mm.
The arrangement of the electrodes is as shown in FIG. 1 of the embodiment. The ratio of the electrode 6 to the upper surface of the pressure chamber is 100
%, if the annular electrode 8 is present around the pressure chamber 4, the present invention will still be effective, or the maximum strain stress will increase. If the ratio of the electrode 6 to the upper surface of the pressure chamber 4 is too small, the portion sandwiched between the annular electrodes 8 and 9 will become convex.
This acts to cancel out the concave effect of the portion sandwiched between the pressure chambers 7 and 7, and the amount of change in volume of the pressure chamber 4 as a whole decreases.

Therefore, the area occupied by the electrode 6.7 in the upper surface tank of the pressure chamber 4 of the diaphragm 1 becomes largest when the volume of the pressure chamber 4 changes from 36% to 100%.

In addition, in this embodiment, the pressure chamber 4 is cylindrical,
This can be realized as long as the pressure chamber has a volume larger than the ejected ink droplet and is formed of at least a part of the inner wall of a diaphragm or a member that transmits vibrations of the diaphragm.

In addition, the number of electrodes 6 and 7 and the annular electrode 8 and annular electrode 9
Even if the number of electrodes on one side is not the same and one or more common electrodes are used, it is possible to realize the same.

FIGS. 5(A) to 5(C) are enlarged views of electrode portions of another embodiment of the present invention.

In FIGS. 5(A) to 5(C), 51 is a diaphragm formed by bonding two piezoelectric elements having polarization directions in the directions of arrows P1 and P2, and a common electrode 13 is provided on the pressure chamber 4 side.
Or is provided. 52 is a diaphragm in which two piezoelectric elements having polarization directions in the directions of arrows P1 and P2 are bonded with a common electrode 13 sandwiched between them; 53 is a diaphragm in which two piezoelectric elements having polarization directions in the direction of arrow P2 are bonded. It is a diaphragm made of material. 2 is a channel substrate, 4 is a pressure chamber, 6 is an electrode, 7 is an electrode, 8 is an annular electrode, and 9 is an annular electrode, which are the same as those in the previous embodiment, so their explanation will be omitted.

The operation of the diaphragm displacement of the inkjet head configured as above will be explained below.

As shown in FIG. 5(A), when the common electrode 13 is set to a reference potential and voltages of opposite positive and negative voltages are applied to the electrode 6 and the annular electrode 8, the polarization directions P1 and P2 of the piezoelectric element forming the diaphragm 51 change Since the direction to the axis is perpendicular, the electrode 6 side of the part sandwiched between the electrode 6 and the common electrode 13 contracts in the direction perpendicular to the direction of the electric field due to the transverse effect of the piezoelectric element, and the common electrode 13 side contracts in the direction perpendicular to the direction of the electric field. It extends perpendicular to the direction. Furthermore, the electrode 8 side of the portion sandwiched between the annular electrode 8 and the common electrode 13 extends in a direction perpendicular to the direction of the electric field, and the common electrode 13 side contracts in a direction perpendicular to the direction of the electric field. Therefore, the diaphragm 5
A force is applied to the portion sandwiched between the electrode 6 and the common electrode 13 of 1 to make it concave, and a force is applied to the portion sandwiched between the annular electrode 8 and the common electrode 13 to make it convex. Since the peripheral portion of the diaphragm 51 forming the inner wall of the pressure chamber 4 is convex and the central portion is concave, the portion of the diaphragm 51 forming the inner wall of the pressure chamber 4 bends in the direction of arrow G1.

As shown in FIG. 5(B), when a voltage is applied to the electrode 6 and the annular electrode 8 with the common electrode as a reference potential, the polarization directions P1 and P2 of the piezoelectric element forming the diaphragm 52 and the direction of the electric axis is vertical, so the portion sandwiched between the electrode 6 and the common electrode 13 extends in a direction perpendicular to the direction of the electric field due to the lateral effect of the piezoelectric element.

Further, the portion sandwiched between the annular electrode 8 and the common electrode 13 extends in a direction perpendicular to the direction of the electric field. Therefore, the diaphragm 5
A force acts on the portion sandwiched between the second electrode 6 and the common electrode 13 to make it concave, and a force acts on the portion sandwiched between the annular electrode 8 and the common electrode I3 to make it convex. Since the peripheral portion of the diaphragm 52 forming the inner wall of the pressure chamber 4 is convex and the central portion is concave, the portion of the diaphragm 52 forming the inner wall of the pressure chamber 4 bends in the direction of arrow G1.

As shown in FIG. 5(C), when voltages of opposite positive and negative polarities are applied to the electrode 6.7 and the annular electrode 8.9 with the common electrode at a reference potential, the polarization direction P2 of the piezoelectric element forming the diaphragm 53 is applied.
Since the direction is perpendicular to the electric axis, the part sandwiched between the electrode 6 and the common electrode 13 shrinks in the direction perpendicular to the direction of the electric field due to the transverse effect of the piezoelectric element, and the part sandwiched between the electrode 7 and the common electrode 13 shrinks in the direction perpendicular to the direction of the electric field. The extended portion extends perpendicular to the direction of the electric field.

Further, the part sandwiched between the annular electrode 8 and the common electrode 13 extends in a direction perpendicular to the direction of the electric field, and the part sandwiched between the annular electrode 9 and the common electrode 13 extends in a direction perpendicular to the direction of the electric field. Shrink. Therefore, a force acts to make the part of the diaphragm 53 sandwiched between the electrode 6.7 and the common electrode 13 concave, and the part sandwiched between the annular electrode 8.9 and the common electrode 3 becomes convex. Forces work to make it happen. The peripheral part of the diaphragm 53 forming the inner wall of the pressure chamber 4 is convex and the central part is concave, so the part of the diaphragm 53 forming the inner wall of the pressure chamber 4 is indicated by the arrow G.
Deflects in one direction. In the embodiments shown in FIGS. 5(a) to 5(c), the mechanism of ejecting ink droplets is the same as that in the embodiment shown in FIG. 2, so a description thereof will be omitted.

Effects of the Invention The present invention is configured such that a voltage opposite to that applied to the first region of the telescoping member of a diaphragm that expands and contracts in response to an electric field is applied to the second region surrounding the first region. By changing the elastic member, the diaphragm can be made convex under the electric field of one electrode and concave under the electric field of the other electrode, making it possible to obtain a large displacement of the diaphragm.

[Brief explanation of drawings]

FIG. 1(a) is an explanatory diagram of the operation of an inkjet head in an ink embodiment according to an embodiment of the present invention, and FIG.
A) is a conventional inkjet head, FIGS. 4A to 4D are explanatory diagrams of the operation of a conventional inkjet head, and FIGS. 5A to C are enlarged views of the electrode portion of another embodiment of the present invention. Figure 6 shows the electrode 6 and the electrode 1...the diaphragm, 2.
...Flow path substrate, 3...Ink flow path, 4.
...Pressure chamber, 5...Nozzle, 6.7. Old... Electrode, 8.9... Annular electrode, 10. Group.
Meniscus, 11... Paper, 12... Ink drop. Name of agent: Patent attorney Haruaki Koba Cutaway cross-sectional views of two people, Figures 2 (a) to (d) are cross-sectional views of the present invention - Figure (f) (Figure 2 (a)

Claims (5)

[Claims] (1) By joining the diaphragm and a substrate having a concave portion, a space that becomes an ink flow path including a pressure chamber and a nozzle is formed, and the portion of the diaphragm that forms the pressure chamber expands and contracts due to an electric field. The inkjet head has a member, and a diaphragm is displaced by applying a voltage to the elastic member, wherein a first area of the elastic member and a second area surrounding the first area are mutually connected to each other. An inkjet head characterized by being configured to apply a reverse voltage. (2) The inkjet head according to claim 1, wherein the diaphragm is made of an elastic member. (3) The inkjet head according to claim 1, wherein the diaphragm is provided with an elastic member. (4) The inkjet head according to claim 1, wherein one of the electrodes has an area of 36% to 100% of the area of the portion of the diaphragm forming the pressure chamber. (5) The inkjet head according to claim 1, wherein the elastic member is a piezoelectric element.