JP3255178B2 - Inkjet head - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recording head of an on-demand type ink jet printer which forms an ink image on a recording medium such as recording paper by discharging ink droplets in response to a print signal.

[0002]

2. Description of the Related Art A recording head of a so-called on-demand type ink jet printer which flies ink droplets according to a print signal is disclosed in Japanese Patent Publication No. 2-455985 and Japanese Patent Publication No. 2-526.
As shown in Japanese Patent Publication No. 25, one end of a piezoelectric element having one end fixed to a base is elastically contacted via a leg with an elastic wall of a container forming a pressure generating chamber. There is. In this recording head, the elastic wall is bent in advance to the pressure generating chamber side, the piezoelectric element is contracted from this state, the bending of the elastic wall is returned, and the piezoelectric element is extended again, so that the ink in the pressure generating chamber is discharged from the nozzle. Discharge as droplets.

According to this, although the displacement of the piezoelectric element can be transmitted to a predetermined position on the elastic wall, the size of the recording head can be reduced,
When the piezoelectric element and the pressure generating chamber are miniaturized due to the high density, the elastic wall is largely deformed in the vertical direction in order to cause a change in the volume of the pressure generating chamber sufficient to discharge sufficient ink droplets. It is necessary. As a result, a large driving voltage is applied to the piezoelectric element ,
Large displacement will result in a large burden,
The reliability is reduced due to fatigue of the elastic wall .

[0004]

DISCLOSURE OF THE INVENTION The present invention has been made in view of such a problem.
It is an object of the present invention to provide an ink jet recording head capable of converting a displacement of a piezoelectric element which expands and contracts in an axial direction into a change in volume of a pressure generating chamber with high efficiency, thereby achieving low voltage driving and extending the life of an elastic wall.

[0005]

In order to solve such a problem, the present invention provides a piezoelectric element which expands and contracts in the longitudinal direction, is elongated and has a smaller sectional area than the piezoelectric element.
In an ink-jet head for ejecting ink droplets from nozzles by displacing an elastic wall forming a part of a large pressure generating chamber, the elastic wall has an elastically deformable plate sealing the pressure generating chamber, and a row of the piezoelectric elements. smaller width than alignment direction of the thickness, also be configured as a laminated structure of the large islands than perpendicular width in the column arrangement direction of the piezoelectric element Tei
You.

[0006]

The cross-sectional area of the piezoelectric element that expands and contracts in the longitudinal direction generates pressure.
Even if it is smaller than the raw chamber, the island-shaped part makes the longitudinal direction of the pressure chamber
To transmit large displacements locally
Without changing the volume of the rectangular pressure generating chamber
Therefore, fatigue of the elastic wall is reduced.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below with reference to the illustrated embodiments. 1 and 2 show an embodiment of a recording head according to the present invention, in which a nozzle substrate 1 provided with a plurality of nozzles 2, a reservoir 4 and a pressure generating chamber 5 are formed, and a cavity forming substrate 3 is formed. And a later-described elastic plate 8 are laminated to form a channel unit. The flow path unit is fixed to the head frame 11 by bringing the elastic plate 8 into contact with the tip of the piezoelectric element 12 housed in the head frame 11.

A piezoelectric element 22 serving as a driving source of ink droplet ejection
Is fixed to the fixed base 21 on one side in the longitudinal direction, and the other end not fixed is joined to the elastic plate 8. An electric field is applied to the piezoelectric element 22 by the control board 13 via the lead frame 25 on which the wiring pattern 24 is provided on the fixed base 21. The head frame 11 has a mounting hole 12 formed therethrough, and supports the fixed base 21 so as to position the piezoelectric element 22 at a predetermined position.

The head frame 11 has an ink supply tube 32 press-fitted and adhered thereto. The ink supply tube 32 passes through the ink connection port 32 and the ink introduction port 33 of the elastic plate 8 to the reservoir 4 of the cavity forming substrate 3 and further to the pressure generating chamber 5. The ink 51 is configured to be supplied from outside.

The piezoelectric element 22 has a front end in contact with the insulating member 7 of the elastic plate 8 with the control board 13
To the head frame 11. The piezoelectric element 22 has a positive external electrode 41 for supplying a drive signal to an internal electrode constituting the piezoelectric element 22 and a negative external electrode 42 formed on the front and back surfaces of the piezoelectric element 22. The external electrode 41 on the positive electrode side is electrically connected to the wiring pattern 24 on the fixing base 21, and the external electrode 42 on the negative electrode side is connected in common by the conductive plate 23, and then on the fixing base 21 via the conductive plate 23. The wiring pattern 24 is also connected.

Cavity forming substrate 3 which characterizes the present invention
The elastic plate 8 that seals the lower surface will be described. A thin metal plate 6 formed to a thickness of 5 μm or less by nickel electroforming is coated with a photosensitive resin as an insulating member 7 to form a laminated structure plate, and the metal thin plate 6 secures mechanical strength. Ink is prevented from leaking to the piezoelectric element side, and the insulating member 7 prevents the positive electrode 41 from contacting the thin metal plate 6 to prevent a short circuit between adjacent piezoelectric elements.

The insulating member 7 is formed as an island-like portion 7a which passes through substantially the center in the longitudinal direction of the pressure generating chamber 5 and is slightly smaller than the projection surface of the pressure generating chamber 5.
That is, the width W1 smaller than the thickness D of the piezoelectric element 22
And the length L is larger than the width W2 of the piezoelectric element 22. These width W1 and length L
Are selected so that the distances Δd1, Δd2, and Δd3 between the elastic plate 8 and more specifically, the partition wall that partitions the pressure generating chamber 5 can be secured to the extent that the thin metal plate 6 can be bent.

The ink jet recording head thus configured receives an electric field from the control substrate 13 to the positive electrode 41 and the negative electrode 42 of the piezoelectric element 22 through the lead frame 25 and the wiring pattern 24 in response to a print signal. Is applied only in the longitudinal direction (vertical direction in the figure)
To shrink.

At this time, the lower half of the piezoelectric element 22 is fixed to the fixed base 21 held on the head frame 11 and cannot be contracted and displaced. On the other hand, the upper half of the piezoelectric element 22 is contracted and displaced because it is not subjected to another constraint, and the contraction force pulls the elastic plate 8 through the island-shaped portion 7a.

In the thin metal plate 6 of the elastic plate 8 pulled by the piezoelectric element 22, a region longer than the width W2 of the piezoelectric element 22 bends downward, and the volume of the pressure generating chamber 5 expands. When the pressure generating chamber 5 expands, the ink 51 flows from the reservoir 4 through the ink supply port 3a. Next, when the application of the electric field to the piezoelectric element 22 is released, the piezoelectric element 22 expands to its original length and compresses a large area of the pressure generating chamber 5 via the island-shaped portion 7a. An ink droplet is ejected from the nozzle 2 at this pressure.

As described above, the displacement of the piezoelectric element 22 is
Therefore, the pressure generating chamber 5 is transmitted to the metal thin plate 6 through the a, so that the peripheral portion of the pressure generating chamber 5 of the metal thin plate 6 is made to be a bent region, so that a wide area of the pressure generating chamber 5 can be deformed. The displacement can be converted to a change in volume of the pressure generating chamber 5 with high efficiency.

[0017]

As described above , according to the present invention, a region wider than the cross-sectional area of the piezoelectric element can be deformed, and the displacement of the piezoelectric element can be changed with high efficiency to the volume change of the rectangular pressure generating chamber. Conversion can be performed, ink droplets can be reliably ejected, and low-voltage driving and extension of the life of the elastic wall can be achieved.

[Brief description of the drawings]

FIG. 1 is an assembled perspective view showing one embodiment of an ink jet recording head of the present invention.

FIG. 2 is a partial cross-sectional view of the recording head.

FIG. 3 is an enlarged perspective view showing a contact area between a piezoelectric element and an elastic plate of the recording head.

FIG. 4 is a plan view of an elastic plate of the recording head.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Nozzle board 3 Cavity 5 Pressure generating chamber 6 Metal thin plate 7 Insulating member 7a Island 8 Elastic plate 11 Head frame 21 Fixed plate 22 Piezoelectric element

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) B41J 2/045 B41J 2/055

Claims (3)

(57) [Claims] 1. An ink jet head which ejects ink droplets from nozzles by displacing an elastic wall which forms a part of a pressure generating chamber which is elongated and is larger than a cross-sectional area of the piezoelectric element by a piezoelectric element which expands and contracts in a longitudinal direction. At
The elastic wall has an elastically deformable plate that seals the pressure generating chamber, and a width smaller than a thickness of the piezoelectric element in a row direction,
Further, an ink jet head configured as a laminated structure with an island-shaped portion having a width larger than a width in a direction perpendicular to a direction in which the piezoelectric elements are arranged. 2. The ink jet head according to claim 1, wherein said elastically deformable plate is made of metal, and said island-shaped portion is made of an insulating material. 3. The elastically deformable plate is made of stainless steel.
2. The ink jet head according to claim 1, wherein said island portion is made of a photosensitive resin.