JPH04282254A - Piezoelectric head for ink jet printer - Google Patents

Abstract

PURPOSE:To shorten response time from the generation of a pressure wave to the ejection of ink by forming a nozzle plate with an ink jet orifice on a surface which is parallel with the width direction of an ink groove and also parallel with a longitudinal direction. CONSTITUTION:If an electric field is applied to a drive electrode 13 formed on both side surfaces of a piezoelectric ceramic wall 11, the wall 11 becomes shear-deformed without being accompanied by a dimensional change in a height direction (thickness direction), because the polarization direction of the wall 11 crosses the direction of an applied electric field. Next, the wall 11 of the piezoelectric ceramics wall 11 is restored to an initial state by removing the applied electric field. In this case, the volume of an ink flow path (pressure chamber) formed by an ink groove 12 changes, and a pressure wave generated in a pressure chamber propagates through the ink flow path following the volume change, and an ink droplet is ejected from an ink jet orifice 15 formed at an ink nozzle.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric head for an inkjet printer, and more particularly to a piezoelectric head for an inkjet printer using a piezoelectric actuator element.

0002

[Prior Art] Conventionally, a piezoelectric head for an inkjet printer using shear deformation of a piezoelectric material was disclosed in Japanese Patent Laid-Open No. 63-2
It is described in Publication No. 47051. The piezoelectric head for an inkjet printer includes an ink jet nozzle plate having a large number of ink jet holes, a large number of ink grooves (pressure chambers) connected to the nozzle plate for supplying ink, and drive electrodes formed on both sides. It consists of a shear deformation piezoelectric actuator element having multiple walls of piezoelectric material, and a liquid supply mechanism for ink replenishment. In the piezoelectric head for an inkjet printer, when an electric field is applied to the drive electrode, the wall of the piezoelectric material causes shear deformation, and then, by removing the electric field, the wall of the piezoelectric material is restored to its initial state. At this time, the volume of the ink groove changes. As a result, the hydraulic pressure of the ink in the ink groove changes, causing ink to be ejected from the ejection holes of the nozzle plate.

When applying such a piezoelectric actuator element to an inkjet printer head, the ink grooves are designed to ensure the minimum required ink groove volume and volume change amount of the ink grooves, and to improve the degree of integration of ink ejection holes. A large number of ink grooves arranged in parallel are formed so that the longitudinal dimension is sufficiently larger than the width and depth dimensions of the ink groove. In the conventional example, the ink nozzle plate 16 having the ink ejection holes 15 is arranged in the width direction 2 of the ink groove 12 as shown in FIG.
1 and parallel to the depth direction 23, and the ink jetting direction was along the longitudinal direction 22 of the ink groove 12. In other words, a large number of ink jet holes 1
5 in the width direction 2 of the piezoelectric ceramic wall 11 of the piezoelectric actuator element 14.
1 and parallel to the height direction 23.

0004

[Problems to be Solved by the Invention] However, when the longitudinal dimension of the ink groove is large in the conventional ink jetting direction, pressure waves are generated in the ink groove due to the restoration of the shear deformation of the piezoelectric material wall to the initial state. The propagation time of the ink to the nozzle varies depending on the distance to the nozzle, resulting in a decrease in jetting efficiency. Another problem is that pressure waves generated at a long distance to the injection hole have a large propagation loss.

The present invention has been made to solve the above-mentioned problems, and provides a piezoelectric head for an inkjet printer that improves ink jetting efficiency and shortens the response time from generation of pressure waves to ink jetting. The purpose is to provide.

[0006]

[Means for Solving the Problems] In order to achieve this object, the piezoelectric head for an inkjet printer of the present invention has a plurality of parallel walls made of piezoelectric material, and a parallel piezoelectric head formed by adjacent walls of piezoelectric material. A large number of ink grooves lined up in the
An ink having a piezoelectric actuator element constituted by drive electrodes formed on both sides of the wall of the piezoelectric material, and a large number of ink ejection holes joined to a surface parallel to the width direction and parallel to the longitudinal direction of the ink groove. Consists of a nozzle plate.

[0007]

[Operation] The wall of the piezoelectric material of the piezoelectric actuator element in the piezoelectric head for an inkjet printer of the present invention having the above-mentioned configuration is polarized in the height direction (thickness direction), so that the polarization is parallel to the direction of the electric field applied to the drive electrode. The directions are perpendicular, and the application of an electric field causes shear deformation in the piezoelectric material wall. The ink groove formed between the walls of the piezoelectric material changes its volume by restoring the shear deformation of the wall of the piezoelectric material to its initial state, and acts as a kind of pressure chamber and an ink flow path. . A pressure wave generated by a change in the volume of the ink groove due to shear deformation of the wall of the piezoelectric material is propagated to the ink ejection hole provided in the ink nozzle plate, and ink droplets are ejected from the ink ejection hole.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment embodying the present invention will be described below with reference to the drawings.

FIG. 1 shows a schematic diagram of the piezoelectric head for an inkjet printer according to this embodiment. In the piezoelectric head for an inkjet printer of this embodiment, piezoelectric ceramics having a polarization direction 24 in the thickness direction is used as the piezoelectric material. The piezoelectric ceramic plate includes a large number of piezoelectric ceramic walls 11 arranged in parallel, a large number of ink grooves 12 arranged in parallel formed between adjacent piezoelectric ceramic walls 11, and both sides of the piezoelectric ceramic walls. Longitudinal direction 22
A drive electrode 13 is formed along the piezoelectric actuator element 14 .

[0010] An ink nozzle plate 1 having an ink ejection hole 15 near the center of the longitudinal direction 22 of the ink groove 12.
6 is bonded to the top surface 20 of the piezoelectric ceramic wall 11 of the piezoelectric actuator element via a strip seal (which has a sealing effect against ink leakage but does not inhibit the deformation of the piezoelectric ceramic wall). Therefore, the ink jetting direction is along the depth direction 23 of the ink groove 12. A side plate 17 is bonded to one side of a surface parallel to the width direction 21 and parallel to the depth direction 23 of the piezoelectric ceramic wall, and a block 19 having an ink supply port 18 is bonded to the opposite surface.

The operation when an electric field is applied to the drive electrode 13 of the piezoelectric actuator element will be described below with reference to FIG. When an electric field is applied to the drive electrodes 13 formed on both sides of the piezoelectric ceramic wall 11, the piezoelectric ceramic wall will move in the height direction ( Shear deformation (also called thickness shear deformation) occurs without any dimensional change in the thickness direction. Next, the applied electric field is removed to restore the piezoelectric ceramic wall to its initial state. At this time, ink groove 1
The ink flow path (pressure chamber) formed by 2 causes a volume change. The pressure waves generated in the pressure chamber accordingly propagate within the ink flow path, and ink droplets are ejected from ink ejection holes formed in the ink nozzle plate.

If the ejection efficiency is 100%, the change in the volume of the pressure chamber required for ejecting ink should be the same as the volume of the ink droplets ejected, but in reality, the change in the volume of the pressure chamber required for ink ejection is the same as the volume of the ink droplets ejected. Ejection efficiency decreases due to the compliance ratio of the ink in the chamber, the return of ink from the ink supply port, etc. Therefore, in order to achieve proper ink ejection, it is necessary to generate a volume change within the pressure chamber that is considerably larger than the volume of the ink droplet to be ejected. Moreover, the volume of the pressure chamber is required to be several hundred to several thousand times larger than the volume change.

On the other hand, since the ink jet printer head is required to have highly integrated ink jet holes 15, it is necessary to reduce the width of the piezoelectric ceramic wall and the ink groove. The height dimension of the piezoelectric ceramic wall (the depth dimension of the ink groove) must also be reduced due to technical limitations in groove formation and the demand for miniaturization of the element. Therefore, when driving with a practical driving voltage is considered, the longitudinal dimension of the ink groove 12 needs to be sufficiently larger than the width and depth dimensions in order to ensure the volume and volume change of the pressure chamber. In reality, the width, depth, and longitudinal dimensions of the ink groove 12 are 0.02 to 0.2 mm, 0.05 to 0.5 mm, and 10 to 10 mm, respectively.
It is about 40mm.

In the conventional piezoelectric head for an inkjet printer, the ink nozzle plate 16 is joined to the piezoelectric actuator element 14 such that the ink jetting direction is in the longitudinal direction 22 of the ink groove 12, so that the longitudinal dimension of the ink groove 12 is If it becomes large, the delay in the propagation time of the pressure waves generated at a position away from the ink ejection hole 15 and the propagation loss of the pressure waves cannot be ignored.

In the piezoelectric head for an inkjet printer of this embodiment, the ink nozzle plate 16 is bonded to the upper surface of the piezoelectric ceramic wall via a strip seal. Furthermore, since the ink jet holes 15 provided in the ink nozzle plate 16 are located at approximately half the longitudinal dimension of the ink groove 12 (near the center), the piezoelectric actuator element 1
When the shape of the ink jet hole 15 is fixed, the distance between the ink jet hole 15 and each point of the ink groove 12 is approximately half that of the conventional example, and the propagation time of the pressure wave generated at a position away from the ink jet hole 15 is reduced. The delay can be reduced to about half compared to conventional piezoelectric heads for inkjet printers, and the propagation loss of pressure waves can be reduced to about half. In other words, high pressure waves can be instantaneously supplied to the ink ejection holes 15 of the ink nozzle plate 16. Therefore, the piezoelectric head for an inkjet printer of this embodiment has excellent ink jetting efficiency, and the response time from generation of pressure waves to ink jetting is reduced.

[0016]

Effects of the Invention As is clear from the above explanation, the piezoelectric head for an inkjet printer of the present invention has a plurality of walls of piezoelectric material with drive electrodes formed on both sides in order to generate shear deformation of the piezoelectric material. The piezoelectric actuator element has a plurality of ink grooves formed between adjacent piezoelectric material walls, and an ink nozzle plate having ink ejection holes formed on the upper surface of the piezoelectric material wall is joined via a strip seal. With this structure, it is possible to provide a piezoelectric head for an inkjet printer that has high ink jetting efficiency and shortens the response time from generation of pressure waves to ink jetting.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of the configuration of a piezoelectric head for an inkjet printer according to the present embodiment.

FIG. 2 is a schematic diagram showing how a piezoelectric actuator element deforms when an electric field is applied.

FIG. 3 is a schematic diagram of a conventional piezoelectric head for an inkjet printer.

[Explanation of symbols]

11 Piezoelectric material wall 12 Ink groove 13 Drive electrode 14 Piezoelectric actuator element 15 Ink injection hole 16 Nozzle plate 21 Width direction 22 Longitudinal direction

Claims (1)

[Claims] 1. A plurality of walls of piezoelectric material having drive electrodes formed on both sides to generate shear deformation of the piezoelectric material, and a plurality of ink grooves formed between adjacent walls of the piezoelectric material. In a piezoelectric head for an inkjet printer that utilizes a piezoelectric actuator element, a nozzle plate having ink ejection holes is formed on a surface parallel to the width direction of the ink groove and parallel to the longitudinal direction. A piezoelectric head for inkjet printers featuring