JPH04284253A - Piezoelectric head for ink-jet printer - Google Patents

Abstract

PURPOSE:To improve the injection efficiency of ink by constituting a driving electrode of at least two or more of divided electrodes in the longitudinal direction of the wall of a piezoelectric material in a piezoelectric actuator element. CONSTITUTION:A piezoelectric ceramic board is composed of a large number of piezoelectric ceramic walls 11 arranged in parallel, a large number of ink grooves 12 formed among the adjacent piezoelectric ceramic walls 11 and disposed in parallel, and driving electrodes 14a, 14b, 14c divided into three and formed along the direction of injection 18 of ink on both side faces of the piezoelectric ceramic walls. Leading-out electrodes 15a, 15b are shaped on the bases 13 of the ink grooves 12 in order to input driving signals at every two split electrode in positional relationship oppositely faced while holding the ink grooves 12 in the divided driving electrodes.

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 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, it is necessary to ensure the minimum required ink groove volume and volume change amount of the ink groove, and to improve the degree of integration of ink ejection holes. It is necessary to form a large number of parallel ink grooves whose length in the ink jetting direction is sufficiently larger than the width and depth of the grooves. Furthermore, in order to cause shear deformation of the piezoelectric material, it was necessary to form the drive electrodes 19 on both sides of the walls of the adjacent piezoelectric materials 11 forming the ink grooves 12, as shown in FIG.

0004

[Problems to be Solved by the Invention] However, in conventional drive electrodes, as the piezoelectric material returns to its initial state, the wall of the piezoelectric material simultaneously deforms at various locations in the ink jetting direction. The propagation time to the ink ejection hole varied depending on the distance to the ejection hole, and the ejection efficiency was reduced. 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 an object of the present invention is to realize a piezoelectric head for an inkjet printer with improved ink jetting efficiency.

[0006]

[Means for Solving the Problems] In order to achieve this object, a piezoelectric actuator element utilized in a piezoelectric head for an inkjet printer of the present invention has a plurality of parallel walls made of piezoelectric material, It consists of a large number of ink grooves arranged in parallel formed by the wall of the piezoelectric material, and drive electrodes divided in the longitudinal direction and formed on both sides of the wall of the piezoelectric material.

[0007]

[Operation] The piezoelectric actuator element of the present invention having the above structure causes shear deformation in the wall of the piezoelectric material by applying an electric field. The ink groove formed between the walls of the piezoelectric material changes its volume due to shear deformation of the wall of the piezoelectric material, and acts as a kind of pressure chamber and as an ink flow path.

[0008]

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

A schematic diagram of the piezoelectric actuator element of this embodiment is shown in FIG. 1, and a detailed diagram of the divided electrode portion is shown in FIG. The piezoelectric actuator element 16 of this embodiment uses piezoelectric ceramics having a polarization direction 17 in the thickness direction as a 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. Drive electrodes 14a, 14b, and 14c formed on a surface by dividing into three along the ink jetting direction 18 (longitudinal direction), and each of the divided drive electrodes facing each other across the ink groove 12. It consists of extraction electrodes 15a and 15b formed on the bottom surface 13 of the ink groove 12 for inputting drive signals for each of the two divided electrodes.

FIG. 3 shows a schematic diagram of a configuration example of a piezoelectric head for an inkjet printer using the piezoelectric actuator element 16 of this embodiment. The piezoelectric actuator elements 16a and 16b having the above configuration are joined together on the upper surface of the piezoelectric ceramic wall 11, and two ink grooves 12 each form an ink flow path (pressure chamber). Multiple ink jet holes 4
An ink nozzle plate 42 with 1 is joined to the front side of the piezoelectric actuator element.

The operation when a drive signal is input to the divided drive electrodes of the piezoelectric actuator element will be described below with reference to FIG. When an electric field is applied to the drive electrodes formed on both sides of the piezoelectric ceramic wall 11, the piezoelectric ceramic wall will move in the height direction (thickness Shear deformation (also called thickness shear deformation) occurs without any dimensional change in direction). Next, the applied electric field is removed to restore the piezoelectric ceramic wall to its initial state.

At this time, the volume of the ink flow path (pressure chamber) formed by the two ink grooves 12 changes. The pressure waves generated in the pressure chamber along with this propagate within the ink flow path, and ink droplets are ejected from the ink ejection holes 41 formed in the ink nozzle plate 42. If the ejection efficiency is 100%, the change in the volume of the pressure chamber required to eject ink should be the same as the volume of the ejected ink droplets, but in reality, the change in volume of the pressure chamber required for ink ejection is the same as the volume of the ejected ink droplets. Ejection efficiency decreases due to ink compliance ratio, ink return 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.

[0013] Furthermore, 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 an inkjet printer head is required to have highly integrated ink ejection holes, 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 considering driving at a practical driving voltage, in order to ensure the volume and volume change of the pressure chamber, it is necessary to make the length of the ink groove (ink jetting direction) sufficiently larger than the width and depth. There is. In reality, the width, depth, and longitudinal dimensions of the ink groove are 0.02 to 0.2 mm and 0.05 mm, respectively.
~0.5mm, about 10-40mm. As the longitudinal dimension of the ink groove increases, the delay in the propagation time of pressure waves generated at a position away from the ink ejection holes and the propagation loss of pressure waves cannot be ignored.

In this embodiment, the driving electrode is divided into three parts, and first, the electric field of the divided electrode 14c that is farthest from the ink injection hole is removed (the electric charge charged in the piezoelectric ceramic is discharged). ), causing shear deformation in a portion of the piezoelectric ceramic wall. The electric field of the divided electrode 14b is removed by delaying the timing of removing the electric field in accordance with the propagation timing of the pressure wave generated at this time. Similarly, the timing is further delayed to remove the electric field of the divided electrode 14a. By delaying the timing and sequentially removing the electric field of the divided electrodes as described above, the delay in the propagation time of the pressure wave generated at a position away from the ink jetting hole 41 is apparently reduced, and the propagation loss of the pressure wave is reduced. This makes it possible to instantaneously supply high pressure waves to the ink ejection holes 41 of the nozzle plate 42. Therefore, the piezoelectric head for an inkjet printer of this embodiment has excellent ink jetting efficiency.

[0015]

As is clear from the above explanation, the piezoelectric actuator element of the present invention has a plurality of walls of piezoelectric material on which drive electrodes are formed on both sides in order to generate shear deformation of the piezoelectric material. A piezoelectric actuator element having a plurality of ink grooves formed between adjacent walls of piezoelectric material, wherein drive electrodes formed on both sides of the wall of piezoelectric material are arranged in the longitudinal direction of the wall of piezoelectric material (ink droplets). injection direction)
Second, since the ink droplet is composed of at least two divided electrodes, the electric field applied to the divided electrodes is sequentially removed in the ink droplet jetting direction with a delayed timing, thereby improving the ink droplet jetting efficiency. Accordingly, it is possible to provide a piezoelectric head for an inkjet printer with high jetting efficiency.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of the configuration of a piezoelectric actuator element in which divided electrodes of this embodiment are formed.

FIG. 2 is a schematic diagram of the configuration of a piezoelectric actuator element in which divided electrodes of this embodiment are formed.

FIG. 3 is a schematic diagram showing the configuration of an inkjet printer head using the piezoelectric actuator element of this embodiment.

FIG. 4 is a schematic diagram showing the deformation of a piezoelectric actuator element when an electric field is applied.

FIG. 5 is a schematic diagram showing a conventional example of a piezoelectric actuator element.

[Explanation of symbols]

11 Piezoelectric material wall 12 Ink groove 14 Split electrode 16 Piezoelectric actuator element 18 Ink droplet jetting 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 the piezoelectric head for an inkjet printer using a piezoelectric actuator element having a piezoelectric actuator element, the piezoelectric actuator element has at least two drive electrodes formed on both sides of the wall of the piezoelectric material in the longitudinal direction of the wall of the piezoelectric material. A piezoelectric head for an inkjet printer characterized by comprising electrodes divided into the above.