JPS63242555A - Ink jet head - Google Patents

Abstract

PURPOSE:To avoid bubbles from invading further into a small-diameter vertical part or remaining here, by providing a bubble-removing branch path vertically connecting from the middle of an ink supply path to an opening formed on the top part. CONSTITUTION:A bubble invading into an ink supply path 15 from an external ink supply mechanism, e.g. an ink bottle, through a joint 15c immediately moves up to a ceiling part of a horizontal part 15b due to its buoyancy. The bubble moves slowly toward a vertical part 15a along the wall surface of the ceiling as an ink flows according to the ink supply. Such a bubble invades into a path 15d with a relatively large diameter connecting from the middle of the horizontal part 15b to an opening 17 on the upper part of a head before reaching to the small-diameter vertical part 15a. After moving upwards due to the buoyancy inside, the bubble is discharged outside the head out of the opening 17 of the top part, thus never adversely affecting the ink supply.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention This invention relates to an inkjet head installed in an inkjet printer.

2. Description of the Related Art Inkjet printers, which perform printing by ejecting ink droplets and flying them to the surface of recording paper, have various advantages such as less noise than the currently mainstream dot impact printers. There are two types of inkjet heads installed in such inkjet printers: continuous jet type and drop-on-demand type.
The latter type is considered to be promising in terms of the small size and simplicity of the device.

There are various types of drop-on-demand type inkjet heads, but a type having an ink reservoir in front of an orifice as shown in FIG. 2 has been developed as a high-performance head.

This inkjet head includes an orifice 21, an ink reservoir 22 having a rear end face including the orifice 21 and a front end face in contact with the atmosphere, and a pressure chamber 2 filled with ink and pressurized by an electromechanical conversion element 26.
4, a pressure propagation path 23 that extends from the pressure chamber 24 forward and is connected to the ink reservoir 22 via the orifice 21, and approaches the ink reservoir 22 from below and is connected to the ink reservoir 22 at its peripheral portion. The ink supply path 25 is also provided.

In this inkjet head, by forming an ink reservoir 22 in front of the orifice 21, it is possible to control the direction and speed of ink droplet jetting that occurs when excess ink adheres to the vicinity of the orifice in an inkjet head that does not have this. The structure is designed to effectively prevent fluctuations and stabilize the injection characteristics.

Problems to be Solved by the Invention In the conventional inkjet head described above, an ink reservoir is formed in front of an orifice, and ink is supplied from an ink supply path into a pressure chamber via this ink reservoir and the orifice. This stabilizes the direction and speed of droplet jetting.

On the other hand, in the structure shown in FIG. 2, since it is necessary to secure a space for forming the pressure chamber and the electrical/mechanical conversion element, the vertical portion 25a of the ink supply path 25 is extended from the horizontal portion 25b formed near the bottom of the head to the top. The nearby ink reservoir 22 is approached from below over a long distance. The inner diameter of the vertical portion 25a of this ink supply path is set to a fairly small value in order to draw up the ink by capillary force.

Therefore, if air bubbles enter the ink supply path 25 through the joint 25c with an external mechanism (not shown) for some reason, they will pass through the horizontal portion 25b and enter the vertical portion 25c.
5a, the ink accumulates in the middle of the vertical portion, as exemplified by B in FIG. 2, and the subsequent ink supply is obstructed.

Means for Solving the Problems The inkjet head of the present invention is configured to include a branch path for removing air bubbles that vertically connects the ink supply path from a midway point to an opening formed at the top. ing.

Operation In the inkjet head of the present invention, air bubbles that have entered the ink supply path are discharged to the outside of the head through a branch path that exits from the middle of the ink supply path to the top of the head. This prevents air bubbles from penetrating into the small-diameter vertical portions or staying there, and adverse effects on ink supply are effectively avoided.

Hereinafter, further details of the present invention will be explained in detail together with examples.

Embodiment FIG. 1 is a sectional view showing the structure of an inkjet head according to an embodiment of the present invention.

This inkjet head includes an orifice 11 and an ink reservoir 12 having a rear end face including the orifice 11 and a front end face in contact with the atmosphere. Furthermore, this inkjet head has a pressure chamber 14 that is filled with ink and pressurized by an electromechanical transducer 16.
, a pressure propagation path 13 extending from the pressure chamber 14 to the front thereof, and an ink supply path 15 connected to the ink reservoir 12 in a peripheral portion thereof.

Because it is necessary to secure a space for forming the pressure chamber 14 and pasting the electrical/mechanical transducer 16, the ink supply path 15 connects a joint 15c with an external mechanism (not shown) and a horizontal portion 15b connected to the head. A small diameter vertical portion 25 is formed at the bottom and rises from the horizontal portion 15b of the bottom.
a is brought close to the upper ink reservoir 12 and communicated with the surrounding area. Horizontal portion 15b of this ink supply path 15
An opening 1 formed in the top of this head from a midway point
A branch path 15d for removing air bubbles is formed which connects up to 7 in the vertical direction.

Such a change in the cross-sectional shape along the ejection direction can be easily realized by configuring the inkjet head as a laminated structure formed by stacking thin plates.

Note that this inkjet head is installed so that the pressure propagation path 13 is horizontal under normal usage conditions. Therefore, in this normal usage state, the vertical portions 15a of the ink supply path 15 are arranged in the vertical direction as indicated by the number 7.

A pulsed electrical signal is intermittently applied to an electrical/mechanical conversion element 16 made up of a piezo element or the like attached to the rear outer wall surface forming the pressure chamber 14, and a pressure wave is generated within the pressure chamber 14. Occur. This pressure wave is propagated through the pressure propagation path 13 to the orifice 11, from where it breaks through the front ink reservoir 12 and ejects an ink droplet. Immediately after this ink droplet is ejected, the negative pressure generated in the pressure chamber 14 causes the pressure propagation path 13 to flow from the ink reservoir 12 through the orifice 11.
Ink is sucked into the printer. The ink in the ink reservoir 12, which tends to be insufficient due to this suction, is supplied from the ink supply path 25 in the peripheral portion.

Air bubbles that enter the ink supply path 15 through the joint 15C from an external ink supply mechanism (not shown) such as an ink bottle immediately move to the ceiling portion of the horizontal portion 15b due to their buoyancy. The bubbles slowly move in the direction of the vertical portion 15a along the wall surface of the ceiling as the ink flows as the ink is supplied. Before reaching the small-diameter vertical portion 15a, such bubbles enter the relatively large-diameter branch passage 15d that communicates with the opening 17 at the top of the head from the middle of the horizontal portion 15b, and rise inside the branch passage 15d due to buoyancy. Thereafter, the ink is discharged to the outside of the head through the opening 17 at the top, so that it does not adversely affect the ink supply.

Effects of the Invention As explained in detail above, the inkjet printer of the present invention
Since the head is configured to include a branch path for removing air bubbles that vertically connects the middle part of the ink supply path to the opening formed at the top of the head, even if air bubbles enter the ink supply path, The ink is easily discharged to the outside of the head through the branch passages, thereby effectively preventing adverse effects on the ink supply.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the structure of an inkjet head according to an embodiment of the present invention, and FIG. 2 is a sectional view showing the structure of a conventional inkjet head. 11... Orifice, 12... Ink reservoir, 13.
... Pressure propagation path, 14 ... Pressure chamber, 15 ... Ink supply path, 15a ... Vertical portion, 15b ... Horizontal portion, 15c ... Joint with external mechanism, 15d ... Branch road,
16... Electrical/mechanical conversion element, 17... Opening at the top of the head. Patent applicant: NEC Home Electronics Co., Ltd.

Claims (1)

[Scope of Claims] A pressure chamber filled with ink and pressurized by an electrical/mechanical conversion element, a pressure propagation path extending from the pressure chamber forward thereof, and a rear end connected to the pressure propagation path. an ink reservoir having an end face and a front end face in contact with the atmosphere; an ink supply path that approaches the ink reservoir from below and is connected to the ink reservoir at its peripheral portion; An inkjet head characterized by having a branch path for removing air bubbles that vertically connects up to the opening.