Ink Accelerating Unit For Use In Ink Jet Printer

Abstract

Upon one or both surfaces of an accelerating electrode having a center aperture is overlaid and fixed concentrically a disk member or members each having a center aperture tapered so as to converge toward the accelerating electrode. Unnecessary ink attached to the accelerating electrode may be sucked through the interface or interfaces between the disk member or members and the accelerating electrode under capillary action and ink attached to the disk members may readily flow toward the interfaces along the tapered peripheral surfaces or walls of the center apertures of the disk members. Grooves may be formed in the surfaces of the disk members in contact with the accelerating electrode so as to facilitate the collection and discharge of unnecessary ink sucked into the interfaces under capillary action. Removal of ink attached to the accelerating electrode may be much facilitated, thus assuring the stable operation of the accelerating electrode. In addition, fabrication of the accelerating electrode structure may be much facilitated and simplified yet with a higher degree of accuracy.

Description

BACKGROUND OF THE INVENTION

The present invention relates to an ink jet recording device and more particularly an accelerating electrode structure for ink jet recording devices capable of preventing the contamination by unnecessary or excess ink.

In the ink jet recording devices of the type in which the ink jet stream is horizontally and vertically deflected under the electrostatic force, electromagnetic force or vibrations caused by ultrasonic waves so as to write the characters or the like on a recording medium, the ink jet stream is liquid opposed to the electron beam or the like so that various parts in the ink jet recording devices are frequently contaminated by ink and their functions are adversely affected by the contamination. As a consequence the stable recording operation of the devices is not attained. Especially in the ink jet recording device of the type in which the stream of electrically charged ink droplets is accelerated by an accelerator and horizontally and vertically deflected by the electrostatic force so as to write the characters and the like on a recording medium, charged ink droplets tend to attach to the accelerating electrode due to the secondary emission, vibrations and some other reasons so that the ink accumulated upon the accelerating electrode causes the disturbance of the electric field, thereby causing the distortions of the characters and the like printed on the recording medium. The secondary emission cannot be eliminated or overcome from the theoretical point of view, and there is no guarantee at all that the attachment of ink to the accelerating electrode due to the vibrations and other reasons may be effectively prevented. To overcome this problem, the prior art generally disposes an accelerating electrode in front of a nozzle in spaced-apart relation therewith, the accelerating electrode with a thickness of 0.5 mm having a center aperture with a diameter of 1.5 mm. The center aperture of the accelerating electrode is tapered so as to diverge toward the nozzle so that the ink droplets in the outer peripheral portion of the ink droplet beam or stream, that is undesired or unnecessary ink droplets caused to fly due to the secondary emission may be prevented to pass through the center aperture of the accelerating electrode by the tapered peripheral wall surface of the center aperture. By this arrangement the prior art intends to provide the uniform electric field distribution between the orifice of the nozzle and the accelerating electrode. The tapered peripheral wall surface of the center aperture of the accelerating electrode must be sufficiently polished so that the undesired ink attached to the tapered surface may readily fall off therefrom. The prior art accelerating electrode structure of the type described above, however, has the following disadvantages:

1. Ink attached to the accelerating electrode may be removed only by gravity.

2. Machining of the accelerating electrode is difficult (a) because formation of the center aperture and polishing of the tapered peripheral surface thereof are difficult as the dimensions are 0.5 mm in thickness and 1.5 mm in inner diameter, and (b) because machining tolerance for forming the center aperture is very severe.

Because of the reasons described above, it has been extremely difficult to fabricate the ideal accelerating electrode of the type described. As a result, the stable ink jet writing operation has not been attained due to the attachment of undesired or unnecessary ink.

One of the objects of the present invention is therefore to provide an improved accelerating electrode structure for ink jet printers.

SUMMARY OF THE INVENTION

According to one aspect of the present invention a plate or disk member is attached to one surface of an accelerating electrode so that unnecessary ink attached to the accelerating electrode may be sucked and discharged through the interface between the plate or disk member and the accelerating electrode.

According to another aspect of the present invention, plate or disk members are attached on both surfaces of the accelerating electrode so that attached unnecessary ink may be sucked and discharged through the interfaces between the plate or disk members and the accelerating electrode.

According to another aspect of the present invention, grooves for collecting and discharging sucked unnecessary ink are formed in the surfaces of the plate or disk members in contact with the accelerating electrode, thereby facilitating the discharge of unnecessary ink out of the accelerating electrode structure.

According to another aspect of the present invention, the center apertures of the plate or disk members attached to the accelerating electrode are tapered so as to converge toward the accelerating electrode so that unnecessary ink attached to the plate or disk members may readily flow toward the interfaces.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic diagram illustrating a writing part of an ink jet recording device to which is applied the present invention in one form;

FIG. 2 is a schematic diagram of electrical components for producing desired electric fields between the associated parts of ink jet recording device;

FIG. 3 is a longitudinal sectional view of an accelerating electrode structure in accordance with the present invention;

FIG. 4 is an exploded view on enlarged scale and in cross section, thereof;

FIG. 5 is a cross section taken along the line A'--A' in FIG. 4 illustrating a first disk member; and

FIG. 6 is a cross section taken along the line B'--B' in FIG. 4 illustrating a second disk member.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, an ink jet writing head 10 is carried for reciprocal movement by a wire 13 wrapped around a pair of pulleys 11 and 12 which are driven by a motor 14. When the writing head 10 is displaced in one direction, the ink jet is ejected and impinged upon a recording medium (not shown) in response to the control signals, thereby synthesizing the characters or the like.

FIG. 2 is a diagrammatical view illustrating the principle of generating the electrostatic fields between the ink nozzle 20 and the acceleration electrode 21 and between the nozzle 20 and a platen 22. A positive electrode is placed in the nozzle 20 made of a glass. The electrically conductive ink to be supplied into the nozzle 20 is applied with a positive potential. Both of the acceleration electrode 21 and the platen 22 are grounded. A power source 23 has a high voltage of the order of for example 2,700 V. As in the case of the conventional cathode ray tube, the vertical and horizontal deflecting electrodes 24 and 25 are disposed forwardly of the acceleration electrode 21. The ejected ink droplets are accelerated by the acceleration electrode 21, then deflected by the vertical and horizontal electrodes 24 and 25 in response to the control signals applied thereto and impinged at a desired position upon a recording medium 26 placed upon the platen 22. Thus, the characters each consisting of a dot pattern may be sequentially synthesized upon the recording medium 26 by the ink droplets ejected in the aforementioned fashion.

FIG. 3 is a sectional view of an accelerating electrode structure in accordance with the present invention in which an accelerating electrode is a metal disk having a thickness of 0.03 mm, an inner diameter of 1.5 mm and an outer diameter of 7.2 mm and a center aperture 31. A first perforated disk member 32 comprises a metal disk having a thickness of 0.2 mm, an inner diameter of 2.4 mm and an outer diameter of 7.2 mm and a center aperture 33, which is tapered as shown by 35 so as to converge toward the center aperture 31 of the accelerating electrode 30. A second perforated disk member 36 comprises a metal disk with a thickness of 0.2 mm, an inner diameter of 3 mm and an outer diameter of 7.2 mm and having a center aperture 37 which is also tapered as indicated by 39. The first perforated disk member 32, the accelerating electrode 30 and the second perforated disk member 36 are laminated in the order named in concentrical relation with each other and secured to each other for example by spot welding. The assembly consisting of the first perforated disk member 32, the accelerating electrode 30 and the second perforated disk member 36 is mounted upon a supporting structure 40.

In the accelerating electrode structure in accordance with the present invention, the capillary action at the interfaces between the first perforated disk member 32 and the accelerating electrode 30 and between the accelerating electrode 30 and the second perforated disk member 36 is used to sucking the unnecessary ink. In this specification the suction caused by the capillary action will be referred to as the "capillary suction" hereinafter for brevity.

As shown in FIGS. 5 and 6, both of the first and second disk members 32 and 36 are provided with annular and straight grooves 34 and 38 respectively formed in the surfaces in contact with the accelerating electrode 30 in order to further increase the capillary suction. It is appreciated that the present invention is not limited to the annular and straight grooves 34 and 38 and that any suitable grooves may be formed for increasing the capillary suction. Because of the construction of the accelerating electrode structure in accordance with the present invention, almost all of the unnecessary or undesired ink is attached to the accelerating electrode 30. From the foregoing description it is seen that the tapered center aperture 33 is provided for relaxing the effect of the electric field and that the ink will not adhere to the tapered surface of the center aperture 33 so that the tolerance in machining may be relaxed. The second disk member 36 is provided for sucking under the capillary suction the unnecessary ink attached to the rear surface (opposing to the recording medium) of the accelerating electrode 30 although the attachment of the ink to the rear surface is very rare. Concurrently the second disk member 36 serves to simplify and facilitate the operation of joining the first disk member 32, the accelerating electrode 30 and the second disk member 36 together for example by spot welding.

In the accelerating electrode structure in accordance with the present invention, the unnecessary ink is attached to the periphery of the center aperture 31 of the accelerating electrode 30 and is sucked into the interface between the first disk member 32 and the accelerating electrode 30 under the capillary suction. In this case a large suction area may be provided because the first and second disk members 32 and 36 are overlaid upon the accelerating electrode 30 over the whole inner periphery thereof. The unnecessary ink sucked into the interfaces between the first and second disk members 32 and 36 on one hand and the accelerating electrode 30 on the other hand may be collected into the grooves 34 and 38 and discharged out of the accelerating electrode structure under the gravity into a suitable sump or the like (not shown) through fine wires (not shown) inserted into the grooves 34 and 38. The ink in the grooves 34 and 38 will not adversely affect the electric field applied to the accelerating electrode structure.

The advantages of the accelerating electrode structure in accordance with the present invention may be summarized as follows:

1. The collection and discharge of the unnecessary ink are much facilitated because not only the gravity but also the capillary suction are used. The unnecessary ink is completely discharged so that the sediment of ink will not remain in the accelerating electrode structure and will not adversely affect the electric field applied thereto. Therefore the deformation of the printed characters may be prevented.

2. The maximum ink suction area is provided so that the capillary suction of unnecessary ink may be much facilitated.

3. The thickness of the accelerating electrode is less so that the center aperture may be formed advantageously by a mechanical press with ease and a higher degree of accuracy.

4. The maching tolerance of the first disk member may be much relaxed as compared with the prior art disk member.

From the foregoing description it is seen that the present invention improves the suction of unnecessary ink and simplifies the fabrication of the accelerating electrode structure.

In the instant embodiment, the first and second disk members and the accelerating electrode have been described as being in the form of disk, but it is appreciated that the present invention is not limited thereto and that they may be in any suitable form.

Claims

I claim:

1. An accelerating electrode structure for ink jet recording devices characterized in that upon one surface of a center-apertured thin accelerating electrode is overlaid concentrically and securely fixed a first member having a center aperture whose diameter is larger than said center aperture of said accelerating electrode and which is tapered so as to converge toward said accelerating electrode, whereby the unnecessary ink attached may be sucked into the interface between said first member and said accelerating electrode.

2. An accelerating electrode structure for ink jet recording devices characterized in that upon one surface of a center-apertured thin accelerating electrode is overlaid concentrically and securely fixed a first member having a center aperture whose diameter is larger than said center aperture of said accelerating electrode and which is tapered so as to converge toward said accelerating electrode, and upon the other surface of said thin accelerating electrode is overlaid concentrically and securely fixed a second member having a center aperture whose diameter is larger than that of said center aperture of said accelerating electrode and which is tapered to converge toward said accelerating electrode, whereby unnecessary ink attached may be sucked into the interfaces between said first and second members on one hand and said accelerating electrode on the other hand.

3. An accelerating electrode structure according to claim 1 wherein grooves for facilitating the suction of said unnecessary ink are formed in one surface of said first member in contact with said accelerating electrode.

4. An accelerating electrode structure according to claim 2 wherein grooves for facilitating the suction of said unnecessary ink are formed in one surfaces of said first and second members in contact with said accelerating electrode.