Jet Printer, Particularly For An Ink Ejection Printing Mechanism

Abstract

In a jet printer including a compression chamber having one end provided with a discharge nozzle via which printing ink is propelled onto the surface of paper to be printed, and its other end communicating with an ink reservoir, the volume of the compression chamber being made to vary by an exciter system, a fluidic component having a non-reciprocal flow characteristic is disposed in the ink flow path between the reservoir and the chamber to cause the resistance to flow from the chamber toward the reservoir to be higher than in the opposite direction.

Description

BACKGROUND OF THE INVENTION

The present invention relates to a jet printer, particularly for an ink ejection printing mechanism, including a chamber whose end facing the paper to be printed is provided with a discharge nozzle, whose other end is provided with an intake for the printing liquid coming from a reservoir, and whose volume can be varied by temporary pressure surges produced by an exciter system.

Devices of this type are known in which the ink, which is under pressure in an ink reservoir, is transferred to a tube having a discharge nozzle. With the aid of electromechanical transducers, the tube, is subjected to periodic elongations, and thus constrictions in diameter, which cause the ink to exit from the housing in the form of ink droplets. The electromechanical transducers here consist of piezoelectric quartz crystals which are polarized so that they axially contract or expand when a voltage is applied.

The structure of this known device is very complicated and requires, inter alia, an arrangement for producing an excess pressure. Moreover, since the stream of ink droplets can not be abruptly cut off, it must be electrically charged so that it can be deflected when no printing is to take place. Thus an additional deflection system must be provided similar to that used for the electron beam in cathode-ray tubes.

An apparatus has been proposed for producing pressure pulses in a chamber filled with a liquid matter where the chamber, on the other hand, is closed off by a membrane and, on the other hand, is in communication with a discharge channel and an intake channel for the printing liquid coming from a reservoir.

The volume in this chamber can be varied by driving the movable membrane by means of an electromechanical transducer. In conjunction with a hydrodynamic decoupling of the liquid streams at the discharge nozzle, individual ink droplets are produced in this manner. The drawback is here the complicated filling of the capillary chambers with liquid, which must take place in a vacuum. Moreover, the structure is still rather complicated.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a jet printer in which the refilling of the capillary chambers with liquid can take place without the need of a vacuum, which is extremely dependable, and which permits rapid operation with uniform printing quality.

This is accomplished, according to the present invention, in that a fluidic component is disposed at the point where the intake channel for the printing liquid opens into the chamber, the flow resistance of this fluidic component being very high in the direction from the chamber to the intake channel and very low in the opposite direction. The non-reciprocal, or diode effect of these fluidic components is produced only by physical effects of the stream deflection or by mutual influence of the liquid streams. Such fluidic components have been found to permit a simple and compact structure for an ink ejection head.

In an advantageous embodiment, the fluidic component is a nozzle impact plate system at the intake side. The fluidic component can also be made to produce a diode effect through a mutual influencing of liquid streams in that the component is provided with two channels which end at one side in the discharge nozzle and at the other side in an intake channel to the reservoir, which channel is perpendicular to the above-mentioned two channels. The opening of the channels into the intake channel may either be perpendicular or tangential and the channels maybe directed toward one another. The particular advantage of these fluidic components is that they are particularly simple and robust in structure. They also permit refilling the reservoir without a vacuum.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a first embodiment of the present invention.

FIG. 2 is a cross-sectional view of a second embodiment of the present invention, with two channels which open into the intake channel in a perpendicular direction.

FIG. 3 is a view similar to that of FIG. 2, but with mutually tangentially directed channel openings.

FIG. 4 is a cross-sectional view of a third embodiment.

FIG. 5 is a detail view, to an enlarged scale of part of the device of FIG. 4.

FIG. 6 is a plan view of the embodiment shown in FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The embodiment shown in FIG. 1 includes an axially symmetrical housing 1 whose axis is horizontal in the drawing and whose axial end facing the printed paper is provided with a nozzle body 3 with a discharge nozzle 5. This discharge nozzle 5 is preceded by a chamber 7 into which an elastic tube 9 is inserted. The other end of this tube 9 is connected with a chamber 11 of a second nozzle body 13 which is kept at a distance from the first nozzle body 3 in housing 1 by a spacer ring 15. The chambers 9, 11 are connected with chamber 19 constituting in the space beween the cylindrical body 40 and the elastic tube 9.

In the space 17 between the nozzle bodies 3 and 13 the elastic wall constituting the tube 9 is enclosed by a piezotoroid 21 serving as the exciter system. The elastic wall 9 and the exciter system may of course also have different structures.

The chamber 11 in nozzle body 13 includes an intake nozzle 23 which is in communication with a reservoir 29 via an intermediate chamber 25 and a connecting channel 27. The intermediate chamber 25 is disposed between the nozzle body 13 and an end piece 39 spaced from nozzle body 13 by a distance defined by a spacer ring 37. In the intermediate chamber 25 the end piece 39 has a protrusion in the form of an impact plate close to and facing intake nozzle 23.

If a signal source 35 transmits voltage pulses through line wires 31 and 33 to the piezotoroid 21, the latter contracts radially due to its polarization. Thus mechanical pressure pulses are given to the elastic tube so that the volume in the compression chambers 7, 11, 19 is reduced. Because of the nozzle impact plate systems 23, 41 constituting the fluidic component on the intake side of the compression chamber the flow resistance is greater at the intake side of the compression chamber when fluid is displaced than on the outlet side of the compression chambers 7, 11, 19, at which the discharge nozzle 5 is disposed.

When the piezotoroid 21 swings back into its starting position a subatmospheric pressure is produced in the compression chambers 7, 11, 19 which causes ink to be sucked through the intake nozzle 23 from the reservoir 29 via channel 27 and intermediate chamber 25. During this operation, the flow resistance on the outlet side 5 of the compression chamber is greater than on the intake side 23. During this suction phase the capillary force of the ink in the discharge nozzle 5 must be great enough that no air is sucked into the compression chambers 7, 11, 19. Coaction of the nozzle impact plate arrangements 23, 41 at the intake side with the discharge nozzle 5 on the outlet side thus produces a hydrodynamic valve.

In order to achieve a high operating speed, an advantageous embodiment of the present invention, as shown in FIG. 1, includes a cylindrical body 40 which is fixed to body 13, by suitable means, such as circumferentially spaced, radially projecting struts, and which is arranged in the elastic tube 9 in such a way as to define an annular compression chamber therewith. This produces a high volume change or compression ratio for the compression chamber, this ratio being determined by the chamber volume corresponding to the starting position and the contracted position, respectively, of piezotoroid 21.

The arrangement of the nozzle impact plate system on the inlet side and the discharge nozzle at the outlet side of compression chambers 7, 11, 19 produces a jet printer which is simple in structure and operation and in which it is possible to fill the capillary chambers without maintaining a vacuum.

The present invention is in no way limited to the embodiment of FIG. 1. Rather, deviations from the embodiment shown in FIG. 1 are possible within the scope of the invention, these deviations being represented by structural modifications which conform to the required conditions and dimensions.

Thus, for example, the fluidic component at the intake of the chamber may include two channels 43 and 45 as shown in FIG. 2, each of which has an inlet end which opens into a supply channel 51 which is perpendicular to these channels and which leads to a reservoir (not shown).

The other ends of the channels 43 and 45 are in communication with a discharge nozzle 57 via respective compression chambers 52 and 54. The inlet opening of the channels 43 and 45 may here be perpendicular to the supply channel as shown in FIG. 2, so that the diode effect is created by a nozzle impact plate arrangement.

On the other hand, in the embodiment shown in FIG. 3, channels 63 and 65 are arranged tangentially to one another and open into supply channel 61. The pressures are here compensated by the oppositely directed flows of the ink toward channel 61 in such a way that the ink in the compression chamber 62 and 64 is forced to flow in the direction of the discharge nozzle 67.

To produce ink droplets it is of course also sufficient to have only one compression chamber in communication with the discharge nozzle 57.

In the embodiments of FIGS. 2 and 3, the compression chambers 52, 54 and 62, 64 are formed of two channels which are parallel to each other between their ends. In these areas, the compression chambers 52, 54 and 62, 64 have elastic walls 53, 55 and 73, 75, respectively, the pair of walls of each chamber being disposed opposite one another and driven by a common oscillation exciter 56 or 66, which may be a piezocrystal. The compression chambers 52, 54 and 62, 64 may of course also be driven by separate exciter systems. In order to realize a valve effect on the intake side during the ejection of an ink droplet it is necessary for both exciter systems to be driven simultaneously.

FIGS. 4, 5 and 6 show an ink injection head for a printing mechanism including a cylindrical body 83 with a continuous fluid chamber 85. This fluid chamber 85 is covered by a plate 87 at the end facing the printing paper, the cover being provided with a discharge nozzle 89. The cylindrical body 83 is inserted into a base body 81 and permanently connected therewith, for example by a solder connection. The base body 81 is also permanently connected with a membrane 93 which is closely opposite the body 83 in order to form therewith a circular capillary chamber 95. The membrane 93 is part of a cover plate 91 and is arranged to be driven, or deflected by means of a piezoelectric crystal 97 in order to displace a volume of liquid from the capillary chamber 95.

On its periphery the capillary chamber 95 has a contiguous slit opening 99 which communicates with annular inlet channels 101, 103. These inlet channels 101, 103 include interconnected annular channels 101 and 103 which are bounded by bodies 81 and 83 and by the plane 104, between body 83 and cover plate 91 and plane 106 between bodies 81 and 83.

Between these annular channels 101 and 103 there is disposed an impact plate 105 constituted by a protrusion 107 in base body 81 and located closely opposite the slit opening 99. The annular channel 101 in cover plate 91 is connected with annular channel 103 via a plurality of bores 109 which are distributed around the periphery of the assembly. Furthermore, the annular channel 103 is in communication with an ink reservoir (not shown) via a connecting line 111. The slit opening 99 has the shape of a nozzle in the direction toward intake channels 101 and 103.

The operation of the arrangement of FIGS. 4-6 is as follows:

If a signal source sends a voltage pulse to the piezocrystal 97, the crystal contracts radially due to its polarization and bends through toward the inside. This produces a pressure pulse which is transmitted to the liquid in the capillary chamber 95 and in chamber 85.

The nozzle impact plate system 99, 105 forms a fluidic component and is so designed that this pressure increase in the compression chambers 85, 95 will not cause liquid to be propelled back to the reservoir. Thus the pressure wave in the liquid is advantageously directed toward the outlet nozzle 89, a single droplet being ejected from the outlet nozzle 89 with each pressure pulse.

When the piezocrystal 95 swings back to its starting position, a subatmospheric pressure is produced in compression chambers 85, 95 which causes liquid to be drawn from the reservoir through line 111 and annular channels 101, 103 and to quickly flow into capillary chamber 95.

In order to permit favorable replenishment conditions, the slit opening 99 is disposed in line with the center of impact plate 105, the ratio between the height of the opening 99 and the height of the impact plate 105 both in the direction of the axis of element 83, lying between 1/2 and 1/2.5. During the time when the voltage pulse drops or returns to zero the direction of the fluid stream in the connection channel between the opening 99 and the channels 101. 103 is reversed, the fluid can now sucked in the compression chambers 85, 95 without an affective flow resistance.

On the other hand, these geometric dimensions also establish an effective flow resistance toward the reservoir for the liquid when a droplet is to be ejected from the outlet nozzle 89.

The ejection head consists of simple cylindrical parts and can thus be easily installed. All surfaces of the ejection head which must have close tolerances lie on planes of separation between members. An ejection head having a plurality of ejection units in a single plane also requires only a few simple operating steps for its fabrication.

It will be understood that the above description of the present invention is susceptible to various modifications, changes and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.

Claims

I claim:

1. In a jet printer including a compression chamber having one end, arranged to face the surface to be printed, provided with a discharge nozzle and its other end provided with an inlet for the printing liquid coming from a reservoir, and an exciter system arranged to vary the volume of the chamber in brief pressure surges, the improvement comprising a fluidic component constituted by a nozzle and an associated impact plate disposed at the printing liquid inlet to said chamber and constituting a non-reciprocal flow element presenting a resistance to flow of liquid which has a higher value for flow in the direction from said chamber toward the reservoir than in the opposite direction.

2. Jet printer as defined in claim 1, further comprising a liquid intake channel between said other end of said chamber and the reservoir and wherein said nozzle is disposed at said other end of said chamber and has the form of an intake nozzle, and said impact plate is disposed closely opposite said nozzle with the space therebetween constituting part of said intake channel.

3. Jet printer as defined in claim 1, further comprising a supply channel connected to the reservoir and wherein: said fluidic component comprises two channels each having an inlet end opening into said supply channel; and said compression chamber is constituted by two compression channels each communicating with a respective one of said fluidic component channels, said compression channels being joined together at said discharge nozzle.

4. Jet printer as defined in claim 3, wherein said inlet ends of said fluidic component channels open perpendicularly into said supply channel.

5. Jet printer as defined in claim 3, wherein said inlet ends of said fluidic component channels open tangentially into said supply channel in respectively opposite directions such that said inlet ends point toward one another.

6. Jet printer as defined in claim 3, wherein each of said compression channels has an elastic wall portion arranged to coact with said exciter system in order to produce a change in the volume of said compression channels.

7. Jet printer as defined in claim 1, wherein a portion of said compression chamber is constituted by an elastic tube and said exciter system comprises a piezotoroid enclosing said tube and arranged to contract said tube radially to vary the volume of said compression chamber.

8. Jet printer as defined in claim 7, further comprising a fixed cylindrical body disposed in, and spaced radially from the walls of, said tube to define therewith annular compression chamber region.

9. Jet printer as defined in claim 1, further comprising a cylindrical body in which said chamber is disposed in a manner such that the liquid flow path between said inlet and siad discharge nozzle is along the axis of said body;

a cover plate having a deflectable membrane associated with said exciter system, said membrane being disposed opposite an axial face of said body at the inlet end thereof and being spaced from said axial face to define a circular capillary channel therewith, said channel constituting the printing liquid inlet of said chamber and having an inlet opening in the form of a slit extending around the entirety of its circular outer periphery; and

means defining an annular liquid intake channel communicating between said inlet opening and the reservoir; and

wherein said inlet opening constitutes said nozzle and said impact plate is a circular impact plate disposed in said intake channel facing said inlet opening.

10. Jet printer as defined in claim 9, wherein said inlet opening has the form of an annular nozzle.

11. Jet printer as defined in claim 9 wherein the impact surface of said impact plate has the form of a cylinder normal to, and centered on, the median plane of said circular capillary channel and the height of said plate is between 2 and 2.5 times the height of said inlet opening normal to such plane.

12. Jet printer as defined in claim 9, further comprising a base element having a hollow interior in which said cover plate and cylindrical body are disposed, said cover plate and cylindrical body being rigidly connected to said base element; and wherein said base element, said cover plate and said cylindrical body are formed to define said liquid intake channel between them, and said impact plate is constituted by a member integral with, and protruding into the hollow interior of, said base element.