JPH0471712B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to inkjet devices and, more particularly, to inkjet devices for ejecting droplets of ink from an orifice for printing on print media.

An inkjet device is composed of a plurality of inkjet (orifices for injection) arranged in a closely packed array in order to simultaneously print appropriate parts of a print medium, such as when printing text information. is generally desirable. It is also desirable to configure multiple ink jets in a closely packed array to achieve high quality printing of textual information.

The small size or volume of the transducers used makes it difficult to construct closely packed arrays. There is considerable mechanical crosstalk between channels when arrays are tightly configured.
talk) may occur. That is, in order to properly excite the transducers for the ink jets forming the array, it is necessary to increase the drive voltage; This may lead to undesirable electrical crosstalk.

Stem as an inkjet device
There are techniques such as those disclosed in US Pat. No. 3,747,120 by Mr. Although the Stem patent discloses a single jet and an array of jets, it is generally difficult to construct closely packed arrays using this technique. Because the array cannot be tightly arranged, the transducer becomes a diffuse pressure source for the volume of ink in the inkjet, providing stable, self-contained operation and high ink droplet velocities, such as at low drive voltages. difficult to achieve.

Problems with this and other inkjet technologies are that ink leaks can cause short circuits in the transducer, complex resonance characteristics in the structure in which the transducer is mounted can adversely affect the operating characteristics of the inkjet, and The configuration of energy transfer from the ink to the ink is difficult and unreliable, and so on.

Elmquist's U.S. Patent No.
No. 4,072,959 discloses another technique that helps to create an even more tightly packed array. As disclosed in this patent, a series of elongated transducers are energized by electrodes that apply an electric field transverse to the axis of elongation, and the transducers are placed within a closely packed array of ink jet chambers. It is linked with In this case, the chamber is so small that the Helm-holtz frequency is higher than the resonant frequency of the length mode of each transducer. Such a relationship is undesirable because it is difficult to damp the longitudinal resonant frequency. On top of that,
Due to the dimensions of Elmquest's chamber, proper control of the inlet to the chamber does not improve the relationship between the Helmholtz frequency and the longitudinal resonant frequency of the transducer.

It is an object of the present invention to eliminate complex resonances in the transducer mounting structure that adversely affect inkjet operations.

To achieve this object of the invention, the inkjet device of the invention comprises a variable volume chamber comprising an orifice for ejection of ink droplets and an elongation axis responsive to an electric field substantially transverse to the elongation axis. A transducer that expands and contracts along the chamber, and a transducer that is provided to connect the chamber and the transducer.
coupling means for contracting and expanding the chamber in response to said expansion and contraction of the transducer along an elongated axis; suction means for maintaining a substantially constant cross-sectional area of the ink flow path regardless of expansion or contraction of the transducer along the axis; and the coupling means prevents leakage of ink to the side of the transducer. the transducer is isolated from the chamber and the suction means to substantially prevent
The Helmholtz frequency of the chamber is higher than 10 KHz but lower than the length mode resonance frequency of the transducer, thereby preventing resonance between the transducer and the chamber.

Referring to FIG. 1, a demand-responsive or impulse-type inkjet device has a chamber 10 and an orifice 12 communicating with the chamber 10 via a leg 16 forming a movable wall 18. There is. A droplet of ink is ejected from the orifice 12 in response to the voltage applied to the transducer 14. Ink is supplied to the chamber 10 through a plurality of suction ports 20 located at the rear end of the chamber 10 adjacent to the wall 18 and opposite the front end where the orifice 12 is located.

In the present invention, the direction of expansion and contraction of the transducer 14 has at least one component extending parallel to the direction of ejection of the ink drop through the orifice 12. In the embodiment of FIG. 1, the transducer expands and contracts in a direction generally parallel to the axis of droplet ejection from orifice 12. An elongated axis along which the transducer expands and contracts extends through chamber 10 from a location distal to orifice 12 to a location proximal to orifice 12.

An important feature of the invention is that the transducer 14 is elongated in the direction of expansion and contraction, and the electric field due to the applied voltage is applied transversely to the axis of expansion. This structure allows the displacement to be increased simply by increasing the length of the transducer 14, and can also be achieved by increasing the length of the transducer 14, as described in detail below. It is desirable that the density of the array formed by the inkjet shown in FIG. Moreover, there is the advantage that a large displacement can be achieved without applying a high voltage that would cause electrical crosstalk. but,
The transducer 14 is designed to limit undesirable deflection movements that can occur if the transducer becomes too long and thin, and to achieve proper length modal resonance with respect to the Helmholtz frequency discussed below.
It is necessary to limit the length of It is also desirable to limit the length to minimize weight. Generally, to limit this undesirable deflection motion and achieve proper length mode resonance, a suitable ratio of width (i.e. outer diameter) to overall length of a cylindrical transducer is 12 to 1, preferably 7:1. The ratio of the overall length of the cylindrical transducer to the radial wall thickness should not exceed 60:1, with 36:1 being convenient.

Yet another important feature of the invention is that the transducer 14 is generally cylindrical in shape. A cylindrical shape is particularly desirable to minimize the occurrence of deflections and other undesirable vibration modes. A cylinder is also desirable to minimize mechanical or acoustic crosstalk between ink jets in the array.

Another important feature of the invention is that transducer 14 is hollow along a central axis that coincides with the axis of expansion and contraction of transducer 14. Thus, the transducer drive signal voltage is applied to the first
is applied across the thickness of the transducer 14 between the electrode 22 and a ground electrode 26 extending along the outside 28 of the transducer 14 to generate an electric field transverse to the axis of elongation. This shape provides effective electrical shielding, thus minimizing electrical crosstalk. The polarity of the ungrounded hot side electrode is determined so that an electric field is generated in the same direction as the polarization direction of the converter. Thus, when voltage is applied to the hot electrode, the transducer contracts, and when voltage is removed from the hot electrode, the transducer expands. A conductive wire 30 is connected to the electrode 22. A conductive surface 32 is connected to the electrode 26 and extends outwardly from the transducer 14 at the back of a plate of insulating material 34, such as silicone rubber, surrounding the transducer 14. Another lamellar member 54 covers the electrically conductive surface 32.

By using a hollow cylindrical transducer 14, the drive signal voltage is applied uniformly across a relatively thin section of the transducer 14, resulting in relatively large displacements despite the low voltage. can get. The uniform thickness of the thin portion of the transducer 14 results in a substantially uniform electric field. The thickness of the transducer is in the range 0.1 to 1 mm, preferably 0.2 to 0.6 mm;
Change the voltage level applied to the converter from 25 volts to 200 volts
It can be made into a bolt. In particularly preferred embodiments, transducer 14 has a thickness of 0.10 to 0.50 mm, preferably 0.20 to 0.30 mm, and voltages of 25 to 80 volts can be used.

Yet another important feature of the invention is that the leg 16 forming the movable wall 18 constitutes a plug inserted into the hollow end of the transducer 14. As shown, the area of the walls 18 forming the chamber approximately corresponds to the cross-sectional area of the transducer 14 at its outer diameter. The relatively small area of wall 18 allows wall 18 to act as a concentrated rather than diffuse energy source, which provides stable, self-contained, high velocity ink droplet ejection at low drive voltages. The most important thing to do. The total area of wall 18 is 50
mm ² or less, preferably 2 mm ² or less. This area should be as small as possible to achieve high array density and high printing resolution. In any case, the difference in pressure pulse transit time from each point on wall 18 to orifice 12 is less than 1 microsecond. Even with a smaller wall area, the required displacement can be achieved by making the transducer longer. The surface area of the end face of the movable wall communicating with the ink within the chamber 10 can be larger than the cross-sectional area of the transducer 14 to obtain the desired ejection surface. Furthermore,
The area of wall 18 can be adjusted to provide impedance matching between the ink and transducer 14.

Furthermore, the legs 16 are connected to the otherwise hollow transducer 14.
It also acts as a seal to prevent ink from returning to the inside, preventing electrical short circuits. Thus converter 14
The transducer 14 can be brought into direct communication with the ink in the chamber 10 without the use of any intermediate members between the ink and the ink. If such an intermediate member were to be provided, it would have a negative effect on the inkjet operation, or even cause a problem with the inkjet's reproducibility. This embodiment is intended to solve this problem.

As shown in FIGS. 2 and 3, the inlet 20
is composed of a plurality of narrowed open grooves 36 arranged along the entire circumference of the chamber 10. This open groove 36 extends over an annular land 38 of a thin plate member 40 that constitutes the majority of the chamber 10. The surface of the member 40 adjacent to the open groove 36 is in contact with the surface 42 of the land 44 on the plate-shaped insulating member 34, thereby completing the suction port 20. It can be seen that the laminar members 34, 40 greatly facilitate the manufacture of the apparatus of FIGS. 1-3.

In FIG. 1, the ink reservoir 46 is in communication with the atmosphere, i.e., is maintained in a non-pressurized state, and the ink reservoir 46 is in communication with the inlet 20 of a substantially constant ink flow path cross-section. Leaks between the sump 46 and the chamber 10 and other leaks, such as leaks around the legs 16, may be routed to the inlet 20 as long as the leakage is relatively small compared to the size of the inlet 20. Since they are parallel, no untoward results will occur. Therefore, even if ink leakage occurs, the multilayer plate structure shown in FIG. 1 does not cause any serious problems. Also, by locating the inlet 20 at the rear of the chamber 10, construction of the jet as shown herein is greatly facilitated. Additionally, the placement of the inlet 20 behind the chamber alleviates the potential for air bubbles to adversely affect the operation of the inkjet.

Furthermore, as shown in FIG. 1, an orifice plate 48 is also included in the multilayer plate-like structure,
Adjacent to the orifice, it is covered by another thin plate-like member 50 having a truncated conical opening 52. Yet another thin plate-like member 54 is member 3.
4 and extends along a conductive surface 32.

A variety of materials can be used to manufacture the layered structure of FIG. 1, which is greatly simplified by the use of a cylindrical transducer 14. For example, layered members 40, 4
8, 50, and 54 can be made of stainless steel. Instead of glass, manufactured by GE, “Noly1”
Modified polyphenylene oxides known as polyphenylene oxides and glass-doped diallyl phthalates can also be used. The legs 16 are made of plastic or ceramic material and the transducer 14 is made of piezoelectric material.
is glued to.

Referring to the embodiment of FIG. 4, an inkjet device having a wall 18 formed by a transducer 14 and a leg 16 is similar in many respects to the device of FIGS. 1-3. is illustrated. However, the chamber 10 is formed by a single thin plate member 140. The chamber 10 includes an orifice 12 relative to which the chamber 10 tapers. Layered member 134, through which transducer 14 extends, forms with member 140 a reservoir 146. A protruding member 148 is provided between member 134 and member 140 within reservoir 146.
extends and acts as an alignment and attachment means between members 134 and 140.

Fairly dense inkjet arrays can be created by using elongated transducers that expand and contract along their elongation axes. As shown in FIG. 5, the orifice plate 140a has a plurality of orifices 12, and the dashed circle surrounding the orifices is the diameter of the transducer 14 located behind the orifice plate 140a. It shows. Figure 6 shows orifice plate 14
A further array of orifices 12 within 0b is shown. Although the staggered arrangement of the jets 112 is different in FIG. 5 and FIG. It is highly desirable to do this.

Referring now to FIGS. 7-9, a chamber 200 having an orifice 202 ejects a droplet of ink in response to the energization of a transducer 204 for each jet in the array. Transducer 204 expands and contracts along its elongation axis in the direction of the arrows shown in FIG. 8, and this movement is transmitted to chamber 200 by coupling means 206. This connecting means 2
06 comprises a viscoelastic material member 208 connected in parallel to the transducer 204 and a diaphragm 210 preloaded to assume the position of FIGS. 7 and 8.

Ink flows from the non-pressurized reservoir 212 through the constricted suction means. This suction means is constituted by a constricted suction port 214. The suction port 214 consists of an open groove formed in the restrictor plate 216 as shown in FIG. In the present invention, the flow cross-sectional area of the ink entering the chamber through the inlet 214 is such that the flow path area of the ink entering the chamber through the inlet 214 is such that the flow path of the ink entering the chamber through the inlet 214 is such that the flow path area of the ink flowing into the chamber through the inlet 214 is such that the flow path area of the ink flowing into the chamber through the inlet 214 is such that the flow path area of the ink flowing into the chamber through the inlet 214 is such that the flow path area of the ink flowing into the chamber through the inlet 214 is such that the flow path area of the ink flowing into the chamber through the inlet 214 is such that the flow path area of the ink flowing into the chamber through the inlet 214 is such that the flow path area of the ink flowing into the chamber through the inlet 214 is not limited to the flow path of the ink flowing into the chamber 204 even though the inlet 214 is located immediately adjacent to the coupling means 206 and the transducer 204. does not substantially change during expansion and contraction. By appropriately sizing inlet 214 relative to orifice 202 in orifice plate 218, a proper relationship between the inertance at inlet 214 and the inertance at orifice 202 can be maintained. This relationship, as it applies to the embodiments illustrated in FIGS. 1-6, is discussed in more detail below.

As shown in FIG. 7, the chamber plate 220
A reservoir 212 is formed in the reservoir 212 and has a tapered edge 222 leading to the inlet 214 . As shown in FIG. 9, the reservoir 212 is provided with a feed pipe 223 and a relief pipe 225. The reservoir is flexibly configured by a diaphragm 210 to minimize mechanical crosstalk through the ink within the chamber. The diaphragm 210 is arranged in parallel with the restrictor plate 21 in the region of the relief 229 of the plate 226.
It communicates with the ink through a large opening 227 at 6. To minimize fluid crosstalk,
Each jet in the array of Figure 9 is
It is isolated from ink and communicates with a single chamber as shown in the figure.

As shown in FIGS. 7 and 9, each transducer 204 is guided at its distal end;
The middle portion of transducer 204 is essentially unsupported as shown in FIG.

One end of the transducer 204 is connected to the leg 207 and the plate 2.
26 in cooperation with holes 224. Plate 226 as shown in FIG.
The diameter of the hole 224 is slightly larger than the diameter of the leg 207. Therefore, the contact between the leg 207 and the wall of the hole 224 is very slight, but this contact is necessary to position the leg 207 and bring it into contact with the viscoelastic material 208 as shown in FIG. Supports transducer 204. The other end of transducer 204 is flexibly mounted within block 228 by a flexible resilient material 230, such as silicone rubber. The flexible material 230 is positioned within the slot 232 shown in FIG. 9 to provide support for the other end of the transducer 204. Transducer 20 by suitable means such as solder 236
Electrical contact with the transducer 204 is also facilitated by a flexible printed wiring board 234 electrically connected to the transducer 204. As shown in FIG. 7, a conductive pattern 23 is formed on a printed wiring board 234.
8 is formed.

As shown in detail in FIGS. 7 and 9,
Plate 226 has opening 2 at the base of slot 237.
24, the opening 224 receiving the transducer 204. Plate 226 has a receptacle 239 for a heater 240 of Sanderch structure. The heater 240 includes a heater element 2 comprising a coil 244.
42, a holding plate 246, and a plate 246.
and a bearing plate 250 located directly below the heater 240. A thermistor 252 is installed in slot 253 to control the temperature of heater 242. The entire heater 240 is held in a receptacle within plate 226 by cover plate 254.

As can be seen in FIG. 9, the structure consisting of a plurality of stacked plate-like members, the entirety of which extends upwardly through the opening 257, holds the bolt 256 and the printed wiring board 234 in place on the plate 228. They are held together by a bolt 258 extending downwardly through an aperture 259. Although not shown in FIG. 9, a terminal 260 is connected to a printed circuit 238 on a printed wiring board 234, as shown by broken lines in FIG. Viscoelastic layer 20 illustrated in FIGS. 7 and 8
8 is also not shown in FIG.

To achieve the objectives of the present invention, it is desirable to have a very high operating frequency for the inkjet.
Desirably high operating frequencies are achieved if the inkjet chamber is sufficiently small.
That is, the Helmholtz (ie, liquid) resonance frequency f obtained by the following equation increases.

where C _c is the compliance related to the amount of ink in the chamber, C _d is the compliance of the movable wall, L _o is the inertance of the liquid in the nozzle, and L _i is the inertance of the liquid in the suction port.

Specifically, C _c , Lo _{and Li} are respectively C _c =V/ρc ² (where V is the volume of the chamber, ρ is the density of the ink, and c is the acoustic velocity in the ink.) L _o =4ρl _o /3πr ² (In the formula, l _o is the length of the nozzle, and r is the radius of the nozzle.) L _i =kρl _i /nA (In the formula, k is the groove that forms the suction port. A is the cross-sectional area of one open groove constituting the suction port, n is the number of open grooves constituting the suction port, and l _i is the length of one open groove.

It is generally desirable that the Helmholtz resonant frequency be significantly greater than the velocity of ink droplet ejection. Advantageously, the Helmholtz resonant frequency is at least twice the ink ejection velocity.
If expressed numerically, at least 10kHz or more,
It is desirable to have a Helmholtz frequency below 100 kHz, with 25 kHz to 50 kHz being advantageous to obtain high droplet ejection rates on demand.

From the above description, it can be seen that it is generally desirable to form small chambers to achieve high Helmholtz resonant frequencies and obtain high droplet ejection velocities on demand. However, apart from the Helmholtz resonant frequency, the droplet ejection velocity and jet stability depend on the acoustic resonant frequency of the chamber and the transducer resonant frequency along the elongated axis (e.g., the longitudinal or (mode resonance frequency) is lower than necessary. It is therefore desirable that the total length of the chamber does not significantly exceed the maximum cross-sectional dimension of the chamber, for example the diameter in the case of a cylindrical chamber. As used herein, the term overall chamber length refers to the length parallel to the droplet ejection axis, measured from the rear of the chamber on the side remote from the orifice toward the outside of the orifice. 1st a
This dimension is represented by distance X and the maximum cross-sectional dimension is represented by dimension Y as shown.

Generally, it is desirable to have an aspect ratio, ie, the ratio of length to cross-sectional dimension, of 5:1 or less, preferably 2:1 or less. Length X is smaller than cross-sectional dimension Y. By using this aspect ratio, the acoustic resonant frequency of the chamber (i.e. organ pipe resonance) is kept sufficiently high;
As a result, the acoustic resonance frequency of the chamber is
It does not interfere with the formation of a stable inkjet at its operating frequency.

There is a lower limit to the cross-sectional dimension Y unless the overall length of the transducer is increased. As the overall length of the transducer increases, the axial or length mode resonant frequency of the transducer decreases, limiting the operating frequency of the required jet. It was found that the length mode resonance frequency in the axial direction can be maximized by setting the minimum value of Y=0.6. In this case, since the maximum cross-sectional dimension Y of the chamber is reduced, the overall length of the transducer will necessarily increase in order to achieve the required displacement.

As previously mentioned, it is desirable to connect the transducer within the chamber as a point pressure source. In this case,
It is desirable that the difference in pressure pulse transit time from each point on the transducer connection wall is less than 1 microsecond, preferably less than 0.1 microsecond, optimally 0.05 microsecond. Assuming a given ink composition and therefore a given acoustic velocity through the ink in the chamber, the difference in the acoustic path, i.e. the difference from d _nax to d _nix as shown in Figure 1a, is the acoustic velocity at that high frequency. Determined due to interference. In this case, it is desirable that the inkjet operates in the presence of a high frequency component of at least 100 kHz, preferably 1 MHz.
The sound velocity in water is 1.5×10 ⁵ cm/sec and 100kHz
The difference in acoustic path length, i.e., the difference between d _nax and d _nix , is 1.5 mm (60
mil) and should not exceed 0.15mm (6 mil)
The following is convenient. Assuming we use a component with a frequency of 1 MHz, the difference in path length is 0.15 mm (6
mil) should not be exceeded. The difference in passage length is the same for the embodiments shown in FIGS. 7 to 9.

Examples of chambers of various dimensions are provided below to illustrate various features of the invention: Example 1 X = 100 mils Y = 70 mils Sound velocity 1.5 x 10 ⁵ cm /sec 1MHz high frequency component.

Example 2 X = 2.54 mm (100 mils) Y = 1.60 mm (63 mils) Sound velocity 1.2 x 10 ⁵ cm/sec 1 MHz high frequency component (using oil-based ink).

Example 3 X = 1.27 mm (50 mils) Y = 1.27 mm (50 mils) Sound velocity 1.5 x 10 ⁵ cm/sec 1 MHz high frequency component.

From the above discussion, it can be seen that achieving a Helmholtz frequency that is sufficiently high compared to the operating frequency of the inkjet, but sufficiently small compared to the acoustic resonant frequency and the longitudinal or length mode resonant frequency of the transducer 14,204. It can be seen that the cross-sectional dimensions of the chambers 10, 200 must be made sufficiently large in order to achieve this. in this regard,
It has been found that the cross-sectional dimension of the chamber transverse to the axis of droplet ejection must be at least ten times the cross-sectional dimension of the orifice transverse to the axis of droplet ejection. Dimensionally speaking, if the cross-sectional dimension of the orifice is within the range of 0.025 mm to 0.075 mm, it is convenient for the cross-sectional dimension of the chamber to be 0.6 mm or less, and preferably within the range of 0.6 mm to 1.3 mm. preferable.

Another important feature of the invention is that the length X shown in FIG. 1a is shortened so as not to undesirably reduce the Helmholtz frequency. at the same time,
A relatively short chamber results in a relatively high acoustic resonance frequency. As shown, the overall axial length of the transducer is such that the acoustic resonant frequency is higher than the longitudinal or length mode resonant frequency of the transducer.

In general, it is advantageous for the resonant frequency along the coupling axis of the transducer, eg in the longitudinal direction of the transducer, to be at least 25% greater than the Helmholtz frequency. Advantageously, the resonant frequency along the coupling axis is at least 50% greater than the Helmholtz frequency.

Advantageously, the use of a cylindrical transducer 14 reduces the number of resonant modes of the transducer. However, it expands in the direction of elongation but does not have a cylindrical cross-section, e.g., an overall length to minimum width ratio of less than 30 to 1, as shown in FIGS.
Other transducers with a rectangular cross-section having a transverse thickness to length in the range 0.4 mm to 0.6 mm can also be used.

As previously discussed, the inlets 214, 20 maintain a substantially constant flow path area for ink entering the chamber during expansion and contraction of the transducer along the elongated axis. To the extent that the diaphragm 210 moves into the area corresponding to the inlet 214 as shown in FIG. must be significantly larger than the change in length of the transducer as it expands and contracts. In this case, the total height h is within the range of 0.025mm to 0.075mm.
Advantageously, it is less than 0.05 mm, and the transducer 2
The total change in length of 04 is between 0.05 and 0.50 microns, advantageously no more than 0.24 microns. For this reason, the opening groove and orifice that make up the suction port both have an inertance of 10 ⁷ to 10 ⁹ Pa.
It is also important that it is in the range of sec ² /m ³ .

The overall dimensions of the inlet opening must have a certain relationship with the inkjet orifice. In this connection, it is desirable that the minimum cross-sectional dimension of the open groove be kept less than or equal to the diameter or cross-sectional dimension of the orifice. This ensures that the Helmholtz frequency is greater than the operating frequency, but below the length mode or acoustic resonance frequency.

Thus, the present invention provides an inkjet having a Helmholtz (fluid) resonant frequency that is less than, and preferably half of, the length mode resonant frequency of the transducer. At the same time, the Helmholtz frequency is considerably higher than the desired repetition rate of the droplet, i.e. more than 10kHz, preferably 25k
Hz or higher. The Helmholtz frequency is well damped so that resonances of the system at that frequency do not adversely affect the droplet formation process. Furthermore, at Helmholtz frequencies significantly lower than the length mode frequency, the fluid system becomes insensitive to transducer length mode resonances that can cause damping failure. Failure to properly damp this length mode resonance can adversely affect the performance of the device as the fluid system responds to length mode frequencies. In such situations, conventionally, external braking of the transducer array (column) was required, which required a large drive voltage.
Such problems do not occur with the present invention.

As illustrated in the embodiments of FIGS. 1-4 and 7-9, an electric field is applied transversely to the elongated axis of the transducer. Figures 1 and 4
As shown, this is done by electrodes 30, 26, while in FIGS.
This is accomplished by printed circuitry 238 electrically connected to 60,262. These electrodes provide a means for applying an electric field to the transducer so that the transducer contracts along its extension axis, causing the chamber to contract, and when no voltage is applied to the transducer, it expands along its axis. to inflate the chamber. This point is particularly important to prevent premature deterioration of the transducers 14, 204 and, in extreme cases, depolarization.
Conversely, if an electric field is applied transversely to the transducer to cause it to expand, such an electric field will cause depolarization of the transducer, rendering it uncontrollable for at least a period of time. state. It is therefore important that an electric field applied transversely to the transducer is applied to cause the transducer to contract.

Reference is made to FIGS. 10 and 11 for further explanation of how to apply an electric field to the transducer. As shown in FIG. 10, transducer 204 includes an electrode 260 with transducer 204 extending outwardly beyond the tip of electrode 260. As shown in FIG. First electrode 260 is grounded. When the second electrode is not energized, transducer 204 assumes the configuration shown in FIG. When the second electrode 260 described above is excited to a positive voltage as shown in FIG.
(ground), the transducer 204 extends in its thickness direction but contracts along its length. Therefore, the first
It is important that the electric field generated by the applied voltage as shown in FIG. 1 be in the same direction as the polarization of the transducer 204. It goes without saying that the expansion and contraction shown in FIGS. 10 and 11 are exaggerated.

Another important feature of the invention is that the transducer 1
4, 204 and the chamber are connected only by connecting means (legs, diaphragms, etc.). Thus, transducers aligned as shown in FIGS. 5, 6, and 9 are substantially insulated from ink and in exclusive communication with a single chamber or jet. Moreover, sealing means, such as diaphragm 210 as shown in FIG.
This prevents the ink from flowing into the surrounding area of 04, thereby effectively blocking the ink.

As used herein, the term elongate indicates that the length is greater than the width. In other words, the elongation axis, as used herein, is larger than the lateral dimension across which the electric field is applied. Furthermore, the transducer can be elongated in depth so that the total depth is greater than the length. Therefore, the term elongated is a relative term. Moreover, the transducer expands and contracts in other directions as well as along the axis of elongation, but such expansion and contraction is not in the direction of connection, which is not part of the invention. It's irrelevant. In the embodiments shown herein, the axis of connection is the elongation axis. The length mode resonance is therefore in the direction of coupling, and in the illustrated embodiment has a resonant frequency along the elongation axis. However, expansion and contraction can be sufficient along the elongation axis to obtain the maximum amount of ink extrusion.

Although specific embodiments of the invention have been described, other embodiments within the scope of the invention will be apparent to those skilled in the art.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of an inkjet device showing an embodiment of the present invention, FIG. 1a is an enlarged sectional view of the chamber shown in FIG. 1, and FIG.
1 is a sectional view taken along line 2-2, FIG. 3 is a partially enlarged view of the sectional view in FIG. 1, FIG. 4 is a sectional view of another embodiment of the present invention, and FIG. , an orifice plate constructed by arranging a plurality of ink jets as shown in FIGS. 1-4, and FIG.
-4 is an orifice plate of another embodiment constructed by arranging a plurality of ink jets as shown in FIG. The figure is an enlarged view of a part of the cross-sectional view of Fig. 7, and Fig. 9 is an enlarged view of a part of the sectional view of Fig.
FIG. 10 is a schematic diagram of the transducer shown in FIG. 7 in a demagnetized state, and FIG. 10 is a schematic diagram of the transducer of FIG. 10; FIG. (Symbol in the figure), 10,200...Chamber, 1
2,202... Orifice, 14,204... Converter, 16,207... Leg, 18... Movable wall, 20,214... Suction port, 206... Connection means, 36... Opening groove, 210...Diaphragm.

Claims (1)

Claims: 1. A variable volume chamber having an orifice for ejection of ink droplets; a transducer that expands and contracts along an elongation axis in response to an electric field substantially transverse to the elongation axis; , provided for connecting the chamber and the converter,
coupling means for contracting and expanding the chamber in response to said expansion and contraction of the transducer along an elongated axis; suction means for maintaining a substantially constant cross-sectional area of the ink flow path regardless of expansion or contraction of the transducer along the axis; and the coupling means prevents leakage of ink to the side of the transducer. the transducer is isolated from the chamber and the suction means to substantially prevent
The Helmholtz frequency of the chamber is greater than 10 KHz but lower than the length mode resonance frequency of the transducer, thereby preventing resonance between the transducer and the chamber. 2. An inkjet device according to claim 1, wherein said connecting means comprises a substantially rigid leg, said leg being attached to the transducer and forming a wall of said chamber. 3. The inkjet device according to claim 1, wherein the cross-sectional shape of the transducer in the direction transverse to the elongation axis is rectangular. 4. The inkjet device according to claim 1, wherein the cross-sectional shape of the transducer in the direction transverse to the elongation axis is circular.