Ink jet apparatus

(42) Date of commencement of the patent: 15. 1. 1987 (45) Date of issue: 25. 8.1987

<td>(30) Priority:</td><td>(73) Patent owner:</td>

<td>30. 1.1981 US 229994 claims. 4. 1. 1982 US 336603 claims.</td><td>EXXON RESEARCH AND ENGINEERING COMPANY FLORHAM PARK (US).</td>

<td>(56) Documents:</td><td></td>

<td>DE-AS2527647 DE-AS2144892</td><td></td>

(54) Ink Jet Apparatus (57) An ink jet apparatus having a variable volume chamber and an ink droplet ejection nozzle has a transducer that can expand and contract along its longitudinal axis depending on an electric field that is substantially transverse to the longitudinal axis, and an inlet means into the chamber for flowing ink into the chamber upon energization of the transducer. Between the chamber and the transducer is provided a coupling device with a movable wall for reducing and increasing the volume of the chamber depending on the expansion and contraction in the direction of the axis of the transducer. The inlet means into the chamber is restricted to maintain the cross-sectional area of ​​the ink flowing into the chamber substantially constant during expansion and contraction, the Helmholtz resonance frequency being kept smaller than the longitudinal mode resonance frequency of the transducer.

fJ f £ A £ IV

WR 007831S

- 2 Nr.383779

The invention relates to an ink jet apparatus having a variable volume chamber having an ink droplet ejection nozzle, a transducer which can expand and contract in the direction of its longitudinal axis depending on an electric field which is substantially transverse to the longitudinal axis and an inlet means in the chamber to let ink flow into the chamber when the transducer is energized.

Conveniently, an ink jet geometry is used which allows the use of a plurality of ink jets in close-packed arrangement so that a reasonable area of ​​a copy carrier can be printed simultaneously, as for example for the printing of alphanumeric information. It is also desirable to use densely packed arrays of ink jets to achieve high quality alphanumeric character printing, with high speed or high print rate printing.

Difficulties can arise when close packed arrangements are to be achieved, due to the size or volume of the transducers or transducers used. For example, densely packed arrangements can exhibit significant mechanical crosstalk or inter-channel leakage. In addition, large drive voltages may be required to properly energize the transducers of the ink jets in the array, and this may cause undesirable electrical crosstalk, particularly when the jets are densely packed.

At present, the technology described in U.S. Patent No. 3,747,120 is being pursued with considerable effort. Although this US patent describes both a single beam and an array of beams, it is generally considered difficult to provide densely packed arrangements with this technology. In addition, such arrangements may use a transducer configuration that results in a distributed pressure source that acts on an ink volume within an ink jet, which may be undesirable if, in particular, stable satellite free operation and high droplet velocity at low drive voltages is desired.

Other difficulties that are characteristic of this technology, as well as other inkjet technologies, include: ink leaks that short converters, complex resonances in the transducer mounting structure that adversely affect beam operation, manufacturing difficulties, and unreliability in coupling energy from the transducer to the ink ,

Another more dense-assembly-type technology is described in U.S. Patent No. 4,072,959. As noted in this US patent, a series of elongate transducers are energized by electrodes which apply a field transverse to the longitudinal axis, and the transducers are provided in a close-packed array of ink jet chambers. It should be noted in this connection that the chambers are considerably small in order to produce a high Helmholtz frequency compared to the longitudinal resonance frequency of the individual transducers. Such a relationship may be undesirable because it is difficult to attenuate the longitudinal resonant frequency. In addition, given the size of the chambers, the precise control of the inlets to the chambers will not affect the improvement in the relationship between the Helmholtz frequency and the longitudinal resonant frequency of the transducer. Also, in this US patent, each transducer is immersed in a common container such that the excitation of a transducer associated with a chamber can cause crosstalk with respect to an adjacent chamber or chambers. That is, there is no fluid or mechanical separation from chamber to chamber between the various transducers or, more specifically, between segments of a common transducer. In addition, the structure shown in this US patent requires a non-conductive ink.

It is therefore an object of the invention to provide an ink jet apparatus which can be packed in dense arrays with a considerable number of beams, which further requires very little energy, in which crosstalk between ink jets within an array is extremely low, which also causes ink leaks not adversely affect the transducer, which also avoids complex resonances in the transducer mounting structure, which could adversely affect inkjet operation, which is easily manufacturable, which reliably couples energy into ink within an inkjet, with a high ink jet

- 3 Nr.383779

Frequency of ink jet operation utilizing a variety of inks, such as inks having various conductive properties, as well as viscosities and surface temperatures capable of generating an ink jet in high-frequency operation with high-viscosity ink, and eventually providing an ink jet; the injected immediately and not easily delayed.

To achieve this object, the ink jet device according to the invention is characterized by a coupling device between the chamber and the transducer with a movable wall to reduce the volume of the chamber depending on the expansion and contraction in the direction of the axis of the transducer and increase, wherein the inlet device in the Chamber is limited, to keep the cross-sectional area of ​​the ink flowing into the chamber constant substantially during expansion and contraction, and to keep the Helmholtz resonance frequency smaller than the longitudinal mode resonance frequency of the transducer.

In this way, the ink chamber has a Helmholtz or fluid resonance frequency which is greater than the operating frequency of the ink jet but less than the transducer resonance frequency along the axis or in the direction of the coupler.

Another feature of the invention provides that the axis of the transducer extends in a direction having at least one component parallel to the axis of the droplet ejection nozzle.

Another feature of the invention is that the inlet device is located immediately adjacent to the coupling device. In this way, rapid ejection is ensured without significantly affecting the cross-sectional area of ​​the incoming ink by the expansion and contraction of the chamber.

Another feature of the invention provides that the coupling device substantially separates the transducer from the chamber and the inlet device.

Furthermore, it can be provided according to the invention that the coupling device essentially has a rigid foot, which is attached to the transducer and forms the wall of the chamber.

According to a further feature of the invention, the coupling device comprises a membrane.

According to a further feature of the invention it is provided that the movement of the coupling device is limited depending on the expansion and contraction of the transducer to a surface which lies inwardly of the inlet device in the direction of the ejection axis.

In a preferred embodiment of the invention, the Helmholtz frequency is controlled by dimensioning the inlet means so that the inertance of the inlet means

9 3 is maintained between 10 and 10 Ma / M / s / s.

Another feature of the invention is that the inlet means is dimensioned so that the parallel inertance of the nozzle and inlet means maintains a Helmholtz resonance frequency which is greater than the droplet ejection frequency and less than the longitudinal mode resonant frequency of the transducer.

According to one embodiment of the invention, an arrangement of a plurality of transducers, chambers and nozzles is provided, each transducer in the arrangement is substantially in exclusive communication with a single chamber. In this case, preferably, the coupling device comprise a membrane extending over the arrangement substantially transversely to the longitudinal axis of each transducer.

To achieve the Helmholtz frequency can be inventively provided that the cross-sectional dimensions of the chamber perpendicular to the direction of the ejecting droplets are at least about 10 times greater than the cross-sectional dimensions of the nozzle in this direction.

For this purpose, according to the invention it can further be provided that the cross-sectional dimension of the chamber exceeds 0.6 mm and is preferably 0.6 to 1.3 mm, and that the cross-sectional dimensions of the nozzle are between 0.025 and 0.075 mm.

Another feature of the invention provides that the length of the chamber in the direction parallel to the ejecting ink droplets does not substantially exceed the largest cross-sectional dimension of the chamber. In this way, the Helmholtz frequency is smaller than the acoustic or sound resonance frequency.

The invention will be closer to exemplary embodiments with reference to the drawings

- 4 No. 383779 explained. Show it: 2 shows a section 2-2 in FIG. 1, FIG. 3 shows an enlarged detail of the section of FIG FIG. 4 shows a section of another embodiment of the invention, FIG. 5 shows a nozzle plate of an arrangement of ink jets of the type shown in FIGS. Fig. 6 shows another nozzle plate for an arrangement of ink jets of the kind shown in Figs. 1 to 4, Fig. 7 shows a section of an ink jet apparatus according to another embodiment of the invention. Fig. 8 is an enlarged view of a part of that shown in Fig. 7 9 shows the embodiment shown in FIGS. 7 and 8 in exploded perspective, FIG. 10 shows a schematic diagram of the converter shown in FIG. 7 in a de-energized state, and FIG. 11 a schematic diagram of the transducer of Fig. 10 in the energized state.

In Fig. 1, a demand or pulse type ink jet apparatus has a chamber -10- and a nozzle or orifice -12- from which ink droplets are ejected depending on the state of energization of a transducer -14- overflowed with the chamber -10- a coupling device -16- in the form of a foot is in communication, which forms a movable wall -18-. Ink is fed to the chamber -10- via an inlet means -20- having a plurality of inlet ports lying adjacent the wall and at the rear end of the chamber -10- opposite the front end where the nozzle -12- is provided.

According to the invention, the transducer -14- expands and contracts in a direction with at least one component extending parallel to the direction of droplet ejection through the nozzle -12-. In the embodiment of Fig. 1, a transducer expands and contracts in a direction substantially parallel to the axis of droplet ejection from the nozzle -12-. It should be noted that the axis of the transducer, along which the transducer expands and contracts, passes through chamber -10- from a location farther from the nozzle -12- to a location closer to Nozzle -12- is located, extends.

According to another important feature of the invention, the transducer -14- is stretched in the direction of expansion and contraction, and the electric field based on the excitation voltage is transverse to the longitudinal axis. This is particularly desirable because a shift can be made larger by merely increasing the length of the transducer -14-, and an increase in the length of the transducer -14- does not result in any decrease in the density of a device consisting of the formed in Fig.l ink jet, as will be explained in more detail below. In addition, large displacements can be achieved without applying high electrical voltages, which could lead to electrical crosstalk. However, it is desirable to limit the length of the transducer to limit undesirable bending motion that may occur when the transducer becomes too long and thin, and to achieve the appropriate longitudinal mode resonance to the Helmholtz frequency. as will be explained in more detail below. It is also desirable to limit the length so that the weight is as small as possible. In general, a total length / width (ie, outer diameter) ratio of 12: 1 at a preferred ratio of 7: 1 in a cylindrical transducer should be adequate to limit this undesirable bending motion and achieve the proper longitudinal mode resonance. The ratio of the total length to the radial wall thickness of the cylindrical transducer should not exceed 60: 1, with a ratio of 36: 1 being preferred.

According to another significant feature of the invention, the transducer -14- is generally cylindrical in shape. In particular, the cylinder is considered desirable to minimize the onset of bending and other undesirable vibration modes. The cylinder is also preferred to minimize mechanical or acoustic crosstalk between inkwells in an array.

According to another important aspect of the invention, the transducer is hollow along its axis which coincides with the extension and withdrawal axes of the transducer -14-. Thereby, a transducer drive signal voltage across the thickness of the transducer between a first electrode -22- inside a cylindrical opening -24- and a ground electrode -26-

5 # 383779, which extends along the exterior of the transducer -14- to create an electric field transverse to the axis. This configuration leads to effective electrical shielding and thus makes the electrical crosstalk as small as possible. The polarity of the hot electrode (as opposed to ground) is such that the applied electric field is in the same direction as the polarization of the transducer. This results in contraction of the transducer depending on the energization of the hot electrode and expansion depending on deenergization of the hot electrode. A line -30- is connected to the electrode -22-. A conductive surface -32- is connected to the electrode -26- and extends outwardly from the transducer -14- on the back of a potting material -34-, such as silicone rubber surrounding the transducer -14-. Another layered member -54- covers the conductive surface -32-.

The use of the hollow cylindrical transducer -14- allows uniform application of the drive signal voltage to a relatively thin portion of the transducer -14- so that relatively large shifts are obtained at low voltages. The uniformity of the thickness of the thin portion of the transducer results in substantial uniformity of the resulting electric field. Preferably, the thickness of the transducer is in the range of 0.1 to 1 mm, with values ​​of 0.2 to 0.6 mm being preferred so that transducer voltage levels of 25 to 200 V can be applied. In particularly preferred embodiments, the thickness of the transducer -14- at the electrodes may be 0.10 to 0.50 mm, and preferably 0.20 to 0.30 mm, whereby 25 to 80 V may be used.

According to another important aspect of the invention, the foot -16 - which generates the movable wall -18- forms a piston inserted in the hollow end of the transducer -14-. The surface of the foot -18- on the wall -18- in contact with the wall (see Fig.l) is substantially coincident with the cross-sectional area of ​​the transducer -14- at its outside diameter. Due to the relatively small area of ​​the wall -18-, this wall -18- acts as a point energy source as compared to a distributed source, which is of paramount importance for setting stable, satellite free and very fast ejection of droplets at low drive voltages. The total area of ​​the wall -18- is less than 50 mm²and preferably less than 2 mm², The area should be as small as possible in order to obtain the highest packaging capability and thus resolution when printing from an array. In any case, the difference in the pressure pulse transit time from each point on the wall -18- to the nozzle -12- is less than 1 με. Of course, the small areas can be accomplished, since the necessary displacement is achieved by the extension of the transducer. It should be noted that the total area of ​​the foot -16- may be increased from the cross-sectional area of ​​the transducer -14- to provide the desired radiating area of ​​the movable wall in conjunction with ink within the chamber -10-. In addition, the area of ​​the wall -18- may be controlled to cause some sort of impedance or resistance matching between the ink and the transducer -14-.

It will also be appreciated that the foot -16- acts as a seal with respect to any ink that might otherwise leak back into the interior of the hollow transducer -14- thereby avoiding electrical shorting. This allows the transducer -14- to operate in direct communication with the ink within the chamber -10- without the use of any intermediate material between the transducer -14 and the ink which adversely affects the operation of the jet or at least a problem in reproducibility in the manufacture of large-sized ink jets where efforts should be made to reliably bond the intermediate material to the transducer.

As shown in Figs. 2 and 3, a substantial number of inlet ports of the inlet means 20 are formed around the entire circumference of the chamber 10 through the use of open channels 36 through a ring land. extending in a layered member which forms an essential part of the chamber -10-. The surface of the member adjacent the open channels is contacted by the surface of a ridge on the layered member so as to complete the manufacture of the inlet openings. It should be emphasized that layered members -34 and 40- greatly facilitate the manufacture or manufacture of the apparatus shown in Figs.

As shown in Fig.i, is an ink container -46-, which is kept under ambient pressure, that is, is not pressurized, in connection with inlet openings with a substantially constant cross-section. Any leaking between the container -46- and the chamber -10- as well as any other leakage, for example around the foot -16- has no adverse consequences, as long as the leakage is relatively small compared to the inlet openings, since such leakage paths are parallel to the inlet openings , Accordingly, any reference to leakage which might ordinarily escape from a layered construction, as shown in Fig. 1, may be minimized. It should also be noted that the location of the openings of the inlet means -20- on the back of chamber -10- greatly facilitates the construction of the jet in the manner described herein. In addition, the location of the openings of the inlet means -20- on the rear of the chamber reduces the possibility that air bubbles adversely affect the operation of the jet.

As also shown in Fig. 1, the layered construction comprises a nozzle plate -48- which is covered by another layered member -50- which has a frusto-conical opening -52- adjacent the nozzle. Another layered member 54 is attached to the end of the member 34 to extend along the conductor surface 32-.

A variety of materials may be used to make the layered construction shown in Fig. 1, which is greatly facilitated by the use of the cylindrical transducer -14-. For example, the layered members -40, 48, 50 and 54- may be made of stainless steel. Alternative materials include glass, a modified polyphenylinoxide manufactured by GE and known by the trade name Noryl, and a glass filled diallyl phthalate. The foot -16- may be made of plastic or ceramic, which is connected to the transducer -14-, which may be made of piezoelectric material.

In the embodiment of Fig. 4 there is shown an ink jet apparatus which in many respects corresponds to the apparatus shown in Figs. 1-3, including the transducer -14- and the wall -18- formed by the foot -16. However, chamber -10- consists of a single layered member -140-. The chamber -10- comprises the nozzle -12-, into which the chamber -10- tapers. A laminated member -134- through which the transducer -14- passes forms an ink reservoir -146- together with the member -140-. A projection -148- extends between the member -134- and the member -140- within the container -146- and serves for adjustment and attachment between the members -134 and 140-.

It will be readily apparent that the use of elongated transducers that expand and contract in the direction of the longitudinal axis allows the production of a considerably dense array of ink jets. As shown in Fig. 5, the nozzle plate -140a comprises a plurality of nozzles -12-, with dashed circles surrounding the nozzles -12- indicating the diameter of the transducers -14- located behind the nozzle plate -140a. lie. Fig. 6 shows another arrangement of nozzles -12- in the nozzle plate -140b-. Although the manner of staking or displacing the rays deviates in Figs. 6 and 5, in both cases the rays are densely packed, which is highly desirable when achieving high quality alphanumeric printing with an ink jet array shall be.

In the embodiment of Figs. 7-9, a chamber 200 with a nozzle ejects droplets of ink 202 -204, depending on the state of excitation of a transducer -204- for each beam in an array. The transducer -204- expands and contracts in directions indicated by arrows in the longitudinal direction shown in Fig. 8, and the movement is coupled to the chamber 200- by a coupling device -206- having a foot - 207-, a viscoelastic material -208- adjacent to the transducer -207- and a diaphragm -210- biased to the position shown in Figs.

Ink flows into the chamber -200 from an unpressurized container 212 via restricted inlet means provided through a restricted opening -214-. The inlet -214- includes an opening in a restrictor plate -216- which is best seen in FIG. According to the invention, the cross-sectional area of ​​the in the chamber

No.383779 through the inlet -214- substantially during the expansion and contraction of the transducer -204- regardless of the position of the inlet -214 · - immediately adjacent to the coupling device -206- and the converter -204- constant. By providing the inlet -214- with a suitable dimension relative to the nozzle -202- in a nozzle plate -218-, the appropriate relationship between the mass effect at the inlet -214- and the mass action at the nozzle -202- can be maintained. This relationship, which also applies to the embodiments of Fig.l to 6 will be explained in more detail below.

As shown in Fig. 7, the container -212- formed in a chamber plate -220- has a tapered edge -222- leading into the inlet -214-. As in

9, the container -212- is supplied with an inlet pipe -223 and a ventilation pipe -252-. In order to minimize the mechanical crosstalk by the ink in the chamber, the container is yielding thanks to the membrane which is in communication with the ink through a large opening -227- in the restrictor plate -216- which adjoins one Surface of a relief or recess -229- lies in the plate -226-. To that

In the arrangement of Fig. 9, each jet is separated from the ink and connected to a single chamber as shown in Figs. 1-6.

Each of the transducers -204- shown in Figs. 7 and 9 is guided at its ends, with intermediate portions of the transducers -204- being substantially unsupported, as best seen in Fig. 7.

One end of the transducers -204- is guided by the interaction of the foot -207- with a hole -224- in the plate -226-. As can be seen from Figure 7, the hole -224- in the plate -226- has a slightly larger diameter than the diameter of the foot -207-. As a result, there must be very little contact between the foot -207 and the wall of the hole -224-, with the contact mass locating the foot -207- thus supporting the transducer -204- from the viscoelastic material -208 - exists, as can be seen from Fig.8. The other end of the transducer -204- is resiliently supported in a block -228- by means of a resilient material, such as silicone rubber. The compliant material lies in slots -232- (see Fig. 9) ³⁰ to make such a bearing for the other end of the converter. Electrical contact with the transducer -204- also occurs in a compliant manner by means of a compliant printed circuit -234- which is electrically coupled to the transducer -204- by suitable means, such as solder -236-. As can be seen from Fig. 7, conductive patterns -238- are provided on the printed circuit -234-.

³⁵ As shown in detail in Figs. 7 and 9, the plate -226- including the hole -224- at the base of a slot -237- accommodating the transducer -204- also comprises a vessel -239- for one Heater liner -240- including a heater element -242- with coils -244-, a bottom retainer plate -246-, a plate -246- associated spring -248- and a support plate -250- which lies just below the heater -240- , Around⁴⁰ To control the temperature of the heater -242-, a thermistor -252- is provided, which is received in the slot -253-. The entire heater -240- is held in the vessel of plate -226- by means of a cover plate -254-.

As can be seen from FIG. 9, the entire construction of the device, including the various plates, is effected by means of screws -256- extending upwards through openings. ⁴⁵ extend in the assembly, and held together by means of screws -258- which extend down through openings -259-, so as to hold the printed circuit board -234- in place on the plate -228-. Not shown in Fig. 9 but indicated by dashed lines in Fig. 7 are connections -260- to the printed circuits -238- on the printed circuit board -234-. It should also be noted that the viscoelastic layer -208-,⁵⁰ which is shown in Figures 7 and 8, not shown in Figure 9.

In accordance with an object of the invention, it is desirable to achieve very high frequency operation of the ink jet. It has been found that a desired high operating frequency can be achieved if the chamber of the ink jet is sufficiently small, so that a high Helm8

No. 3,837,77, which is given by the following equation:

f =

<img file="AT383779B_D0001.tif" />

with C_c = resiliency or spring action associated with the ink jet volume in the chamber, C_d = resilience or spring action associated with the movable wall, L_n = Mass effect of the liquid in the nozzle, Lj = mass effect of the liquid in the inlet restrictor.

Furthermore, apply toC_c, L_n and L .:

Where V is the volume of the chamber, Φ the density of the ink, and c the speed of sound in the ink.

In addition:

with L_p = Length of the nozzle and r = radius of the nozzle. In addition:

where k = geometry factor determined by the cross-sectional shape of the constraint channels, A = cross-sectional area of ​​a single constraint channel, n = number of constraint channels, L • = length of a single constraint channel.

In general, it has been found desirable to have a characteristic Helmholtz resonance frequency that is substantially higher than the rate of ink droplet ejection. Preferably, the Helmholtz resonance frequency is at least twice the rate of ink droplet ejection. In numerical values, it is desirable to have a Helmholtz frequency of at least 10 kHz and less than 100 kHz at preferred values ​​of 25 to 50 kHz in order to achieve such high droplet ejection rates on demand.

It follows from the above discussion that it is generally desirable to achieve a small chamber to have a high Helmholtz resonance frequency so as to allow a high droplet ejection rate as needed. However, regardless of the Helmholtz resonance frequency, the ejection droplet rate and beam stability may be adversely affected by undesirably low or low acoustic or acoustic resonance frequencies of the chamber or by undesirably small or low transducer resonance frequencies along the coupling axis, ie, the longitudinal or longitudinal mode resonant frequencies Transducers -14 and 204-, are affected. However, it should be ensured that the total length of the chamber does not greatly exceed the largest cross-sectional dimension of the chamber, ie the diameter in a cylindrical chamber. Here, the term total length of the chamber refers to the length parallel to the axis of droplet ejection from the rear of the chamber remote from the nozzle to the exterior of the nozzle itself. As shown in Fig.la, this dimension is indicated by the distance X, while the largest cross-sectional dimension is indicated by Y.

It is generally preferable that a aspect ratio, ie, a length to cross-sectional dimension ratio, is not more than 5: 1, and preferably not more than 2: 1

No. 383779 becomes. It should also be noted that the length X may be smaller than the cross-sectional dimension Y. By means of this aspect ratio, the sound resonant frequency of the chamber (ie, the organic pipe resonance) remains sufficiently high so that the sonic resonant frequency of the chamber does not unduly limit the operating frequency of stable operation of the beam.

It should also be noted that there is a certain minimum cross-sectional dimension Y that can be achieved without requiring an increase in the overall length of the transducer, which in turn would result in a decrease in the axial or longitudinal mode resonant frequency of the transducer, thus the operating frequency to limit the desired beam. A minimum cross-sectional dimension Y of 0.6 mm is desirable in order for the axial or longitudinal mode resonance frequency to assume their maximum value. In this regard, it should be emphasized that the total length of the transducer necessarily increases to achieve the required displacement when the largest cross-sectional dimension Y of the chamber is reduced.

As explained above, it is desirable to couple the transducer into the chamber as a point source. In this regard, it is preferred that the difference in pressure pulse 15 transit times from each point from the transducer coupling wall be less than 1 gs, and preferably less than 0.1 gs, with 0.05 gs indicating an optimum value. If a given ink composition and therefore a predetermined speed of sound are assumed by the ink in a chamber, the difference in a sound path length or a distance d may be less d_m,_n (see Fig.la) for a given high-frequency noise disturbance. In this regard, it should be emphasized that it is desirable to operate ink jets with high frequency components that are at least 100 kHz and preferably at 1 MHz. If a sound velocity of 1.5 χ 10 cm / s is assumed to be the same as the velocity of sound in water and a high frequency component of 100 kHz, then the difference in the sound path length or distance d_raax less d_nin not exceed 1.5 mm, and preferably be less than 0.15 mm.

Assuming a frequency component of 1 MHz, the difference in the path lengths should not exceed 0.15 mm. The same difference in the path lengths also applies to the embodiment of FIGS. 7 to 9.

The following examples of chambers of various dimensions or dimensions are given to illustrate the various aspects of the invention:

Example 1: X = 2.54 mm; Y = 1.78 mm; Speed ​​of sound = 1.5 χ 10⁵ cm / s; High frequency component of 1 MHz

Example 2: X = 2.54 mm; Y = 1.60 mm; Speed ​​of sound = 1.2 χ 10 cm / s; (Oil-based ink) High frequency component of 1 MHz

Example 3: X = 1.27 mm; Y = 1.27 mm; Speed ​​of sound = 1.5 χ 10 cm / s; High frequency component of 1 MHz.

It follows from the above discussion that the cross-sectional dimension of chamber 10 and 200, respectively, is sufficiently large to achieve a sufficiently high Helmholtz frequency over the operating frequency of the beam, but sufficiently small relative to the sonic resonant frequency and longitudinal mode resonant frequency of the transducers -14 and 204- must be. In this regard, it has been found that the cross-sectional dimension of the chamber should be at least 10 times greater than the cross-sectional dimension of the nozzle transverse to the axis of the droplet ejection, perpendicular or transverse to the axis of the droplet ejection. With regard to the dimensions, in the case of a cross-sectional dimension of the nozzle in the range of 0.025 to 0.075 mm, the cross-sectional dimension of the

Chamber 0.6 mm, preferably in the range of 0.6 to 1.3 mm.

According to another important aspect of the invention, the length X (see Fig.la) is so short that it does not undesirably reduce the Helmholtz frequency in the frequency domain. At the same time, the relatively short chamber causes a relatively high sound resonance frequency. The overall axial length of the transducer is - as shown - such that the sonic resonant frequency is greater than the longitudinal mode resonant frequency of the transducer.

In general, it is preferred that the resonant frequency along the coupling axis of the transducer, such as the longitudinal resonant frequencies of the transducers, be at least 25% higher than the Helmholtz resonant frequency. Preferably, the resonant frequency along the coupling axis is at least 50% greater than the Helmholtz frequency.

Nr.383779

By using the cylindrical transducers -14-, the number of resonance modes of the transducers is desirably reduced. However, it should be emphasized that other transducers can be used which extend longitudinally but have no cylindrical cross-section, such as transducers of rectangular cross-section having a total length to minimum width ratio not exceeding 30: 1, and one thickness perpendicular to the length in the range of 0.4 to 0.6 mm, as shown in Figures 7 to 9.

As explained above, the inlet ports -214 and 20- maintain the cross-sectional area of ​​the ink flowing into the chambers substantially constant during expansion and contraction of the transducer in the direction of the longitudinal axis. To the extent that the membrane moves into the area representing the inlet -214, as shown in Fig. 8, the cross-sectional dimension of the ink represented by the height h of the inlet -214- must be , be substantially greater than the overall change in the length of the transducer as the transducer expands and contracts. In this connection, it should be noted that the total height h is in the range of 0.025 to 0.075 mm, with a value smaller than 0.05 mm being preferred, while the total change in length at the transducer is -204- 0.05 to 0.50 gm is, where one

Value less than 0.24 gm is preferred. For this purpose, it is also important that the 7 9 3

Inlet restrictor and the nozzle mass action parallel in the range of 10 to 10 Pa / M / s / s.

It should also be emphasized that the overall dimension of the inlet restrictor must have some relationship with the ink jet nozzle. In this connection, it is desirable that the minimum or minimum cross-sectional dimension of the restrictor be kept smaller than or equal to the nozzle diameter or the cross-sectional dimension. This ensures a Helmholtz frequency greater than the operating frequency, but less than the longitudinal mode or sonic resonance frequency.

In the above discussion, it has been emphasized that the apparatus of the present invention provides an ink jet having a Helmholtz (fluid) resonant frequency that is less than the transducer longitudinal mode resonant frequency, and preferably is one-half that frequency. At the same time, the Helmholtz frequency is much higher than the required drop-beat rates or frequencies, ie greater than 10 kHz and preferably greater than 25 kHz. Since the Helmholtz frequency tends to be adequately attenuated, vibrating or ringing the device at the frequency does not adversely affect the stability of the drop formation process. Even with a Helmholtz frequency substantially less than the longitudinal mode frequency, the fluid system can not respond to the longitudinal mode swing of the transducer, which tends to be weakly damped. This low attenuation longitudinal mode swing can exert a detrimental effect on the performance of the device when the fluid system is responsive to the longitudinal mode frequency. This situation requires external damping of the transducer assembly, which often increases the drive voltage, but this is not the case with the invention.

As shown in the embodiments of Figures 1 to 4 and 7 to 9, an electric field is perpendicular or transverse to the longitudinal axis of the transducer. As shown in Figs. 1 and 4, this is achieved by electrodes -30 and 26-, while in Figs. 7 to 9, this is done by printed circuit elements -238- which are electrically connected to electrodes -260 and 262- , These electrodes provide means for applying an electric field to the transducer so that the transducer contracts along the axis, thereby contracting the chamber, and so that the transducer expands along the axis to expand the chamber when an electric field not on the converter. This is particularly important to avoid accelerated aging of transducers -14 and 204- and, in extreme cases, depolarization. That is, if an electric field is across the transducer to expand the transducer, then such an electric field tends to depolarize or de-polarize the transducer so that it will not operate for at least a period of time. It is therefore important that the electric field acting transversely to the transducer be applied so that the transducer is contracted.

Nr.383779

In order to deepen the understanding of the manner in which the electric field is applied to the transducers, FIGS. 10 and 11 will be discussed in more detail below. As shown in Fig. 10, the transducer -204- has electrodes or electrical connections -260-, with the transducer -204- extending outwardly beyond the tip of the electrodes -260-. If one of the electrodes -260- is grounded and the other electrode is not energized, then the converter -204- takes the voltage shown in FIG. 10 shown configuration or shape. On the other hand, if one of the electrodes -260- is energized with a positive voltage (see Fig.11) and the other electrode -260- is grounded, then the transducer -204- actually expands across its thickness but retreats in the direction of it Length together. It should be emphasized that the electric field generated by voltage applied in the manner shown in Fig. 11 has the same direction as the polarization of the transducer -204-. Of course, the extent and contraction are exaggerated in Figs. 10 and 11 for clarity of illustration.

According to another important aspect of the invention, the only connection between the transducers -14 and 204- via the coupling device in the chamber, for example via the foot or the membrane. Thus, in arrangements as shown in Figs. 5, 6 and 9, the transducers are substantially isolated or separated from the ink and in exclusive communication with a single chamber or beam. In addition, a seal is provided between the chamber and the transducers, such as through the membrane shown in Fig. 9, to prevent ink from flowing upwardly into and around the transducer, such as transducer -204-.

With the term stretched or in the longitudinal direction is here indicated that the length is greater than the width. That is, the longitudinal axis extends here in the direction of the length which is greater than the transverse dimension, over which the electric field is applied. In addition, it should be emphasized that the particular transducer can be stretched in a different direction, which could be referred to as the depth, and the total depth can be greater than the length. It follows that the term longitudinal direction is a relative designation. It should also be emphasized that, in addition to the longitudinal axis, the transducer can expand and contract in other directions as well, but such expansion and contraction are not of interest since they do not take place in the coupling direction. In the embodiments shown here, the coupling axis is the longitudinal axis. Accordingly, it will be appreciated that the longitudinal mode resonance occurs in the coupling direction and, in the embodiments shown, represents the resonant frequency in the direction of the longitudinal axis. However, the expansion and contraction in the direction of the longitudinal axis are sufficient to make the displacement of the ink as large as possible.