JPH0221946B2 - - Google Patents

Abstract

An elongated acoustic waveguide (20) couples a transducer (18) to an ink jet chamber (14) including an outlet orifice (16) through which droplets of ink are ejected. In one embodiment, the waveguide (20) is directly coupled to ink within the chamber (14). Arrays are formed utilizing such ink jet chambers (14) and waveguides (20). Because the transducers (18) are located separately from the ink jet chambers (14), the latter can be arranged in a very compact array.

Description

[Detailed description of the invention]

The present invention relates to an inkjet device, and more particularly to an inkjet device that ejects ink particles from an ejection opening for the purpose of recording on a recording medium. It may be advantageous in some cases to use parallel inkjet rows to write alphanumeric characters or numerical symbols. From this purpose,
It is often desirable to provide a dense array of ink jets. However, in many cases the stimulator elements or transducers of such arrays are too bulky, placing severe limitations on the density with which the individual inkjet units can be arrayed. This situation generally causes these transducers to be constructed with certain limited dimensions. For this purpose, the energy and displacement movement necessary to generate a change in the volume of the ink jet chamber are applied, and the ink particles are ejected from the ejection opening formed in the ink jet chamber. It must also be noted that attempts to create dense inkjet arrays may create undesirable crosstalk problems between aligned inkjet units. This problem results, at least in large part, from the relatively close spacing between the inkjet arrays. In designs where an effort is made to achieve high density arrays, the inkjet transducers are incorporated in close association with the fluidic components of the inkjet unit or chamber and its ejection openings. As a result, any defects that occur in the inkjet unit fluid system, which is a much more common problem than transducer defects, eliminate the need for alignment across the entire system, i.e., both the fluid system and the transducer system. It is approved. It is an object of the present invention to provide a high density inkjet alignment arrangement. Another object of the present invention is to provide an inkjet arrangement device that minimizes the occurrence of crosstalk between inkjet units. Yet another object of the present invention is to provide a parallel inkjet system that increases the efficiency of arranging the inkjet fluid path system independent of the inkjet system transducers. Another object of the present invention is to provide an ink supply system which minimizes air ingress and cavitation in the ink supply system leading to the ink jet system. Yet another object of the present invention is to encapsulate the aligned waveguides in a suitable material to prevent flexural vibrations that can cause crosstalk between adjacent fluid supply chambers. According to the above objects and other objects of the present invention, one inkjet device includes an inkjet chamber having an ink introduction port for introducing ink into the inkjet chamber and an ejection opening for ejecting ink particles from the chamber. further provided with one transducer at a position remote from the ink jet chamber, the ink jet and the transducer being connected by a solid or hollow elongated acoustic waveguide, Furthermore, the acoustic waveguide transmits the acoustic pulses generated in the transducer to the inkjet chamber so that the volume of the inkjet chamber can be varied depending on the energization state of the transducer. According to the invention, an acoustic pulse is transmitted along the waveguide with the following behavior. That is, when the transducer is energized, the side end portions of the transducer undergo axial deformation by an amount determined by the voltage transmitted to the transducer. If one end portion of the transducer is integrated into a solid back plate, the other end is movably displaced relative to the joining end of the waveguide. The junction end of the waveguide will then be driven in that direction by an amount corresponding to the amount of movement of the end of the transducer. If the driving voltage pulse occurs suddenly, i.e. the voltage reaches its final voltage value within a short time, the end of the waveguide will rapidly move in response to the voltage, and the waveguide will therefore Only a portion of the tube undergoes sudden movement, while the remainder of the waveguide remains stationary. The first deformed waveguide end is subjected to a pressing action and the subsequent section along the waveguide relaxes with an elastic deformation action. The successive displacements of this elastic deformation eventually reach the far end portion of the waveguide. The final end of the waveguide exerts a compressive action on the fluid within the ink jet chamber, so that a jet of fluid particles is generated from the jet opening. The physical properties employed in the present invention utilize the properties of the waves themselves propagating along the length of the waveguide, and do not utilize the properties of the push rod. That is, it does not take advantage of the property that when one end of the push rod is moved, the other end is moved together with it. An important cosmetic feature of the invention is that a number of inkjet units are used in an array configuration, where the center-to-center spacing between the transducer groups is substantially the same as that of the jet aperture. They are substantially larger than their mutual axial spacing. The waveguides are arranged in such a way that the relative spacing between the transducers toward the jet aperture group decreases compared to the spacing of the jet aperture group. Furthermore, according to other important cosmetic features of the present invention:
All of the transducers are located on one side of the jet aperture axis at the outermost end of the ink jet array. Yet another important feature is that the waveguide groups have different lengths along the longitudinal axis. A further important feature is that the waveguides are tapered such that the diameter of the waveguide located at the end remote from the transducer is substantially smaller than the diameter at the transducer end. It is. This tapering of the waveguides helps to space the waveguides even closer together, allowing their waveguide density to be further increased. Yet another important feature is that the tapered ends of the waveguides are molded with tubular material to form a fluid supply ink passageway for filling the inkjet chamber with fluid. That's what I did. A still further important feature is that the ink passageway of the fluid supply has a cross-section that is much smaller than the cross-sectional area of the fluid passageway, thereby acting as a restriction for controlling the flow of fluid therethrough. can. Yet another important feature is that the ink jet chamber is provided with a diaphragm connected to the waveguide, which diaphragm has at least one diaphragm parallel to the axis of the injection opening, depending on the energization state of the transducer. The retraction and expansion of the diaphragm takes place in one direction with a component. Yet another important feature is that each waveguide is bonded to a transducer and a metal or ceramic wedge connects the transducer end and the waveguide end together in a mating manner. It is that you are. A final important feature is that each acoustic waveguide is elongated and the overall dimension along the longitudinal axis is much larger than the dimension of the waveguide perpendicular to the axis. be. Hereinafter, the present invention will be explained in detail according to preferred embodiments. In FIG. 1, a set of inkjet rows includes a plurality of inkjet units arranged in a row so as to asynchronously eject ink droplets 12 in a required amount. The ink jet 10 has an inlet port 15 and an ink droplet 1.
It has an injection chamber 14 having an injection opening 16 for ejecting 2. According to the invention, the ejection chamber 14 expands and contracts depending on the energization conditions of an electro-mechanical transducer 18 , which is connected to the ejection chamber 14 via an acoustic waveguide 20 . Furthermore, as shown in FIG. 2, the waveguide 20 is actually inserted into the injection chamber 14 by a distance d _i . Furthermore, when installing the waveguide 20, a wedge tube 21 made of ceramic or metal is used to connect it to the transducer, so that the inkjet 10 does not impose any restrictions on the spatial arrangement of the transducer 18. This makes it possible to arrange them even closer together without having to do so. In particular, the distance d _c between the central axes of the injection chambers 14 is configured to be substantially smaller than the distance d _t between the central axes of the transducers 18 . This allows an increase in the arrangement density of the inkjet rows to be achieved regardless of the shape or size of the transducer 18. According to the invention, acoustic pulses are transmitted along the waveguide in the following manner. That is, when the transducer 18 is subjected to an electrical biasing force, the end portion of the transducer 18 moves in the axial direction, that is, in a direction parallel to the axis of extension of the waveguide 20.
is displaced by an amount determined according to the magnitude of the voltage applied to it. Since one end of the transducer 18 is integrated into the solid back plate, the other end is displaced against the joining end of the waveguide 2. The junction end of the waveguide 20 is then driven in the same direction by an amount corresponding to the displacement of the end of the transducer 18. If the drive pulse has an abrupt shape, i.e. the voltage reaches its final value within a short time, the transducer end moves quickly and the waveguide end similarly moves quickly. Thus, only a portion of the waveguide 20 follows the sudden movement. The other parts of the waveguide are therefore held stationary. The end of the waveguide that is initially deformed presses against the subsequent portion along the elastically deforming waveguide 20 and becomes relaxed. The sequential displacement of this elastic deformation finally reaches the far end of the waveguide 20. Next, the final end portion of the waveguide is the injection chamber 1.
It acts to compress the fluid within 4 so that the ink droplets are ejected from the ejection opening. The physics utilized in the present invention are those of a true propagating wave that propagates along the length of the waveguide, and the nature of the piston, i.e., when one end of the piston rod is moved, the other end is moved. It is not a property of being moved in unison with. According to one of the important cosmetic features of the invention, the injection chamber 14 communicates with a passage 24 in a waveguide 20 terminating in an outlet passage opening 26 at the distal end 22. . The outflow passage opening 26 is formed to have a narrow cross section compared to the cross section of the waveguide, and is located at a position far away from the injection opening 16, and the passage gradually decreases and is formed in a tapered shape. One restraining portion is formed at a portion that becomes an inlet to the injection chamber 14. Perhaps most clearly seen in FIGS. 2, 2a and 2c, ink passes through inlet 28 and enters ink passageway 24 within waveguide 20. The remainder of waveguide 20 is filled with a suitable material 30, such as a metal strip or epoxy encapsulant. In operation of the inkjet array shown in FIGS. 1 and 2, the distal end 22 of the waveguide 20 expands and contracts in one direction 32 with at least one component parallel to the axis of the jet opening 16. Of course, in that case, it can be understood that each of the waveguides 20 always extends in one direction with at least one component parallel to the direction of expansion and contraction of the end portion 22 of the waveguide 20, It will also be appreciated that these waveguides 20 are elongated as shown in FIG. As shown in the figure, the waveguide 20 is formed as elongated as possible so that the overall length along the axis of action of acoustic propagation is much larger than the waveguide dimension in the direction orthogonal to the axis, that is, more than 10 times longer. Designed to. From a practical point of view, the waveguide 20 in FIG.
It is fitted and penetrated towards the inside of. The portion of the waveguide 20 that penetrates into the interior of the injection chamber 14 has the outer diameter of the waveguide 20 and the injection chamber 14 formed as a block 34.
Precise tolerances are maintained between the walls. The block 34 may be made of various materials such as plastic, metal or ceramic. Referring again to FIG. 1 in connection with FIG. Waveguide 20 as shown in
is encapsulated or enclosed within a material by means of a filler material. Alternatively, each waveguide 20 may be surrounded by a sleeve 40, as shown in FIG. 2b. In this case, the sleeve 40 serves to reduce the flexural vibrations or resonance effects occurring in the waveguide 20. In another embodiment, the aforementioned sleeve 40
is omitted and filler material 38 is instead used to dampen the resonant vibrations. Suitable filler materials include elastomers and polyethylene or polystyrene. The filling material 38 is formed separately from the injection chamber wall block 34 by a gasket plate 41 made of elastomer or the like. It goes without saying that the transducer 18 is electrically energized to propagate acoustic pulses along the waveguide 20. Although the conductors connected to the transducer 18 are not shown, it is obvious that such electrical conductors can be provided for energizing the transducer. Referring again to FIGS. 1 and 2, pump 46
A storage chamber 42 communicating through a passage 44 leading to
The ink flows through the ink inlet 28 in each waveguide 20.
It is clear that the inflow occurs through . The pump 46 supplies ink at a suitably controlled pressure from a supply conduit 48 to the ink reservoir 42 . The pressure control action provided by pump 46 is important. This is because, especially in typing technology, significant liquid impact effects and associated changes occur within the reservoir chamber 42 and the channel 44. As shown in FIG.
It is closed by a cover 50 enclosing a leg member 52 that closes the end of the cover 6. As shown in FIG. 1, some of the waveguides 20 are formed to extend substantially straight toward the injection chamber 14. As shown in FIG. Still other waveguides are bent or curved toward the injection chamber. In FIG. 3, a somewhat different configuration of the transducer structure is shown. To describe this in detail, an integrally molded transducer 118 having a plurality of branch legs 118a to 118f is connected to a set of five ink jets 110 of the type shown in FIG. 1 via a waveguide group 120, for example. ing. In this case as well, the form of the block-like transducer 118 is not critical as far as the inkjet arrangement density is concerned. Additionally, the arrangement of parallel ink jets 110 can be varied as opposed to transducer block 118. As shown, all of the transducer sections 118a-118f are located on one side of the axis X of the injection opening of the jet 110 located in the top row of the array, ie, below the axis X as shown. Since the ink jets shown in FIGS. 3 and 1 are arranged obliquely and asymmetrically with respect to one side of the ink jet row 10, it is necessary for printers to improve the visibility of the last character. very suitable for use. Referring now to FIG. 4, a plurality of transducers 218 and jets 210
is provided on the head 200 arranged in two stages. Furthermore, the jets 210 are densely spaced with very close spacing, and the transducers 218 are spaced even more closely apart, so that the waveguides 220 are closely spaced from each other.
From 18 toward the ink jet 210, it becomes a contracted or convergent shape like a fan. FIG. 5 shows a head array in which two or more of the inkjet heads 200 shown in FIG. Thus, it is possible to achieve a multi-row inkjet 210 that improves the resolution of printed characters. 1st
As clearly shown in Figures 3 and 4, the overall length of the waveguide group varies. This is also true for the waveguide groups, but in order to minimize the crosstalk generated between the converter groups, the distance between the converters is separated as much as possible. 6 and 6a, a somewhat different embodiment is shown in which the acoustic waveguide 20 is connected to the ink ejection chamber 14 in a slightly modified form. In particular, at the end of the injection chamber 14 remote from the injection opening 16, a diaphragm 60 is provided which has a protrusion 62 that abuts the waveguide 20. Ink flows into the ejection chamber 14 through a restriction opening 65, FIG. 6a, formed adjacent to the restriction plate 64. The restriction opening 65 communicates with the reservoir chamber 66 in the manner described above. For this purpose, the injection chamber block 34 is formed with a land portion 68 which is joined to the restriction plate 64 to form the aforementioned restriction opening 65 in the injection chamber 14. In operation of the embodiment shown in FIG. 6, a pulse from the transducer propagates through each waveguide 20 at the time the pulse reaches protrusion 62 of diaphragm 60. This propagating pulse causes the diaphragm 60 of the ejection chamber 14 in cooperation with the respective waveguide 20 to deform inwardly and outwardly, changing the volume of the ejection chamber and thereby ejecting the ink droplets 12 from the ejection opening 16. . The diaphragm therefore expands and contracts at the protrusion 62 generally in a direction coincident with and parallel to the longitudinal axis of the waveguide 20. The fluidic reaction in the embodiment described above, including the injection chamber 14, is separate from the waveguide 20, according to one of the important objects of the invention.
It is also possible to correct at the diaphragm 62. Acoustic waveguides applied in various embodiments of the present invention are fabricated from materials such as tungsten, stainless steel, or titanium, or other hard materials such as ceramic or fiberglass may also be used. When selecting an acoustic waveguide, it is particularly important that the waveguide material has the maximum wave transmission capacity for acoustic waves and the maximum intensity thereof. The operating mechanism of the waveguide in conjunction with the transducer can be explained as follows.
That is, when an electrical pulse reaches the transducer, the transducer first contracts and fills with ink, and then expands. The aforementioned contraction cycle accompanied by an expansion cycle produces a displacement of the working surface of the transducer, with the waveguide end in contact with the transducer being exposed to said working surface. During the rise time of the pulse waveform, a portion of the waveguide end is subjected to an elastic compression action. This initial compressive action produces a compressive shock wave within the waveguide material along the waveguide with a velocity equal to the speed of sound. For example, in a 2.54 cm steel waveguide, this shock wave reaches the far end of the waveguide after approximately 2 μsec. In this way, the volume of the ejection chamber is changed to eject ink particles. The physical conversion mechanism for converting the electrical pulse applied to the transducer into a mechanical shock wave will be described below using the single-stage excitation analysis theory or the single-impact excitation analysis theory. For single-stage excitation: Now assume that a constant force F ₀ is suddenly applied to the initially resting waveguide at time t=0. The equation of motion commonly used is as follows. m・d ² x/dt ² +c・dx/dt+kx=F ₀ where t>0. The solution to this ^{equation is} : x=F ₀ / ^k + No. here Therefore, However, ωn = transition frequency (ω = 2π) β = attenuation coefficient (loss) t = time (sec.) F ₀ = applied impact force (dyne) n = mass (gr.) k = deformation of the waveguide Spring constant when assuming that is within the elastic limit of the material k = E・A/l where E = Young's modulus (dy)/cm ² A = cross-sectional area cm ² l = length cm Also, c/ 2m=βωn, where c is the viscosity coefficient. Excitation analysis using unit impact force: Impact force I is strictly defined as a large force that acts in an extremely short time that cannot be achieved in practice. However, this definition is appropriate for understanding the operating state of the waveguide, so the assumption in this case is useful. Therefore, with this assumption, Δt→
At 0, LimI/Δt→∞. This impact force creates a certain initial velocity in the short mass portion m adjacent the transducer end. This initial velocity is V ₀ =I/m, and the displacement x at this time can be considered to be equal to zero. Therefore, the solution to the differential equation for t>0 when the displacement on the right side is equal to zero is as follows. That ^is , ^{x =}

[Formula] Therefore, the displacement x at any time t is The maximum displacement at this time is

Occurs at each time that satisfies [Formula]. The kinetic energy produced by a single impact force at the beginning of the waveguide is: That is, an impact force I received from the transducer strikes some mass of the waveguide, producing a velocity V. Assuming that the waveguide has an initial velocity V ₀ , the velocity change is m(V-V ₀ )=I. Multiplying both sides of this by 1/2 (V + V ₀ ) gives 1/2 mV ² - 1/2 mV ² ₀ = I [1/2 (V - V ₀ ).If we assume that the initial velocity V ₀ =0, 1/2 mV ² = 1/2 I V = Kinetic Energy (CGS units) These descriptions generally describe how a single impulse force is guided into a waveguide. .Along with this, the analysis of the matters derived when the impact force travels along the waveguide is as follows.The amplitude α of one mechanical impact force travels through the waveguide medium. When time t
Assume that one particle has a velocity v and a displacement position x. At this time, the displacement position b of the particle at the initial displacement position ) = Frequency (per second) λ = Wavelength (pulse width between the leading edge and trailing edge of the shock wave) α = Fluctuation amplitude of the particle Also, since v = ·λ and ω = 2π, b = α · sin2/λ (vt−x)=αsinω(t−x/v
) Therefore, particle velocity db/dt=α・ω・cosω(t−x/v
) Here, if the thickness of the layer is dx and the density is ρ, its mass is ρ・dx, and the kinetic energy of the layer is
KE is as follows. dE=ρdx/2(db/dt) ² = 1/2ρdx・α ² ω ² cos ² ω
(t-x/v) However, dE is a minute increase in kinetic energy. Therefore, the kinetic energy KE of the entire shock wave system is E=1/2ρ・α ² ω ² ∫cos ² [ω(t-x/v)]dx The total energy of shock wave motion per unit volume is E-1/2ρα ² ω ⁵ (=Energy density) = 2π ² ρ ² α ^{2 2} Therefore, by using a thin wire, the amount of displacement can be increased, and as long as the energy is not lost from inside the wire, the amount of displacement will be large. transmission becomes possible. The impact intensity I is the amount of energy transmitted per unit area of the wave front per unit second time, which is equal to (energy density E) x (velocity V). That is, I=1/2ρα ² ω ² V=α ² ω ² ·(ρV) Regarding the particle velocity in the wave medium, the varying compression pressure P at any point is as follows. P=ρV・db/dt Therefore, P/db/dt=ρV=K (constant depending on the material) Also, the energy loss lost from inside the waveguide to the outside is calculated as follows. R=R ₂ −R ₁ /R ₂ +R ₁ where R corresponds to both the external world surrounding the waveguide and the energy reflected from the waveguide material. i.e. R ₁
is the energy reflected from the waveguide material,
R ₂ is the energy reflected into the outside world surrounding the waveguide. and R ₁ = ρ ₁ C ₁ where ρ ₁ is the density of the waveguide material (gr/cm ³ ) C ₁ is the wave velocity within the material For steel, R ₁ = ρ ₁ C ₁ = 1.9×52 ×10 ⁵ =4.1×
For 10 ⁶ air, R ₂ = ρ ₂ C ₂ =0.35×10 ⁵ ρ ₂ is the density of the air or material surrounding the waveguide. Therefore, 1-R=0.0164, and this fact shows that the amount of energy lost from a unit length of waveguide is quite small. The energy loss due to bending action is explained by A.E.H., published in Dover magazine in 1944.
It was calculated in Mr. AEH Love's paper on numerical elasticity theory. According to this calculation,
We conclude that if the bending radius is equal to or greater than a quarter wavelength of the vibrational force in the waveguide material, all of the energy will be transmitted along the bent waveguide. has been done.

[Brief explanation of drawings]

FIG. 1 is a sectional view of an ink jet arrangement showing a preferred embodiment of the present invention. Figure a is a cross-sectional view taken along line 1a-1a in Figure 1, and Figure 2 is a cross-sectional view of Figure 1.
Partially enlarged view of the inkjet row shown in FIG. 2.
Figure a is a sectional view taken along line 2a-2a in Figure 2; Figure b is a sectional view taken along line 2b-2b in Figure 2; Figure c shows a sectional view taken along the line 2c-2c in Figure 2, Figure 3 shows a partial schematic view of yet another embodiment of the invention, and Figure 4 shows yet another embodiment. FIG. 5 is a partial schematic diagram of another embodiment of the invention; FIG. 6 is a partial cross-sectional diagram of yet another embodiment of the invention; FIG. ．． Figure a is 6a-6a in Figure 6.
It is a sectional view taken along a line. DESCRIPTION OF SYMBOLS 10... Inkjet unit group, 12... Ejection ink particles, 14... Ejection chamber, 16... Ejection opening, 1
8...Transducer, 20...Acoustic waveguide, 28...Ink inlet, 42...Ink storage chamber, 46...Ink supply pump, 48...Ink supply conduit, 60...Diaphragm, 62...Protrusion.

Claims (1)

Claims: 1. An ink jet chamber having an ink inlet port for receiving ink and an outlet orifice for ejecting ink drops, converting electrical control signals into longitudinal acoustic contractions and compressions. a transducer; a rod-shaped acoustic waveguide having a rear end acoustically coupled to the transducer and a front end plungeably inserted into the ink jet chamber through the ink inlet port; an ink supply chamber disposed proximate a front end of the rod-shaped acoustic waveguide, the front end of the rod-shaped acoustic waveguide having an ink supply passageway, the ink supply passageway having a front end orifice opening into the inkjet chamber; , and a wall orifice opening into the ink supply chamber. 2. The apparatus of claim 1, wherein the front end of the rod-shaped acoustic waveguide extends through an ink supply chamber. 3. The apparatus of claim 1, wherein the front end orifice of the ink supply passage has smaller dimensions than the ink inlet port. 4. The device of claim 1, wherein the rod-shaped acoustic waveguide is curved along its axis. 5 a plurality of ink jet chambers each having an ink inlet port for receiving ink and an outlet orifice for ejecting ink drops; a plurality of transducers for converting electrical control signals into longitudinal acoustic contractions and compressions; a plurality of rod-shaped acoustic waveguides each having a rear end acoustically coupled to the transducer and a front end plungeably inserted into the ink jet chamber through the ink inlet port; an ink supply chamber disposed proximate the front end of the rod-shaped acoustic waveguide, each front end of the rod-shaped acoustic waveguide having an ink supply passageway, the ink supply passageway being connected to a corresponding inkjet chamber. An ink jet row forming a front end orifice that opens and a wall orifice that opens into one ink supply chamber. 6. The inkjet array according to claim 5, wherein the plurality of rod-shaped acoustic waveguides have different lengths. 7. The inkjet array according to claim 5, wherein the plurality of rod-shaped waveguides converge toward the plurality of inkjet chambers. 8. The inkjet array of claim 7, wherein the plurality of inkjet chambers are located closer together than the plurality of transducers. 9. The inkjet array of claim 7, wherein the plurality of transducers are all located on one side of the plurality of inkjet chambers.