JPH038946B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a fluid jet printing apparatus, and more particularly to a print head and method for generating at least one drip stream, the print head being simple in construction and operation. Concerning what is being expressed.

Jet drop printers and coating devices operate by generating a stream of small droplets of ink or paint fluid and controlling the deposition of the droplets onto a print-receiving medium. Typically, the drops are electrically charged and then deflected by an electric field. The drip is formed from a fluid filament emerging from a small orifice. This orifice communicates with a fluid tank in which fluid is maintained under pressure. Each fluid filament tends to break at its tip to form a drip stream. In order for the drops to be accurately deflected by the electric field and selectively deposited on the print receiving medium of the drops, the size of the drops and the spacing between drops within each drip fluid should be substantially uniform. is necessary. Breaking the filament into a drip stream is facilitated by mechanically vibrating some or all of the print head structure in a process called "stimulation".

One conventional stimulation method is U.S. Patent No. 3,739,393 issued June 12, 1973 to Lyon et al.
As shown in the issue, a fluid orifice is provided in a typical thin flexible wall plate of a fluid tank.
This wall board, known as "orifice board",
It is stimulated by moving a series of bending waves along the plate. This method produces approximately uniform drop size and spacing, but the timing of fluid filament breakage varies along the length of the orifice plate.

Another method is to vibrate the entire print head, including the ink manifold structure and orifice plate structure, together. This is US Patent No. 3,586,907 issued June 22, 1971 to Beam et al.
No. This type of arrangement inevitably fatigues the print head mounting structure since it is subject to the same vibrations that are applied to the manifold and orifice plates. Furthermore, the amplitude and phase of the vibratory motion is difficult to control at the frequencies commonly used in jet drop printer operation.

Another method for filament stimulation is described in U.S. Patent No. 1, issued June 13, 1978 to Cha.
It is disclosed in No. 4095232. Using the technique disclosed in this patent, a stimulator attached to the upper portion of the fluid tank generates pressure waves that propagate downward through the fluid. Each stimulator has a pair of piezoelectric crystal elements that vibrate in phase and are mounted on opposite sides of a mounting plate that is aligned with the nodal plane. A reaction mass is disposed at the end of each stimulator opposite the stimulator member that is coupled to the fluid. This reaction mass ensures that the nodal planes are properly positioned.

GB 1422388 discloses a printing head in which a piezoelectric crystal element forms one wall of a single jet inkjet printing head. When a droplet is to be expelled from the orifice, the piezoelectric transducer is electrically actuated to create a strain that forces the droplet out of the orifice.

British Patent Specification No. 25 October 1972
No. 1,293,980, and U.S. Pat. No. 4,198,643 issued to Cha et al. on April 15, 1980, a printing head is disclosed in which a pair of piezoelectric crystal elements is bonded to opposite sides of a support plate. A print head manifold structure is bonded to one of the piezoelectric crystal elements and a counterweight is bonded to the other of the crystal elements. The weight of the counterweight is selected to offset the weight of the print head manifold. Due to this balanced configuration, the support plate is located in the nodal plane when the two piezoelectric transducers are excited synchronously. However, as will be appreciated, the construction of such printheads is relatively complex and it is also difficult to design such printheads to resonate at a desired frequency. Therefore, after construction, the printhead must be adjusted so that its resonant frequency is equal to the desired operating frequency.

Finally, U.S. Pat. No. 3,972,474, issued to Keur on August 3, 1976, shows an ink drop recording device that uses a vibrating nozzle to generate a stream of drops. The length of the nozzle is chosen such that its mechanical resonance frequency is much higher than its driven frequency. The nozzle is in the form of a tube and is surrounded by a piezoelectric ring which, when electrically driven, causes radial contraction and expansion of the tube.

An improved fluid jet print head capable of providing uniform in-phase stimulation to multiple jet drip streams, facilitating print head installation, and simplifying print head construction and design. The need exists.

SUMMARY OF THE INVENTION A fluid jet printing head for generating at least one drip stream comprises an elongated printhead body, the length between a first end surface and a second end surface of the print head body being the length of the printhead body of the print head for generating at least one drip stream. It's considerably larger than that. The body has a fluid receiving tank on a first end thereof and at least one orifice communicating with the fluid receiving tank. Fluid is supplied to the tank under pressure by suitable equipment and exits the tank to form a fluid stream. The transducer device is mounted on the outer surface of the body and extends longitudinally along the body a substantial distance from proximate the support device toward the first and second end faces of the body. The transducer device changes the longitudinal dimension of the body in response to the electrical drive signal, thereby causing mechanical vibration of the body to break the fluid stream into a drip stream.

The transducer device comprises a pair of piezoelectric transducers bonded to opposite sides of the body and extending longitudinally from a position proximate a first end face to a position proximal a second end face of the body. The piezoelectric transducer provides for alternating expansion and contraction of the elongated printhead body in its longitudinal direction.

The transducer arrangement further includes means for electrically connecting a pair of transducers in parallel so that the transducers operate in phase and in a direction substantially parallel to the longitudinal direction of the elongated printhead body. Vibration begins to occur. A support device for the print head locks the print head body intermediately and approximately equidistant from the first and second end faces thereof.

In other cases, the transducer arrangement may include a device for electrically connecting the transducers such that the transducers operate out of phase to produce bending waves. The support device for the printing head locks the printing head body at a distance equal to 0.23 of the respective overall length from each end face thereof.

In the case of longitudinally parallel oscillations, the support device may consist of a pair of relatively thin mounting flanges, each formed integrally with the printhead body. The flange extends from the elongate printhead body on opposite sides thereof and has a first end face and a second end face thereof so as to support the body along the nodal plane.
It is approximately equidistant from the end face. Or, the support device is
The print head body may include a pair of support screws that lock the body on opposite sides of the body at positions approximately equidistant from the first and second end faces of the print head body.

The printhead body includes a device defining a slot in a first end thereof, and an orifice plate device attached to the slot defining device and forming therewith a fluid receiving tank. The orifice plate apparatus includes multiple orifices for generating multiple drip streams. The printhead body further includes a fluid supply opening and a fluid outlet opening communicating with the slot. The fluid jet printing head further includes a fluid conduit connected to the fluid supply opening and the fluid outlet opening. The fluid conduit is formed of a material that exhibits a significantly different vibrational impedance than the printhead body and therefore does not provide substantial power losses. The fluid conduit may be made of, for example, a polymeric material.

The fluid jet printing head further includes means for applying an electrical drive signal of a frequency substantially equal to f ₀ =C/2L, where L is the dimension of the body in the longitudinal direction and C is the speed of sound in the body. It's okay. In this case, the fluid jet printing head is driven at a frequency close to its mechanical resonance frequency.

In the case of bending vibrations, the transducer is driven at a frequency F ₀ =αCa/L ² , where a is the lateral thickness of the printhead body and αΓ=1.7. In this case, the two nodal attachment axes are set at a distance equal to about 0.23 of the length of the printhead body centered between the transducers.

A method for stimulating a rupture in a fluid stream emanating from at least one orifice communicating with a fluid reservoir in a fluid jet printing head consists of the following steps.

(a) providing an elongated printing head with a tank and an orifice on one end; (b) applying fluid to the tank under pressure to produce fluid flow through the orifice; (c) opposite ends of the elongated printing head. (d) alternately extending and retracting the print head substantially at a resonant frequency of the print head; This supports the printing head in the nodal plane and also effectively stimulates the fluid flow to break into drops.

The resonant frequency of the print head may be approximately equal to the resonant frequency of the fluid stream. The printing head can be expanded and contracted by piezoelectric transducers bonded to its outer surface.

Fluid flow may also be stimulated by operating the transducers out of phase to create bending vibrations of the print head. With this stimulation method, the print head is placed at a distance from each edge equal to the length of the print head.
It is installed at a position approximately equal to 0.23 times.

SUMMARY OF THE INVENTION It is therefore an object of the invention to provide a fluid jet printing head for generating one or more drip streams, the printing head comprising an elongated body which is driven to expand and contract in the longitudinal direction thereof. and to provide such a printing head and method in which the printing head is driven by a thin piezoelectric transducer glued to its outer surface, and in which the support for the printing head is provided in the nodal plane. to provide a printing head.

Other objects and advantages of this invention are as follows:
It will become clear from the accompanying drawings and claims.

DETAILED DESCRIPTION OF THE SELECTED CONFIGURATIONS This invention relates to fluid jet printing heads of the type that can be used for inkjet printing, painting, textile dyeing, and other applications. As is known, devices of this type typically operate by electrically charging the drops in one or more jet drip streams and causing the trajectory of some of the drops to be deflected by an electric field. To generate one or more streams of drips, fluid is typically added under pressure to a fluid tank and flows through one or more orifices or nozzles in communication with the tank.
The fluid emerges from the orifice as a fluid filament that, if not perturbed, will break off in a somewhat irregular manner into drops of varying size and spacing. Since it is not possible to charge and deflect such irregular drops, jet infusion devices generally employ some method of mechanically stimulating the fluid filament so that the filament is generally uniform at the desired drop breakage frequency. It is designed to break into drips with the same dimensions and spacing.

A first configuration example of a printing head according to the present invention is a first configuration example of a printing head according to the present invention.
As shown in FIGS. The printing head generally consists of an elongated printing head body 10, the length L of which is considerably larger than the other dimensions a and b. The body 10 has an orifice plate 12 and a block 14 of material. The body 10 includes a fluid receiving tank 16 at a first end thereof, and also includes at least one, and preferably multiple, orifices 18 arranged in a row across the orifice plate 12. The orifice plate 12 is attached with a suitable adhesive.
It is glued to a block 14 of a material such as stainless steel. The block 14 has a slot 20 which together with the orifice plate 12 forms a tank 16. Block 14 further includes a fluid supply opening 22 and a fluid outlet opening 24, both of which communicate with slot 20.

The print head further supplies fluid under pressure to tank 16.
Apparatus is provided for supplying fluid to the orifice 18 to cause it to emerge as a fluid filament, which is broken to create a drip stream. It includes a pump 26 which receives fluid from the source tank 28 and supplies it to the tank 16 by a fluid conduit 30. Conduit 32 connects fluid outlet 24
The fluid is connected to the tank 16 so that fluid can be removed from the tank 16 when the print head is stopped or during cross-flushing of the tank 16. As will become apparent, the end of the print head to which conduits 30 and 32 are attached, as well as the opposite end of the print head, breaks the fluid filament to produce drops of uniform size and spacing. Subjected to mechanical vibration for flow. Conduits 30 and 32 are selected from a number of materials, such as polymeric materials that have a vibrational impedance substantially different than that of stainless steel block 14. Therefore, conduit 30
The power losses in and 32 and the resulting damping of vibrations are minimized.

The print head further includes support devices such as mounting flanges 34. Flange 34 is relatively thin and integrally formed with block 14. Flanges 34 extend from opposite sides of the elongate printhead body 10 and are approximately equidistant from the body's first and second end faces. As a result, the main body 10 can be supported in the nodal plane using this flange. Flange 34 is therefore not subject to substantial vibration.

The print head further includes a transducer arrangement consisting of thin piezoelectric transducers 36 and 38. These transducers are glued to the outside of the body of block 14;
It extends longitudinally a considerable distance from near the support device toward the first and second sides of the body.
Transducers 36 and 38 change dimensions in response to an electrical drive signal applied to line 42 by power source 40, thereby causing mechanical vibration of the body to disrupt the fluid flow and cause drip flow. Make it.

Piezoelectric transducers 36 and 38 are provided with a conductive coating on their outer sides, ie, the side facing away from printing headblock 14, which forms the first electrode for each of them. A generally grounded metal printing headblock 14 provides a second electrode for each of these transducers. The piezoelectric transducer is selected to alternately expand and contract in the longitudinal direction of the print head when driven by an alternating current drive signal. As seen in FIG. 3, transducers 36 and 38 are electrically connected in parallel. Both transducers are oriented to expand and contract simultaneously due to the drive signal on line 42. Since transducers 36 and 38 are glued to block 14, they also expand and contract the block.

If desired, an additional piezoelectric transducer 44 can be glued to one of the narrow sides of the printing head to provide an output voltage on line 46 that varies in response to the expansion and contraction of the printing head block 14. Good too. The amplitude of the signal on line 46 is proportional to the amplitude of the mechanical vibration of block 14.

The mechanism by which the first embodiment of the print head according to the invention operates can be explained as follows. The elongated printhead body is somewhat similar to a conventional coil spring. When such a spring is compressed and then quickly released, it oscillates around its center at a frequency of ₀ , called its fundamental longitudinal resonance frequency. In this state, the ends of the spring move toward and away from the center of the spring, and the center remains stationary. Therefore, if we repeat the above operation with the center of the spring fixed, the spring will vibrate at the frequency F ₀ in the same way.

The steel block 14 forming part of the printhead body can be considered a very stiff spring. Therefore, block 14 can be held in its center, such as by flange 34, when suitably mechanically stimulated, and its ends can be moved alternately toward and away from the center. Because the block is in a nodal plane, the flange 34 is not subject to substantial vibration and therefore the printhead support does not interfere with its movement. When the end face of the print head body 10 forming the fluid receiving tank 16 vibrates, the vibrations are transmitted to the fluid filament exiting the orifice 18, causing a substantially simultaneous uniform drip break. Note that tank 16 is small compared to the overall dimensions of block 14 and is centrally located on the end face of the block. Therefore, the tank 16 does not significantly impede the vibrations of the block 14 and has little effect on the resonant frequency of the print head.

It can be generally stated that the resonant frequency of block 14 is given by ₀ =C/2L=√2. However, C is the speed of sound in the material of the printing head block 14, L is the length of the printing head in the longitudinal direction,
E is the elastic modulus of the material forming the block 14, and ρ is the density of the material forming the block 14. Preferably, the print head is designed to operate at or near its resonant frequency, and this frequency is selected within a suitable fluid jet stimulation frequency range, such as 50 KHz to 100 KHz.

By providing a pair of piezoelectric transducers 36 and 38 on opposite sides of block 14, block 14 expands and contracts without bending vibrations, but if only one piezoelectric transducer were used. If you do, that won't happen. Additionally, the use of two piezoelectric transducers allows for higher power input into the print head for a given voltage, and thus higher maximum power input into the print head body, since the piezoelectric transducers This is because there is a limit to the voltage difference that can be applied to this without destroying it.

As is well known, since E and L are related to temperature, the resonant frequency of the print head changes with changes in temperature. At or near room temperature, the change in ₀ with respect to the temperature change in △T is △=△ ₀ k
ΔT/2, where k is approximately 4×10 ⁻⁴ /C ⁰ for stainless steel.

When dimensions a and b are small compared to L, the print head can be driven at an off-resonance frequency. Figure 5 shows the variation in drive voltage applied to the transducer required to drive a single jet print head for a constant nominal filament length of 4.19 x 10 ^-2 cm (16.5 x 10 ^-3 ''). In general, the nominal filament is a function of drive voltage and drive frequency. For any given drive frequency, the nominal filament length decreases with increasing drive voltage.

As can be seen from FIG. 5, at a resonant frequency of 83 kHz, the print head requires a drive voltage of approximately 20 volts peak. When driving with an oscillator at a frequency on either side of the resonant frequency, the filament length should be 4.19×10 ^-2 cm (16.5×
10 ^-3 ''). On either side of the resonant frequency, the required voltage increases approximately linearly with frequency. However, the voltage applied to the piezoelectric transducer There is a maximum voltage that can be applied, and as long as this maximum voltage is not exceeded, the transducer can be driven in the positive slope part of the curve in Figure 5 or in the negative slope part of the curve.Assuming that the resonant frequency remains constant. For example, such variations can be compensated for by changing the drive frequency synchronously with variations in the speed of the print receiving medium on which the drops from the print head are to be deposited. , the frequency of the drive signal is monitored and the voltage of the drive signal is adjusted appropriately to compensate for frequency deviations and maintain the desired fluid filament length.

If desired, additional piezoelectric transducers 44 can be utilized to monitor the frequency of the drive signal and the amplitude of the printhead vibrations. In Figure 6,
Approximately 2.54× with length of 4.19× ^10-2 cm (16.5× ^10-3 ″)
The voltage output at line 46 is plotted against the frequency of the drive signal to maintain a nominal fluid filament of a single jet printing head of 10 ^-3 cm (approximately 1 x 10 ^-3 '') diameter. Assuming no change in the jet's resonant frequency, line 4
6 and monitor the output voltage and frequency at the 6th
The desired length of the fluid filament can be maintained by adjusting the level of the drive signal required to maintain the output voltage on line 46 at the reference voltage level specified by the curve of the figure. can.

As will be appreciated, many modifications may be made to the disclosed printhead body without departing from the scope of the present invention. For example, flange 34 may be deleted. Other devices, such as support screws, may be provided for attaching the print head to a suitable support structure, provided that the attachment point lies substantially in a nodal plane intermediate the end faces of the print head body 10. do it.

Reference is now made to FIG. 7 illustrating a circuit providing an apparatus for providing electrical drive signals. The output of the fixed frequency oscillator 48 is connected to the voltage controlled attenuator circuit 5.
0, is supplied to converters 36 and 38 via a power amplifier 52 and a step-up transformer 54. The output from transducer 44 on line 46 is used to control the amount of attenuation provided by circuit 50. line 46
The signal at is amplified by an amplifier 56, converted to a DC signal by a converter 58, and compared with a selection reference signal by a summing circuit 60 to produce a signal on line 62, which signal is connected to the circuit. 50. With this feedback arrangement, the amplitude of the drive signal in line 42 and the amplitude of the mechanical vibrations of the print head are precisely controlled.

FIG. 8 is a side view illustrating a second configuration example of the present invention, in which elements corresponding to the printing head of FIG. 1 are given the same reference numerals. In this configuration, transducers 36 and 38 are oriented such that a positive drive signal on line 42 causes one transducer to extend and the other transducer to contract, and a negative drive signal to do the opposite. attached to the print head body. Therefore, the AC drive signal is on line 42.
The print head is caused to vibrate in its first bending mode. This mode of vibration is illustrated by intermediate line 64 in FIG.
This shows the range of movement of the center of printhead body 14, although the bending has been greatly exaggerated for clarity. It should be noted that line 64 intersects at a point approximately 0.23L inwardly from each end face of the printhead body, thus representing a nodal point. The mounting hole 66 is connected to the main body 1 at this node.
4 and a second corresponding pair of mounting holes are drilled on the opposite side of the printhead body.
The provision of a mounting pin extending into hole 66 provides a pivot support that does not impede bending movement of the print head.

This bending mode can be excited by driving the transducer at a frequency F ₀ =αCa/L ² , where α is about 1.76.
This formula is a simplified version of the following resonant frequency equation.

F ₀ =π9CK/8L ² where K is the radius of rotation and is equal to a/2 for the print head shown.

It will further be appreciated that this invention is not limited to the precise method and apparatus configurations disclosed, and that various changes may be made therein without departing from the scope of the invention. .

[Brief explanation of drawings]

FIG. 1 is an exploded view showing a first configuration of a fluid jet printing head according to the present invention. FIG. 2 is a plan view of the print head of FIG. 1 with the orifice plate removed. 3 is a side view of the printhead of FIG. 1 with electrical drive circuitry; FIG. Fourth
The figure is an enlarged partial cross-sectional view taken generally along line 4--4 of FIG. FIG. 5 is a diagram useful in explaining the operation of a printhead according to the invention.
FIG. 6 is a diagram useful in explaining the operation of a printhead according to the invention. FIG. 7 is a schematic diagram illustrating the drive circuitry for a fluid jet printing head. FIG. 8 is a side view of a second embodiment of a fluid jet printing head according to the present invention. In these drawings, 10 is an elongated printing head body, 12 is an orifice plate, 14 is a block,
16 is a fluid receiving tank, 18 is an orifice, 20
22 is a slot, 22 is a fluid supply opening, 24 is a fluid outlet opening, 30 is a fluid conduit, 32 is a conduit, 34 is a mounting flange, 36 and 38 are piezoelectric transducers, and 44 is a monitoring piezoelectric transducer. .

Claims (1)

[Scope of Claims] 1. A fluid jet printing head for generating a stream of at least one drop, comprising: (a) an elongated printing head body, the first of which;
the length between the end face and the second end face is substantially greater than other dimensions thereof, and the first end face includes a fluid receiving tank and at least one fluid receiving tank in communication with the fluid receiving tank. (b) a device for supplying fluid under pressure to said tank such that it exits said orifice and forms a fluid stream; (c) said body having two orifices; (d) a support device for engaging the print head body intermediate the first end surface and the second end surface; a transducer device that changes a longitudinal dimension of said body in response to an electrical drive signal, thereby causing mechanical vibration of said body and said transducer device extending a distance of said fluid flow; a fluid jet printing head comprising: a transducer device for breaking the fluid into a drip stream; 2. A fluid jet printing head according to claim 1, wherein said transducer device is adhered to both sides of said body and extends from a position near said first end surface to said second end surface. A fluid jet printing head consisting of a pair of piezoelectric transducers extending longitudinally to a nearby location. 3. A fluid jet printing head according to claim 2, wherein said pair of piezoelectric transducers provide alternating longitudinal expansion and contraction of said elongated printhead body. 4. A fluid jet printing head according to claim 3, wherein said transducer device further comprises:
A fluid jet printing head comprising a device for electrically connecting said pair of piezoelectric transducers in parallel. 5. A fluid jet printing head according to claim 4, wherein the pair of piezoelectric transducers are connected to expand and contract in phase. 6. A fluid jet printing head according to claim 5, wherein said support device is provided on said printing head body with said first end surface and said second end surface thereof.
engaged at a midpoint substantially equidistant from the end face;
Fluid jet printing head. 7. A fluid jet printing head according to claim 4, wherein the pair of piezoelectric transducers are connected to expand and contract out of phase, thereby preventing bending of the printing head body. A fluid jet printing head is being produced. 8. A fluid jet printing head according to claim 7, wherein said support device pivotally engages said printhead body at a bending node. 9. A fluid jet printing head according to claim 1, wherein said support device comprises a pair of relatively thin mounting flanges, each integrally formed with said printing head body; flanges extending from opposite sides of the elongate printhead body substantially equidistant from the first and second end faces of the body;
A fluid jet printing head, wherein said flange supports said body along a nodal plane. 10. A fluid jet printing head as claimed in claim 1, wherein said support device extends substantially equidistantly from said first and second end surfaces of said printing head body on opposite sides of said body. A fluid jet printing head comprising a pair of support screws engaging said body at points. 11. A fluid jet printing head according to claim 1, wherein the printing head body defines a slot at a first end face thereof;
and an orifice plate arrangement attached to said slot defining arrangement and forming therewith said fluid receiving tank. 12. A fluid jet printing head according to claim 11, wherein said orifice plate arrangement includes a plurality of orifices for producing a plurality of drip streams. 13. A fluid jet printing head according to claim 11, wherein said printing head further comprises a fluid outlet opening in communication with said slot. 14. The fluid jet printing head of claim 13, further comprising a fluid conduit connected to said fluid supply opening and said fluid outlet opening, said fluid conduit connected to said fluid supply opening and said fluid outlet opening. A fluid jet printing head, wherein the fluid jet printing head is constructed of a material exhibiting a vibrational impedance substantially different from that of the printing head body, such that the conduit does not introduce substantial power losses. 15. A fluid jet printing head according to claim 14, wherein said fluid conduit is made of a polymeric material. 16. The fluid jet printing head of claim 1 further comprising a monitoring transducer device attached to an exterior surface of said body for providing an electrical monitoring signal in response to dimensional changes in said body. Equipped with a fluid jet printing head. 17 In the fluid jet printing head according to claim 5, f ₀ =C/2L, where L is the longitudinal dimension of the body and C is the speed of sound in the body. further comprising means for applying an electrical drive signal of a frequency substantially equal to f ₀ to cause the fluid jet printing head to
A fluid jet printing head adapted to be driven at a frequency approximately equal to its mechanical resonant frequency. 18. A fluid jet printing head according to claim 1, including: a monitoring transducer device attached to an exterior surface of said body for providing an electrical monitoring signal in response to dimensional changes in said body; a fluid jet printing head, further comprising: a device responsive to the monitoring transducer device for applying an electrical drive signal to the transducer device with an amplitude dependent on the electrical monitoring signal. 19. A fluid jet printing head according to claim 7, where L is the longitudinal dimension of said body, C is the speed of sound in said body, and K is the radius of rotation of said body. A fluid jet printing head further comprising a device for applying an electrical drive signal of a frequency substantially equal to F ₀ , where F ₀ =9CK/8L ² .