JPH11227184A - Recording head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To record an image with high resolution by jetting micro ink drops. SOLUTION: The recording head 10 has a cantilever structure where a resilient member 12 is supported by a vibration generating means 16 at the base end part 14. When the means 16 is vibrated at a specified frequency, the resilient member 12 resonates to jet an ink drop from the vibratory plane in the vicinity of the forward end part 18 thus recording a dot on a recording sheet. Consequently, a high resolution image can be recorded with micro ink drops. The repeating period of driving signal being applied from a signal generating means 20 to the vibration generating means 16 is set equal to an integer times of the period of residual vibration of the means 16 (synchronized) thus suppressing the effect of residual vibration at the vibration generating means 16. According to the structure, period of driving signal can be shortened resulting in high speed image recording.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recording head for recording an image by discharging droplets such as ink droplets on a recording medium.

[0002]

2. Description of the Related Art A typical example of an ink jet recording system for performing printing by ejecting liquid droplets, particularly ink droplets, onto a recording medium is a system using a nozzle. Molds and continuous flow molds are known.

[0003] The on-demand type is a system in which ink is intermittently ejected from nozzles in accordance with recording information to perform printing, and typical types include a piezo oscillator type and a thermal type. The piezo vibrator type applies a pulse voltage to a piezoelectric element attached to the ink chamber to deform the piezoelectric element, thereby changing the ink liquid pressure in the ink chamber, and ejecting ink droplets from nozzles to form dots on recording paper. It is to be recorded. In the thermal type, ink is heated by a heating element provided in an ink chamber, and ink droplets are ejected from nozzles by bubbles generated thereby to record dots on recording paper.

On the other hand, in the continuous flow type, ink is continuously ejected from a nozzle by applying pressure to ink, and at the same time, vibration is applied by a piezo vibrator or the like to form a protruding ink column into droplets. The recording is carried out by selectively charging and deflecting.

However, recently, 600 times have been required for image recording.
High resolution such as up to 720 dpi (dot / inch) has been demanded. In order to satisfy such demands, it is necessary to reduce the dot diameter on the recording medium,
In the above-mentioned nozzle type recording method, it is necessary to reduce the diameter of the nozzle to reduce the diameter of the ink droplet ejected.

However, when the nozzle diameter is reduced,
Nozzle clogging due to dust or dust, nozzle clogging due to drying of the ink surface in the nozzle, and a change in the ink ejection direction due to such clogging are likely to occur, resulting in a defect in the image quality on the recording medium. Therefore, it is difficult to achieve a dot diameter corresponding to the required resolution by reducing the nozzle diameter.

Therefore, as a method of solving the problem caused by such a nozzle, a recording method in which ink droplets are ejected onto a print surface by using a vibration or an acoustic wave without using a nozzle, and printing is performed, Some have been proposed.

As a first recording method without using a nozzle, for example, as shown in US Pat. No. 4,308,547, a concave-curved piezoelectric body shell having a spherical shape is arranged in ink. There is a recording method in which a voltage is applied to a piezoelectric shell via an electrode. In this method, longitudinal waves radiated into the ink from the piezoelectric shell are collected at one point on the free ink surface, and ink droplets are ejected from the free ink surface.

Further, as shown in Japanese Patent Publication No. 6-45233, a spherical concave portion is provided on a substrate such as glass, which is used as an acoustic lens, and a piezoelectric body and a voltage There is also a recording method in which a vibrator composed of electrodes for applying a voltage is formed and the vibrator is arranged in ink.

Further, Japanese Patent Application Laid-Open No. 3-200199 discloses a recording system in which a thin-film flat plate-shaped phase Fresnel lens is provided on a substrate instead of a concave lens as an inexpensive and sharper focusing lens. It is shown.

In the above-described system in which a longitudinal wave is focused on the free ink surface and ink droplets are ejected from the free ink surface, the diameter of the ink droplet is substantially equal to the focused diameter of the longitudinal wave, and the focused diameter d is If the drive frequency of f is f and the F value of the lens is F, d to F / f. When the wavelength of the longitudinal wave propagating in the ink is λ and the propagation speed is v, there is a relation v = f · λ between these and the driving frequency f of the vibrator.

Therefore, for example, in a case where a very small ink droplet having a diameter (converging diameter) d of about 15 μm is to be ejected, if the F value of the lens is set to 1, the conventional low-viscosity and water-soluble Since the propagation velocity v of the longitudinal wave in the ink is approximately 1500 m / s, the driving frequency f of the vibrator must be set to a very high frequency such as about 100 MHz. Since it is practically difficult to make the F value of the lens extremely small due to various problems, the diameter d of the ink droplet
If one wishes to reduce, the vibrator must generally be driven at a higher frequency.

As described above, in the first recording method using no nozzle, a plurality of vibrators must be driven at a high frequency of about 100 MHz, which generally causes a cost problem that the driving means becomes expensive. At the same time, the ink viscosity changes due to heat generation and the drop diameter fluctuates,
There is a serious problem that the ink itself may be dried or solidified in the recording apparatus and the ink cannot be ejected.

As a second recording method that does not use a nozzle, there is a method in which the vibration generated by the vibration generating means is focused on one point on the free surface of the ink by an acoustic horn to discharge ink droplets.

For example, see the above-mentioned US Pat. No. 4,308,547.
In the specification, vibration is focused by an acoustic horn formed on vibration generating means instead of a concave lens, and the vibration is applied to an ink thin film conveyed on a belt in contact with the tip of the acoustic horn. It is shown that ink droplets are ejected. Here, a discharge force is generated at the tip of the acoustic horn.

A similar prior art is disclosed in Japanese Unexamined Patent Publication No.
Japanese Patent Application Publication No. 168050 discloses a recording device 83 in which a sound collector 80 is provided on a vibration generating means 82 as shown in FIG. The vibration generating means 82 is formed of a piezoelectric body 84 and electrodes 86 a and 86 b for applying a voltage to the piezoelectric body 84, and is disposed in an ink reservoir 90 holding an ink 88 together with the sound collector 80. As shown in FIG. 14, the sound collector 80 submerged in the ink 88 is provided with a tapered tip toward the ink free surface 92.

Here, from the vibration generating means 82 to the sound collector 80
When the vibration is incident on the bottom of the sound collector 80, its amplitude is amplified as it propagates through the sound collector 80, and the large-amplitude wave collected by the sound collector 80 hits the ink 88 and is generated there. The longitudinal wave pushes up the free ink surface 92, and the ink droplet 94 is ejected.

However, in US Pat. No. 4,308,547 and JP-A-4-168050, a sound collector or an acoustic horn is used, but its size, driving conditions, vibration mode, etc. are further reduced. It is not stated whether ink droplets can be formed.

Regarding the acoustic horn, generally in the field of acoustics, a sound collector (or acoustic horn) is generated by resonance.
When trying to obtain the ink droplet ejection force by vibrating so that the amplitude of the tip of the sound collector increases, the length (height) of the sound collector in the vertical section direction is an integral multiple of 1/2 of the wavelength of the vibration wave. It is known that it must be.

Therefore, in the conventional method as shown in FIG. 14, if the sound collector 80 is to be made smaller in order to produce a high-density recording element, the wavelength of the vibration wave must be shortened. The driving frequency of the generating means 82 must be increased.

Therefore, in order to manufacture a recording element having a realistic density, it is necessary to drive the vibration generating means at a high frequency of several tens MHz to about 100 MHz, as in the above-described first recording method using no nozzle. There is. For this reason, while the energy attenuation in ink is large,
The drive circuit becomes expensive. Also, U.S. Pat.
As disclosed in Japanese Patent No. 8547, it is practically difficult to stably transport an ink thin film using a belt in contact with the tip of an acoustic horn, and the diameter of an ink droplet to be ejected tends to vary.

Further, as a third recording method using no nozzle, there is a so-called electrostatic suction method using electrostatic force as a discharge force, and a method using vibration to form an ink meniscus (ink bulge) is also known. Are known.

For example, Japanese Patent Application Laid-Open No. 92-222853 discloses that a recording needle is made to protrude from the surface of ink to give ultrasonic energy that propagates in the axial direction. According to this, an ultrasonic stream (acoustic streamin)
g) Due to the phenomenon, the ink in contact with the recording needle moves toward the tip of the recording needle, and a convex ink meniscus is formed at the tip of the recording needle. In this state, an electrostatic field is applied between the recording needle and the back electrode to tear off the ink, and the ink droplet lands on the recording medium disposed between the recording needle and the back electrode. According to this method, since an ink meniscus is formed at the tip of a recording needle, smaller ink droplets can be formed as compared with the conventional electrostatic suction method.

However, in the electrostatic suction method, there is a problem that the diameter of the formed drop varies due to a variation in the thickness of the dielectric of the recording medium due to humidity or a variation in the roughness of the surface of the recording medium. Furthermore, in the electrostatic suction method, a problem arises in that, by discharging charged ink droplets, dot position variation is increased due to residual charges of preceding dots on a recording medium.

As a prior art other than the above, Japanese Patent Application Laid-Open No.
Japanese Patent No. 40070 discloses a new on-demand type recording method. This is to resonate a beam of cantilever structure by bending vibration, generate sufficient amplitude at the tip of the beam and fly ink, and it is possible to eject ink at a relatively low excitation frequency and low voltage. This is a recording method that has characteristics. However, this recording method uses a mechanism that forms ink droplets through nozzles provided at the tip of the beam, and the diameter of ink droplets is determined by the nozzle diameter, as in the various nozzle-type recording methods described above. When the diameter is reduced, there is a problem that a change in the ink ejection direction occurs due to nozzle clogging and adhesion of ink residue to the nozzle circumference. The technique disclosed in Japanese Patent Application Laid-Open No. 6-340070 is one of the technical problems to be solved to reduce the possibility of nozzle clogging as compared with the conventional method. Because it is determined by the nozzle diameter, it cannot be a fundamental solution.

As yet another prior art, a method of forming fine particles of a liquid by applying vibration energy, which is not an ink jet recording method, is disclosed in Japanese Patent Application Laid-Open No. 3-154665.
No., published in Japanese Patent Application Publication No. This method is intended to be applied to an atomizing device, and includes a vibrator including a piezoelectric ceramic,
The vibrating part is fixed to the vibrator and bends and vibrates in the form of a cantilever. A part of the vibrating part is immersed in a liquid, and mist-like liquid droplets are generated by radiation of ultrasonic waves. However, with the technology used in this atomizing device, although it is possible to generate minute diameter ink droplets without using a nozzle,
Since a large number of ink droplets that are not controlled temporally and spatially are generated, the method cannot be applied to an ink jet recording head that needs to accurately land ink droplets at a predetermined position on a recording medium.

[0027]

As described above, in recent years, high-resolution image recording on a recording medium has been increasingly required. However, any conventional recording method or technology in another field such as an atomizing apparatus is used. However, it is difficult to meet these demands. At the same time, there is a strong demand for faster image recording.

The present invention has been made in order to solve the above problems.
It is an object of the present invention to provide a recording head capable of discharging minute ink droplets without using a nozzle and capable of recording a high-resolution image at a high speed.

[0029]

According to a first aspect of the present invention, there is provided a vibration generating means which vibrates according to image information, and a cantilever structure which vibrates according to the vibration of the vibration generating means. An elastic member that is in contact with the ink, wherein the vibration generating means sets an interval from the end of the main vibration for causing ink droplets to fly from the ink thin film formed on the surface of the elastic member to the start of the next main vibration. , Characterized by being an integral multiple of the period of the residual vibration continued after the main vibration.

The operation of the present invention will be described. The elastic member vibrates due to the excitation (main vibration) of the vibration generating means corresponding to the image information. Due to the vibration of the elastic member, ink droplets fly from the ink thin film formed on the elastic member. As described above, since fine ink droplets can be generated without using a nozzle, ink droplets can be stably fly without clogging. As a result, high-resolution image recording becomes possible.

At this time, the vibration generating means repeats the main vibration at intervals of an integral multiple of the period of the residual vibration. In other words, in order to synchronize the interval between the end of one main vibration and the start of the next main vibration and the period of the residual vibration, even if the main vibration is started while the residual vibration is continuing, The vibration state of the means is stabilized. Therefore, the interval between the main vibrations can be reduced,
High-speed image recording can be achieved.

According to a second aspect of the present invention, there is provided a vibration generating means which vibrates according to image information, and a cantilever structure which vibrates according to the vibration of the vibration generating means, and is in contact with the ink. An elastic member, wherein the vibration generating means repeats main vibration for causing ink droplets to fly from an ink thin film formed on the surface of the elastic member at a cycle that is an integral multiple of the cycle of the main vibration.

The operation of the present invention will be described. The elastic member vibrates due to the excitation (main vibration) of the vibration generating means corresponding to the image information. Due to the vibration of the elastic member, ink droplets fly from the ink thin film formed on the elastic member. As described above, since fine ink droplets can be generated without using a nozzle, ink droplets can be stably fly without clogging. As a result, high-resolution image recording becomes possible.

At this time, the vibration generating means repeats the main vibration at a period that is an integral multiple of the period of the main vibration. That is, since the cycle of repeating the main vibration and the cycle of the main vibration are synchronized, even if the main vibration is started while the remaining vibration is continuing, the vibration state of the vibration generating means is stabilized. Therefore, the interval between the main vibrations can be reduced,
High-speed image recording can be achieved.

[0035]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment A recording head according to a first embodiment of the present invention will be described with reference to FIGS.

First, a brief description of the recording head according to this embodiment will be given. FIG. 1 and FIG. 2 are a side view and a front view of the recording head 10. FIG. 2 does not show the ink chamber walls 30a and 30b shown in FIG. 1 for easy understanding.

The recording head 10 has a cantilever structure in which the elastic member 12 is supported by the vibration generating means 16 at the base end 14 and the tip 18 is a free end. Vibration generating means 16
Is excited based on a drive signal from the signal generating means 44, and the excitation causes the elastic member 12 to resonate. On this occasion,
The ink 22 supplied to the ink chamber 20 from an ink supply source (not shown) reaches the elastic member 12 to the distal end portion 18 by surface tension. Therefore, the ink droplet 48 flies from the thin film of the ink 22 formed in the vicinity of the distal end portion 18 due to the bending vibration of the elastic member 12, and the dot is recorded on the recording paper as the recording medium.

Next, each member constituting the recording head 10 will be described in detail. When viewed from the front, the elastic member 12 has a tapered substantially triangular shape in the vicinity of the distal end portion 18,
When viewed from the side, the plate has a uniform thickness. Elastic member 12
Has a cantilever structure in which the base end portion 14 is sandwiched and fixed between the ceramic substrates 24a and 24b. Therefore, when bending vibration is performed by excitation of the vibration generating means 16, the distal end portion 18 which is a free end is It will have the largest amplitude.
Further, a part of the elastic member 12 is configured to contact the ink 22 held in the ink chamber 20.

The elastic member 12 may be a member capable of converting the vibration of the vibration generating means 16 into bending vibration and generating a sufficient amplitude near the tip 18 for ink droplet ejection. Although not particularly limited, metal materials such as SUS and Ni, inorganic materials such as SiO ₂ and Al ₂ O ₃ , polyimide resins, PET (polyethylene terephthalate), epoxy resins, cyanoacrylate resins, etc. Are preferred.

For the purpose of protecting the elastic member 12 from deterioration, corrosion, adhesion of foreign substances, etc., it is not possible to coat the surface with a metal such as gold, platinum, palladium, rhodium and a thin film such as PTFE (polytetrafluoroethylene). It is effective.

The vibration generating means 16 is composed of a piezoelectric ceramic thin film 26 made of PZT (lead zirconate titanate) and electrodes 28a and 28b for applying a voltage thereto. The vibration generating means 16 includes ceramic substrates 24a, 24
b is fixed to a lower surface (the opposite side to the ink chamber 20 side) (hereinafter referred to as a lower surface), and is in contact with the base end portion 14 of the elastic member 12. The piezoelectric ceramic thin film 26 made of PZT is subjected to a polarization process, and vibrates in a direction perpendicular to the lower surfaces of the ceramic substrates 24a and 24b when a voltage is applied between the electrodes 28a and 28b.

Further, the piezoelectric ceramic thin film 2 of the present embodiment
6, PZT was selected as the piezoelectric material, but other materials such as quartz, barium titanate BaTiO ₃ , lead niobate PbNb ₂ O ₆ , bismuth germanate Bi ₁₂ GeO ₂₀ , lithium niobate LiNbO ₃ , lithium tantalate LiTaO _3, etc. Polycrystalline or single crystal, or piezoelectric thin film such as ZnO or AlN, or polyurea, PVDF
A piezoelectric polymer such as (polyvinylidene fluoride) or a copolymer of PVDF, or a composite of an inorganic piezoelectric substance such as PZT and a piezoelectric polymer can also be used. Of course, when designing the recording head, it is necessary to select an optimum piezoelectric material according to the driving frequency. For example, if the applied AC frequency is between several tens kHz to 1 MHz, PZT
When driving at a higher frequency, a piezoelectric thin film corresponding to a high frequency, such as ZnO, is selected. In any case, it is necessary to have a vibration characteristic that is stable and exhibits sufficient vibration. The elastic member 12 is made of the piezoelectric material itself constituting the vibration generating means 16.
May be formed.

The vibration generating means 16 is not limited to a piezoelectric material, but may be any as long as it generates vibration in accordance with an electric signal input from the signal generating means 44 which has received image information. Actuators, actuators applying electrostatic force, and the like are applicable.

The ink chamber 20 includes a ceramic substrate 24a,
Ink chamber wall 3 made of ceramic material on 24b
0a, 30b, a partition wall 42, and a top plate 32. The ink 22 is supplied to the ink chamber 20 from an ink supply source (not shown) through an ink supply path 34. At this time, physical properties such as surface tension and viscosity of the ink 22 are set so that the tip end 18 of the elastic member 12 is wetted by the ink 22.
Alternatively, the wettability of the elastic member 12 is adjusted. The hole formed by the ink chamber wall 30a, the partition wall 42, and the top plate 32 becomes the ink droplet ejection port 36.

The lower part of each ink chamber 20 (the ceramic substrate 2)
4a and 24b), each elastic member 12 is provided with a corresponding vibration generating means 16. The piezoelectric ceramic thin films 26 in the vibration generating means 16 may be individually formed and driven, but in the present embodiment, they are shared as shown in FIG. In the case where the electrodes are shared, an insulating member 38 is provided between the electrodes 28a for insulation, and
The piezoelectric ceramic thin film 26 is fixed by the support substrate 40 made of an aluminum plate so that the vibration generated by any of the vibration generating means 16 does not excite the elastic member 12 on the other vibration generating means 16. Is desirable. Each ink chamber 20 is separated by a partition wall 42 so that the vibration of the ink liquid level by the elastic member 12 does not affect the ink liquid level of the adjacent ink chamber 20.

Ceramic substrate 2 constituting ink chamber 20
4a, 24b, ink chamber walls 30a, 30b, top plate 32,
The partition walls 42 are desirably made of the same ceramic material, and may be formed by any method of integrally molding or individually forming and then bonding. Further, a plastic substrate may be used instead of the ceramic substrate.

Next, the operation of the recording head 10 will be described with reference to FIG.
This will be described with reference to FIG. FIG. 3 is a side view showing a state of the elastic member 12 when the vibration is generated by the vibration generating means 16. FIG. 4 is an enlarged side view of the distal end portion 18 of the elastic member 12 undergoing bending vibration.

First, an image signal is input to the signal generating means 44 one pixel at a time. As a result, a drive signal having an alternating voltage waveform having a drive frequency f is applied from the signal generation means 44 to the vibration generation means 16, and the drive signal
Is excited.

Here, the drive frequency f may be any value, but it is preferable to drive at the resonance frequency f _O of the vibration generating means 16 or a frequency f that is an integral multiple of the resonance frequency f _O, because vibration can be efficiently performed. Here, the resonance frequency f _O is a ceramic substrate 24a, 24b of the rigid, the thickness of the piezoelectric ceramic thin film 26 is determined from the piezoelectric characteristics.

The excitation of the vibration generating means 16 is performed every time the number of excitations required for the flight of one ink droplet is completed so that the flying of one ink droplet is realized according to the drive signal input from the signal generating means 44. It intermittently separates the excitation.

That is, when the vibration generating means 16 is excited,
A drive signal (see FIG. 8A) in which at least one waveform having one excitation cycle is connected is used, and a burst wave is used in which these are intermittently applied according to an image signal. However, the burst wave is not limited to the illustrated sine wave, and may be a rectangular wave, a triangular wave, or the like.

The energy for ejecting the ink droplets 48 is determined by the number of waveforms (the number of bursts) of which one cycle is the excitation cycle of the vibration generating means 16 and the applied voltage. The voltage value V of the alternating voltage applied to the vibration generating means 16 and the number of burst waves are determined by conditions such as the viscosity of the ink used and the thickness of the ink thin film (hereinafter referred to as ink liquid thickness) t (see FIG. 4). .

When the vibration generating means 16 is excited in this manner, the elastic member 12 resonates and the ceramic substrate 2
Bending vibration is performed in the direction of arrow A (refer to FIG. 3, hereinafter referred to as A direction) around the base end portion 14 sandwiched between 4a and 24b.

Here, the elastic member 12 has a unique resonance frequency f _e determined by its rigidity, size, manner of contact with ink, and the like. Therefore, the unique resonance frequency f _e
Alternatively, the rigidity of the elastic member 12 is set so that the value of the integral multiple of this value matches the drive frequency f that excites the vibration generating means 16.
If you adjust the size, how to contact the ink, etc.,
The elastic member 12 can be efficiently bent and vibrated.

As described above, the elastic member 12 bends and vibrates, whereby a plane perpendicular to the vibration direction of the distal end portion 18 (hereinafter, referred to as a plane).
When the thickness t of the ink liquid in the vibration surface 45 is within a predetermined range (several μm to several hundred μm), a capillary wave 46 is generated on the ink surface (see FIG. 4). The ink 22 is, for example, a black aqueous ink having a viscosity of 2 mPa · s. The ink liquid thickness t can be adjusted by controlling the shape of the tip 18 of the elastic member 12, the liquid level of the ink 22 in the ink chamber 20, the wettability of the tip 18 with the ink 22, and the like.

The state where the capillary wave 46 is generated is shown in FIGS.
This will be described with reference to FIG. FIG. 5 is an enlarged front view of the vicinity of the distal end portion 18 of the elastic member 12, and FIGS.
FIG. 3 is a sectional view taken along line XX of FIG.

The capillary wave 46 is generated in a direction perpendicular to the bending vibration direction of the elastic member 12 (arrow B direction, hereinafter referred to as B direction). At a certain time t, FIG.
As shown in (2), two peaks of the capillary wave 46 are generated such that the wavelength λ is W = 2λ with respect to the width W of the elastic member 12 in the B direction. At time t + Δt after the elapse of the minute time Δt, as shown in FIG. 7, one peak of the ink ridge is formed between the two peaks of the capillary wave 46, and this is separated and one ink droplet flies.

As the vibration generating means 16 repeatedly excites, the ink droplets 48 fly continuously from the elastic member 12 one by one.

As described above, in order to cause the ink droplets 48 to fly stably one by one, the width of the elastic member 12 on the vibration surface 45 near the distal end portion 18 of the elastic member 12 is set to W.
When the value calculated by the following equation is λ, the tip 1
It is desirable that the width W of at least a portion near 8 is approximately 2λ.

Λ = [8πσ / (ρf _e ² )] ^1/3 × 10 ⁴ (μm) (1) where σ is the ink surface tension (mN / m) and ρ is the ink density ( g / cm ³ ) f _e is the excitation frequency (Hz) The above equation (1) is described in general reference books, for example, Chiba Chika, “Ultrasonic Spraying” (Sankaido), Chapter 7, Section 2 It is described as an equation giving the wavelength.

The width W is preferably as close as possible to the value of 2λ, and is preferably in the range of 1.2λ to 2.4λ. The minute ink droplet 48 generated in this manner is moved in a direction perpendicular to the vibration surface 45 from the ink flying point P near the distal end portion 18 of the elastic member 12 by a driving signal having an appropriate waveform input to the vibration generating means 16. Flies stably and records dots on recording paper.

The vibration surface 45 near the tip 18
Is less than about 1λ, it is difficult for capillary waves to be generated in the thin film of the ink 22, and ink droplets do not fly unless the excitation voltage of the vibration generating means 16 is increased or the number of bursts is increased. Further, even when the ink droplet is caused to fly, the ink droplet does not fly stably.

Also, when the width W of the vibrating surface 45 is about 3λ or more, a capillary wave is hardly generated. As above,
Capillary waves can be generated by increasing the excitation voltage of the vibration generating means 16 or increasing the number of bursts. In this case, three or more peaks of the capillary waves are generated, and a plurality of ink droplets fly. become,
It is difficult to stably fly one ink droplet.

As described above, the recording head 10 in which the vibration generating means 16 is excited by the drive signal input from the signal generating means 44 to bend and vibrate the elastic member 12 has the tip 1
The ink droplets 48 are stably fly one by one onto the recording paper from the vibrating surface 45 near the width W = 2λ near 8.

As described above, in the recording head 10, by sufficiently increasing the amplitude of the distal end portion 18 of the elastic member 12, the ink bulge of the capillary wave 46 flies as an ink droplet 48. The diameter of the ink drop 48 is typically about 2
0 μm.

In the recording head 10, since the tip 18 is caused to fly only in one direction (toward the ink droplet discharge port 36), the ink liquid thickness t on the non-flying side (toward the ink chamber wall 30b) is increased. To suppress the generation of capillary waves. As a method of increasing the ink liquid thickness t, the wettability of the ink on the ink chamber wall 30b may be controlled,
A convex portion may be provided on the side wall surface of the ink chamber 20 of the ink chamber wall 30b to regulate the liquid level of the ink.

As another method for causing the ink droplet 48 to fly in only one direction, a configuration in which the ink 22 is not supplied at all to the tip portion 18 on the non-flying side can be considered.

Further, in order to limit the region where the capillary wave 46 is generated on the vibrating surface 45, the shape of the tip portion 18 is a sharp triangular shape as shown in FIG. The configuration was such that the droplet 48 was ejected.

The recording head 10 thus configured is
After the ink droplets 48 fly from the elastic member 12, residual vibrations having substantially the same cycle as the drive frequency f are generated in the vibration generating means 16. The time until the next drive signal is input (hereinafter,
If the stop time does not become an integral multiple of the cycle of the residual vibration (the drive signal and the residual vibration are not synchronized), the vibration of the elastic member 12 that bends and vibrates due to the excitation of the vibration generating means 16 becomes unstable, Drop flight is likely to be unstable.

Therefore, in this embodiment, the signal generating means 4
4 stabilizes the vibration of the elastic member 12 by applying a drive signal to the vibration generating means 16 after an integral multiple of the period of the residual vibration (synchronizes the drive signal with the residual vibration).
As a result, the ink droplets 48 can be made to fly at short intervals, thereby enabling high-speed image recording.

The operation for speeding up image recording will be described in detail below. First, the effect of residual vibration when a normal drive signal is applied from the signal generating means 44 to the vibration generating means 16 will be described.

FIG. 8A shows an alternating voltage waveform of the drive signal. In the present embodiment, the driving frequency f and the applied voltage V
A sinusoidal alternating voltage of 1 (highest and lowest amplitude) is applied as a burst wave to the vibration generating means 16 for an application time t1 to excite. In other words, this means that a sinusoidal alternating voltage having the driving frequency f is applied for 5 bursts.

The application of the driving signal (alternating voltage) is stopped after the ink droplets 48 have been ejected, and after the elapse of the stop time t2, the driving signal (alternating voltage) is applied again to eject the next ink droplets 48. Let it. That is, the ink is repeatedly applied in the ejection period T (t1 + t2) of the ink droplet.

FIG. 8B shows a vibration state of the vibration generating means 16 to which such a drive signal is applied. This is because the vibration of the elastic member 12 does not stop immediately even when the application of the drive signal (alternating voltage) stops, so that the residual vibration continues during the decay time t3. A drive signal (alternating voltage) for ejecting the next ink droplet is applied before the residual vibration stops (t2 <t3).
This causes problems such as variations in the size of ink droplets, ejection of a plurality of ink droplets, and non-ejection of ink droplets. Therefore, it is necessary to wait for the application of a drive signal (alternating voltage) for discharging the next ink droplet until the residual vibration naturally attenuates and returns to the initial state once (t2 ≧ t3). In this case, the ejection frequency for ejecting ink droplets is at most several kilohertz.
It is about z.

In order to reduce the influence of the residual vibration, the signal generation means 44 oscillates the next drive signal after an integral multiple (n · Tr) of the period Tr of the residual vibration after terminating the application of the drive signal. It is applied to the generating means 16 (the drive signal and the residual vibration are synchronized) (see FIG. 9A). Here, a new drive signal is applied to the vibration generating means 16 while the residual vibration is continuing because the stop time t2 = n · Tr <t3 is set.

In this case, the stop time t2 is a time that is an integral multiple of the cycle Tr of the residual vibration. That is, since the drive signal and the residual vibration are synchronized, the influence of the residual vibration is reduced,
As shown in FIG. 9B, the drive signal is
, The vibration generating means 16 instantaneously enters a stable vibration state.

The period Tr of the residual vibration is determined by the elastic member 12
Although it is preset in the signal generator 44 based on the physical properties of the ink 22 and the drive frequency f of the drive signal, the detection may be performed by providing a detector.

As described above, even if the stop time t2 from the end of application of the drive signal to the start of application of the next drive signal is shorter than the decay time t3 of the residual vibration (t2 <t3), stable ink droplets are obtained. Is guaranteed, so that the ejection cycle T can be shortened. Therefore, the speed of image recording can be increased. [First Embodiment] A first embodiment will be described. The configuration of the recording head is the same as in the first embodiment.

Here, only the effect of increasing the speed of image recording (reducing the effect of residual vibration) will be described with reference to FIGS. First, the present embodiment will be described, and then a comparative example will be described.

As shown in FIG. 9A, the drive signal of this embodiment has a drive frequency f = 192 kHz and an applied voltage V1 =
A sinusoidal alternating voltage of 35 V _pp (maximum and minimum amplitudes) is applied as a burst wave to the vibration generating means 16 for an application time t1 = 26 μsec. The stop time t2 is
The period of the residual vibration Tr = 26 μsec, which is five times the 5.2 μsec.

FIG. 9B shows a vibration waveform of the vibration generating means 16 to which such a driving signal is applied from the signal generating means 44.
Shown in As described above, the vibration generating unit 16 receives the new drive signal during the residual vibration, but the stop time t2 (<t3).
Is an integral multiple of the cycle Tr of the residual vibration (the drive signal and the residual vibration are synchronized), so that a normal vibration state (vibration waveform) is instantaneously obtained. As a result, the discharge cycle T (t1 +
At t2) = 52 μs, the ink droplet stably flies, and high-resolution image recording was performed. In addition, the ejection frequency for ejecting ink droplets has been increased to about 20 kHz.

Next, a comparative example will be described. The drive signals of the comparative example are all the same as the drive signal of the present embodiment except for the stop time t2.

The stop time t2 of the drive signal is 12.5 μsec, which is about 2.4 times the period Tr of the residual vibration. That is, since the stop time t2 is not an integral multiple of the cycle Tr of the residual vibration, the applied drive signal and the cycle of the residual vibration are not synchronized. As a result, the vibration based on the drive signal is easily affected by the residual vibration, and unless the application time t1 of the drive signal (alternating voltage) is extended, it is impossible to discharge ink droplets in the flying direction in a stable manner.

Therefore, when image recording is performed with the stop time t2 of the drive signal not being an integral multiple of the period Tr of the residual vibration (the drive signal and the residual vibration are not synchronized),
Due to the influence of residual vibration, the discharge frequency could be increased only up to about 3 kHz.

As described above, the drive signal is transmitted to the vibration generating means 16.
After the ink droplets are ejected to discharge the ink droplets, the stop time t2 until the next drive signal is input is set to an integral multiple of the period Tr of the residual vibration (the drive signal and the residual vibration are synchronized). It was confirmed that the recording speed was increased. [Second Embodiment] A recording head according to a second embodiment of the present invention will be described. The basic configuration and operation of the recording head according to the present embodiment are the same as those of the first embodiment, and thus description thereof will be omitted, and only the speeding up of image recording will be described with reference to FIGS. In this case, the same components as those in the first embodiment are denoted by the same reference numerals,
A detailed description thereof will be omitted.

FIG. 10 shows an alternating voltage waveform of the drive signal.
In the present embodiment, the driving frequency f, the applied voltage V1
A (sinusoidal) alternating voltage having the highest and lowest amplitudes is applied as a burst wave to the vibration generating means 16 for an application time t1 to excite. That is, a sinusoidal alternating voltage having the driving frequency f is applied for 10 bursts.

The application of the driving signal (alternating voltage) is stopped after the ink droplets 48 are ejected, and after the elapse of the stop time t2, the driving signal (alternating voltage) is applied again to eject the next ink droplets 48. Let it. That is, the discharge cycle T (t1 +
It is repeatedly applied at t2).

Here, the ejection cycle T and the cycle T _{v of the} drive signal (alternating voltage) are set so that T = n · T _v (n is an integer). This is to reduce the influence of residual vibration by synchronizing the next ejection cycle with the cycle of the drive signal in consideration of the phase shift between the cycle of the drive signal and the cycle of the ejection cycle in the vibration generating means 16. is there.

Even after the application of the drive signal is completed, the vibration generation means 16 continues the residual vibration having substantially the same cycle as the cycle of the drive signal. Here, by inputting the drive signal while synchronizing the cycle of the drive signal and the ejection cycle, even if the vibration generating means 16 is in the residual vibration, the vibration is instantaneously brought into the normal vibration state (see FIG. 11). The droplet flies stably and a high-resolution image is recorded. As described above, since the next drive signal can be applied even when the residual vibration is attenuated, the speed of image recording can be increased.

[0090] Thus, by setting the period T of the ejection frequency to an integral multiple of the period T _v of the driving signal (AC voltage), the vibration of the vibration generating means 16 by application of the driving signal affected by the residual vibration It was confirmed that the possibility of high-speed printing was higher than before. [Second Embodiment] A second embodiment will be described. The configuration of the recording head is the same as in the second embodiment.

Here, only the effect of increasing the speed of image recording (reducing the effect of residual vibration) will be described with reference to FIGS. First, the present embodiment will be described, and then a comparative example will be described.

As shown in FIG. 10, the drive signal of this embodiment has a drive frequency f = 325 kHz and an applied voltage V1 = 40.
Vibration generating means 1 with a sinusoidal alternating voltage of V _pp (highest and lowest amplitude) as a burst wave for an application time t1 = 31 μsec.
6 is applied. Note that the driving signal cycle T _v =
3.1 μs.

The ejection cycle T is the cycle of the drive signal T _v =
It is 46.5 μsec which is 15 times 3.1 μsec.

FIG. 11 shows a vibration waveform of the vibration generating means 16 to which such a drive signal is applied. Vibration generating means 16 thus is a new drive signal during the remaining vibration is applied, since the stop time t2 (<t3) is taken period T _v and synchronization of the drive signal, the ink droplet instantaneously It becomes a normal vibration state for discharging. As a result, the discharge cycle T (t1 +
At t2) = 46.5 μsec, the ink droplet stably flies, and high-resolution image recording was performed. As a result, the ejection frequency for ejecting ink droplets was increased to about 20 kHz.

Next, a comparative example will be described. The drive signals of the comparative example are all the same as the drive signals of the embodiment except for the ejection period T.

The discharge cycle T is about 1 of the drive signal cycle _Tv .
It is 7.6 times, 54.6 μsec. That is, the discharge cycle T
Is not an integral multiple of the cycle T _v of the drive signal (the ejection cycle T and the cycle T _{v of the} drive signal are not synchronized), the vibration based on the drive signal is easily affected by the residual vibration, and the application time of the alternating voltage If the length of the ink droplet was not long, it was not possible to discharge a stable ink droplet in the flight direction.

[0097] Therefore, when the ejection cycle T is an integral multiple of without the relationship of the period T _v of the drive signal (period T _v of the ejection cycle T and the drive signal synchronizes without taken) images were recorded, the remaining Under the influence of vibration, the discharge frequency could be increased only up to a few kHz.

As described above, the drive signal is transmitted to the vibration generating means 16.
The ejection cycle T to be applied to an integral multiple of the period T _v of the drive signal in (period T _v of the ejection cycle T and the driving signal is synchronized)
It was confirmed that the speed of image recording was increased. [Third Embodiment] Next, a recording apparatus provided with the recording head described in the first and second embodiments will be described. The same components as those in the first and second embodiments are denoted by the same reference numerals, and detailed description thereof will be omitted.

First, an array head which is a main part of the recording apparatus will be described. FIG. 12 is a perspective view of the array head.

The array head 50 includes recording heads 52a to 52d vertically stacked in four stages, and an ink supply unit 5 attached to the back of the recording heads 52a to 52d.
4a to 54d. Recording head units 52a-5
The support substrate 40 is provided between 2d and between the ink supply units 54a to 54d. Each of the recording head units 52a to 52d has an ink supply unit 54a to 54d.
d, black, yellow, magenta, and cyan inks 22 stored one by one are supplied, and ink droplets 48 of a predetermined color fly from the ink droplet ejection ports 36 based on the operation described in the first embodiment. . FIG. 13 shows a recording apparatus 60 on which the recording head 10 of the first embodiment is installed. In the recording device 60, the array head 50 shown in FIG. 12 is fixed to the carriage 62 and connected to the ink cartridge 64. The ink cartridge 64 holds four color inks 22 of black, yellow, magenta, and cyan. The carriage 62 reciprocates while being guided by the guide 66. The recording paper 68 is wound around a roller 70, and an image is recorded over the entire surface of the recording paper 68 by the rotation of the roller 70 and the movement of the carriage 62.

In this case, in the recording apparatus 60, the array head 50 is moved in the paper width direction by the carriage 62, and the ink drops from the recording heads of the first and second embodiments stably fly onto the recording paper 68. Image recording of resolution can be performed.

[0102]

As described above, according to the present invention, fine droplets can be ejected without using a nozzle, so that a problem such as clogging of a nozzle does not occur and the height of an image can be improved. The requirement for higher resolution can be satisfied. further,
By synchronizing the driving frequency of the vibration generating means with the frequency of the residual vibration generated on the vibration generating means, the influence of the residual vibration on the vibration waveform at the start of image recording can be reduced, so that the ejection cycle can be shortened, High-speed recording is possible.

[Brief description of the drawings]

FIG. 1 is a side view of a recording head according to a first embodiment of the present invention.

FIG. 2 is a front view of the recording head according to the first embodiment of the present invention.

FIG. 3 is a side view illustrating a state in which an elastic member is vibrated by a vibration generating unit of the recording head according to the first embodiment of the present invention.

FIG. 4 is an enlarged view of a side surface when the elastic member according to the first embodiment of the present invention is bending and vibrating.

FIG. 5 is an enlarged front view of the vicinity of the distal end of the elastic member according to the first embodiment of the present invention.

FIG. 6 is a view showing a state of a capillary wave, taken along line XX in FIG. 5;
It is a line sectional view.

FIG. 7 is a view showing a state of a capillary wave, taken along line XX in FIG. 5;
It is a line sectional view.

8A is a diagram showing an alternating voltage waveform of a drive signal applied from the signal generation unit to the vibration generation unit according to the first embodiment of the present invention, and FIG. FIG. 4 is a diagram illustrating a vibration state in which a unit vibrates based on the drive signal.

9A is a diagram illustrating an alternating voltage waveform of a drive signal applied from the signal generation unit to the vibration generation unit according to the first embodiment of the present invention, and FIG. FIG. 4 is a diagram illustrating a vibration state in which a unit vibrates based on the drive signal.

FIG. 10 is a diagram showing an alternating voltage waveform of a drive signal applied from a signal generation unit to a vibration generation unit according to a second embodiment of the present invention.

FIG. 11 is a diagram illustrating a vibration state of the vibration generation unit according to the second embodiment of the present invention, which is caused by the drive signal.

FIG. 12 is a perspective view showing an array head of a printing apparatus provided with a print head according to a third embodiment of the present invention.

FIG. 13 is a perspective view showing a recording apparatus according to a third embodiment of the present invention.

FIG. 14 is a diagram illustrating a recording apparatus without a nozzle according to a conventional example.

[Explanation of symbols]

 Reference Signs List 10 recording head 12 elastic member 16 vibration generating means 22 ink 48 ink droplet

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yasushi Suwabe 430 Nakaicho Sakai, Ashigara-gun, Kanagawa Green Tech Nakai Inside Fuji Xerox Co., Ltd. Inside

Claims (2)

[Claims] A vibration generating unit that vibrates in response to image information; a cantilever structure that vibrates in response to vibration of the vibration generating unit; and an elastic member that is in contact with ink. The vibration generating means sets an interval from the end of the main vibration for causing ink droplets to fly from the ink thin film formed on the surface of the elastic member to the start of the next main vibration to the cycle of the remaining vibration continued after the main vibration. A recording head characterized by being an integral multiple. 2. A vibration generating means that vibrates in response to image information, and an elastic member that has a cantilever structure that vibrates in response to vibration of the vibration generating means and is in contact with ink, A recording head according to claim 1, wherein said vibration generating means repeats a main vibration for causing ink droplets to fly from an ink thin film formed on a surface of the elastic member at a cycle of an integral multiple of the cycle of said main vibration.