JP2002120364A - Acoustic wave ink jet recording head and acoustic wave ink jet recorder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To record an image with a high image quality at a high rate by performing drop modulation while sustaining a stabilized flying state of ink drop. SOLUTION: When a switch 50 is turned on/off depending on image information, a high frequency voltage is applied to a high frequency applying electrode 48 from a high frequency amplifier 36 corresponding to a specified burst frequency to generate an acoustic wave. The acoustic wave is radiated from a piezoelectric element 26 and focused through an acoustic lens 34 to fly an ink drop 40 from a gas-liquid interface 30B. Although the focal length of the acoustic lens 34 depends on the burst frequency, ink drops 40 having different drop volumes can be flied at a constant repetitive frequency by setting the liquid level distance L of the acoustic lens 34 and the gas-liquid interface 30B between the focal length at a burst frequency for flying a largest ink drop and the focal length at a burst frequency for flying a smallest ink drop.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acoustic wave ink jet recording head and an acoustic wave ink jet recording apparatus, and more particularly, to an acoustic wave ink jet recording head which focuses an acoustic wave on a free surface of a liquid to fly droplets. The present invention also relates to an acoustic wave ink jet recording apparatus including the acoustic wave ink jet recording head.

[0002]

2. Description of the Related Art An ink jet recording method for recording an image by ejecting ink droplets onto an image recording medium generates a small amount of noise at the time of image recording, is easy to colorize, can be recorded on a so-called plain paper, and is fixed. Since it has advantages such as no need for processing, it has attracted attention in recent years. In particular, in the so-called on-demand type ink jet recording method, since the size of the ink jet recording head can be easily reduced, the ink jet recording method has been widely applied to home and office ink jet recording apparatuses and has become widespread.

[0003] The on-demand type ink jet recording method is roughly classified into a method using thermal energy and a method using vibration energy of a piezoelectric element (piezo element) depending on a method of ejecting (discharging) ink droplets. You.

In an on-demand type ink jet recording method using thermal energy, a heating element provided in a nozzle is heated according to image information, and an ink droplet is formed by the pressure of a generated bubble. Since the heating elements can be reduced in size, they can be arranged at a high density. However, it takes a long time until the generated bubbles naturally disappear, and a long time is required until the next injection. That is,
The on-demand type ink jet recording method using thermal energy can arrange the nozzles at a high density, but has a problem that the time interval of ink ejection becomes long and it is difficult to achieve high-speed image recording. Also, in order to perform so-called gradation printing by changing the amount of ink droplets,
Although it has been proposed to provide a plurality of heating elements in one nozzle, providing a plurality of heating elements in nozzles arranged at high density lowers the yield in producing an ink jet recording head.

On the other hand, in an ink jet recording method using the vibration energy of a piezoelectric element, a piezoelectric element provided in an ink flow path is vibrated according to image information, and an ink droplet is formed by distortion of the piezoelectric element. In comparison with the above-described method using thermal energy, a large area of the piezoelectric element is required to form an ink droplet, so that it is difficult to increase the density and increase the number of nozzles. However, by controlling the waveform of the voltage applied to the piezoelectric element, it is possible to control the meniscus of the ink ejection port and the re-supply of the ink after ejection, so that driving at a high frequency (ink ejection) and ink Gradation recording in which the amount of the droplet is changed becomes possible.

As an ink jet system different from the above, there is a system using an acoustic wave. For example,
No. 102377 describes an ink jet recording method using an acoustic wave in which an acoustic wave radiated by a vibrator is focused on an ink surface and ink droplets fly by the acoustic energy. In such a method, since a fine ink droplet can be made to fly by narrowing the spot diameter of the focused acoustic wave, it is not necessary to reduce the diameter of the nozzle to form a fine ink droplet, and the reliability is reduced due to clogging. There is no problem of the decrease. In addition, in the ink jet recording method using such an acoustic wave, a liquid level holding plate having an opening for maintaining a constant distance between the ink surface and the acoustic lens is generally provided. A water pool without capillaries is provided between the substrate and the substrate on which the acoustic lens is formed, and has a high repetition frequency because of excellent ink resupply properties. Further, since the vibrator for radiating the acoustic wave requires only a small area, it is easy to increase the number and density of the vibrator, and is excellent in speeding up image recording.

However, when minute ink droplets are formed in order to achieve high image quality, it is necessary to perform multiple overstrikes when forming a high-density image, which impairs high speed operation. Occurs. Therefore, according to the image density to be formed,
The so-called “drop modulation” that changes the size of a flying ink droplet is an effective means for achieving both high image quality and high speed.

For example, in the drop modulation in the ink jet method using an acoustic wave described in JP-A-63-166545, the burst width, amplitude and burst frequency of a burst wave applied to a vibrator for acoustic wave radiation are modulated. Although methods and overstrikes have been proposed, they lack specificity and have the following problems.

That is, in the method of modulating the burst width, as the burst width becomes longer, the optimum flight range between the burst width giving the threshold value of the ink droplet flight and the burst width in which the satellite mist appears becomes narrower, and the stable flight range becomes stable. It becomes difficult to find the driving burst width.

In the method of modulating the amplitude, it is necessary to change the amplitude promptly in accordance with the pixel information, but the driving circuit becomes expensive.

Further, in the method of modulating the burst frequency, the energy required for the flight is changed by changing the impedance of the vibrator according to the burst frequency and changing the focal length of the acoustic lens according to the burst frequency. Fluctuates, and the optimal driving conditions cannot be set.

On the other hand, Japanese Patent Application Laid-Open No. H10-128968 describes a configuration in which a higher-order standing wave is generated on a liquid surface and drop modulation is performed by changing the order thereof. Droplets fly, and the droplets cannot be individually controlled. When an image is formed with a plurality of droplets as described above, there is a problem that a thin line or the like cannot be sharply expressed.

[0013]

SUMMARY OF THE INVENTION In consideration of the above-mentioned circumstances in an ink jet method using acoustic waves, the present invention provides high speed and high image quality by performing drop modulation while maintaining a stable flying state of ink droplets. An object of the present invention is to provide an acoustic wave ink jet recording head capable of recording an image and an acoustic wave ink jet recording apparatus having the acoustic wave ink jet recording head.

[0014]

According to a first aspect of the present invention, there is provided an acoustic ink jet recording head for converging an acoustic wave on a free surface of a liquid to fly a droplet, wherein the liquid is applied to a desired liquid surface. Holding means for holding at a height, a piezoelectric element for radiating the acoustic wave, an acoustic lens for focusing the acoustic wave, and applying a burst wave to the piezoelectric element to generate the acoustic wave, and at least a burst frequency And a driving means capable of changing the size of the droplet by changing the height of the liquid droplet. Is set between a focal length corresponding to the acoustic wave that causes the largest droplet to fly and a focal length corresponding to the acoustic wave that causes the largest droplet to fly.

That is, in this acoustic wave ink jet recording head, an acoustic wave is generated when the driving means applies a burst wave to the piezoelectric element. Further, the acoustic wave is radiated by the piezoelectric element and focused on the free surface of the liquid (ink) by the acoustic lens, so that the droplet (ink droplet) flies and an image can be recorded.

In the acoustic wave ink jet recording head, the size of the flying droplet can be changed by changing the burst frequency of the burst wave applied by the driving means.

In general, when the burst frequency changes, the focal length of the acoustic lens also differs for each acoustic wave corresponding to the burst frequency.

Here, in the acoustic wave ink jet recording head of the present invention, the liquid surface height of the liquid held by the holding means, that is, the distance from the acoustic lens to the liquid surface, makes the smallest droplet fly among the droplets. The focal length is set between the focal length corresponding to the acoustic wave to be caused and the focal length corresponding to the acoustic wave causing the largest droplet to fly. Therefore, even if the focal length of the acoustic lens changes for each acoustic wave due to the change in the burst frequency, sufficient energy is applied to focus the acoustic wave near the liquid surface of the held liquid and fly the ink droplet. It is possible to fly ink droplets of individual sizes on demand according to a desired image pattern. That is, drop modulation is performed while maintaining a stable flying state of ink droplets, and an image can be recorded at high speed and with high image quality.

According to a second aspect of the present invention, in the first aspect of the present invention, the driving means controls the energy of the burst wave to control the flying energy of the droplet for each of the burst frequencies. It is characterized by the following.

As described above, by controlling the energy of the burst wave, the flying energy of the droplet whose size changes in response to the burst frequency can be set to an optimum value for each size of the droplet. Even if the ink droplets have different sizes, the ink droplets can be made to fly under the optimum flying conditions.

According to the third aspect of the present invention, there is provided an acoustic wave ink jet recording head for converging an acoustic wave on a free surface of a liquid and flying a droplet, wherein the liquid is held at a desired liquid level. Means, a piezoelectric element that radiates the acoustic wave, an acoustic lens that focuses the acoustic wave, and a burst wave is applied to the piezoelectric element to generate the acoustic wave, and at least the frequency of the burst wave is changed. Driving means capable of changing the size of the droplet and controlling the energy of the burst wave to control the flying energy of the droplet for each burst frequency.
Of the burst frequencies, regarding the burst frequency at which the threshold value of the flying energy of the droplet is minimized, the flying energy at the burst frequency is controlled to be equal to or less than the flying energy at another burst frequency. .

That is, in this acoustic wave ink jet recording head, an acoustic wave is generated when the driving means applies a burst wave to the piezoelectric element. Further, the acoustic wave is radiated by the piezoelectric element and focused on the free surface of the liquid (ink) by the acoustic lens, so that the droplet (ink droplet) flies and an image can be recorded.

In this acoustic wave ink jet recording head, the size of the flying droplet can be changed by changing the burst frequency of the burst wave applied by the driving means.

Here, in the acoustic wave ink jet recording head of the present invention, the flying energy of the droplet can be controlled for each burst frequency by controlling the energy of the burst wave. In other words, by controlling the energy of the burst wave, the flying energy of the droplet whose size changes in response to the burst frequency can be set to an optimal value for each individual size of the droplet. Even ink droplets can be made to fly under the optimum flight conditions. That is, by performing drop modulation while maintaining a stable flying state of ink droplets, an image can be recorded at high speed and with high image quality.

In the acoustic wave ink jet recording head of the present invention, with respect to the burst frequency at which the threshold value of the flying energy of the droplet among the burst frequencies is minimum, the flying energy at this burst frequency is converted to the burst energy at another burst frequency. It is controlled to be less than the flight energy.
Accordingly, appropriate flying energy can be given to each ink droplet, and optimal flying conditions can be secured.

According to a fourth aspect of the present invention, there is provided an acoustic wave ink jet recording head for converging an acoustic wave on a free surface of a liquid to fly a droplet, wherein the liquid is held at a desired liquid level. Means, a piezoelectric element that radiates the acoustic wave, an acoustic lens that focuses the acoustic wave, and a burst wave is applied to the piezoelectric element to generate the acoustic wave, and at least the frequency of the burst wave is changed. Driving means capable of changing the size of the droplet and controlling the energy of the burst wave to control the flying energy of the droplet for each burst frequency.
Of the burst frequencies, regarding the burst frequency at which the threshold value of the flying energy of the droplet is maximized, the flying energy at the burst frequency is controlled to be equal to or higher than the flying energy at another burst frequency. .

That is, in this acoustic wave ink jet recording head, an acoustic wave is generated when the driving means applies a burst wave to the piezoelectric element. Further, the acoustic wave is radiated by the piezoelectric element and focused on the free surface of the liquid (ink) by the acoustic lens, so that the droplet (ink droplet) flies and an image can be recorded.

In this acoustic wave ink jet recording head, the size of the flying droplet can be changed by changing the burst frequency of the burst wave applied by the driving means.

Here, in the acoustic ink jet recording head of the present invention, the flying energy of the droplet can be controlled for each burst frequency by controlling the energy of the burst wave. In other words, by controlling the energy of the burst wave, the flying energy of the droplet whose size changes in response to the burst frequency can be set to an optimal value for each individual size of the droplet. Even ink droplets can be made to fly under the optimum flight conditions.

In the acoustic wave ink jet recording head of the present invention, with respect to the burst frequency at which the threshold value of the flying energy of the droplet among the burst frequencies is maximized, the flying energy at this burst frequency is converted to the burst energy at another burst frequency. It is controlled so that it is higher than the flight energy.
Accordingly, appropriate flying energy can be given to each ink droplet, and optimal flying conditions can be secured.

In the inventions according to the second to fourth aspects, the method of controlling the energy of the burst wave is not particularly limited. For example, as described in the fifth aspect, the energy of the burst wave is If the adjustment is made by changing at least one of the amplitude and the burst time, the energy control of the burst wave is easy.

According to a sixth aspect of the present invention, in any one of the second to fifth aspects of the present invention, the energy of the burst wave is set so that the flying energy of the droplet is not less than a threshold and not more than a satellite generation value. Is controlled for each burst frequency.

As a result, ink droplets having a desired flying energy can be surely caused to fly, and at the same time, generation of satellites can be prevented and a high-quality image can be formed.

According to a seventh aspect of the present invention, in any one of the first to sixth aspects of the present invention, an inductance component is connected to the piezoelectric element, and one or more resonance components are provided for the flying energy of the droplet. Generating a frequency.

Thus, the energy efficiency from the driving means to the piezoelectric element can be improved.

According to the invention described in claim 8, in the invention described in any one of claims 1 to 7, between the acoustic lens and the liquid, the acoustic impedance between the acoustic lens and the acoustic impedance of each of the liquids is set. An acoustic matching layer having an acoustic impedance and having a thickness between the thickness determined by the burst frequency of the acoustic wave flying the smallest droplet and the thickness determined by the burst frequency of the acoustic wave flying the largest droplet is provided. It is characterized by the following.

By providing such an acoustic matching layer, it is possible to prevent the acoustic wave radiated by the piezoelectric element from being reflected at the interface between the acoustic lens and the liquid, thereby preventing energy loss.

Further, since the acoustic matching layer exists between the member on which the acoustic lens is formed and the ink, the member does not come into direct contact with the ink, so that the member can be prevented from being corroded.

In the first to eighth aspects of the present invention, the acoustic lens is not particularly limited as long as the acoustic wave can be focused. For example, a Fresnel lens may be used. By using a spherical lens, it is possible to further improve the focusing efficiency.

According to the tenth aspect of the present invention,
According to a ninth aspect of the present invention, there is provided the image forming apparatus, wherein the spherical lens has a spherical lens array formed by being two-dimensionally arranged.

Thus, high-speed and high-accuracy image recording can be performed.

[0042] According to the eleventh aspect of the present invention, in the first aspect,
The invention according to claim 10 is characterized in that the spherical lens array is formed by embossing a base material.

Thus, a spherical lens array in which acoustic lenses are arranged at high density can be manufactured at low cost.

In the invention according to the eleventh aspect, the material of the base material is not particularly limited as long as a spherical lens having a desired shape can be formed in a desired arrangement. Or a resin as described in claim 13 can be used. When glass is used, the durability of the substrate increases. In contrast, when a resin is used, molding of the base material becomes easier.

According to the fourteenth aspect of the present invention,
An acoustic wave inkjet recording head according to claim 13.

Since the acoustic wave ink jet recording head according to any one of claims 1 to 13 is used, drop modulation is performed while maintaining a stable flying state of ink droplets, thereby recording an image at high speed and high image quality. it can.

[0047]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [First Embodiment] FIG. 1 shows an acoustic ink jet recording head 1 according to a first embodiment of the present invention.
Acoustic wave ink jet recording device 12 with 0 is shown partially cut away. FIG. 2 shows the acoustic ink jet recording head 10 partially enlarged.

As shown in FIG. 1, the acoustic wave ink jet recording apparatus 12 includes an acoustic wave ink jet recording head 10.
Has a carriage 14 mounted thereon. The carriage 14 moves in a main scanning direction (direction of arrow M) along a shaft 16 provided in the acoustic wave ink jet recording apparatus 12. The acoustic wave ink jet recording head 10
Are arranged corresponding to a plurality of colors. For example, a full-color image is formed by ejecting ink droplets of four colors of K (black), C (sian), M (magenta), and Y (yellow). It is possible to record.

The acoustic wave ink jet recording apparatus 12
Is provided with a transport roller 20 for transporting the recording paper 18. The recording paper 18 is conveyed while being nipped by the conveyance rollers 20, and moves in the sub-scanning direction. In the drawings, the moving direction (main scanning direction) of the acoustic wave ink jet recording head 10 is indicated by an arrow M, and the moving direction (sub-scanning direction) of the recording paper 18 is indicated by an arrow S.

The ink jet recording head 10 is provided with an ink tank 22, and the ink jet recording head 10 is arranged on the side of the ink tank 22 facing the recording paper 18.

In the following, for convenience of explanation, there are places where specific numerical values and materials are given, but it goes without saying that the present invention is not limited to these specific examples.

As shown in FIGS. 2 and 3, the acoustic wave ink jet recording head 10 has a substrate 24 on which a spherical acoustic lens array 32 is formed by arranging a plurality of spherical acoustic lenses 34 two-dimensionally. A piezoelectric element 26 for radiating acoustic waves, an aperture plate 28 for holding the stored ink 30 at a desired height, and a substrate 24;
It is constituted by a holding member (not shown) that holds the piezoelectric element 26 and the aperture plate 28 integrally.
The holding member has a side wall surrounding the substrate 24 and the aperture plate 28 to prevent the stored ink 30 from inadvertently flowing out and drying.

The substrate 24 and the aperture plate 28
A water pool without capillaries is provided between them, and the ink droplets 40 can be made to fly at a high repetition frequency because the water 30 is excellent in re-supply properties of the ink 30.

The ink 30 is supplied from the ink tank 22 and stored between the substrate 24 and the aperture plate 28. Then, an acoustic wave generated by a signal from a high-frequency amplifier 36 described later is radiated by the piezoelectric element 26,
Further, the laser beam is focused by the acoustic lens 34 and the ink 30
The ink droplet 40 flies from the gas-liquid interface 30B. An ink discharge port 38 is formed in the aperture plate 28 at a position corresponding to the acoustic lens 34 so as not to hinder the discharge of the flying ink droplet 40.

The material and manufacturing method of the substrate 24 are not particularly limited. However, in order to enhance the shape stability and durability of the acoustic lens 34, it is preferable to use a glass material. In the present embodiment, soda glass was produced by an embossing method in an atmosphere (about 700 ° C.) slightly higher than its softening point. As other glass materials, borosilicate glass, aluminum silicate glass, aluminum borosilicate glass, silica glass, or the like can be used. In addition, it is possible to facilitate the production of the substrate 24 by using a material having high workability. From such a viewpoint, polyethylene, polystyrene, tetrafluoroethylene, polycarbonate, polyacetal which can be extruded without increasing the temperature relatively is used. , Polypropylene, polyphenylene oxide, polybutylene terephthalate, and other resins (particularly high-molecular resins) are most suitable. Regardless of which material is used, manufacturing cost can be reduced by manufacturing the substrate 24 by embossing.

The acoustic lens 34 of this embodiment has an aperture diameter of 3
With an F value of 1.10 and an F value of 1.10, 128 bits were arranged at a pitch of 339 μm for one line on the straight line (each line in which the acoustic lens 34 was arranged in the sub-scanning direction). Further, the spherical acoustic lens array 32 of 16 rows is configured by disposing the rows at regular intervals in the main scanning direction while shifting the rows by 21 μm in the sub-scanning direction. Therefore, the resolution of the acoustic wave ink jet recording head 10 is as a whole as can be seen from the fact that 16 acoustic lenses 34 are arranged at a length of 339 μm in a region E shown by a halftone dot in FIG. The resolution is 1200 dpi.

As shown in FIGS. 3A and 3B, the surface of the substrate 24 located on the ink side (the surface on which the acoustic lens 34 is formed) has an acoustic wave radiated by the piezoelectric element 26. An acoustic matching layer 42 is provided to prevent (or reduce the reflectance) from reflecting at the interface between the acoustic lens 34 and the ink 30. This acoustic matching layer 4
2, the acoustic impedance Z ₂ must be between the acoustic impedances Z ₁ and Z ₃ of the material of the acoustic lens 34 and the ink 30 in order to achieve the above-described effect. In particular, the geometric average value Z ₂ = √ (Z ₁ · Z ₃ ). In the present embodiment, polyimide is used as the material of the acoustic matching layer 42, and the design value of the acoustic impedance is Z ₂ = 4.4 × 10 ⁶ [kg / sec ·
m ² ]. Polyimide is used depending on the baking temperature.
Since the acoustic impedance can be adjusted within a range of 0 to 7.0 × 10 ⁶ [kg / sec · m ² ], it is suitable as a material of the acoustic matching layer 42. As an example of a method of forming the acoustic matching layer 42, after the substrate 24 is formed by the above-described embossing, a polyimide precursor is uniformly spray-coated and spin-coated on the surface of the substrate 24,
A desired acoustic impedance can be obtained by forming in a baking process in a 300 ° C. atmosphere.

The acoustic matching layer 42 also serves to prevent the acoustic lens material (base 24) from being corroded by the ink.

The thickness of the acoustic matching layer 42 is determined from the burst frequency of the acoustic wave as shown in Table 1.

[0060]

[Table 1]

In this embodiment, as will be described later in detail, burst waves of different burst frequencies are used for drop modulation for flying ink droplets 40 of different sizes. Therefore, the thickness of the acoustic matching layer 42 is
It is preferable to design between a thickness optimized for the burst frequency giving the maximum drop and a thickness optimized for the burst frequency giving the minimum drop.
In the present embodiment, the thickness of the acoustic matching layer 42 is 5 μm
Therefore, when flying ink droplets of any size, the reduction in energy efficiency due to the reflection of acoustic waves is reduced by about 30 to 4 compared to the case where the acoustic matching layer 42 is not provided.
0% improvement is possible.

It is sufficient that the acoustic matching layer 42 is formed so as to cover only the acoustic lens 34 only to prevent the energy efficiency from being reduced by the reflection of the acoustic wave. However, as described above, the acoustic matching layer 42 also has a role of preventing the acoustic lens material (base material 24) from being corroded by the ink 30, so that the acoustic lens 34 is required to sufficiently exhibit this effect.
Is preferably formed on the base material 24 so as to cover all the portions where the ink 30 comes into contact, including the portions where no ink is formed.

After the acoustic matching layer 42 is formed on the substrate 24 in this manner, a control electrode 44 for acoustic lens addressing is deposited on the surface opposite to the surface on which the acoustic matching layer 42 is formed. As shown in the figure, the image was drawn obliquely crossing the main scanning direction. As a material of the control electrode 44, a desired material can be selected as long as it has a low resistance and can make an ohmic contact with the material of the piezoelectric element 26. In this embodiment, TaTi is applied to the back of the surface on the ink 30 side by 1.0 × 10
Deposited to a thickness of ^-7 m.

After depositing the control electrode 44, a vibrator 46 for radiating an acoustic wave is deposited so as to be in contact with the acoustic matching layer 42, and as shown in FIG. Draw to match. The material of the vibrator 46 is not particularly limited as long as it can radiate an acoustic wave. In this embodiment, the piezoelectric element 26 of 19 μm is formed by depositing ZnO by a sputtering method. Generally Z
nO is suitable because it has a high vibration efficiency and a high crystal orientation can be obtained by a deposition method using sputtering. In particular, it is desirable that the (001) plane be oriented so as to be perpendicular to the substrate surface. The material of the piezoelectric element 26 may be P
A piezoelectric material having a perovskite structure such as ZT or a piezoelectric material such as PVDF (polyvinylidene fluoride) is used.

Further, since the vibrator 46 can radiate an acoustic wave even if it has a relatively small area, it is possible to arrange a large number of vibrators 46 at a high density, thereby achieving high quality image recording and high speed. Can be achieved.

Thereafter, the high-frequency application electrode 48 was deposited (along the sub-scanning direction) so as to be substantially orthogonal to the control electrode 44 in plan view, and was drawn as shown in FIG. As can be seen from FIG. 3A, a high-frequency amplifier 36 corresponding to each frequency is connected to the high-frequency application electrode 48, and a high-frequency voltage from a specific high-frequency amplifier 36 is applied by opening and closing a switch 50. In this embodiment, TaTi is used as the high frequency application electrode 48 by sputtering.
0 × 10 ⁻⁶ m and 1 μm of Al were further deposited, and drawing was performed so that the longitudinal direction was the sub-scanning direction, as shown in FIG.

FIG. 2 shows the control electrode 44 and the vibrator 4.
6 and only a part of the high-frequency application electrode 48 are shown, but in practice, the control electrodes 4 correspond to all the acoustic lenses 34.
4, a vibrator 46 and a high-frequency application electrode 48 are provided.

As shown in FIG. 3A, a coil 52 is interposed between the high-frequency amplifier 36 and the high-frequency application electrode 48 as an element for providing an inductance. FIG. 4 shows the burst frequency and phase difference (burst frequency and piezoelectric element 26) of the burst wave (see FIG. 6) applied to the high-frequency application electrode 48 when the coil 52 is interposed and when it is not interposed. Is shown. In this graph, the broken line indicates the case where only the piezoelectric element 26 is interposed without the coil 52, and the solid line indicates the case where the coil 52 is interposed. As can be seen from the broken line in this graph, in the piezoelectric element 26 alone,
The phase difference is shifted by almost 90 degrees at all frequencies,
The energy from the high frequency amplifier 36 cannot be efficiently transmitted to the piezoelectric element 26 to the vibrator. On the other hand, as can be seen from the solid line in the graph, the resonance point appears by interposing the coil 52 (at least at a certain frequency, the phase difference approaches 0 ° by interposing the appropriate coil 52). Can increase energy efficiency.

By the way, in the ink jet recording head using the acoustic wave, like the acoustic wave ink jet recording head 10 of the present embodiment, it is possible to fly the ink droplets 40 having different sizes (drop modulation). I have. FIG. 5 shows the relationship between the burst frequency of the burst wave applied to the ink 30 and the volume of the ink droplet 40 flying by the burst wave. As can be seen from this graph, the drop volume of the ink droplet 40 can be uniquely determined depending on the burst frequency.
For example, at a burst frequency of 90 MHz, the resolution is 1200.
A drop volume of 6 pl corresponding to dpi and a drop volume of 1 pl corresponding to a resolution of 2400 dpi at a burst frequency of 170 MHz can be ensured.
A pictorial image equivalent to dpi can be output at high speed. In the present embodiment, as an example, drop modulation is performed by setting the burst frequency to 90, 120, or 170 MHz, and the 6, 3, 1 pl ink droplet 40 is caused to fly according to a desired image pattern corresponding to each frequency. Like that.

FIG. 7 shows the acoustic lens 34 with respect to the burst frequency of the burst wave acting on the ink 30.
Are shown. As can be seen from this graph, even when the same acoustic lens 34 is used, the focal length decreases depending on the burst frequency. For example, when the burst frequency is 50 MHz and 200 MHz, the focal length is more than 20 μm. There is a difference. Therefore, as in the present embodiment, the burst frequencies are set to 90, 120, 17
In a configuration in which drop modulation is performed at 0 MHz, for example, the liquid surface distance L between the acoustic lens 34 and the gas-liquid interface of the ink 30 is L.
Is adjusted to the focal length when the burst frequency is 90 Hz (see the gas-liquid interface 30B shown by the two-dot chain line in FIG. 8), when the burst frequency is 170 MHz, the focal length of the acoustic lens 34 and the above Since the deviation from the liquid level distance L becomes large, the burst frequency 170M
Hz cannot be made to fly.
Conversely, even if the liquid level distance L is adjusted to the focal length when the burst frequency is 170 Hz (see the gas-liquid interface 30B shown by the dashed line in FIG. 8), when the burst frequency is 90 MHz, the acoustic lens Since the difference between the focal length of L and the liquid level distance L becomes large, the ink droplet corresponding to the burst frequency of 90 MHz cannot be made to fly. This is because the difference in spot height of the focal region, that is, the difference in height of a portion where the acoustic energy density is concentrated (generally a pseudo-cylindrical shape) so that the acoustic wave can converge and fly the ink droplet 40, It is understood that it is at most about 10 μm, which means that between the focal length corresponding to the burst frequency for flying the largest ink drop and the focal length corresponding to the burst frequency for flying the smallest ink drop,
If the liquid level distance L between the acoustic lens 34 and the gas-liquid interface 30B is set, the ink droplets 4 corresponding to all burst frequencies are set.
0 means that it can fly. In the acoustic wave ink jet recording head 10 of the present embodiment, FIG.
As shown in (A) and (B), the aperture plate 2
By appropriately setting the position 8, the liquid level distance L can be adjusted between the focal length corresponding to the burst frequency at which the largest ink droplet 40 flies and the focal length corresponding to the burst frequency at which the smallest ink droplet 40 flies. (See the gas-liquid interface 30B shown by the solid line in FIG. 8). In this way, by applying a burst wave having sufficient energy to the flight of the ink droplet 40, the large, medium, and small ink droplets 40 are caused to have a constant repetition frequency (for example, 30 MHz).
In z), it is possible to fly according to a desired pattern.

FIG. 9 shows a burst time (in one unit of a burst wave for ejecting one ink droplet 40,
The relationship between the burst frequency and the threshold voltage is shown when the time during which the burst wave acts is substantially constant (see FIG. 6). FIG. 10 shows the relationship between the burst frequency and the threshold energy when the burst frequency is kept constant. Here, the “threshold voltage” and “threshold energy” refer to the minimum voltage (voltage applied to the piezoelectric element 26) and the minimum energy, respectively, required to cause the ink droplet 40 to fly. As can be seen from FIG. 9, the threshold amplitude when the burst time is constant indicates a specific distribution corresponding to the burst frequency. When the burst frequency is 90, 120, or 170 MHz as in the present embodiment, the threshold amplitude is highest at 90 Hz, and is 120 MHz.
It can be seen that the threshold amplitude is the lowest at z. Also, from FIG. 10, the threshold energy when the burst time is fixed also shows a specific distribution corresponding to the burst frequency. When the burst frequency is 90, 120 or 170 MHz, the threshold energy is the highest at 90 Hz. It can be seen that the threshold energy is the lowest at 120 MHz. Therefore, it is preferable to appropriately correct the flying energy for each burst frequency.

In this embodiment, since the liquid surface distance L between the acoustic lens 34 and the gas-liquid interface 30B is constant,
When the focal length of the acoustic lens 34 changes according to the burst frequency, the flying energy of the ink droplet 40 also changes. Therefore, from such a viewpoint, it is preferable to appropriately correct the flying energy for each burst frequency.

For this reason, in the present embodiment, by setting the flying energy of the ink droplet 40 at the burst frequency of 120 MHz when giving the minimum threshold energy to the minimum energy, other burst frequencies of 90 and 170 MHz can be obtained.
The flying energy of the ink droplet 40 at the time is adjusted by adjusting the amplitude of the burst wave and the burst time (see FIG. 6). That is, the burst frequency is 90 MHz or 170 MHz higher than when the burst frequency is 120 MHz.
At MHz, a desired flying energy can be obtained by increasing the amplitude of the burst wave or increasing the burst time. Burst frequency is 12
The flying energy of the ink droplet 40 at 0 MHz is preferably at least 1.02 times the threshold energy in order to stably eject the ink droplet 40. In order to prevent the occurrence of “satellite” which will be described in detail later, it is preferable that the threshold energy is not more than 3.00 times,
More preferably, it is 2.00 times or less.

On the contrary, the flying energy of the ink droplet 40 at the burst frequency 90 MHz when the maximum threshold energy is given is set to the maximum energy, and the ink droplet 4 at the other burst frequencies 120 and 170 MHz is set.
The flying energy of 0 may be corrected by adjusting the amplitude of the burst wave and the burst time.
In this case, when the burst frequency is 120 MHz or 170 MHz than when the burst frequency is 90 MHz, the desired flying energy can be obtained by reducing the burst wave amplitude or shortening the burst time. .

FIG. 11 shows the relationship between the burst time and the power of the ink droplet 40 at a specific burst frequency. In general, when the flying energy of the ink droplet 40 is increased by, for example, increasing the burst time, if the flying energy is too large, a so-called “satellite” is used.
May occur. The satellite is shown in FIG.
As shown in FIG. 7, when a single ink droplet 40 flies, a small droplet 40S is generated in addition to the ink droplet (main droplet 40M) that originally contributes to image recording.
May land on a recording medium, image quality may be degraded. On the other hand, when the flying energy applied to the ink droplet 40 is equal to or less than the threshold, as shown in FIG.
Although the ink 30 rises from the gas-liquid interface 30B, the ink 30 does not have enough energy to completely separate the ink droplet 40 from the ink 30, and cannot fly the ink droplet 40. In consideration of these, in the present embodiment,
The burst time is set so that the power of the ink droplet 40 at the burst frequency of 90 MHz and 170 MHz is equal to or more than the threshold value and less than the satellite generation (in the graph of FIG. I have.

The minute droplets 40S that cause the generation of satellites are determined based on the image quality required and the main droplets 40S.
Depending on the magnitude relationship between M and the minute droplet 40S, there may be no substantial problem. Therefore, it is desirable to set the burst time in consideration of these facts and prevent the generation of satellites.

Further, as shown in FIG.
Is dependent on the burst time, and the volume increases with an increase in the burst time, but the increase is small, and the size of the ink droplet 40 is corrected (optimized) by the burst time.
Has little effect on the volume change of the ink droplet 40. In addition, the acoustic wave ink jet recording head 10 of the present embodiment
When the acoustic wave ink jet recording apparatus 12 (see FIG. 1) is configured by using the above method, an excessively high voltage amplitude (that is, the amplitude of the burst wave) is not desirable because the cost of the driving circuit is increased and is corrected by the burst time. (A necessary energy can be obtained by increasing the burst time and the voltage amplitude is reduced). From this viewpoint, the burst time is 0.5
It is desirable that the time be between μsec and 10 μsec. In the present embodiment, by setting the burst time to 1.0 to 7.0 μsec (preferably 2.0 to 5.0 μsec), 120
The ink droplet 40 can be stably ejected with the energy of nJ.

In the acoustic ink jet recording head 10 of the present embodiment having such a configuration, the specific high-frequency amplifier 3 is opened and closed by opening and closing the switch 50 corresponding to the image information.
6 is selected, a high-frequency voltage is applied to the high-frequency application electrode 48, and an acoustic wave is generated. This acoustic wave is applied to the piezoelectric element 26.
The ink droplet 40 flies from the gas-liquid interface 30 </ b> B and lands on the recording paper 18 (see FIG. 1). As shown in FIG. 1, the carriage 14 moves in the main scanning direction while the ink droplets are ejected, and the recording paper 18 is conveyed in the sub-scanning direction. Is formed.

Here, in the acoustic ink jet recording head 10 of the present embodiment, the gas-liquid interface 3
Liquid level distance L to 0B, burst frequency is 90MHz
The gas-liquid surface 30B is held by the aperture plate 28 so as to be between the focal length of the acoustic lens 34 when the burst frequency is 170 MHz and the focal length of the acoustic lens 34 when the burst frequency is 170 MHz. Therefore, if the burst frequency is at least in the range of 90 to 170 MHz, the ink droplet 40 can be made to fly. Then, as the high frequency amplifier 36, 90 MHz, 120 MH
The high-frequency voltage is applied to the high-frequency applying electrode 48 by a specific high-frequency amplifier 36 selected from three types of z and 170 MHz
So that 6 pl, 3 pl, and 1 pl ink droplets 40 corresponding to these burst frequencies respectively fly according to a desired image pattern.
Images can be recorded at high speed and with high image quality.

To fly the ink droplets 40 of different sizes in this manner, the flying energy at the burst frequency of 120 MHz that gives the minimum flying energy is set to the minimum energy, and the burst energy of other burst frequencies is set. At times, a desired flying energy is obtained by adjusting the amplitude of the burst wave or the burst time. In addition, the flying energy is set so that the power of the ink droplet 40 is not less than the threshold value and not more than the satellite generation value. For this reason, the ink droplet 40 can be made to fly under optimal flying conditions without generating satellites.

[Second Embodiment] FIG. 14 shows an acoustic ink jet recording head according to a second embodiment of the present invention. In the second embodiment, the basic configuration of the acoustic ink jet recording head is substantially the same as that of the first embodiment, but as can be seen from FIG. 14A, the coil 52 is connected in parallel. Are different. The inductance of each coil 52 has a burst frequency of 90, 12
It is set so as to give a resonance point every 0 and 170 MHz. Thereby, the high frequency vibration from the high frequency amplifier 36 can be efficiently transmitted to the piezoelectric element 26. Second
In the embodiment, as an example, by using an inductance in the range of 1 nM to 100 nH, a large, medium, and small drop can be made to fly with an energy of 1/2 to 1/3 in the present embodiment compared to the first embodiment.

[0082]

According to the present invention having the above-described structure, high-speed and high-quality image recording can be performed by performing drop modulation while maintaining a stable flying state of ink droplets.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an acoustic wave ink jet recording apparatus according to the present invention with a part thereof cut away.

FIG. 2 is a plan view partially showing the acoustic wave ink jet recording head according to the first embodiment of the present invention.

3A and 3B partially show an acoustic wave inkjet recording head according to a first embodiment of the present invention, and FIG.
FIG. 3B is a cross-sectional view taken along a line A, and FIG.

FIG. 4 is a graph showing a relationship between a burst frequency of a burst wave applied to a high-frequency application electrode and a phase difference between a vibration frequency of the piezoelectric element and a burst frequency of the burst wave applied to the high-frequency application electrode in the acoustic wave inkjet recording head according to the first embodiment of the present invention. is there.

FIG. 5 is a graph showing a relationship between a burst frequency of a burst wave applied to ink and a volume of an ink droplet flying by the burst wave in the acoustic wave inkjet recording head according to the first embodiment of the present invention.

FIG. 6 is an explanatory diagram showing a waveform of a burst wave.

FIG. 7 is a graph showing the relationship between the burst frequency and the focal length of the acoustic lens in the acoustic wave inkjet recording head according to the first embodiment of the present invention.

FIG. 8 is an explanatory diagram showing the relationship between the focal length at each burst frequency and the distance from the acoustic lens to the liquid level in the acoustic wave inkjet recording head according to the first embodiment of the present invention.

FIG. 9 is a graph showing a relationship between a burst frequency of a burst wave and a threshold voltage in the acoustic wave ink jet recording head according to the first embodiment of the present invention.

FIG. 10 is a graph showing a relationship between a burst frequency of a burst wave and a threshold energy in the acoustic wave inkjet recording head according to the first embodiment of the present invention.

FIG. 11 is a graph showing the relationship between the burst frequency of a burst wave and the power of ink droplets in the acoustic wave ink jet recording head according to the first embodiment of the present invention.

FIGS. 12A and 12B are explanatory diagrams showing how ink droplets fly in the acoustic wave ink jet recording head according to the first embodiment of the present invention, wherein FIG. 12A shows a case where the power of the ink droplets is equal to or less than a threshold, and FIG. This is the case where satellites are generated.

FIG. 13 is a graph showing a relationship between a ratio of a burst time to a threshold value and a volume ratio of an ink droplet to a threshold value in the acoustic wave ink jet recording head according to the first embodiment of the present invention.

FIGS. 14A and 14B show an acoustic ink jet recording head according to a second embodiment of the present invention, wherein FIGS.
FIGS. 3A and 3B are cross-sectional views each showing the same cross section as that of FIG.

[Explanation of symbols]

 Reference Signs List 10 acoustic wave ink jet recording head 12 acoustic wave ink jet recording device 26 piezoelectric element 28 aperture plate (holding means) 32 spherical acoustic lens array 34 acoustic lens 36 high frequency amplifier (driving means) 42 acoustic matching layer 52 coil (inductance component)

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Naoki Morita 2274 Hongo, Ebina-shi, Kanagawa Prefecture Fuji Xerox Co., Ltd. Ebina Works F-term (reference) 2C057 AF01 AF39 AG62 AG68 AG82 AM15 AM40 AN01 AP11 AP21 AR16 BF06 CA01 5C051 AA02 CA04 DB02 DB07 DC07 DE03

Claims (14)

[Claims] 1. An acoustic wave ink jet recording head that focuses an acoustic wave on a free surface of a liquid and causes a droplet to fly, comprising: holding means for holding the liquid at a desired liquid level; A piezoelectric element that radiates, an acoustic lens that focuses the acoustic wave, and a burst wave applied to the piezoelectric element to generate the acoustic wave, and to change at least a burst frequency to change the size of the droplet. And a driving unit that is capable of: a liquid surface height of the liquid held by the holding unit being a focal length and a maximum corresponding to the acoustic wave that causes the smallest one of the droplets to fly. An acoustic wave inkjet recording head, which is set between a focal length corresponding to the acoustic wave that causes the droplet to fly. 2. The acoustic wave ink jet recording head according to claim 1, wherein the driving unit controls the energy of the burst wave to control the flying energy of the droplet for each of the burst frequencies. . 3. An acoustic wave ink jet recording head that focuses an acoustic wave on a free surface of a liquid and causes a droplet to fly, comprising: holding means for holding the liquid at a desired liquid level; A piezoelectric element that radiates, an acoustic lens that focuses the acoustic wave, and a burst wave applied to the piezoelectric element to generate the acoustic wave, and at least change the frequency of the burst wave to reduce the size of the droplet. And a driving unit capable of controlling the energy of the burst wave to control the flying energy of the droplet for each of the burst frequencies. With respect to the burst frequency at which the threshold value becomes minimum, the flying energy at the burst frequency is controlled to be equal to or less than the flying energy at another burst frequency. An acoustic wave ink jet recording head characterized in that: 4. An acoustic wave ink jet recording head that focuses an acoustic wave on a free surface of a liquid and causes a droplet to fly, comprising: holding means for holding the liquid at a desired liquid level; A piezoelectric element that radiates, an acoustic lens that focuses the acoustic wave, and a burst wave applied to the piezoelectric element to generate the acoustic wave, and at least change the frequency of the burst wave to reduce the size of the droplet. And a driving unit capable of controlling the energy of the burst wave to control the flying energy of the droplet for each of the burst frequencies. Regarding the burst frequency at which the threshold value becomes maximum, the flying energy at the burst frequency is controlled to be equal to or higher than the flying energy at another burst frequency. An acoustic wave ink jet recording head characterized in that: 5. The acoustic wave according to claim 2, wherein the energy of the burst wave is adjusted by changing at least one of an amplitude and a burst time of the burst wave. Ink jet recording head. 6. The burst wave according to claim 2, wherein the energy of the burst wave is controlled for each burst frequency so that the flying energy of the droplet is not less than a threshold and not more than a satellite generation value. 3. The acoustic wave ink jet recording head according to claim 1. 7. The sound according to claim 1, wherein an inductance component is connected to the piezoelectric element to generate one or more resonance frequencies with respect to the flying energy of the droplet. Wave inkjet recording head. 8. A liquid having an acoustic impedance between the acoustic lens and the liquid between the acoustic lens and the liquid, and a thickness and a maximum liquid determined by a burst frequency of an acoustic wave flying on the smallest droplet. The acoustic wave ink jet recording head according to any one of claims 1 to 7, further comprising an acoustic matching layer having a thickness between a thickness determined by a burst frequency of an acoustic wave flying through the droplet. . 9. The acoustic wave ink jet recording head according to claim 1, wherein the acoustic lens is a spherical lens. 10. The acoustic wave ink jet recording head according to claim 9, further comprising: a spherical lens array formed by arranging the spherical lenses two-dimensionally. 11. The acoustic ink jet recording head according to claim 10, wherein the spherical lens array is formed by embossing a base material. 12. The acoustic wave ink jet recording head according to claim 11, wherein the base material is glass. 13. The acoustic wave ink jet recording head according to claim 11, wherein the substrate is a resin. 14. An acoustic wave ink jet recording apparatus comprising: the acoustic wave ink jet recording head according to any one of claims 1 to 13.