JPH1170651A - Ink jet recording apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably eject ink droplets regardless of a change in use environmental temp. by regulating the liquid level of the ink in an ink holding chamber so as to compensate the converging position of ultrasonic waves fluctuated by a change in peripheral temp. SOLUTION: A lid plate 18 provided with a circular opening part 19 is constituted of bimetals (metals 181, 182). That is, the bimetals (metals 181, 182) are constituted so that the lid plate is curved inside when temp. rises and curved outside when temp. drops. Now, the liquid level of ink can be moved by utilizing that the liquid level of the ink by the surface tension at the opening part 19 is held to move the lid plate 18 up and down in the periphery of the opening part 19. Therefore, by the above mentioned constitution, an ink jet recording apparatus 10 can regulate the liquid surface of the ink so as to compensate the fluctuations of the focal distance of a Flesnel acoustic lens 141 by the change of the peripheral temp. (the temp. change of an ink liquid 15).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink jet recording apparatus for recording an image by forming liquid ink into liquid droplets and flying the liquid ink on a recording medium, and more particularly, to an ultrasonic beam emitted from a piezoelectric element. The present invention relates to an ink jet recording apparatus that records ink on a recording medium by discharging ink droplets by pressure.

[0002]

2. Description of the Related Art An apparatus for recording an image by forming an image spot by forming liquid ink into small particles called ink droplets and flying on a recording medium has been put to practical use as an ink jet printer. To date, a number of ink jet printer systems have been devised. In particular, the pressure of steam generated by the heat of a heating element disclosed in Japanese Patent Publication No. 56-9429 and Japanese Patent Publication No. 61-59911 is disclosed. Method of flying ink droplets by using
A method of flying an ink droplet by a pressure pulse due to displacement of a piezoelectric body disclosed in Japanese Patent No. 2138 or the like is typical.

However, since these ink jet printers employ a method in which ink is ejected from the tip of a nozzle, the ink is easily concentrated locally due to volatilization of a solvent in the ink. This may cause clogging of thin nozzles.

In order to overcome these drawbacks, there has been proposed a system using ultrasonic waves in which ink droplets fly from an ink liquid surface using the pressure of an ultrasonic beam generated from a thin-film piezoelectric material (IBM). TDB, vol.
No. 4,1168 (1973-10), JP-A-63
JP-A-162253, JP-A-63-166548,
JP-A-63-212157, JP-A-2-1844
43, etc.). Since this ultrasonic method is a so-called nozzleless method that does not require a nozzle for each individual dot or a partition between ink flow paths, the problem of clogging, which was a major obstacle in forming a line head, is solved. You.
In addition, this method can stably fly an ink droplet having a very small diameter, and is therefore suitable for high resolution.

However, in a conventional ultrasonic ink jet recording apparatus, the radiation pressure of the ultrasonic beam generated by the piezoelectric element is kept constant under a wide operating temperature environment, and ink droplets are stably ejected to achieve a high pressure. It has been difficult to obtain high quality images.

[0006]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an ink jet recording apparatus which makes ink droplets fly by radiation pressure of ultrasonic waves is provided.
It is an object to maintain a high-quality image by stably ejecting ink droplets regardless of a change in a use environment temperature.

[0007]

Means for Solving the Problems In order to solve the above-mentioned problems, the inventors of the present invention have made intensive studies. It can be seen that there are mainly two causes of the inability to stably eject and fly. The first major cause is based on the fact that the focus position (focal length) of the ultrasonic wave fluctuates as a result of a change in the temperature of the ink liquid due to a change in the use environment temperature. That is, the lower the temperature of the ink liquid, the lower the velocity of the ultrasonic wave propagating in the ink liquid, the longer the focal length, and the less the ultrasonic wave is focused on the ink liquid surface.

Therefore, in the present invention, in order to eliminate the first cause and stably eject ink droplets irrespective of a change in a use environment temperature (ambient temperature), an ink jet recording apparatus is provided with an ambient temperature change. Means is provided for adjusting the ink level in the ink holding chamber so as to compensate for the fluctuating focus position of the ultrasonic waves.

That is, according to the present invention, first, an ink holding chamber for holding an ink liquid, an ultrasonic generating means acoustically connected to the ink liquid and including a piezoelectric element, and a drive of the ultrasonic generating means Driving means, and an ultrasonic focusing means including an ultrasonic focusing lens member formed on the ultrasonic generating means and focusing an ultrasonic wave generated from the ultrasonic generating means near a liquid surface of the ink liquid. An ink jet recording apparatus provided with means for adjusting an ink liquid level in the ink holding chamber so as to compensate for a focus position of an ultrasonic wave that fluctuates due to a change in ambient temperature. Things.

The ink level adjusting means may be provided by including a lid plate of the ink holding chamber having an opening at a position where the ultrasonic wave is focused, and the lid plate is made of a bimetal.

Alternatively, the ink liquid level adjusting means includes a lid plate of the ink holding chamber having an opening at a position where the ultrasonic wave is focused, and a side wall of the ink holding chamber which expands and contracts due to a change in ambient temperature. It can also be constituted by a lever member that moves the lid plate in response to the expansion and contraction of the side wall.

A second cause of the inability of the ink droplet to be stably ejected and fly due to a change in the use environment temperature is based on the fact that the electrical impedance of the piezoelectric element fluctuates in proportion to the change in the ambient temperature. That is, the intensity of the ultrasonic beam has an almost linear relationship with the voltage applied to the piezoelectric element and the power determined by the electrical impedance of the piezoelectric element. As a result, the intensity of the ultrasonic beam was changed, and it was found that stable ejection and flying of ink droplets could not be achieved.

Therefore, according to the present invention, the piezoelectric element is driven via a circuit element having a temperature coefficient having a sign opposite to that of the impedance of the piezoelectric element so as to compensate for a change in the electrical impedance of the piezoelectric element due to a change in ambient temperature. I did it.

That is, according to the present invention, secondly, there is provided an ink holding chamber for holding an ink liquid, ultrasonic generating means acoustically connected to the ink liquid and including a piezoelectric element, and driving the ultrasonic generating means. Driving means, and an ultrasonic focusing means including an ultrasonic focusing lens member formed on the ultrasonic generating means and focusing an ultrasonic wave generated from the ultrasonic generating means near a liquid surface of the ink liquid. In the ink jet recording apparatus provided, the driving means, via a circuit element having a temperature coefficient of the opposite sign to the impedance of the piezoelectric element so as to compensate for the variation of the electrical impedance of the piezoelectric element due to a change in ambient temperature, There is provided an ink jet recording apparatus which is connected to the piezoelectric element. The circuit element can be constituted preferably by a capacitor or a resistance element, and more preferably by a capacitor.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. Throughout the drawings, the same portions are denoted by the same reference numerals, and a detailed description of such repetition for each drawing may be omitted from the following description.

First, referring to FIGS. 1 to 7, the present invention is provided with a means for adjusting the ink liquid level in the ink holding chamber so as to compensate for the focus position of the ultrasonic wave which fluctuates due to a change in ambient temperature. An embodiment of the ink jet recording apparatus will be described.

FIG. 1 is a sectional view showing an ink jet recording apparatus according to an embodiment of the present invention, and FIG. 2 is a plan view of a portion of the apparatus shown in FIG. 1 excluding a cover plate 18 and an ink liquid. is there.

The ink jet recording apparatus 10 shown in FIGS. 1 and 2 is of a single head type. This ink jet recording apparatus 10 has a piezoelectric element 13 constituting an ultrasonic wave generating means on a support 11 via a suitable adhesive 12. Ultrasonic focusing means 14 is provided on the piezoelectric element 13. An ink liquid holding chamber 16 for storing and holding the ink liquid 15 includes a peripheral wall 17 formed by side walls 171 to 174 and a lid plate 18 having a circular opening 19 formed therein.
Consists of

The support 11 can be made of glass or the like. The piezoelectric element 13 provided on the support 11 via the adhesive 12 is not particularly limited as long as it can generate ultrasonic waves. The piezoelectric element 13 includes a plate-shaped piezoelectric body 131 and electrodes 132 and 133 formed entirely on both surfaces thereof. Examples of the piezoelectric material constituting the piezoelectric body 131 include ZnO, Pb (Z
rTi) O ₃ , LiNbO ₃ , quartz, piezoelectric polymers such as a copolymer of vinylidene fluoride and ethylene trifluoride, and the like. Also, the electrodes 132 and 1
33 can be formed as a thin film by vapor deposition or sputtering of titanium, nickel, aluminum, copper, gold, or the like, and can also be formed by plating. Alternatively, the electrodes 132 and 133 can be formed by a baking method in which silver paste is applied by screen printing and sintered. The piezoelectric element 13 has two electrodes 132, 1
A voltage is applied to the piezoelectric body 131 via the
1 is resonated to generate ultrasonic waves.

The frequency of the generated ultrasonic waves varies depending on the type and shape of the piezoelectric material of the piezoelectric element 13, and the diameter of the flying ink droplet (not shown) varies depending on the magnitude of the frequency. The smaller the ink droplet diameter, the higher the resolution (high quality) of the image. In order to obtain a high quality image, it is preferable that the diameter of the ink droplet is 3 to 150 μm. In order to obtain such an ink droplet diameter, it is preferable to select the piezoelectric material and shape so that the resonance frequency of the piezoelectric element 13 is about 10 to 500 MHz.

In the present invention, the ultrasonic focusing means converts the ultrasonic wave generated from the piezoelectric element 13 from the piezoelectric element 13 to the liquid surface of the ink 15 acoustically connected thereto (the lid of the ink liquid holding chamber in FIG. 1). There is no particular limitation as long as the light is focused on the opening 19) of the plate 18, and a Fresnel acoustic lens 141 as shown in FIG. 1 can be used. The Fresnel acoustic lens 141 includes a plurality of annular grooves (grooves 142 to 14 in FIG.
4) can be formed by providing concentrically. Such an acoustic lens 141 is preferably formed of a material having an acoustic impedance intermediate between the acoustic impedance of the piezoelectric element 13 and the acoustic impedance of the ink liquid 15 because attenuation of ultrasonic waves can be reduced.

In the present invention, the ink liquid 15 is not particularly limited as long as an ink droplet is ejected by the pressure of the ultrasonic beam focused on the liquid surface to record an image on a recording medium. Used. For example, a dye ink and a pigment ink using water as a solvent can be used, but it is desirable to use a pigment ink having excellent water resistance and fading property.

An opening 19 formed in the cover plate 18 of the ink liquid holding chamber 16 for containing and holding the ink liquid 15 is located at the focal point of the sound wave focusing means 14. The ink droplet is ejected from the opening 19. If the opening 19 is narrow, it becomes possible to maintain the ink liquid level at the position of the opening 19 by the surface tension even if the supply of the ink liquid changes. The narrower the opening 19 is, the greater the ink liquid level holding force is. However, it is desirable that the width of the opening 19 be larger than three times the size of the ink droplet to be ejected. By doing so, the ultrasonic waves focused by the ultrasonic focusing means 14 raise the ink surface to form a meniscus,
When the ink droplet flies from the top of the meniscus, the meniscus can be smoothly grown. Figure 1
In the ink jet recording apparatus shown in FIG. 2, the opening 19 has a circular shape in order to eject ink droplets from one place, and the diameter thereof corresponds to the above width. When the diameter of the opening 19 is 1.5
If it is less than 1 mm, a sufficient ink liquid holding force can be obtained by the surface tension, and if it is 1 mm or less, a stronger ink liquid holding force can be obtained.

The ink jet recording apparatus 10 is provided with, in addition to the components described above, means for adjusting the ink liquid level by compensating for a change in the ultrasonic focus position (focal length) due to a change in temperature. I have.

As described above, the main factor of the fluctuation of the ultrasonic focusing position is a change in the speed of the sound wave propagating in the ink liquid due to a change in the temperature of the ink liquid. For example, in the case of the aqueous ink, the sound speed in the ink liquid at 5 ° C. is 1450 m / sec, but increases to 1500 m / sec at 20 ° C. Thus,
For example, when the focal length is 2.6 mm (20 ° C.) and the temperature of the ink liquid 15 reaches 5 ° C., the focal length increases to 2.7 mm and 0.1 mm. (Such a relationship is almost proportional in a practical ink liquid temperature range (5 ° C. to 40 ° C.).) Therefore, in this case, when the temperature of the ink liquid changes, the ink droplets are efficiently formed. For stable ejection, it is necessary to raise the ink level by 0.1 mm. vice versa,
When the temperature of the ink liquid 15 rises, it is necessary to lower the ink liquid level accordingly. Such movement of the ink liquid level is achieved by moving the lid plate 18 up and down at least around the opening 18 by utilizing the fact that the ink liquid level is held by the surface tension at the opening 19 of the lid plate 18. Thus, the ink level can be moved. By installing the ink tank so that an appropriate negative pressure is applied to the ink liquid 15 in the ink chamber 16, the ink liquid surface can move more stably.

In the ink jet recording apparatus 10 shown in FIGS. 1 and 2, the cover plate 18 is made of a bimetal (metal 181).
And 182). Such a bimetal is not particularly limited as long as it is a combination of metal materials that bends due to a change in temperature. However, a combination of brass (30 to 40% zinc) and 34% nickel steel, and a combination of brass (30 to 4
0% zinc) and amber (36% nickel steel), Monel metal (nickel copper alloy) and 34-42% nickel steel, 20% nickel steel and 42-54
% Nickel steel and the like can be preferably exemplified. Needless to say, when the temperature rises,
Are bent inward, and the bimetal is configured so that the lid plate 18 is bent outward when the temperature decreases. Thus, the ink liquid level is adjusted so as to compensate for a change in the focal length due to a change in the ambient temperature (a change in the temperature of the ink liquid 15).

FIG. 3 schematically shows a cross section of another ink jet recording apparatus having the same structure as that of the ink jet recording apparatus shown in FIG. 1 except that the means for adjusting the ink level according to the temperature change is different. FIG. 4 is a plan view of a portion of the recording apparatus in FIG. 3 from which a cover plate 18 and an ink liquid 15 are removed. In the ink jet device 30, the upper lid 18 of the ink liquid chamber 16 is formed of a normal plate-like body made of, for example, stainless steel.

Now, in the ink jet recording apparatus 30 shown in FIGS.
1 to 174, adjacent to the side walls 171 to 17
Lever members 31 to 34 for lowering and raising the cover plate 18 based on the principle of leverage when 4 expands and contracts due to a temperature change are provided. Each of the lever members 31 to 34 is formed of a plate having substantially the same height and length as the inner exposed surfaces of the peripheral side walls 171 to 174.
The lower end face is joined to the Fresnel lens 141. Each of the lever members 31 to 34 is formed with a thin portion acting as a hinge on the upper side thereof (thin portions 311 and 331 are shown in FIG. 3, but the same thin portion is used as a lever). It is also provided on members 32 and 34). In this case, the side wall 17 is preferably formed of a material having a large coefficient of thermal expansion, and the lever members 31 to 34 are preferably formed of a material having a small coefficient of linear thermal expansion.

When the temperature rises, the side wall 17 is moved to the lever members 31-31.
When it extends beyond 34, the lid plate 18 is pushed down by the action of the lever members 31-34, and conversely, when the side wall shrinks from the lever members 31-34 due to a temperature drop, the lever members 31-34.
By the action of 34, the cover plate 18 is pushed upward. Thus, the ink liquid level is adjusted so as to compensate for a change in the focal length due to a change in the ambient temperature (a change in the temperature of the ink liquid 15).

FIGS. 5 to 7 show an ink jet recording apparatus having piezoelectric elements divided into an array, FIG. 5 is a schematic perspective view thereof, and FIG. 6 is a view showing the piezoelectric elements and ultrasonic focusing. FIG. 7 is a cross-sectional view of the means taken along the YZ plane of FIG. 5, and FIG. 7 is a cross-sectional view of the piezoelectric element and the ultrasonic focusing means taken along the XZ plane of FIG.

That is, the ink jet recording apparatus 5
Numeral 0 has a rectangular parallelepiped shape as a whole, and has a piezoelectric element 43 constituting an ultrasonic focusing means on a support (substrate) 11.
The piezoelectric element 53 is a flat piezoelectric member 5 made of the same piezoelectric material as the piezoelectric element 13 described with reference to FIGS.
31.

As shown best in FIG. 6, on the lower surface of the piezoelectric body 531, a plurality of striped individual electrodes (24 individual electrodes 532a to 532 in FIG.
x) are formed to have the same length as the width of the piezoelectric body 531 in the X direction (corresponding to the sub-scanning direction) (hereinafter, the individual electrodes may be collectively referred to as individual electrodes 532). The piezoelectric body 531 is formed by these individual electrodes 532.
It is functionally divided into a plurality of piezoelectric elements. On the other hand, on the upper surface of the piezoelectric body 531, an integral common electrode 533 is formed over the entire surface.

A plurality of Fresnel acoustic lenses 541 as ultrasonic focusing means 54 formed on the piezoelectric element 53 are arranged at a predetermined pitch based on the Fresnel's ring theory at a symmetrical position from the center thereof. 5 (FIGS. 5 and 7 show six grooves 542 to 547, and 542 and 5
43, 544 and 545, 546 and 547 are formed symmetrically, respectively) in parallel with the arrangement direction of the piezoelectric elements divided by the individual electrodes 532 (Y direction: corresponding to the main scanning direction). ing. The depth of each groove is (2m + 1) / 4 times (m is 0 or more) the wavelength of the ultrasonic wave in the lens 541 so that the phase of the ultrasonic wave emitted from the top and bottom surfaces of the groove is shifted by a half wavelength. (Integer). The grooves 542 to 547 are formed in parallel with the arrangement direction (Y direction: corresponding to the main scanning direction) of the piezoelectric elements divided and formed by the individual electrodes 532.

A plurality of array electrodes 55 are formed at one end of the support 11 at the same intervals as the individual electrodes 532 formed on the lower surface of the piezoelectric body 531. The array electrode 55 and the individual electrodes 532 on the lower surface of the piezoelectric body 531 are aligned and crimped via a conductive adhesive, and are electrically connected. The array electrode 55 on the support 11 is connected to driving circuits 56 and 57 disposed on the end of the support 11 by bonding wires 58, and a common electrode 533 formed on the upper surface of the piezoelectric body 531.
Are connected to the drive circuits 56 and 57 by wiring (not shown).

In the case of such an ink jet recording apparatus 50, an ultrasonic lens is focused by an acoustic lens on the YZ plane as shown in FIG. 6, and a plurality of continuous individual electrodes shown in FIG. Group (532a-5 in FIG. 7)
The ink droplets (not shown) are simultaneously driven on the five individual electrodes 32e at timings such that the phases of the ultrasonic waves generated from the respective piezoelectric elements become the same at one point on the ink liquid surface. Can fly from the surface. In this case, by setting a plurality of simultaneous drive electrode groups, ink droplets can be caused to fly from a plurality of places at the same time.

In the ink jet recording apparatus shown in FIGS. 5 to 7, the cover plate 18 is made of bimetal as described with reference to FIGS. By providing the lever members 32 to 33 (not shown in FIGS. 5 to 7) adjacent to the inner wall surface of the chamber 16, FIGS.
The same effects as those described above can be obtained.

In an ink jet recording apparatus having piezoelectric elements arranged in an array as shown in FIGS. 5 to 7, the following is compared with the single head type ink jet recording apparatus shown in FIGS. There are significant advantages.

That is, when a two-dimensional image is formed using a single head, the head itself is usually moved mechanically in a direction perpendicular to the moving direction of the recording medium.
In this method, when mechanical vibration is generated or when the pixel density is increased, fine adjustment or complicated control is required for the movement of the head, which may cause problems such as an increase in complexity and size of the apparatus. . On the other hand, when the piezoelectric elements are arranged in an array as in the ink jet recording apparatus shown in FIGS. 5 to 7, the flying position of the ink droplet can be controlled by electronic control, so that the above problem can be avoided.

That is, for example, a simultaneous drive electrode group (for example, the electrodes 532a to 532e of the individual electrodes in FIG. 6) is used to fly the ink liquid from a predetermined point.
The ultrasonic wave is driven at a timing such that the phase of the ultrasonic wave becomes the same on the ink level immediately above. Next, the electrodes 532b to 532
If the electrode group consisting of f is driven at such a timing that the phase of the ultrasonic wave becomes the same on the ink liquid level immediately above the electrode 532d, the flying position of the ink droplet can be shifted by one individual electrode.

At this time, the focus of the ultrasonic wave on the ink liquid surface is such that if the focus on the ink liquid surface is of a degree necessary for the ink droplet to fly, the focal point of the ultrasonic focusing means will be It may be different. Specifically, the difference Δd between the distance between the ink liquid surface and the focusing means and the focal length female is λ ≦ Δd ≦ 20 with respect to the wavelength λ of the ultrasonic wave in the ink liquid 15.
If it is in the range of λ, it can be said that the ultrasonic wave is substantially focused on the ink liquid surface.

Ultrasonic focusing means 5 as shown in FIGS.
In the case of an ink jet recording apparatus having four, it is possible to discharge ink droplets from a plurality of locations, and the opening 19 can be formed in a slit shape as shown in FIG. Thus, even when the opening 19 is a slit, if the width of the slit is 1.5 mm or less, a sufficient ink liquid holding force can be obtained with surface tension. If the width is 1 mm or less, a stronger ink liquid can be obtained. A holding force can be obtained.
The length of the slit-shaped opening 19 is not particularly limited, but is usually 300 mm or less.

8 to 17, a circuit element having a temperature coefficient having a sign opposite to that of the impedance of the piezoelectric element so as to compensate for a change in the electrical impedance of the piezoelectric element due to a change in ambient temperature. An embodiment according to the ink jet recording apparatus of the present invention, which is configured to drive a piezoelectric element via the device, will be described.

FIG. 8 is a sectional view showing the structure of an example of the ink jet recording apparatus according to the present invention. FIG. 9 is a plan view of the ink jet recording apparatus shown in FIG. The figure is shown.

The ink jet recording apparatus 80 shown in FIGS. 8 and 9 has the same configuration as the ink jet recording apparatus 10 shown in FIG. That is, as described in detail with respect to the ink jet recording apparatus 10 shown in FIGS.
On the support 11 via a suitable adhesive (not shown), and an ultrasonic focusing means 14 is provided on the piezoelectric element 13. Similarly, the ink liquid holding chamber 16 for storing and holding the ink liquid 15 is composed of an outer peripheral side wall 17 and a lid plate 18 having a circular opening 19 formed therein. However, the cover plate 18 is not formed of a bimetal but is formed of a normal material such as stainless steel as described with reference to FIGS. Hereinafter, the device portion excluding the correction circuit portion is referred to as a recording portion.

In the ink jet recording apparatus 80 shown in FIGS. 8 and 9, a correction circuit element 81, which will be described in detail later, is provided on the support (substrate) 11 so as to face the recording section. When the pressure of the ultrasonic beam focused near the ink liquid level exceeds a threshold value, the ink droplet is ejected by a part of the ink liquid column on the ink liquid surface being separated. As a main cause of the instability of the ejection of the ink droplets, in addition to the above-described fluctuation of the focal length, a fluctuation of the ultrasonic beam intensity due to a temperature change was found. The intensity of the ultrasonic beam has a substantially linear relationship with the power applied to the piezoelectric element. The power is
It is determined by the voltage applied to the piezoelectric element and the electrical impedance of the piezoelectric element. In general, the characteristics of the piezoelectric element, such as the electrical impedance, change with a change in temperature. In particular, the temperature coefficient of the relative permittivity of the piezoelectric element is large, and tends to be substantially the same as the temperature coefficient of the electrical impedance.
Therefore, when the electric impedance of the piezoelectric element is an electric impedance estimated from the capacitance, the ultrasonic beam intensity can be controlled by controlling the applied voltage corresponding to the temperature coefficient of the capacitance.

FIG. 16 is a graph schematically showing the temperature dependence of the electric impedance, capacitance, and input power of the piezoelectric element. In FIG. 16, line a is for the electrical impedance of the piezoelectric element, line b is for the capacitance of the piezoelectric element, and line c is for the input power. As shown in FIG. 16, the temperature coefficients of the input power (line c) and the capacitance (line b) have the same sign (both are positive). Therefore, it is understood that the piezoelectric element 13 may be driven via the circuit element 81 that changes the applied voltage according to the change in the capacitance of the piezoelectric element. The simplest method for that is to connect in series a correction circuit element 81 having a temperature coefficient of a sign (negative) opposite to that of the electric impedance of the piezoelectric element 13.

That is, the circuit element 81 according to the present invention comprises:
A device having a temperature coefficient having a temperature coefficient opposite to that of the electrical impedance of the piezoelectric element 13 and capable of controlling a drive signal voltage applied to the piezoelectric element 13 so as to keep the intensity of the ultrasonic wave fluctuated by a temperature change constant. If used, it is used without particular limitation. For example, a capacitor or a resistor having a temperature coefficient having a sign opposite to that of the capacitance of the piezoelectric element 13 can be used. In the piezoelectric element of the present method for applying an AC signal, in particular, a capacitor can easily obtain a desired capacitance and temperature coefficient by appropriately selecting a derivative material thereof, and has a small power loss. It is more preferable because of the advantages such as the following.

More specifically, in the ink jet recording apparatus shown in FIGS. 8 and 9, the circuit element 81 having a temperature coefficient having a sign opposite to that of the electric impedance of the piezoelectric element 13 is a capacitor or a resistance element. It consists of. The capacitor or resistance element 81 is constituted by a dielectric or resistance body 811 and electrodes 812 and 813 formed on the side surfaces thereof, and one electrode 813 is connected by a lower electrode 132 of the piezoelectric element and a wiring electrode 82. I have.

The upper electrode 133 and the electrode 81 of the piezoelectric body 131
3 is supplied with a predetermined drive signal from the drive circuit 83.
The case where the correction circuit element 81 is a capacitor will be described in more detail by way of example. First, the temperature coefficient αi of the ultrasonic radiation intensity I and the temperature coefficient αc of the capacitance C of the piezoelectric element 13 are described.
Αi = 5100 (ppm / ° C.), αc = 4800
(Ppm / ° C). Note that αi and αc are respectively

[0050]

(Equation 1) It is. In this case, in the equivalent circuit shown in FIG. 10, for example, the capacitance C of the piezoelectric element 13 increases,
It is assumed that a temperature change occurs such that the ultrasonic radiation intensity I of No. 3 increases. At this time, the capacitor 81 connected in series
Since the temperature coefficient of the ultrasonic radiation intensity I (capacitance) of the piezoelectric element 13 is opposite to the temperature coefficient of the piezoelectric element 13, this capacitor 81
Of the capacitance C1 decreases. Therefore, the voltage applied to the piezoelectric element 13 decreases, and the control is performed in a direction to reduce the ultrasonic radiation intensity I. The same applies when the temperature change is reversed.

As described above, by using the capacitor 81 having the temperature coefficient of the opposite sign to the temperature coefficient of the capacitance C of the piezoelectric element 13, a sufficient expected effect can be obtained.
However, the temperature coefficient (αc1) of the capacitance of the capacitor 81 is expressed by the following equation: αc1 = − (C1 (T0)) / (C (T0)) · αc (A) (where αc is the static value of the piezoelectric element 13). Capacitance temperature coefficient T0 satisfies the relationship represented by the following expression: reference temperature C1 (T0), capacitance C (T0) of capacitor 81 at temperature T0, capacitance C (T0) of piezoelectric element 13 at temperature T0. Or expression αc1 = − (C1 (T0)) / (C (T0)) · αs (B) (where αs is the temperature coefficient T0 of the ultrasonic radiation intensity I of the piezoelectric element 13 and the reference temperature C1 (T0) satisfies the relationship expressed by the following equation: C (T0) is the capacitance of the capacitor 81 at the temperature T0, and the capacitance C (T0) is the capacitance of the piezoelectric element 13 at the temperature T0. all right.

As shown in FIGS. 8 to 10, the piezoelectric element 13 (capacitance C) and the capacitor 81 (capacitance C1)
Are connected in series to apply the voltage (V0), the voltage (V) applied to the piezoelectric element 13 is represented by the following equation (1).

V = C1 / (C1 + C) .V0 (1) The ultrasonic radiation intensity I of the piezoelectric element is expressed by the following equation (2), where S is the voltage sensitivity.

I = S · V (2) Therefore, the ultrasonic radiation intensity at the temperature T is given by the following equation (1).
(2) is calculated as follows.

[0055]

(Equation 2) here,

[0056]

(Equation 3) Then, equation (5) becomes as follows: αI = αs + C / (C1 + C) · (αc1−αc) (6) In order to eliminate the temperature change of the ultrasonic radiation intensity I of the piezoelectric element, αI = αs = 0, and αs is α
If it is almost equal to c, the following equation is obtained from equation (6).

Αc1 = −C1 / C · αc (7) αc1 = −C1 / C · αs (8) Further, C1 and C are represented by the following equations.

C1 (T) = C1 (T0) + C1 (T0) · αc1 · ΔT (9) C (T) = C (T0) + C (T0) · αc · ΔT (10) In general, αc is Since it is as small as 2000 to 10000 ppm / ° C., the following relationship is established: αc1 = −C1 (T0) / C (T0) · αc (11) (= C1 (T0) / C (T0) · αs (11 ′)) I do.

Therefore, if the capacitor 81 having such αc1 is used, the temperature change of the ultrasonic radiation intensity can be made almost zero. Further, if the allowable error in the temperature difference ΔT is 100 · a%, the relationship of −a ≦ ΔT · α1 ≦ a (12) may be satisfied.

Therefore, from the equation (6), the following equation is obtained: -a / ΔT · (C1 + C) ≦ C1αc + Cαc1 ≦ a / ΔT · (C1 + C) (13) Calculating in the same manner as equation (11), -C1 (T0) / C (T0) · αc-a / ΔT (1 + C1 (T0) / C (T0)) ≦ αc1 ≦ −C1 (T0) / C (T0 ) · Αc + a / ΔT (1 + C1 (T0) / C (T0)) (14)

For example, if C1 (T0) is almost equal to C (T0), the relationship of -αc-2a / ΔT ≦ αc1 ≦ -αc + 2a / ΔT should be satisfied.

By setting a to a value of ΔT · αs or less, the effect of temperature compensation by the capacitor is exhibited. Although it is desirable to use a capacitor for the circuit element 81, when a desired capacitor cannot be obtained, for example,
The same holds true for the above-described capacitor for the resistance element. However, in the case of using a resistance element, it is necessary to consider problems such as power consumption and heat generation of the resistance element.

FIG. 11 is a schematic sectional view showing an ink jet recording apparatus 110 having the same structure as the ink jet recording apparatus 80 described with reference to FIGS. 8 to 9 except that the piezoelectric element 13 and the circuit element 81 are integrated. .

That is, as shown in FIG. 11, a circuit element 1110 provided with a dielectric or resistor 1111 having the same size as the piezoelectric element is provided below the piezoelectric element 13. Electrodes 1112 and 1113 are formed on the entire upper and lower surfaces of the dielectric or resistor 1111. The drive signal from the drive circuit is applied to the electrode 1 of the piezoelectric element.
33 and the electrode 1112 of the circuit element 1110.
The ink jet recording apparatus having this structure also operates in the same manner as the ink jet recording apparatus 80 described with reference to FIGS. In addition, the ink jet recording apparatus 110 has the advantages of being smaller in size and easier to control than the ink jet recording apparatus 80 of FIGS.

FIGS. 12 to 14 show an ink jet recording apparatus having a structure in which a correction circuit element is integrated with a piezoelectric element as shown in FIG. 11 in an ink jet recording apparatus having a structure similar to that shown in FIGS. FIG. 12 is a schematic perspective view thereof, and FIG. 13 is a diagram showing a correction circuit, a piezoelectric element, and an ultrasonic focusing means.
FIG. 14 is a cross-sectional view of the correction circuit, the piezoelectric element, and the ultrasonic focusing means taken along the X-Z plane of FIG.

That is, the ink jet recording apparatus 1
When simply repeated, 200 has a piezoelectric element 53 on a support (substrate) 11 which has a rectangular parallelepiped shape as a whole and constitutes an ultrasonic focusing means. The piezoelectric element 53 includes a plate-shaped piezoelectric body 531, and a plurality of striped individual electrodes (532 a to 532 x) are formed on the lower surface of the piezoelectric body 531. An integral common electrode 5 is provided on the upper surface of the piezoelectric body 531.
33 are formed over the entire surface. On the piezoelectric element 53, a Fresnel lens 5 having a plurality of parallel grooves 542 to 547 formed at a predetermined pitch based on the ring theory.
41 are provided. Note that the inner surface of the side wall 17 of the ink holding chamber 16 of this recording apparatus is inclined so as to unite upward, and forms a slit-shaped opening 19.

Under the piezoelectric element 53, a flat dielectric or resistor 121 having the same planar shape as the piezoelectric 531 is provided.
The stripe-shaped individual electrodes 1212 (1212a to 1212x) having the same width and length as the individual electrodes 532 of the piezoelectric element 53 are formed on the lower surface thereof at the same intervals.

On one end side of the support 11, each individual electrode 1 formed on the lower surface of the dielectric or resistor 1211 is provided.
A plurality of array electrodes 55 are formed at the same interval as 212. Each array electrode 55 on the support 11 and each individual electrode 1212 on the lower surface of the dielectric or resistor 1212 are
They are aligned and crimped via a conductive adhesive and are electrically connected. The array electrodes 55 on the support 11 are shown in FIGS.
Similar to the structure of FIG. 7, the common electrodes 53 connected to the driving circuits 56 and 57 disposed on the ends of the support 11 by bonding wires 58 and formed on the upper surface of the piezoelectric body 531 are formed.
3 is also connected to the drive circuits 56 and 57 by wiring (not shown). In this case, the individual electrode 532 is
31 and the dielectric or resistor 1212.

Such an ink jet recording apparatus 120
Also in the case of 0, as in the case of the ink jet recording apparatus 50, ultrasonic waves are focused by an acoustic lens on the YZ plane as shown in FIG.
A plurality of continuous individual electrode groups shown in FIG.
The ink droplets (not shown) are simultaneously driven on the five individual electrodes 2a to 1212e at timings such that the phases of the ultrasonic waves generated from the respective piezoelectric elements become the same at one point on the ink liquid surface. It can fly from the ink level. In this case, by setting a plurality of simultaneous drive electrode groups, ink droplets can be caused to fly from a plurality of places at the same time. Needless to say, the inkjet recording device 12
00 is also different from the single-head type ink jet recording apparatus described with reference to FIGS.
The ink jet recording apparatus shown in FIG. 7 has all of the above advantages that the single head type ink jet recording apparatus has.

In the ink jet recording apparatus of the present invention, the driving circuit (the driving circuit 5 in FIGS. 5 and 12) is used.
6, 57, and the drive signal applied from the drive circuit 83 in FIGS. 8 and 10 is not particularly limited as long as it is a drive signal that applies a voltage so that an ink droplet is ejected corresponding to the image recording signal. Used. For example, using the example of the drive signal waveform shown in FIG. 15 to describe a case where one ink droplet is ejected, the piezoelectric elements 13 and 53 have a predetermined length, for example, the wavelength of the sound wave in the ink is 3 to 150 μm. By applying an intermittent high-frequency voltage (burst wave) at a frequency of about 0.5 to 200 μsec for an application time,
A standing wave is generated between the piezoelectric elements 13 and 53 or the acoustic lenses 14 and 54 formed on the piezoelectric elements 13 and 53 and the ink liquid level. This standing wave is focused on the ink surface by the focusing means. At the focus position of the ultrasonic wave, the ink surface rises in a conical shape to form a meniscus, and before the standing wave is attenuated, an ink droplet having a diameter corresponding to the wavelength of the ultrasonic wave separates and flies from the top of the meniscus, and the standing wave Disappears.

Although the embodiments of the present invention have been described with reference to the drawings, the present invention is not limited to these embodiments. For example, FIGS. 1 to 4 and FIG.
9 and 11, the ultrasonic focusing means 14 is constituted by the Fresnel acoustic lens 141. However, the ultrasonic focusing means 14 can be constituted by a concave acoustic lens, or the ultrasonic focusing means The means 14 can also be used as the piezoelectric element 13 by processing the upper surface of the piezoelectric element 13 into a concave surface. Also, the ink level adjusting means described with reference to FIGS. 1 to 7 and FIGS. 8 to 9, FIGS.
The circuit elements described with reference to FIG. 14 can be used in appropriate combination, and they also belong to the scope of the present invention.

[0072]

The present invention will be described below with reference to examples. Example 1 In this example, an ink jet recording apparatus having the structure shown in FIGS. 1 and 2 was manufactured.

As the piezoelectric body 131, a lead titanate ceramic was used, and the thickness was adjusted such that the resonance frequency of the thickness vibration became 50 MHz. Ti / Au laminated electrodes 132 and 133 were formed on both surfaces of the piezoelectric body 131 by sputtering at a thickness of 0.05 μm and 0.3 μm, respectively, and polarization treatment was performed. The effective aperture of the piezoelectric element 13 was 1.4 mm. The acoustic lens 141 is a glass Fresnel lens having grooves of a predetermined pitch based on the Fresnel zone design, and the grooves are formed by reactive ion etching (RIE) so that the focal length becomes 2.7 mm. The ink holding chamber 16 has a size that does not hinder the focusing of ultrasonic waves by the acoustic lens, and is installed outside the lens.

The ink holding chamber 16 is composed of a lid plate 18 provided with a circular opening 19 for keeping the liquid level near the focal length and a side wall 17. The lid plate 18 is made of a brass plate and a 34% nickel steel with a brass plate placed on top. Then, the bimetal having a thickness of 0.2 mm and bonded to each other was processed into a shape capable of obtaining a desired curvature. The diameter of the opening was 0.3 mm, and the side wall 17 was dimensioned such that the cover plate 18 was arranged at the focal position of the acoustic lens 141 when the temperature of the ink liquid was 20 ° C.

Finally, a driving circuit was connected to the piezoelectric element 13 and the ink liquid 15 was filled to complete a recording apparatus. An intermittent continuous sine wave (burst wave) was applied to the piezoelectric element 13 of such a recording apparatus to form an ink dot, and an image was obtained. At this time, the interval between the burst waves was appropriately changed depending on the image data. In this embodiment, at an ambient temperature of the inkjet recording apparatus of 20 ° C., an applied voltage of 20 Vpp,
Ink droplets were ejected at a burst wave number of 1600.

Using such an ink jet recording apparatus, the stability of the ink droplet ejection with respect to the temperature change of the ink liquid was examined. For comparison, an ink jet recording apparatus (Comparative Example 1) similar to the above recording apparatus was prepared except that the cover plate 18 was formed of a SUS plate.

These ink jet recording apparatuses were filled with a dye ink liquid, and the apparatus was set in an image recording standby state. And
The same image data was sent to these inkjet recording apparatuses at an applied voltage at which ink droplets were ejected, and printing was performed. The ambient temperature is changed in the range of 5 ° C to 30 ° C, and for each evaluation temperature,
Printing was performed.

As a result of evaluating 1,000 dots of recorded image points, dots were missing in the ink jet recording apparatus of Comparative Example 1 in a temperature environment of 10 ° C. or lower, and a maximum of 3% of ink droplets were not ejected. Further, even at 30 ° C., dot omission occurred.

On the other hand, in the ink jet recording apparatus according to the first embodiment, the dot omission occurred in a temperature environment of 15 ° C. or less, but the degree was only 0.5% at the maximum, and all the dots in the other temperature range did not. It was printed.

Example 2 In this example, an ink jet recording apparatus having the structure shown in FIGS.

The structure and specifications of this ink jet recording apparatus are the same as those of the recording apparatus of the first embodiment, except that the cover plate 18 is formed of a SUS plate having a thickness of 0.1 mm and the diameter of the opening 19 is 0.1 mm.
3 mm. The lever members 31 to 34 are formed of an invar alloy having a small linear thermal expansion coefficient, provided with a hinge portion (311 or the like), and provided so as to control expansion and contraction of the outer wall due to a temperature change to substantially the same position as fluctuation of the ink liquid level. It was joined to the plate 18. The side wall 17 was formed of polyester having a linear thermal expansion coefficient of 12 × 10 ⁻⁶ .

In order to compare the stability of ink droplet ejection due to temperature change, the side wall 17 is formed of a SUS plate having a thickness of 2 mm, and the lid plate 18 is formed of a 0.1 mm SUS plate having an opening 19 having a diameter of 0.3 mm. An ink jet recording apparatus having the same structure as in Example 2 except that was provided (Comparative Example 2).

The initial temperature was set at 20 ° C., and these ink jet recording apparatuses were adjusted. The applied voltage for stable ejection of ink droplets is 25 Vpp and the burst wave number is 15
00. The same image data was sent to two ink jet recording apparatuses at an applied voltage at which ink droplets were ejected, and printing was performed. Changing the ambient temperature in the range of 5 ° C to 30 ° C,
Printing was performed for each evaluation temperature.

As a result of evaluating 1,000 dots of recorded image points, it was confirmed that all the dots were recorded in the temperature range of 10 to 30 ° C. in the ink jet recording apparatus of Example 2. On the other hand, the inkjet recording apparatus of Comparative Example 2 having the conventional structure has
At a temperature of 15 ° C. or lower, about 1.3% of missing dots occurred with respect to the recording signal.

Example 3 In this example, an ink jet recording apparatus having the structure shown in FIGS.

The piezoelectric body 131 was formed of a lead titanate-based ceramic, and its thickness was adjusted so that the resonance frequency of the thickness vibration became 50 MHz. Ti / Au laminated electrodes 132 and 133 were formed to a thickness of 0.05 μm and 0.3 μm, respectively, on both surfaces of the piezoelectric body 131 by sputtering, and polarization treatment was performed. The effective aperture of the piezoelectric element 13 was 1.4 mm. The acoustic lens 141 is a glass Fresnel lens having grooves of a predetermined pitch based on the Fresnel zone theory,
A groove was formed by RIE so that the focal length female became 3.3 mm. The ink holding chamber 16 has a size that does not hinder the focusing of ultrasonic waves by the acoustic lens, and is installed outside the lens. Further, a cover plate 18 having a circular opening 19 for keeping the liquid level near the focal length was provided.

As the circuit element 81, a ceramic capacitor having substantially the same capacitance as the piezoelectric element 13 and having a temperature coefficient opposite to that of the piezoelectric element 13 is used.
This was mounted on a substrate 11. The capacitance of the ceramic capacitor was 10 pF, and a chip capacitor having a temperature coefficient of capacitance of −5000 ppm / ° C. in a temperature range of 5 ° C. to 30 ° C. was used.

Finally, the driving circuit 83 was connected to the electrode 133 of the piezoelectric element 13 and the electrode 812 of the circuit element 81, and the ink liquid 15 was filled to complete the recording apparatus. FIG. 15 shows the piezoelectric element 13 of the ink jet recording apparatus thus obtained.
An ink dot was formed by applying an intermittent continuous sine wave (burst wave) as shown in (1), and an image was obtained (in FIG. 15, a symbol Vrf is a burst peak value, a symbol tb is a burst time, and a symbol tc is a burst. Application cycle). The interval between the burst waves was appropriately changed depending on the image data. In the present embodiment, at an ambient temperature of the inkjet recording apparatus of 20 ° C., an applied voltage of 40 Vpp and a burst wave number of 1
At 500, an ink droplet was ejected. When both ends of the circuit element 81 (ceramic capacitor) were short-circuited, ink droplets were ejected at an applied voltage of 20 Vpp.

The stability of ink droplet ejection with respect to the temperature change of the piezoelectric element was examined using these ink jet recording apparatuses (the case where both ends of the circuit element were not short-circuited (the present invention) and the case where the both ends were short-circuited (Comparative Example 3)). These ink jet recording apparatuses were filled with a dye ink liquid to be in an image recording standby state, and the same image data was sent to these ink jet recording apparatuses at the applied voltage at which ink droplets were ejected, and printing was performed. As a result of evaluating 1,000 dots of recorded image points, both ink jet recording apparatuses recorded all image points with respect to the recording signal.

Based on this condition, the ambient temperature is set to 5 ° C.
Printing was performed for each evaluation temperature by changing the temperature in the range of 30 ° C. Similarly, as a result of evaluating 1000 dots of recorded image points, in the ink jet recording apparatus of Comparative Example 3, dots were missing in a temperature environment of 15 ° C. or lower, and a maximum of 3% of ink droplets were not ejected. At 30 ° C., a phenomenon that the dot diameter becomes large occurred.

On the other hand, in the ink jet recording apparatus of the present invention in which a voltage is applied via the circuit
Dot missing occurred in the following temperature environment.
The maximum value was 0.5%, and the phenomenon of increasing the dot diameter did not occur.

Example 4 In this example, an ink jet recording apparatus having the structure shown in FIG. 11 was manufactured. The configuration and specifications of the ink jet recording apparatus are the same as those of the recording apparatus of the third embodiment.
As shown in FIG. 5, the piezoelectric element 13 and the circuit element 1110 are integrated.

Since the circuit element 1110 has substantially the same shape as the piezoelectric element 13, the temperature coefficient is −5000 ppm /
A ceramic material having a relative dielectric constant of 200 ° C. and a dielectric material 11
The thickness is adjusted so that the capacitance becomes almost the same as that of the piezoelectric element 13, and Ti / Au laminated electrodes are formed on both surfaces thereof by sputtering at 0.05 μm and 0.3 μm, respectively.
It was formed to a thickness of μm. The circuit element 1110 and the piezoelectric element 13 were stacked.

An experiment similar to that of Example 3 was performed using this recording apparatus. As a result, the voltage applied to stably eject ink droplets was 45 Vpp, and the burst wave number was 1500. When both ends of the circuit element 1110 were short-circuited (Comparative Example 4), the applied voltage was 23 Vpp and the burst wave number was 1500.

In these two ink jet recording apparatuses,
The same image data is sent at the applied voltage at which ink droplets are ejected,
Printing was performed. Printing was performed at 20 ° C. As a result of evaluating 1000 dots of recorded image points, all of the two ink jet recording apparatuses recorded all image points with respect to the recording signal.

Based on this state, the ambient temperature is set to 5 ° C.
Printing was performed for each evaluation temperature by changing the temperature in the range of 30 ° C. Similarly, as a result of evaluating 1,000 dots of recorded image points, all the image points were recorded by the inkjet recording apparatus of the present invention in which a voltage was applied via the circuit element 110. In contrast,
In the ink jet recording apparatus of Comparative Example 4 in which both ends of the circuit element 1110 were short-circuited, dots were missing in a temperature environment of 15 ° C. or less, and about 3% of ink droplets were not ejected. At 30 ° C., a phenomenon image in which the dot diameter was large occurred.

[0097]

As described above, according to the present invention, there is provided an ink jet recording apparatus capable of stably ejecting ink droplets irrespective of a change in ambient temperature and forming a stable quality image. Is done.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of an ink jet recording apparatus according to a first embodiment of the present invention.

FIG. 2 is a plan view of a part of the ink jet recording apparatus shown in FIG.

FIG. 3 is a schematic sectional view of an ink jet recording apparatus according to a second embodiment of the present invention.

FIG. 4 is a plan view of a part of the ink jet recording apparatus shown in FIG.

FIG. 5 is a schematic perspective view of an ink jet recording apparatus according to a third embodiment of the present invention.

FIG. 6 shows a part of Y of the ink jet recording apparatus shown in FIG.
Sectional drawing along the -Z plane.

FIG. 7 shows a part X of the ink jet recording apparatus shown in FIG.
Sectional drawing along the -Z plane.

FIG. 8 is a schematic sectional view of an inkjet recording apparatus according to a fourth embodiment of the present invention.

9 is a plan view of a part of the ink jet recording apparatus shown in FIG.

FIG. 10 is an equivalent circuit diagram of a piezoelectric element and a circuit element of the ink jet recording apparatus shown in FIG.

FIG. 11 is a schematic sectional view of an inkjet recording apparatus according to a fifth embodiment of the present invention.

FIG. 12 is a schematic perspective view of an ink jet recording apparatus according to a sixth embodiment of the present invention.

FIG. 13 is a cross-sectional view of a part of the inkjet recording apparatus shown in FIG. 12 along the YZ plane.

14 is a cross-sectional view of a part of the ink jet recording apparatus shown in FIG. 12, taken along the XZ plane.

FIG. 15 is a graph showing the electrical impedance and capacitance of a piezoelectric element and the temperature dependence of input power.

FIG. 16 is a drive voltage waveform diagram that can be used in the ink jet recording apparatus of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 11 ... Support body 13, 53 ... Piezoelectric element 12 ... Adhesive 14, 54 ... Ultrasonic focusing means 15 ... Ink liquid 16 ... Ink chamber 17, 171-174 ... Ink chamber side wall 18 ... Ink chamber lid plate 19 ... Lid Plate openings 31-34 Lever members 56, 57, 83 Driving circuits 81, 1110 Compensation circuit elements 131, 531 Piezoelectric bodies 132, 133, 532, 533, 1112, 111
3, 1212 ... electrode 311, 331 ... hinge part of lever member 142-144, 542-547 ... Fresnel lens groove 811, 1211 ... dielectric or resistor

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Kenichi Mori 1st Toshiba R & D Center, Komukai, Kawasaki City, Kanagawa Prefecture (72) Inventor Hitoshi Yagi Komukai Toshiba, Saiwai District, Kawasaki City, Kanagawa Prefecture No. 1 Town, Toshiba R & D Center (72) Inventor Noriko Yamamoto No. 1, Komukai Toshiba Town, Koyuki-ku, Kawasaki, Kanagawa Prefecture, Japan Toshiba R & D Center

Claims (5)

[Claims] 1. An ink holding chamber for holding an ink liquid, an ultrasonic generating means acoustically connected to the ink liquid and including a piezoelectric element, a driving means for driving the ultrasonic generating means, and the ultrasonic wave And an ultrasonic focusing means including an ultrasonic focusing lens member formed on the generating means and focusing the ultrasonic waves generated from the ultrasonic generating means near the liquid surface of the ink liquid. An ink jet recording apparatus, comprising: means for adjusting an ink liquid level in the ink holding chamber so as to compensate for a focus position of an ultrasonic wave that fluctuates due to a change in temperature. 2. The ink liquid level control means includes a lid plate of the ink holding chamber having an opening at a position where ultrasonic waves are focused, and the lid plate is made of bimetal. Item 2. An inkjet recording apparatus according to Item 1. 3. The ink level control means includes: a lid plate of the ink holding chamber having an opening at a position where an ultrasonic wave is focused; and a side wall of the ink holding chamber, which expands and contracts due to a change in ambient temperature. 2. An ink jet recording apparatus according to claim 1, further comprising a lever member for moving said lid plate in response to said expansion and contraction of the side wall. 4. An ink holding chamber for holding an ink liquid, ultrasonic generating means acoustically connected to the ink liquid and including a piezoelectric element, driving means for driving the ultrasonic generating means, and the ultrasonic wave An ultrasonic focusing unit including an ultrasonic focusing lens member formed on a generating unit and focusing an ultrasonic wave generated by the ultrasonic generating unit near a liquid surface of the ink liquid; Driving means is connected to the piezoelectric element via a circuit element having a temperature coefficient having a sign opposite to that of the impedance of the piezoelectric element so as to compensate for a change in electrical impedance of the piezoelectric element due to a change in ambient temperature. An ink jet recording apparatus comprising: 5. An ink jet recording apparatus according to claim 1, wherein said circuit element is a capacitor or a resistance element.