JPH1177995A - Ink jet recording device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable application of uniform voltage to all piezoelectric elements by providing a means to make an impedance uniform for an electrical impedance in each of subgroups, in an ink jet recording device which discharges an ink droplet under the pressure of an ultrasonic beam to be emitted by the piezoelectric elements. SOLUTION: This ink jet recording device selects plural pieces (e.g. 16 pcs) of piezoelectric element excepting piezoelectric elements located on both ends as simultaneous drive elements and drives 16 pieces of the piezoelectric element by allocating these elements into a first subgroup comprising 10 pieces of the piezoelectric element and a second subgroup comprising 6 pieces of the piezoelectric element, based on a Fresnel ring belt theory. In this case, a burst wave generated by a burst wave generator 31 is separated into two burst waves whose phase is reversed 180 deg. by a phase reactor 32. Further, the first and the second burst wave are amplified and these amplified burst waves are applied to the individual electrodes 13 of the piezoelectric elements related to the first and the second subgroups respectively by turning switches SW111-SW128 and SW211-SW218 ON/OFF.

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 ink droplets into droplets and flying them onto a recording medium, and more particularly, to an ultrasonic beam radiated by a piezoelectric element. The present invention relates to an ink jet recording apparatus that ejects ink droplets by pressure to fly on a recording medium.

[0002]

2. Description of the Related Art An apparatus for recording an image by forming an image point by making an ink liquid into small particles called droplets and flying on a recording medium has been put to practical use as an ink jet printer. This ink-jet printer has the advantages that it has less noise than other recording methods and does not require processing such as development and fixing, and has been attracting attention as a plain paper recording technique.

[0003] A number of ink jet printer systems have been devised up to now. In particular, a system in which ink droplets fly by the pressure of steam generated by the heat of a heating element, or a method in which ink droplets are formed by pressure pulses due to displacement of a piezoelectric body. The method of flying is typical.

[0004] These ink jet printers fly ink from the tip of a nozzle. For this reason, there is a problem that local concentration of the ink occurs due to evaporation and volatilization of the solvent in the ink, and the nozzle is clogged. Further, in the conventional ink jet printer, it is difficult to reduce the particle size of the ink droplet to be ejected (for example, a diameter of 20 μm or less), and it is difficult to increase the resolution.

In order to overcome these drawbacks, a method has been proposed in which ink is ejected from an ink liquid surface using the pressure of an ultrasonic beam generated by a piezoelectric element constituted by a thin film piezoelectric layer. However, in the conventional ultrasonic beam system, it has been found that, for example, if the number of simultaneously driven piezoelectric elements is different, the flying efficiency and flying stability of ink droplets are reduced.

[0006]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an ink jet recording apparatus in which the flying efficiency and flying stability of ink droplets are not reduced even when the number of simultaneously driven piezoelectric elements is different. As an issue.

[0007]

In order to solve the above problems, the present invention provides an ink liquid holding chamber for holding an ink liquid,
Including a piezoelectric element array constituted by a plurality of piezoelectric elements arranged at predetermined intervals, an ultrasonic wave generating means for generating ultrasonic waves propagating in the ink liquid, and a piezoelectric element constituting the piezoelectric element array Selecting a plurality of simultaneously driven piezoelectric elements as a simultaneously driven group, distributing the plurality of simultaneously driven piezoelectric elements into a plurality of simultaneously driven subgroups, applying a drive signal having a phase difference to each of the simultaneously driven subgroups; Driving means for simultaneously driving the ultrasonic waves generated from the simultaneously driven piezoelectric elements of the simultaneously driven group to the liquid surface of the ink liquid, and impedance for equalizing the total electric impedance of each of the subgroups to each other Provided is an ink jet recording apparatus comprising a uniforming means.

[0008] The impedance equalizing means may include a variable capacitance element. In this case, a capacitance corresponding to the difference in the capacitance is applied to the drive signal to the sub-group having a small number of piezoelectric elements so that the total capacitance becomes the same as the total capacitance of the sub-group having the largest number of piezoelectric elements. Thus, the impedance between the subgroups can be made uniform.

The impedance equalizing means is provided in an acoustically unconnected state with the ink liquid, and one or more dummy piezoelectric elements to which a driving signal is applied simultaneously with the simultaneously driven piezoelectric elements by the driving means. Can be included. In this case, the same drive signal as the drive signal to the subgroup consisting of the smaller number of piezoelectric elements is applied to the dummy piezoelectric elements corresponding to the difference in the number of the piezoelectric elements in the subgroup, whereby each subgroup is The impedance between them can be made uniform.

A plurality of simultaneously driven piezoelectric elements are selected as a simultaneously driven group from the piezoelectric elements constituting the piezoelectric element array for generating ultrasonic waves, and the plurality of simultaneously driven piezoelectric elements are divided into a plurality of simultaneously driven subgroups. When the ultrasonic waves generated from the piezoelectric elements of the simultaneous driving group are focused on the liquid surface of the ink liquid, the piezoelectric elements belonging to the simultaneous driving sub group are simultaneously driven by giving a phase difference to each of the simultaneous driving sub groups. It is important that the flight efficiency and flight stability of ink droplets do not decrease even when the number of sub-groups differs between subgroups. In particular, when using a driving method of doubling the resolution by making the number of simultaneously driven piezoelectric elements selected from the piezoelectric element array odd or even, or connecting a plurality of piezoelectric element arrays in the array direction. Efficient and stable even when the number of piezoelectric elements to be driven changes during the recording of one image, such as when driving the connecting part when a long line head is manufactured. The ink drops must fly.

The present inventors have sought to determine the cause of the drop in the ink flying efficiency and flying stability when the number of piezoelectric elements belonging to each sub-group driven simultaneously is different between the sub-groups. As a result, if the number of piezoelectric elements belonging to each sub-group to be simultaneously driven is different between the sub-groups, the cause is that the electrical impedance of each simultaneously driven sub-group viewed from the driving source differs between the sub-groups. I found Therefore, in the present invention, an impedance equalizing means for equalizing the electrical impedance of each of the subgroups is provided.

According to this method, even when the number of piezoelectric elements in each of the simultaneously driven element groups is different, it is possible to uniformly apply a voltage to all the piezoelectric elements.
The intensity of the ultrasonic beam at the focal position is improved, and the stability and reliability of ink flying can be improved. Further, stable flight of ink droplets can be realized with a lower applied voltage, and the efficiency of ink flight can be improved.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. Throughout the drawings, the same members are denoted by the same reference numerals. <First Embodiment> FIG. 1 is a schematic perspective view of a head portion of an ink jet recording apparatus according to an embodiment of the present invention. In FIG. 1, a flat plate-shaped piezoelectric body 12 constituting the ultrasonic wave generating means has a support member 11 in which a groove 11a described later is formed.
Above, it is provided across the groove 11a.

The piezoelectric body 12 is made of a ceramic material such as lead titanate (PT), zircon / lead titanate (PZT), or a mixture of vinylidene fluoride and ethylene trifluoride depending on the frequency of ultrasonic waves and the size of the element. It can be formed of a polymer material such as a polymer, a single crystal material such as lithium niobate, or a piezoelectric semiconductor material such as zinc oxide.

The support member 11 can be formed of a material such as glass. A plurality of striped individual electrodes 13 separated from each other are formed on the lower surface of the piezoelectric body 12.
The piezoelectric body 12 is functionally divided into a plurality of piezoelectric elements by the individual electrodes 13. On the other hand, on the upper surface of the piezoelectric body 12, an integral common electrode 14 is formed over the entire surface. These electrodes 13 and 14 are made of titanium, nickel,
A metal material such as aluminum, copper, or gold can be formed as a thin film by vapor deposition or sputtering. Alternatively, these electrodes 13 and 14 can also be formed by printing a mixture of glass frit and silver paste by a screen printing method and baking it.

On one end of the support member 11, a plurality of array electrodes 15 are formed at the same intervals as the individual electrodes 13 formed on the lower surface of the piezoelectric body 12.
The array electrodes 15 on the first electrode 1 and the individual electrodes 13 on the lower surface of the piezoelectric body 12 are aligned and pressure-bonded via a conductive adhesive (not shown), and are electrically connected. The array electrode 15 on the support member 11 is connected to a drive circuit 16 disposed on an end of the support member 11 by a bonding wire 17, and the common electrode 14 formed on the upper surface of the piezoelectric body 12 is also , Driving circuit 16.

A one-dimensional Fresnel lens 18 serving as an acoustic lens also serving as an acoustic matching layer is provided on the piezoelectric body 12 with the common electrode 14 interposed therebetween. The Fresnel lens 18 has a plurality of grooves (six grooves 18a to 18 in FIG. 1) at a predetermined pitch based on Fresnel's ring zone theory.
8f), the phase of the ultrasonic wave radiated from the top and bottom surfaces of the groove is shifted by a half wavelength,
Each of the grooves 18 a to 18 f is formed in parallel with the arrangement direction (main scanning direction) of the piezoelectric elements divided by the individual electrode 13. The acoustic matching layer is used for acoustic matching between the piezoelectric element and the ink liquid in order to minimize the attenuation of the ultrasonic wave when the ultrasonic waves generated from the piezoelectric element are propagated into the ink liquid. The acoustic impedance Z _{m of the} layer is the acoustic impedance Z of the piezoelectric body.
It is desirable to use a material having an acoustic impedance close to the square root of the product of _p and the acoustic impedance Z _i of the ink liquid (Z _m = (Z _p × Z _i ) ^1/2 ). Examples of such an acoustic matching material include a polymer material such as epoxy resin and polyimide, or a mixture of the polymer material and a powder such as fiber or alumina or tungsten for adjusting acoustic impedance. . In the example of FIG. 1, the Fresnel acoustic lens 1
Since 8 also functions as an acoustic matching layer, it is desirable to form it from such a material.

Further, on the support member 11, an ink liquid holding chamber 19 for containing and holding the ink liquid 20 with the Fresnel lens 18 as a bottom is provided. The ink liquid holding chamber 19 is inclined such that the side walls surrounding the ink liquid 20 meet upward from both ends of the Fresnel lens,
The upper part is closed by a lid plate 21 having a slit 21a. Note that the upper surface of the ink liquid holding chamber 19 may directly constitute a slit without providing the cover plate 21.

In the ink jet recording apparatus shown in FIG. 1, each individual electrode 13 formed on the lower surface of the piezoelectric body 12 has a length equal to the width of the piezoelectric body 12. However, the common electrode 14 formed on the upper surface of the piezoelectric body 12
Are formed only in portions excluding both ends of the piezoelectric body 12 so as to cover the effective width of the Fresnel lens 18 as an acoustic lens. Therefore, the portion of the piezoelectric body 12 that functions as each piezoelectric element is only a region corresponding to the common electrode 14. In other words, the piezoelectric body 12 extends on both sides of the piezoelectric element, and the piezoelectric body 12 is supported by the support member 11 at the extended portion. Further, the groove 11 a provided in the support member 11 has a width substantially matching the width of the common electrode 14. That is, the piezoelectric element composed of the portion of the piezoelectric body 11 sandwiched between the individual electrode 13 and the common electrode 14 has a groove 11a on the lower side, that is, the lower side of the piezoelectric element has a hollow structure. Therefore, it is placed in a non-contact state with the support member 11. When recording, individual electrodes 1
And simultaneously driving some drive element groups of the plurality of piezoelectric elements divided by 3 to focus ultrasonic waves near the ink liquid level,
At this time, the ultrasonic wave radiated from the piezoelectric element to the back surface side is canceled by air normally present in the groove 11a located on the back surface of the piezoelectric element, and is reflected toward the ink liquid 20 side. Nothing. However, it is not necessary to provide such a groove 11a.

Next, an example of a method of focusing ultrasonic waves generated from the piezoelectric elements and a method of driving the piezoelectric elements in the above-described ink jet recording apparatus will be described. First, the individual electrode 1
As a method of converging ultrasonic waves in the array arrangement direction (main scanning direction) of the piezoelectric elements divided into an array from 3, a predetermined simultaneous driving element is selected from the piezoelectric element array based on the Fresnel zone theory. , And these are divided into a plurality of simultaneous driving element subgroups, and a driving method is used in which each of the simultaneous driving element subgroups is given a predetermined phase difference and driven simultaneously. For example, the simultaneous driving elements selected from the piezoelectric element array are divided into two (first and second) simultaneous driving element subgroups,
Is driven by inverting the phase by 180 ° with respect to the second simultaneous driving subgroup. As described above, by controlling the phase of the ultrasonic wave radiated from each piezoelectric element, the intensity of the ultrasonic wave is locally increased in the vicinity of the ink liquid level, so that the focal point is formed.

On the other hand, the focusing of ultrasonic waves in a direction (sub-scanning direction) orthogonal to the arrangement direction of the piezoelectric elements is performed by an acoustic lens, here, a Fresnel lens 18. In this way, by focusing the ultrasonic waves from the two directions, the ink droplets are ejected and fly from an arbitrary position on the ink liquid surface by the ultrasonic pressure. The flying position of the ink droplet can be changed by electronically scanning the simultaneous driving element. Further, by selecting a plurality of the simultaneous driving element groups from among the piezoelectric elements arranged in an array, a plurality of ink droplets can be caused to fly at the same time.

FIG. 2 shows an example of a driving circuit in the head of the ink jet recording apparatus shown in FIG. The drive circuit (drive means) 16 includes a burst wave generator 31 that generates a burst wave of an arbitrary waveform at a predetermined frequency and for a predetermined output duration. On the one hand, the burst generator 31 has a line L connected to the grounded common electrode 14.
1 and on the other hand to the phase inverter 32 via line L2. From this phase inverter 32, two lines L3 and L4 are branched.

The phase inverter 32 has, on the one hand, a line L3
Is connected to a first amplifier (power amplifier) 33 via a line L5, and the first amplifier 33 is connected to a corresponding switch SW111 to SW128 via a line L5, and on the other hand, via a line L4. The second amplifier (power amplifier) 34 is connected to this second amplifier 3
4 is a corresponding switch SW211 via a line L6.
To SW228. Each pair of switches SW
111 and SW211, SW112 and SW212 ... SW
128 and SW228 are individually electrodes 13 (1) to
13 (18). Hereinafter, the individual electrodes 13
The piezoelectric elements defined by (1) to 13 (18) are denoted by reference symbols T (1) to T (18).

Each of the lines L5 and L6 has a corresponding one of the switches SW111-SW128 and SW211-SW228.
, An impedance conversion element (variable capacitance element) 35 via switches SW3 and SW4, respectively.
And 36 are connected. The variable capacitance elements 35 and 36 are each grounded.

In the above configuration, the piezoelectric elements T at both ends are
Sixteen piezoelectric elements except two of (1) and T (18) are selected as simultaneous driving elements, and these sixteen piezoelectric elements are composed of a total of ten piezoelectric elements based on the Fresnel zone theory. The case where the driving is divided into the first sub-group and the second sub-group composed of a total of six piezoelectric elements will be described below.

First, the burst wave generated by the burst wave generator 31 is separated by the phase inverter 32 into two burst waves whose phases are inverted by 180 degrees from each other. One of the first burst waves (this phase is represented by 0, and FIG.
The symbol “0” is assigned to the individual electrode to which the zero-phase burst wave is applied in the first sub-group. This is amplified by the amplifier 33 and then appropriately opened and closed by the switches SW111 to SW128. Piezoelectric element T belonging to
(3), T (4), T (6), T (8) to T (11),
Individual electrodes 1 of T (13), T (15) and T (16)
3 (3), 13 (4), 13 (6), 13 (8) to 13
(11), 13 (13), 13 (15) and 13 (1
6) is applied.

The other second burst wave (this phase is represented by π, and the individual electrode to which the π-phase burst wave is applied in FIG. 2 is denoted by “π”) is After being amplified by the amplifier 34, the switches SW211-SW
By appropriate opening and closing of 218, the piezoelectric elements T (2), T (5), T (7), T (1) belonging to the second sub-group
2), individual electrodes 13 of T (14) and T (17)
(2), 13 (5), 13 (7), 13 (12), 13
(14) and 13 (17).

At this time, the number of piezoelectric elements differs between the first sub-group and the second sub-group (in this example,
The total capacitance of the piezoelectric elements of the first sub-group is equal to that of the piezoelectric elements of the second sub-group because the number of the piezoelectric elements of the sub-group is four more than the piezoelectric elements of the second sub-group. Is larger than the total capacitance of the piezoelectric elements by an amount corresponding to the difference in the number of piezoelectric elements (four in this example). Now, let the capacitance of one piezoelectric element be αpF
(Picofarad), 4 × αp
The capacitance of F is applied from the second variable capacitance element 36 to the second subgroup of piezoelectric elements via line L6.
In this way, the total electric capacity of the piezoelectric elements of the first sub-group and the total electric capacity of the second sub-group are equalized, and the electrical impedance of both sub-groups is equalized. Voltage can be applied to the ink jet recording apparatus, and the stable flight of the ink droplet can be realized with a lower power supply voltage, and the flying efficiency of the ink can be improved. <Second Embodiment> FIG. 3 shows the ink jet recording apparatus shown in FIG. FIG. 8 is a perspective view showing a piezoelectric element array and a Fresnel lens part which can be used in place of the piezoelectric element array and the Fresnel lens part in the head part. The structure of the ink liquid holding chamber, the support, and the arrangement of the drive circuit are the same as those in FIG.

However, rectangular notches 41 and 42 are provided at both ends of the Fresnel lens in the longitudinal direction (sub-scanning direction) of the individual electrodes 13 (1) to 13 (18). A groove formed between the base 42 and each end of the underlying common electrode includes an acoustic non-matching layer 4.
3 and 44 are provided, and the individual electrodes 13 (1) to 13 (3) and 13 (16) to 13
The piezoelectric elements (T (1) to T (1) to T
The ultrasonic waves generated from (3) and T (16) to T (18)) are not acoustically connected to the ink liquid. That is, even if a drive signal is applied to these piezoelectric elements, their ultrasonic waves do not propagate to the ink liquid, and these piezoelectric elements become dummy (in FIG. D "). The acoustic non-matching layers 43 and 44 are preferably formed of a material having an acoustic impedance of a value as far as possible from the value of the square root of the product of the acoustic impedance of the piezoelectric material and the acoustic impedance of the ink liquid. The acoustic non-matching layers 43 and 44 can be formed of, for example, silicone rubber.

FIG. 4 shows the driving circuit 16 in FIG. 1 of the head section of the ink jet recording apparatus described with reference to FIG. 2. This driving circuit does not include the impedance conversion elements 35 and 36, and therefore, has the switch SW3 and the switch SW3. The configuration is the same as that shown in FIG. 2 except that SW4 is not provided.

In the above configuration, the piezoelectric elements T (1) to T (1)
T (18), the central ten piezoelectric elements T (5) to
T (14) is selected as a simultaneous driving element, and the ten piezoelectric elements are composed of a first subgroup of a total of six piezoelectric elements and a total of four piezoelectric elements based on the Fresnel zone theory. The case of driving by distributing to the first sub-group will be described below.

First, as described in the first embodiment, the burst wave generated from the burst wave generator 31 is separated by the phase inverter 32 into two burst waves whose phases are inverted by 180 degrees from each other. . One of the first
(The phase is represented by 0, and the individual electrode to which the 0-phase burst wave is applied is denoted by “0” in FIG. 4). By appropriately opening and closing SW111 to SW128, the piezoelectric elements T (6) belonging to the first sub-group,
Individual electrodes 13 of T (8) to T (11) and T (13)
(6), 13 (8) to 13 (11) and 13 (13)
Is applied.

The other second burst wave (this phase is represented by π, and the individual electrode to which the π-phase burst wave is applied in FIG. 4 is denoted by the symbol “π”) is referred to as the second burst wave. After being amplified by the amplifier 34, the switches SW211-SW
By appropriately opening and closing 228, the piezoelectric elements T (5), T (7), T (12) and T
The individual electrodes 13 (5), 13 (7), 13 (1) of (14)
2) and 13 (14).

At this time, the number of piezoelectric elements differs between the first sub-group and the second sub-group (in this example,
The two sub-groups have two more piezoelectric elements than the second sub-group. Therefore, the electric impedance of the first sub-group is equal to the electric impedance of the second sub-group. Than the two piezoelectric elements. Therefore, according to the present invention,
One element (for example, T (2)) from the dummy piezoelectric elements T (1) to T (3) and the dummy piezoelectric elements T (16) to
From T (18), a π-phase burst wave signal as a second burst wave is applied to one element (for example, T (17). In this case, dummy piezoelectric elements T (2) and T (2) are applied).
(17) hardly emits ultrasonic waves into the ink liquid due to the ultrasonic shielding effect of the acoustic non-matching layers 43 and 44, but the number of driving elements in the first simultaneous driving subgroup and the second simultaneous driving subgroup is made equal. And make the electrical impedance uniform. Thus, also in the second embodiment, ink droplets fly efficiently and stably. Then, as in the first embodiment, as a result of equalizing the electrical impedance, the voltage applied to the piezoelectric element is made uniform, so that the intensity of the ultrasonic beam at the focal position is increased, and a stable flight of the ink droplet is achieved. The required power supply voltage is reduced.

The embodiment of the present invention has been described above.
The present invention is not limited to them. For example,
The piezoelectric element array can be constituted by individually manufactured piezoelectric elements. Further, the individual electrodes can be arranged on the piezoelectric body, and the common electrode can be arranged below the piezoelectric body. Further, in the second embodiment, the acoustic non-matching layer may be formed on the acoustic matching layer and acoustic lens. Also,
A space may be provided instead of the acoustic non-matching layer. In practice, providing voids makes the fabrication process difficult,
It is very excellent as an ultrasonic wave blocking effect. In short, in the second embodiment, one or more dummy piezoelectric elements which are provided in an acoustically unconnected state with the ink liquid and to which a driving signal is applied simultaneously with the group of simultaneously driven piezoelectric elements by the driving means. Only needs to be present.

[0036]

EXAMPLES Examples of the present invention will be specifically described below. Example 1 In this example, an ink jet recording apparatus having a head having the structure shown in FIGS. 1 and 2 was manufactured.

First, plate-shaped lead titanate (PbTiO ₃ )
Ti / Au electrodes were fabricated by forming Ti and Au on one side of the piezoelectric ceramic body to a thickness of 0.05 μm and 0.5 μm, respectively, by sputtering. Continue 4kV / mm
A piezoelectric ceramic element having ferroelectricity was produced by applying the electric field of the above and performing a polarization treatment. The relative dielectric constant after polarization was about 215. Thereafter, the width is 60 μm and the electrode interval is 25 μm by chemical etching (the arrangement pitch is 85 μm).
m) Individual electrodes 13 were formed. On the other hand, after a Ti / Au array electrode having a width of 60 μm and an electrode spacing of 25 μm is formed on the glass substrate 11, a depth of 0.2 mm is formed by machining to form a hollow structure between the substrate and the piezoelectric element. A groove 11a having a size of 2.2 mm in width was formed. Then, while positioning the individual electrodes 13 formed on the ceramic piezoelectric body and the array electrodes formed on the glass under a microscope, the electrodes were adhered with an epoxy resin, and the electrodes were made conductive. Next, in order to set the frequency of the ultrasonic waves to 50 MHz, the ceramic piezoelectric body was polished to a thickness of 45 μm, and Al was subjected to electron beam evaporation to form the common electrode 14.
At this time, the length of the electrode in the sub-scanning direction, that is, the aperture is 2 m.
m.

For the acoustic matching layer / acoustic lens 18, a mixture of epoxy resin and alumina powder was used. First,
The mixing ratio was adjusted so that the sound speed was around 3 × 10 ³ m / sec, the density was 2.20 × 10 ³ kg / m ³ , and the sound speed was 2.95 ×
To obtain a 10 ³ m / s. This was applied to the surface of the common electrode 14, cured, and polished to a thickness of about 45 μm. Thereafter, the depth 1 is adjusted so that the focal length becomes 1.8 mm.
The Fresnel lens 18 was formed by forming a groove having a half wavelength (about 30 μm) in parallel with the main scanning direction. Then, a side wall (ink liquid holding chamber 19) in which the distance between the ultrasonic wave emitting surface and the ink liquid surface is approximately 1.8 mm is formed.
To complete the ink jet recording apparatus.

Using the ink jet recording apparatus thus manufactured, an ink flying experiment was performed by the driving method according to the present invention. That is, in order to form one recording dot, as described in the first embodiment, the center 16 piezoelectric elements are selected, and the ultrasonic beam is applied in the main scanning direction based on the Fresnel zone theory. To converge, these 16 selected piezoelectric elements are connected to switches SW111 to SW111.
Using SW128 and SW211 to SW228, the first and second simultaneous driving subgroups each including ten piezoelectric elements were divided into the second simultaneous driving subgroup including six piezoelectric elements.

More specifically, the burst wave generator 31
Then, a burst wave of a sine wave having a frequency of 50 MHz and an output duration of 30 μs was generated, and this was separated by a phase inverter 32 into two burst waves whose phases were inverted by 180 °. These burst waves are transmitted to power amplifiers 33, 3
After the amplification in step No. 4, the ink droplet flying experiment was performed by applying the voltage to the first and second simultaneous driving subgroups.

In the ink jet recording apparatus of this embodiment, the capacitance of one piezoelectric element is about 10 pF
Met. Therefore, the switch SW4 of the circuit for driving the second simultaneous driving subgroup is turned on, the impedance conversion element (variable capacitance element) 36 is operated, and the capacitance is added by about 40 pF. In addition, the impedance between the simultaneously driven subgroups was made uniform.

When the flying state was observed with an ultra-high speed camera, the output voltage of the burst generator 31 was required to be about 1.8 V in order for the ink droplets to fly stably. About 15 to each piezoelectric element
It was confirmed that a voltage of V was applied.

Comparative Example 1 A flying experiment of an ink droplet was performed in exactly the same manner as in Example 1 except that no electrostatic capacitance was applied from the variable capacitance element 36. As a result, in order for the ink droplet to fly stably, the output voltage of the burst wave generator 31 needs to be 2.2 V. In this case, the applied voltage to the first simultaneous drive subgroup is about 12 V, The applied voltage to the second simultaneous drive subgroup was about 20V.

Comparative Example 2 An ink drop flying experiment was performed in exactly the same manner as in Comparative Example 1, except that the number of piezoelectric elements in the first simultaneous driving sub-group and the second simultaneous driving sub-group were equal to eight. went. As a result, in order for the ink droplet to fly stably, the output voltage of the burst wave generator 31 is sufficient to be 1.4 V. In this case, as in the case of the first embodiment, all the 16 piezoelectric piezoelectric elements driven simultaneously are used. A voltage of about 15 V was uniformly applied to the device.

From the results of Example 1 and Comparative Examples 1 and 2, the number of elements of the simultaneous driving element groups that are simultaneously driven by giving a phase difference as in Comparative Example 1 is different. If there is a difference in the target impedance, the applied voltage to each piezoelectric element varies, and it has been found that the power supply voltage needs to be further increased to stably fly the ink droplet. On the other hand, when there is a difference in the electrical impedance as in the first embodiment, the power supply for achieving the stable flight of the ink droplets by operating the impedance conversion element to make the electrical impedance uniform. It was confirmed that the voltage could be reduced. The reason why the power supply voltage required for the stable flight of the ink droplet in Example 1 is low is that the applied voltage to the piezoelectric element is made uniform,
It is considered that the intensity of the ultrasonic beam at the focal position is increased. In the case of Comparative Example 2, since the number of elements of the simultaneous driving element groups that are simultaneously driven by giving a phase difference are equal and the electrical impedance as viewed from the driving source is originally equal, the ink is applied at the same applied voltage as that of the present example. A stable flight of the drops was confirmed. Example 2 In this example, an ink jet recording apparatus having the configuration described with reference to FIGS. 3 and 4 was manufactured.

This ink jet recording apparatus is the same as that of the first embodiment except that after forming the common electrode 14, the acoustic non-matching layers 43 and 44 are formed and the acoustic matching layer and acoustic lens 18 are formed. Met.

The acoustic impedance of the piezoelectric body and the acoustic impedance of the ink liquid used in this embodiment were about 35 × 10 ⁶ kg /
m ² · s and about 1.5 × 10 ⁶ kg / m ² · s, and the square root of the product is 7.2 × 10 ⁶ kg / m ² · s. On the other hand, the acoustic impedance of the mixture of the epoxy resin and the alumina powder used as the acoustic matching layer and acoustic lens in the present embodiment is about 6.5 × 10 ⁶ kg / m ² · s, which is a value close to the ideal value. ing. In addition, as a material of the acoustic non-matching layers 43 and 44, a silicone rubber having an acoustic impedance of about 1.4 × 10 ⁶ kg / m ² · s was used, and had a thickness of about 20 μm.

Using the ink jet recording apparatus thus manufactured, an ink flying experiment was performed by the driving method according to the present invention. That is, as described in the second embodiment, the central 10 piezoelectric elements are selected from the 18 piezoelectric elements to form one recording dot, and the main scanning is performed based on the Fresnel zone theory. Switches SW111 to SW128, SW so that the ultrasonic beams are focused in the directions.
Ten piezoelectric elements selected using 211 to SW228 were divided into a first simultaneous driving subgroup including six piezoelectric elements and a second simultaneous driving subgroup including four piezoelectric elements. A burst wave generator 31 generated a sine burst wave having a frequency of 50 MHz and an output duration of 35 μs. The burst wave was separated by a phase inverter 32 into two burst waves whose phases were inverted by 180 °.
After the burst waves were amplified by the power amplifiers 33 and 34, they were applied to the first and second simultaneous driving subgroups, thereby performing an ink droplet flight experiment.

Here, each of the two ends from both ends of the piezoelectric element array
The second dummy piezoelectric element was simultaneously driven in the same phase as the second simultaneous driving subgroup. Observation of the flying state with an ultra high-speed camera revealed that the output voltage of the burst wave generator was 1.6 V in order for the ink droplet to fly stably.
In this case, it was confirmed that a voltage of about 18 V was uniformly applied to all 12 piezoelectric elements that were simultaneously driven.

Comparative Example 3 An ink drop flying experiment was performed in exactly the same manner as in Example 2 except that no drive signal was applied to the two dummy piezoelectric elements. As a result, in order for the ink droplet to fly stably, the output voltage of the burst wave generating device needs to be 2.1 V. In this case, the applied voltage to the first simultaneous drive sub-group is about 16 V, and the second simultaneous drive The voltage applied to the subgroup was 23V.

As described above, the power supply voltage required for stable flight of ink droplets in Example 2 is lower than that in Comparative Example 3 because the electrical impedance is equalized, and the voltage applied to the piezoelectric element becomes uniform. This is considered to be due to an increase in the intensity of the ultrasonic beam at the focal position.

[0052]

As described above, according to the present invention, in order to focus an ultrasonic beam in the main scanning direction, a predetermined simultaneous driving element is selected from a piezoelectric element array, and a plurality of simultaneous driving element groups are selected. When driving by giving a predetermined phase difference to these multiple simultaneous drive element groups,
By equalizing the electrical impedance of each group of simultaneous driving elements as viewed from the driving source, even when the number of piezoelectric elements of each group of simultaneous driving elements is different, it is possible to apply a voltage uniformly to all the piezoelectric elements. It becomes possible. As a result, the intensity of the ultrasonic beam at the focal position is improved, and the stability and reliability of ink flying can be improved. In addition, by making the applied voltage uniform, stable flight of ink droplets can be realized with a lower applied voltage, and the efficiency of ink flight is improved.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing a configuration of a driving circuit of a head unit shown in FIG. 1;

FIG. 3 is a perspective view illustrating a part of a head unit of an ink jet recording apparatus according to a second embodiment of the invention.

FIG. 4 is a diagram showing a configuration of a driving circuit of a head unit shown in FIG. 2;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 ... Support member 11a ... Groove 12 ... Piezoelectric body 13 ... Individual electrode 14 ... Common electrode 15 ... Array electrode 16 ... Drive circuit 18 ... Ultrasonic focusing means 19 ... Ink liquid holding chamber 21a ... Slit 20 ... Ink liquid 31 ... Burst wave Generator 32 Phase inverter 35, 36 Variable capacitance element 33, 34 Amplifier 43, 44 Acoustic non-matching layer

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Isao Amemiya 1st, Komukai Toshiba-cho, Saiwai-ku, Kawasaki-shi, Kanagawa Prefecture Inside Toshiba R & D Center (72) Inventor Noriko Yamamoto Toshiba Komukai, Kochi-ku, Kawasaki-shi, Kanagawa (72) Inventor Kenichi Mori Kenichi Mori 1st place in Komukai Toshiba-cho, Saiwai-ku, Kawasaki-shi, Kanagawa Prefecture In-house Toshiba R & D Center

Claims (3)

[Claims] An ultrasonic wave including an ink liquid holding chamber for holding an ink liquid, and a piezoelectric element array constituted by a plurality of piezoelectric elements arranged at a predetermined interval, and generating ultrasonic waves propagating in the ink liquid. Generating means, selecting a plurality of simultaneously driven piezoelectric elements as a simultaneously driven group from the piezoelectric elements constituting the piezoelectric element array, distributing the plurality of simultaneously driven piezoelectric elements into a plurality of simultaneously driven subgroups, A driving unit that focuses ultrasonic waves generated from the simultaneously driven piezoelectric elements of the simultaneously driven group by applying a drive signal having a phase difference to each of the subgroups and simultaneously driving the same, and An ink jet printer comprising: impedance equalizing means for equalizing the total electric impedance of each of the subgroups. Unit recording device. 2. The ink jet recording apparatus according to claim 1, wherein said impedance equalizing means includes a variable capacitance element. 3. The one or more dummy units, wherein the impedance equalizing unit is provided acoustically disconnected from the ink liquid, and a driving signal is applied simultaneously with the simultaneously driven piezoelectric element by the driving unit. The ink jet recording apparatus according to claim 1, further comprising a piezoelectric element.