JPH1177994A - Ink jet recording apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ink jet recording apparatus capable of flying an ink liquid at an interval equal to or less than the array pitch of piezoelectric elements while having a merit of a linear electron scanning system and capable of enhancing resolution still more. SOLUTION: A second drive means for bisecting a plurality of piezoelectric elements selected from the piezoelectric elements constituting a piezoelectric element array in the arranging direction of the piezoelectric element array on the basis of the focal position of the ultrasonic beam emitted from a first piezoelectric element to form two piezoelectric element sub-groups [T(1)-T(n/2)] and T(n/2+1)-T(n) and driving second piezoelectric element groups at the same time so that the ultrasonic beams emitted from the respective piezoelectric element sub-groups become different in energy quantity at the focal position is provided in addition to a first drive means for driving a plurality of predetermined piezoelectric elements at the same time and an ink droplet flying direction is deflected to a Px direction from a vertical direction P0 by the second drive means.

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 flying an ink liquid as small droplets by a focused ultrasonic beam.

[0002]

2. Description of the Related Art An ink jet printer which forms recording dots by flying an ink liquid onto a recording medium has been conventionally known. 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. To date, a number of ink jet printer systems have been proposed. In particular, a system in which ink droplets fly by the pressure of steam generated by the heat of a heating element (for example, Japanese Patent Publication No. 56-9429, Japanese Patent Publication No. 61-5991)
No. 1) and a method in which an ink droplet is caused to fly by a pressure pulse due to displacement of a piezoelectric body (for example, Japanese Patent Publication No. 53-12)
No. 138 publication) is typical. These recording heads have been put to practical use mainly as serial scanning heads that are mounted on a carriage and repeat scanning in a direction orthogonal to the recording paper conveyance direction.

On the other hand, instead of mounting the recording head on a carriage, a recording head having the same size as the width of the paper is manufactured to reduce the size of the movable part and improve the recording speed. Are also known, but their fabrication is not easy. That is, in the line scanning method, there is a problem that local concentration of ink is apt to occur due to evaporation and volatilization of a solvent, and individual nozzles corresponding to respective resolutions are narrow, so that the nozzles are easily clogged. Especially,
In the method using steam pressure, insoluble matter adheres due to thermal or chemical reaction with the ink, and in the method using pressure due to displacement of the piezoelectric material, the complicated structure in the ink channel etc. becomes more clogged. Is easily induced. A serial scanning printhead using tens to hundreds of tens of nozzles can reduce the frequency of clogging, but a line scan printhead that requires thousands of nozzles has a low probability. Clogging occurs quite frequently,
This is a major problem in terms of reliability. Further, the line scanning method is not suitable for improving the resolution. That is,
It is difficult to generate ink droplets having a diameter of 20 μm or less (this corresponds to a recording dot having a diameter of about 50 μm on recording paper) using the pressure of steam, and the pressure due to the displacement of the piezoelectric material is used. In the method, it is difficult to produce a high-resolution head in terms of processing technology due to its complicated structure.

In order to overcome these drawbacks, there has been proposed a method 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.
4,1168 (1973-10), U.S. Pat.
08,547, US Pat. No. 4,697,195.
No. 4,751,529, U.S. Pat. No. 4,751,530, U.S. Pat.
041,849, JP-A-62-66943, JP-A-63-162253, JP-A-63-1
No. 66545, JP-A-63-166546, JP-A-63-166546
JP-A-3-166548, JP-A-63-212157, JP-A-2-184443, JP-A-3-200
199, JP-A-4-296562, JP-A-4-296563, JP-A-4-356328, JP-A-5-278218, etc.). This ultrasonic method is a nozzleless method that does not require a nozzle for each individual dot or a partition of the ink flow path, so it is important to prevent and recover from clogging, which was a major obstacle in making a line head. And has a valid structure. Further, since an ink droplet having a very small diameter can be stably ejected, it is suitable for high resolution. However, this method
Since an acoustic lens having a diameter larger than the recording pixel or the resolution, for example, 30 times as large as the recording pixel, is used, it is not possible to obtain the required resolution with only one array of the recording head, and several lines are required. It is necessary to use a so-called staggered arrangement in which spaces are filled using a head made of an array. A head having a staggered structure has many problems in terms of image quality, such as periodic density unevenness and slight displacement from adjacent dots.

Therefore, as another means for converging ultrasonic waves, a plurality of piezoelectric elements arranged in an array excite ultrasonic waves, each of which is phase-controlled, to concentrate on one point near the ink liquid level. A method has been proposed (see JP-A-2-184443). This method can change the flying position of the ink droplet without being limited by the arrangement pitch of the piezoelectric elements. However, in order for droplets to fly at each position on the ink liquid surface, it is necessary to accurately calculate and control the delay time of each piezoelectric element so that the ultrasonic waves are focused at each position, and drive The circuit becomes complicated and expensive.

To cope with such a problem, some of the piezoelectric element groups in the piezoelectric element array are simultaneously driven to cause one ink droplet to fly, and the positions of the simultaneously driven piezoelectric element groups are sequentially shifted so that the ink droplets are shifted. There has been proposed a linear electronic scanning method for moving the flying position of a camera. In this method, since the delay time for each piezoelectric element is set to be symmetrical with respect to the center of the piezoelectric element group, the ink droplet always flies straight in the direction perpendicular to the liquid surface. In addition, if the number of simultaneously driven piezoelectric element groups is fixed, scanning can be performed only by switching the combination of the piezoelectric element groups. Therefore, the driving circuit does not need to control complicated delay time, and one group is not required. It is only necessary to control the delay time pattern of the piezoelectric element. Furthermore, as a method of setting the delay time in the linear electronic scanning method, the piezoelectric element array is further divided into two groups based on the Fresnel diffraction theory, instead of setting the quadratic function of the delay time used in the normal electronic focusing method. A simpler method has been proposed in which the delay time is set so that the phases are different from each other by half a wavelength. However, in such a linear electronic scanning method, the flying position of the ink droplet depends on the arrangement pitch of the piezoelectric elements, and the ink droplet cannot fly below the pitch, and it is difficult to further improve the resolution.

[0007]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to make it possible to fly an ink liquid at an interval equal to or less than the arrangement pitch of piezoelectric elements while having the advantage of a linear electronic scanning system, thereby achieving a higher resolution. An object of the present invention is to provide an ink jet recording apparatus capable of improving the recording quality.

[0008]

In order to solve the above problems, the present invention provides an ink holding chamber for holding an ink liquid, and a plurality of piezoelectric chambers acoustically connected to the ink liquid and arranged at predetermined intervals. An ultrasonic wave generating means including a piezoelectric element array constituted by elements, and a first comprising a plurality of piezoelectric elements selected from the piezoelectric elements constituting the piezoelectric element array.
A first driving unit for simultaneously driving the piezoelectric element group so that the ultrasonic waves generated from the first piezoelectric element group are focused on a predetermined position on the surface of the ink liquid; and the piezoelectric element array. With respect to a second piezoelectric element group consisting of a plurality of piezoelectric elements selected from among the piezoelectric elements to be constituted, the ultrasonic beam generated from the second piezoelectric element group is moved to the predetermined position on the liquid surface of the ink liquid. So that the second piezoelectric element group is divided into two in the array direction of the piezoelectric element array based on the predetermined position.
, So that the amount of energy at the predetermined position of the ultrasonic beam radiated from each of the piezoelectric element subgroups is different.
And a second driving means for simultaneously driving the piezoelectric element group.

The present inventors have found that an ink jet recording apparatus that records an image by ejecting ink droplets from an ink liquid surface by means of the radiation pressure of an ultrasonic beam and flying over a recording medium cannot be achieved by the conventional method. In order to achieve higher recording speed and higher resolution, a plurality of piezoelectric elements are arranged at predetermined intervals to form a piezoelectric element array, and a part of the piezoelectric element groups is given a predetermined phase difference and driven. To focus the ultrasonic beam near the ink surface to fly the ink droplets,
There has been proposed an ink jet recording apparatus based on a linear electronic scanning system in which a combination position of a part of the piezoelectric element groups is moved. However, as mentioned above,
In such a linear electronic scanning method, the flying position of the ink droplet depends on the arrangement pitch of the piezoelectric elements, and the ink droplet cannot fly below the pitch, and the resolution cannot be further improved.

In the ink jet recording apparatus based on the above-mentioned linear electronic scanning system, the present inventors have proposed a driving device which groups piezoelectric element arrays and linearly drives the piezoelectric elements (first piezoelectric element group) of each group simultaneously. In addition, a plurality of piezoelectric elements selected from the piezoelectric elements constituting the piezoelectric element array are bisected in the arrangement direction of the piezoelectric element array based on the focal position of the ultrasonic beam radiated by the first piezoelectric element. And a second driving means for simultaneously driving the second piezoelectric element group so that the ultrasonic beams emitted from the respective piezoelectric element sub groups have different energy amounts at the focal position. As a result, it is possible to change the flying position variously regardless of the arrangement pitch of the piezoelectric elements, and it is possible to record an image with extremely high resolution. Found that, it has led to the completion of the present invention.

More specifically, in the present invention, assuming that a piezoelectric element array is composed of, for example, more than n piezoelectric elements, first, a total of n piezoelectric elements from the first to the n-th are arranged. These n piezoelectric elements are simultaneously driven by a first driving means as a first piezoelectric element group. At this time, an ultrasonic beam radiated from the n piezoelectric elements at a point where an axis perpendicular to the center in the arrangement direction of the first piezoelectric element group (hereinafter, referred to as a central axis of the piezoelectric element group) intersects the ink liquid level. Are driven to converge. In this case, the ink droplet flies perpendicularly to the center axis of the piezoelectric element group, that is, a plane including the piezoelectric element array (hereinafter, such driving by the first driving unit may be referred to as a vertical flying driving mode. ). Next, the constituent piezoelectric elements of the first piezoelectric element group are shifted, for example, by one piezoelectric element, and fly vertically to n new first piezoelectric element groups including the second to (n + 1) th piezoelectric elements. The new first piezoelectric element group is simultaneously driven in the drive mode. By sequentially repeating the vertical flying drive mode, ink droplets can be sequentially caused to fly in the vertical direction at intervals corresponding to the arrangement pitch of the piezoelectric elements along the arrangement direction of the piezoelectric element array. Thereby, the recording dots can be formed in a line shape in the main scanning direction.

In the driving by the second driving means, the piezoelectric element group (second piezoelectric element group) including the first to n-th piezoelectric elements is bisected by the central axis of the piezoelectric element group. That is, the second piezoelectric element group is divided into a first piezoelectric element sub-group composed of the first to (n / 2) th piezoelectric elements and (n / 2 +
1) A second piezoelectric element subgroup including the nth to nth piezoelectric elements. Then, all the piezoelectric elements belonging to the second piezoelectric element group are simultaneously driven so as to be focused to a point corresponding to the focal point of the ultrasonic beam in the vertical flight drive mode by the first driving means. The total energy amount (E1) of the ultrasonic beam from the first piezoelectric element subgroup is set to be different from the total energy amount (E2) of the ultrasonic beam from the second piezoelectric element subgroup. Then, the ink droplet flies in a direction deviated from the vertical direction from the focal point of the ultrasonic beam from the second piezoelectric element group (hereinafter, such driving by the second driving means is referred to as a deflection flying driving mode). Sometimes). That is, according to the second driving means, it is possible to cause ink droplets to fly regardless of the arrangement pitch of the piezoelectric element array. Therefore, it is possible to form recording dots between recording dots formed in the vertical flying driving mode. Thereby, the resolution can be further improved.

The deflecting flight driving mode by the second driving means may be performed on any of the recording dots formed in the vertical flight driving mode by the first driving means. For example, the constituent piezoelectric elements of the second piezoelectric element group are shifted by, for example, one piezoelectric element, and deflection flying drive is performed for n new second piezoelectric element groups including the second to (n + 1) th piezoelectric elements. In this mode, the new second piezoelectric element group can be simultaneously driven (in this case, the new first piezoelectric element subgroup is constituted by the second to ((n + 2) / 2) th piezoelectric elements). , The second piezoelectric element subgroup is ((n
(+2) / 2 + 1) th to (n + 1) th piezoelectric elements).

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, the first driving means is configured such that the first driving means is driven by a two-phase driving signal having a uniform driving voltage and a uniform application time and having opposite phases to each other.
And a driving unit for driving the piezoelectric element group. Further, in the present invention, the second driving means includes:
(1) driving means for driving the second piezoelectric element group so that some of the piezoelectric elements belonging to the first piezoelectric element subgroup or the second piezoelectric element subgroup are not driven;
(2) driving means for driving the second piezoelectric element group such that at least one of a drive voltage and an application time is different between the first piezoelectric element subgroup and the second piezoelectric element subgroup; or 3) A part of the piezoelectric elements belonging to the first piezoelectric element subgroup or the second piezoelectric element subgroup is driven by a driving signal having a phase opposite to a driving signal applied by the first driving means. Driving means.

Hereinafter, embodiments of the present invention will be described more specifically with reference to the drawings. <First Embodiment> FIG. 1 is a perspective view showing a configuration of a head section of an ink jet recording apparatus according to a first embodiment of the present invention. A recording head 10 shown in FIG. 1 has a piezoelectric element array 12 on a lower surface of a substrate 11 such as a glass plate.
The piezoelectric element array 12 includes a long plate-like piezoelectric layer 13 having a uniform thickness, and a common electrode 1 formed on both surfaces thereof.
4 and a plurality of striped individual electrodes 15 (1) to 15 (n).

The common electrode 14 is formed on the upper surface of the piezoelectric layer 13 over the entire surface. On the other hand, stripe-shaped individual electrodes 15 (1) to 15 (n) (hereinafter, individual electrodes 1
5 (1) to 15 (n) are collectively referred to simply as the individual electrodes 15
Have the same length as the width of the piezoelectric layer 13 and are arranged at a constant pitch in the longitudinal direction of the piezoelectric layer 13. The piezoelectric layer 13 is functionally divided into a plurality of piezoelectric elements by the individual electrodes 15 opposed to the common electrode 14, and constitutes a one-dimensionally arranged piezoelectric element array 12.

The piezoelectric layer 13 is made of a ceramic piezoelectric material such as zircon / lead titanate (PZT), or vinylidene fluoride and ethylene trifluoride, depending on the frequency of the emitted ultrasonic waves and the size of the element. And various piezoelectric materials such as a single crystal piezoelectric material such as lithium niobate and a piezoelectric semiconductor such as zinc oxide. In addition, the common electrode 14 and the individual electrode 15 can be formed as a thin film of titanium, nickel, aluminum, copper, gold, or the like by vapor deposition or sputtering, or can be formed by plating. Alternatively, the electrodes 14 and 15 can be formed by a baking method in which silver paste mixed with glass frit is applied by screen printing and sintered. Each piezoelectric element has two electrodes 1
Ultrasonic waves are generated by applying a voltage to the piezoelectric layer 13 via 4 and 15 to resonate the piezoelectric layer 13.

An acoustic lens 16 is formed in an upper surface area of the substrate 11 corresponding to the piezoelectric layer 13. The acoustic lens 16 can be formed by forming the above-described upper surface region of a substrate such as a glass plate into a concave surface, in which case it functions as a concave acoustic lens.

A plate 17 is provided on the upper surface of the substrate 11. A groove having an inverted V-shaped cross section is formed in the plate-like body 17 along the longitudinal direction of the piezoelectric body so as to form a side wall surface of the ink holding chamber 18 having the concave surface of the concave acoustic lens 16 as a bottom. ing. The opposite side surfaces 19a and 19b of the inverted V-shaped groove forming the side wall surface of the ink holding chamber 18 are inclined so as to meet upward, and the top is opened in a slit shape to form a slit-shaped opening 20. I have. A predetermined ink liquid 21 is stored in the ink holding chamber 18.

On the lower surface of the glass substrate 11, a drive circuit (hereinafter, referred to as a drive IC) 22 provided as an IC is provided at a position facing the piezoelectric element array 12. The drive IC 22 is connected to the common electrode 14 and each individual electrode 15 via a wiring pattern (not shown) formed on the lower surface of the glass substrate 11. As described in detail below, the drive IC 22 selects the piezoelectric element array 12 adjacent to the array direction (the arrangement direction of the piezoelectric elements, which corresponds to the main scanning direction in the present invention) according to the image data to be recorded. The linear electronic scanning is performed by sequentially driving the piezoelectric element group including a plurality of piezoelectric elements as one group (first piezoelectric element group) for each group.

Specifically, by supplying a high-frequency drive signal having a predetermined delay time difference (phase difference) to the selected piezoelectric element group, and simultaneously driving the first piezoelectric element group, The ultrasonic beam emitted from the piezoelectric element array 12 is focused in the array direction, that is, in the main scanning direction. The position of the piezoelectric element group that is driven simultaneously is shifted by one piezoelectric element at a time, and the simultaneous driving is repeated, whereby the radiation direction of the focused ultrasonic beam is moved linearly in the main scanning direction.

The ultrasonic beam radiated from the piezoelectric element array 12 and focused in the main scanning direction is further
The acoustic lens 16 also converges in a direction (sub-scanning direction) orthogonal to the main scanning direction, and finally converges at a predetermined position on the liquid surface of the ink liquid 21. In this way, the pressure (radiation pressure) generated by the ultrasonic beam focused on the ink liquid surface causes a conical meniscus to grow on the ink liquid surface, and the ink droplet is eventually ejected from the tip of the meniscus. The ejected ink droplets fly and adhere to a recording medium (not shown), and are dried and fixed, thereby performing image recording. In this driving mode, the ink droplet flies in the direction of the center axis of the first piezoelectric element group (vertical flying driving mode).

The size of the ink droplet flying as described above can be determined by the frequency of the ultrasonic wave. Since the piezoelectric element array 12 emits ultrasonic waves using resonance in the thickness direction of the piezoelectric layer 13, the ultrasonic frequency is determined by the thickness of the piezoelectric layer 13. Since the thickness is inversely proportional to the frequency, the thickness of the piezoelectric layer 13 decreases as the frequency increases. That is, the higher the resolution of the ink jet recording apparatus, the higher the frequency of the ultrasonic waves required to be obtained, and the type and forming method of the piezoelectric layer 13 are selected accordingly.

Next, the driving means and method of the piezoelectric element array 12 in the first embodiment shown in FIG. 1 will be described more specifically with reference to FIGS. 2, 3 and 4. Note that the acoustic lens 16 is omitted in FIGS. 2 to 4 for easy understanding.

As shown in FIG. 2, the piezoelectric elements T (1) to T (n + 1) constituting the piezoelectric element array 12 are:
The piezoelectric elements are arranged in the main scanning direction at a predetermined pitch d, and each piezoelectric element is connected to each delay circuit 32, and each of the delay circuits 32 is connected to the drive signal power supply 31.
Needless to say, the drive signal source 31 and the delay circuit 32
Are components of the drive circuit 22 in the printing apparatus shown in FIG. The drive signal source 31 generates a high-frequency drive signal, and the delay circuit 32 outputs the drive signal delayed by a delay time set by a control circuit (not shown) to the piezoelectric element array 12.
To a predetermined piezoelectric element.

First, the vertical flight drive mode by the first drive means will be described with reference to FIG. Piezoelectric element array 12
Of the piezoelectric elements constituting the piezoelectric elements T (1) to T (1)
(N) is a first piezoelectric element group. The amount of energy of the drive signal supplied to each piezoelectric element of the first piezoelectric element group is equal. Specifically, the drive signal to each piezoelectric element is applied from the drive signal source 31 with the same drive voltage and the same application time. Here, the first to n-th piezoelectric elements T
(1) -The phase of the ultrasonic wave radiated from T (n) is the first
A on the liquid surface of the ink 21 on the central axis of the piezoelectric element group
By driving the delay circuit 32 by setting the delay time so that the points coincide with each other, the ink droplet flies vertically from the point A.

Next, a new first element composed of n piezoelectric elements T (1) to T (n) shifted by one piezoelectric element from the piezoelectric elements T (1) to T (n).
Similarly, if the respective piezoelectric elements T (2) to T (n + 1) of the piezoelectric element group are driven with the delay time being set, the ink is shifted from the point C which is shifted from the point A by the arrangement pitch d of the piezoelectric elements. Fly vertically.

FIG. 3 shows that each ultrasonic beam (indicated by a broken line in the figure) emitted from the first piezoelectric element group driven by the first driving means is focused on the liquid surface 21a of the ink liquid 21. Is shown. That is, each piezoelectric element T
(1) The ultrasonic waves radiated from T (n)
Focusing is performed at the point P of 1a, and the ink droplet flies in a predetermined direction (a direction perpendicular to the ink liquid surface 21a) P0. Here, the center axis of the first piezoelectric element group (when n is an even number, the piezoelectric element T (n / 2) and the adjacent piezoelectric element (T (n / 2 +
1) is P0.

Next, the deflection flight drive mode by the second drive means will be described. In this drive mode, as described above,
A first piezoelectric element subgroup bisected by the central axis of the piezoelectric element group (consisting of piezoelectric elements T (1) to T (n / 2))
And the second group of piezoelectric elements (piezoelectric elements (T (n / 2 + 1) to
T (n)), the second piezoelectric element group consisting of the first and second piezoelectric element subgroups is simultaneously set so that the total energy amount at the focal point of the ultrasonic beam radiated from The second piezoelectric element group is driven so that some of the piezoelectric elements belonging to the first piezoelectric element subgroup or the second piezoelectric element subgroup are not driven. Drive.

More specifically, as shown in FIG.
Of the piezoelectric elements T (1) to T (n /
In 2), for example, only the piezoelectric element T (2) is set in the non-drive state.

As described above, the second piezoelectric element group is moved to the focal point P
The flying position of the ink when driven so that there is a difference in the amount of ultrasonic energy of the liquid surface radiated and focused from the piezoelectric element in the area bisected with reference to
Is different from the direction Px. That is, the ink droplet can be caused to fly to a position different from the ink droplet in the first drive mode described with reference to FIG. Further, the difference between the total energy amount (E1) of the ultrasonic beam irradiated from the first piezoelectric element subgroup and the total energy amount (E2) of the ultrasonic beam irradiated from the second piezoelectric element subgroup is changed. By driving in such a manner, the flying position of the ink droplet can be changed. As described above, when driven by the second driving unit, the ink droplet flies in a direction deflected from the direction perpendicular to the liquid surface.

Next, a more specific example will be described in detail. The specifications regarding the piezoelectric element array 12 include a driving frequency of 100 MHz, a focal length (a depth of the ink liquid).
Was set to 3 mm, the arrangement pitch d of the piezoelectric elements was set to 50 μm, and the number of piezoelectric elements of the first piezoelectric element group to be driven simultaneously was set to 36. In this case, the speed of sound in the ink liquid is 1.5 km / sec, which is almost the same as the speed of sound in water, so the wavelength of the ultrasonic wave in the ink liquid is 15 μm. Piezoelectric element array 1
2 has a drive signal waveform of 100 as shown in FIG.
A square wave burst of MHz with a wave number of 500 (5 μs),
The voltage was 30 V0 _-P .

As a method of setting the phase (delay time) of the ultrasonic wave radiated from each piezoelectric element in the first drive mode described with reference to FIG. 3, a method of dividing into two types based on the Fresnel diffraction theory was used. . Specifically, the radius of Fresnel zoning is determined using the following equation (1) or equation (2).

[0034]

(Equation 1)

[0035]

(Equation 2)

Here, r (1) is the radius of the Fresnel zoning, λw is the ultrasonic wavelength in the ink, and F is the focal length (the depth of the ink liquid). Table 1 below shows the radius r (1) (0 to 1) of each Fresnel zoning obtained from the equation (1).
9) is shown. However, when i = 0, r (0) = 0.

Next, assuming that a distance between the center points of the piezoelectric elements with respect to the center position of the piezoelectric element group (arrangement pitch of the piezoelectric element array) is d, r (2n) <d <F (2n +
The piezoelectric element existing in the range of 1) is r (2n + 1) <d
The delay time is set so that the phase is shifted by a half wavelength with respect to the piezoelectric element existing in the range of <r (2n + 3).

As described above, the delay time τ (n) (n = 1 to 1) of the first piezoelectric element group determined based on the Fresnel diffraction theory
36) is shown in Table 2 below. By simultaneously driving the first piezoelectric element group including the 36 piezoelectric elements, the ink liquid level 21 on the intermediate point between the 18th piezoelectric element and the 19th piezoelectric element can be obtained.
At the point P of a, the ink droplet flies in the P0 direction. this is,
This corresponds to point A in FIG. If the positions of the n piezoelectric element groups are shifted by one piezoelectric element and driven by the same delay time pattern, the ink droplets can fly in a line at the same interval as the arrangement pitch d of the piezoelectric elements. . When the piezoelectric element is driven by the first driving means while being shifted by one piezoelectric element, FIG.
The ultrasonic beam is focused on a point corresponding to the point C.

[0039]

[Table 1]

[0040]

[Table 2]

On the other hand, the deflection flight drive mode by the second drive means shown in FIG. 4 is based on the vertical flight drive mode by the first drive means and is obtained by calculating the radius of the Fresnel zoning. It can be considered that the setting of the delay time given to each piezoelectric element is the same.

In the second driving mode, of the piezoelectric elements of the second piezoelectric element group including the n piezoelectric elements, the piezoelectric elements are respectively radiated from the piezoelectric elements located in the area divided into two on the basis of the point P. For example, the piezoelectric element T (2) is connected to the drive circuit 2 so that the amount of energy at the focal point of the ultrasonic beam is different.
2 sets a non-drive state. In this case, the piezoelectric element T
The individual electrode 13 of (2) is set at a predetermined DC potential or the same potential as the common electrode 12, for example, a ground potential, and is preferably set to be electrically disconnected from the drive circuit 22.
Thus, the piezoelectric element T belonging to the first piezoelectric element subgroup
The ultrasonic energy (E1) radiated from (1) to T (n / 2) and the piezoelectric element T belonging to the second piezoelectric element subgroup
The ultrasonic energy (E2) radiated from (n / 2 + 1) to T (n) satisfies E1 <E2.

As described above, among the piezoelectric elements of the second piezoelectric element group including the n piezoelectric elements, the focal points of the ultrasonic beams respectively radiated from the piezoelectric elements in the area bisected with reference to the point P. The flying position of the ink when the piezoelectric element T (2) is driven by the driving circuit 22 so as to be in the non-driving state so that the amount of energy at the first driving means is different from the flying direction P0 of the first driving means. The position is slightly shifted. In the case of this example, it is shifted to the left direction Px in FIG. That is, the ink droplet can be caused to fly to a different position from the ink droplet by the first driving unit shown in FIG.

Further, the recording dots formed by the driving by the first driving means are formed by using the second driving means to form recording dots at peripheral positions slightly shifted from the recording dots, whereby pseudo recording is performed. It is possible to control the gradation of the recorded image by changing the size of the dots, and at the focal point of the ultrasonic beam radiated from each of the piezoelectric elements in the area bisected from the focal point P. By driving while gradually changing the energy amount difference, the flying position of the ink droplet can be gradually changed. Specifically, for example, the piezoelectric elements belonging to the second piezoelectric element sub-group are always driven, and the piezoelectric elements of the first piezoelectric element sub-group are
By changing the number and position of the piezoelectric elements whose driving is stopped as in the advancing method, the flying position of the ink droplet can be gradually changed.

The same effect can be obtained by driving the first sub-group of piezoelectric elements and the second sub-group of piezoelectric elements by the second driving means in a manner opposite to the above example. The focus point P is reversed from the above example.

When the piezoelectric element at a position close to the convergence point P is not driven, the deflection amount at the flying position becomes large. However, since the flight becomes unstable or the size of the ink droplet varies, the piezoelectric element closest to the focal point P in the second driving means is always driven by the second driving means. Is preferred.

As described above, according to the present invention, recording can be performed at a high resolution equal to or less than the arrangement pitch of the piezoelectric elements, and gradation control of a recorded image can be performed. <Second Embodiment> Next, a second embodiment of the present invention will be described.

The basic configuration of the ink jet head unit in this embodiment is the same as that of FIG. 1, and the vertical flight drive mode by the first drive unit is also the same as that of the first embodiment.

The second driving means according to the second embodiment is divided into two parts based on the point P focused by the first driving means, out of the piezoelectric elements of a group of n piezoelectric elements. At least one of the driving voltage and the application time is set to the first piezoelectric element so that the total amount of energy at the focal point of the ultrasonic beam radiated from each of the first piezoelectric element subgroup and the second piezoelectric element subgroup differs. The driving circuit 22 (FIG. 1) drives the element subgroup differently from the second piezoelectric element subgroup.

For example, as shown in FIG. 6, the first piezoelectric element subgroups T (1) to T (n /
Two types of drive signals are applied so that the voltage of the drive signal applied to 2) is 50 V and the voltage of the drive signal applied to the second piezoelectric element subgroups T (n / 2 + 1) to T (n) is 30 V. Drive. Here, the voltage and phase of each drive signal are the same as those of the first drive means.

As described above, by changing the voltage of the drive signal applied to the first piezoelectric element sub-group and the second piezoelectric element sub-group, the flying position of the ink is changed as in the first embodiment. , A slightly different position from the flying direction P0 by the first driving means. In this example, it shifts to the right direction Px. That is, the ink droplet can be caused to fly to a different position from the ink droplet by the first driving unit shown in FIG.
Further, as in the case of the first embodiment, pseudo dots are formed at peripheral positions slightly shifted from the recording dots by the first driving unit by using the second driving unit. It is possible to control the gradation of the recorded image by changing the size of the recorded dots.

Further, of the piezoelectric element sub-groups divided into two parts with reference to the point P, for example, the second piezoelectric element sub-group is fixed at, for example, 30 V, and the voltage of the drive signal applied to the first piezoelectric element sub-group is reduced. By driving linearly, the difference between the total energy amounts E1 and E2 can be changed linearly as in the case of the first embodiment, so that the flying position of the ink droplet can be changed. it can. The same effect can be obtained by driving the first piezoelectric element subgroup and the second piezoelectric element subgroup with the applied voltage reversed from the above example, but the deflection direction of the flying position is Px with respect to P0. In the opposite direction.

When n is an odd number, the driving signal applied to the piezoelectric element T (n + ／) is determined by setting the desired ink droplet flying position and the first piezoelectric element with respect to the point P. It is determined whether to apply a signal to the subgroup or a signal to the second piezoelectric element subgroup.

In the above-described example, the driving is performed by providing a difference between the right and left piezoelectric elements with respect to the point P with the voltage of the driving signal. However, the driving for the first piezoelectric element sub-group and the second piezoelectric element sub-group is performed. Driving may be performed with a difference in the signal application time (burst wave number). For example, the first piezoelectric element subgroups T (1) to T (T)
The application time of the drive signal applied to (n / 2) is 10 μs
c, The driving is performed with the application time of the driving signal applied to the second piezoelectric element subgroups T (n / 2 + 1) to T (n) set to 5 μsec.

As described above, according to the second embodiment of the present invention, it is also possible to perform recording with a high resolution equal to or less than the arrangement pitch of the piezoelectric elements, and it is also possible to control the gradation of a recorded image. .

<Third Embodiment> Next, a third embodiment of the present invention will be described.
An embodiment will be described. The basic configuration of the inkjet head unit according to the third embodiment is the same as that of FIG.
Further, the vertical flight drive mode by the first drive means is also the first flight mode.
This is the same as the embodiment.

The second driving means in the third embodiment applies a part of the piezoelectric elements belonging to the first piezoelectric element subgroup or the second piezoelectric element subgroup by the first driving means. It is driven by a drive signal having a phase opposite to that of the drive signal.

More specifically, as shown in FIG. 7, of the piezoelectric elements of the second piezoelectric element group consisting of n piezoelectric elements,
One or more piezoelectric elements at the position of production of the piezoelectric element group,
For example, the first driving of the piezoelectric element T (3) is performed by the drive circuit 22 (FIG. 1) so that the ultrasonic beam from the piezoelectric element T (3) is not focused on the point P on the liquid surface 21a of the ink liquid 21. It is driven by a drive signal having a phase opposite to that of the means. Originally, in order to converge at the point P in FIG. 7, a driving signal having a delay time of 5 nsec (nanosecond) is applied to the piezoelectric element T (3) as shown in Table 2 above. However, in this example, for example, a drive signal having a delay time of 0
Apply to (3). Therefore, the ultrasonic wave radiated from the piezoelectric element T (3) does not converge on the point P of the ink liquid level 21a, but is rather radiated from another piezoelectric element and the ink liquid level 21a.
Works in a direction to weaken the energy of the ultrasonic wave focused on the point P. That is, in this case, the ultrasonic energy (E1) radiated from the first piezoelectric element sub-groups T (1) to T (n / 2) bisected with respect to the point P, and the second piezoelectric element sub-groups T (n
/ 2 + 1) to ultrasonic energy (E2) emitted from T (n), E1 <E2.

As described above, also in the third embodiment, the first and second parts are divided into two parts on the left and right with respect to the convergence point P.
As a result, the amount of energy at the focal point of the ultrasonic beam radiated and focused from each of the piezoelectric element subgroups is different, so that the flying position of the ink is different from P0 as in the first and second embodiments. Direction. In the present example, it is shifted to the left direction Px in FIG. That is, the ink droplet can be caused to fly to a position different from the position of the ink droplet in the first drive mode shown in FIG.

Further, by using the second driving means to form recording dots at slightly shifted peripheral positions with respect to the recording dots by the first driving means, the size of the recording dots is changed in a pseudo manner. It is possible to control the gradation of the recorded image by changing the difference in the energy amount between the ultrasonic beams respectively radiated from the piezoelectric elements in the left and right bisected regions based on the focal point P. By driving, it is possible to change the flying position of the ink droplet.

Further, when the piezoelectric element located at a position near the convergence point P is driven by the second driving means, the amount of change in the flying position becomes large. However, since the flight becomes unstable or the size of the ink droplet varies, the piezoelectric element closest to the convergence point P in the second driving unit is also driven by the regular driving unit in the second driving unit. It is preferably driven by a signal.

As described above, according to the third embodiment of the present invention, it is also possible to perform recording at a high resolution equal to or less than the arrangement pitch of the piezoelectric elements, and it is also possible to control the gradation of the recorded image. .

Although the embodiments of the present invention have been described with reference to FIGS. 1 to 7, the present invention is not limited to these embodiments. For example, the first to third
Although the embodiment using the ink jet head shown in FIG. 1 has been described in the embodiment, the acoustic lens is not limited to the concave lens shown in FIG. 1, but may be, for example, a Fresnel lens (Fresnel ring) shown in FIG. (Consisting of grooves 81a to 81f formed in parallel with the main scanning direction based on the band theory), and the piezoelectric element itself constitutes a concave lens as shown in FIG. (In this case, the piezoelectric element is provided on a support 91 having a similar concave surface).

[0064]

As described above, according to the present invention, there is provided an ink jet recording apparatus capable of recording at a high resolution equal to or less than the arrangement pitch of piezoelectric elements and capable of controlling the gradation of a recorded image. Provided.

[Brief description of the drawings]

FIG. 1 is a perspective view showing the configuration of an ink jet recording apparatus according to the present invention.

FIG. 2 is a schematic diagram for explaining a method of driving an ink jet recording apparatus by a first driving unit of the present invention.

FIG. 3 is a schematic diagram for explaining focusing of an ultrasonic beam radiated from a piezoelectric element driven by a first drive unit according to the present invention.

FIG. 4 is a schematic diagram for explaining a drive mode by a second drive unit according to the first embodiment of the present invention.

FIG. 5 is a diagram showing a waveform of a drive signal used in the present invention.

FIG. 6 is a schematic diagram for explaining a drive mode by a second drive unit according to the second embodiment of the present invention. .

FIG. 7 is a schematic diagram for explaining a drive mode by a second drive unit according to the first embodiment of the present invention. .

FIG. 8 is a schematic sectional view showing the configuration of another inkjet recording apparatus according to the present invention.

FIG. 9 is a schematic sectional view showing the configuration of still another ink jet recording apparatus according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 ... Substrate 12 ... Piezoelectric element array 13 ... Piezoelectric layer 14 ... Common electrode 15 (1) -15 (n) ... Individual electrode 16 ... Acoustic lens 18 ... Ink holding chamber 21 ... Ink liquid 22 ... Drive circuit 31 ... Drive signal Source 32: delay circuit T (1) to T (n + 1): piezoelectric element

 ──────────────────────────────────────────────────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 Hitoshi Yagi Komukai Toshiba, Sai-ku, Kawasaki-shi, Kanagawa No. 1 Town, Toshiba R & D Center (72) Inventor Noriko Yamamoto No. 1, Komukai Toshiba-cho, Kawasaki City, Kanagawa Prefecture, Japan Toshiba R & D Center

Claims (5)

[Claims] 1. An ink holding chamber for holding an ink liquid, and an ultrasonic wave generating means including a piezoelectric element array constituted by a plurality of piezoelectric elements acoustically connected to the ink liquid and arranged at predetermined intervals; A first piezoelectric element group including a plurality of piezoelectric elements selected from the piezoelectric elements constituting the piezoelectric element array
The first is that the ultrasonic waves generated from the piezoelectric element group are simultaneously driven so as to be focused on a predetermined position on the liquid surface of the ink liquid.
And a second piezoelectric element group consisting of a plurality of piezoelectric elements selected from the piezoelectric elements constituting the piezoelectric element array. The ultrasonic beam generated from the second piezoelectric element group First and second portions corresponding to regions where the second piezoelectric element group is bisected in the arrangement direction of the piezoelectric element array based on the predetermined position so as to focus on the predetermined position on the liquid surface of the liquid. A second driving unit that simultaneously drives the second piezoelectric element group so that the amount of energy at the predetermined position of the ultrasonic beam emitted from each of the two piezoelectric element subgroups is different. Inkjet recording device. 2. The method according to claim 1, wherein the first driving unit drives the first piezoelectric element group by a two-phase driving signal having a uniform driving voltage and a uniform application time and having mutually opposite phases. The ink jet recording apparatus according to claim 1, wherein 3. The second driving unit controls the second driving unit so that some of the piezoelectric elements belonging to the first piezoelectric element subgroup or the second piezoelectric element subgroup are in a non-driving state. 3. The ink jet recording apparatus according to claim 1, wherein the apparatus drives the piezoelectric element group. 4. The second piezoelectric device according to claim 2, wherein the second driving means is configured to change at least one of a driving voltage and an application time between the first piezoelectric element subgroup and the second piezoelectric element subgroup. 2. The ink jet recording apparatus according to claim 1, wherein the apparatus drives an element group. 5. The second driving means applies a part of the piezoelectric elements belonging to the first piezoelectric element sub-group or the second piezoelectric element sub-group by the first driving means. 2. The ink jet recording apparatus according to claim 1, wherein the apparatus is driven by a drive signal having a phase opposite to that of the drive signal.