JP2001179962A - Ink jet recorder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an ink jet recorder employing ultrasonic wave in which gradation control of image is performed by varying the diameter of an ink drop. SOLUTION: A plurality of piezoelectric elements 101 are driven simultaneously by a drive signal applied from a drive means 110 to generate an ultrasonic wave which is converged onto the surface of ink liquid 109 thus ejecting an ink drop by means of an ultrasonic beam. In such an ink jet recorder, m piezoelectric elements 101 are driven simultaneously when an ink drop of small diameter is ejected and m+2 piezoelectric elements 101 are driven simultaneously when an ink drop of large diameter is ejected thus controlling the diameter of an ink drop being ejected.

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, and more particularly to an ink-jet recording apparatus using ultrasonic waves and capable of controlling the diameter of ink droplets.

[0002]

2. Description of the Related Art Conventionally, there has been known an ink jet printer which forms recording dots by discharging an ink liquid onto a recording medium. 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, but in particular, a system in which ink droplets are ejected by the pressure of steam generated by the heat of a heating element, and a system in which ink droplets are ejected by pressure pulses due to displacement of a piezoelectric body. Are typical.

However, in these ink jet printers, the diameter of the ink droplet is determined by the diameter of the nozzle for discharging the ink droplet. Therefore, it is necessary to reduce the diameter of the nozzle in order to increase the resolution. As a result, nozzle clogging occurs. There is a problem that it becomes easier.

In order to overcome these drawbacks, there has been proposed an ultrasonic system in which ink droplets are ejected from an ink liquid surface using the pressure of an ultrasonic beam generated from a thin-film piezoelectric material.

[0005] In the ultrasonic method, a nozzle-less configuration can be adopted, so that clogging of the nozzle does not occur and ink droplets having a very small diameter can be stably ejected.

[0006] Among the ink jet printers of the ultrasonic type, those of the piezoelectric element array type have been proposed. In this method, a part of the piezoelectric elements (piezoelectric element group) arranged in an array are simultaneously driven with a phase-controlled voltage, and the phase-controlled ultrasonic waves are excited from each of the simultaneously driven piezoelectric elements, and the ink liquid level is increased. This is a method that concentrates on one point in the vicinity.
According to this method, linear electronic scanning can be performed in the array direction by sequentially shifting the piezoelectric element groups that are simultaneously driven on the array.

In this method, if the number of piezoelectric element groups driven simultaneously is fixed, scanning can be performed only by switching the combination of the piezoelectric element groups. Therefore, the drive circuit needs to control a complicated delay time. Instead, it is only necessary to control the delay time pattern of one piezoelectric element group.

Further, as a method of setting a delay time in the linear electronic scanning method, a piezoelectric array is further added based on Fresnel diffraction theory instead of setting a quadratic function delay time used in a normal electronic focusing method. A simpler method has been proposed in which the delay time is set so that the phase is divided into two groups and the phases are different from each other by half a wavelength (JP-A-8-132607).

However, since the ink droplet diameter in the ultrasonic ink jet printer is conventionally controlled by the frequency of the ultrasonic wave, that is, the thickness of the piezoelectric element, in order to perform gradation control using the same piezoelectric element array, It is necessary to control the number of ink droplets for forming one pixel. Therefore, there is a problem that the printing speed is reduced.

[0010]

As described above, in the conventional ultrasonic ink jet printer, in order to control the image gradation by changing the size of one pixel,
A plurality of ink droplets must be ejected to one pixel, which causes a problem that the printing speed is reduced.

SUMMARY OF THE INVENTION The present invention has been made in view of such a problem, and it is possible to change the diameter of an ink droplet in accordance with image gradation information, and to reduce the image gradation without lowering the printing speed. It is an object of the present invention to provide an inkjet recording device that can be controlled.

[0012]

An ink jet recording apparatus according to the present invention emits convergent ultrasonic waves toward ink, and ejects ink near the convergence point of the convergent ultrasonic waves as ink droplets to perform recording on a recording medium. In the ink jet recording apparatus, a piezoelectric element array in which a plurality of piezoelectric elements are arranged at a predetermined pitch, and a driving unit that simultaneously drives a piezoelectric element group including a predetermined number of piezoelectric elements in the piezoelectric element array, wherein the driving unit includes And at least one pair of piezoelectric elements symmetrically positioned with respect to the center position of the piezoelectric element group as an ejection amount control element, and the ejection amount control element selects drive / non-drive in accordance with ink droplet diameter information. It has a control means.

The present inventors have confirmed that the particle size of the ink droplet to be ejected changes not only with the wavelength of the ultrasonic wave but also with the amount of energy of the converged ultrasonic wave, and reached the present invention. That is, according to the present invention, gradation control can be performed by changing the number of simultaneously driven piezoelectric elements according to the particle size information of ink droplets.

Further, the discharge amount control means may be a means for applying a DC voltage to the discharge amount control element when not being driven.

Since the piezoelectric elements are usually arranged at a narrow pitch, there is a possibility that undesired vibration may occur due to the influence of the voltage applied to the adjacent piezoelectric elements. By applying a DC voltage to the piezoelectric elements that are not simultaneously driven, the vibration can be suppressed.

The discharge amount control means may be a means for applying a high-frequency voltage having a phase for weakening a convergent sound wave at the convergence point to the discharge amount control element when not being driven.

By generating an ultrasonic wave that weakens the convergent ultrasonic wave in the ejection amount control element when not driven, it is possible to reduce the energy amount of the convergent ultrasonic wave at the ink ejection position. Can be bigger.

Another ink jet recording apparatus of the present invention comprises:
A piezoelectric element in which a plurality of piezoelectric elements are arranged at a predetermined pitch in an ink jet recording apparatus that radiates convergent ultrasonic waves toward ink and ejects ink near the convergence point of the convergent ultrasonic waves as ink droplets to perform recording on a recording medium. An array and driving means for simultaneously driving a piezoelectric element group consisting of a predetermined number of piezoelectric elements in the piezoelectric element array, wherein the driving means controls the number of the piezoelectric elements to be simultaneously driven simultaneously according to ink droplet diameter information. It is characterized by having discharge amount control means for changing.

[0019]

Embodiments of the present invention will be described below with reference to the drawings.

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

An individual electrode (glass plate side) 112 is formed on the upper surface of the glass substrate as the support member 100, and an individual electrode (piezoelectric layer) corresponding to the position of the individual electrode (glass plate side) 112 is formed on the upper surface. A piezoelectric element array 101 including a piezoelectric layer 102 on which a (side) 103 is formed and a common electrode 104 provided on the upper surface thereof is formed. That is, the individual electrodes 112, 1
03 and the common electrode 104, and the piezoelectric layer 1 sandwiched between both electrodes
02 is formed.

The piezoelectric element array 101 on the support member 100
On the side where is formed, an ink liquid holding chamber 107 is attached so as to surround the piezoelectric element array 101, and a slit plate 108 is provided on the upper surface thereof. The inside of the ink liquid holding chamber 107 is filled with an ink liquid 106.

Then, the ultrasonic waves emitted from the piezoelectric elements are converged by the acoustic lens 105, respectively, and the slit plate 108
Is converged on the slit formed by

In this embodiment, the piezoelectric layer 102 of the piezoelectric element array 101 is not divided into an array, and only the individual electrodes 103 are divided into an array, so that the piezoelectric layers 102 are separated into a plurality of piezoelectric elements. I have. In this example, the pointing member
The surface in contact with the piezoelectric element array 101 of the piezoelectric element 100 includes the piezoelectric layer 10
Individual electrodes 112 provided on the glass plate side at the same interval as the individual electrodes 103 provided on the two sides are formed in an array,
The arrayed individual electrodes on the support member 100 are pressed and wired via an adhesive. The array-shaped individual electrodes on the support member 100 are wired to the driving means 110 arranged on the same support member 100 by bonding wires 111. Similarly, the common electrode 104 is also wired to the driving unit 110 by a bonding wire (not shown).

The piezoelectric element array 101 is connected to the driving means 110, so that a part of the piezoelectric elements of the piezoelectric element array 101 are substantially simultaneously adjusted so that the ultrasonic wave converges to a predetermined position near the ink level. By driving, ink droplets are ejected from the ink liquid surface.

Hereinafter, the plurality of simultaneously driven piezoelectric elements will be referred to as a piezoelectric element group.

In this embodiment, as the acoustic lens 105, a one-dimensional Fresnel lens in which irregularities based on the Fresnel zone theory are formed parallel to the main scanning direction (array direction). The thickness of the concave and convex portions of the acoustic lens 105 is (2N + 1) / 4 times (N is 0) the wavelength in the acoustic lens.
(The above integer), and a material having a value close to the square root of the product of the acoustic impedance of the piezoelectric layer 103 and that of the ink liquid 106, such as alumina powder, is dispersed in the acoustic lens material. By using epoxy resin, the acoustic lens 105 also has a function as an acoustic matching layer.

Next, a method of driving the piezoelectric element array 101 will be described.

The driving method of the piezoelectric element array 101 is as follows.
As a method of driving by giving a phase difference to each piezoelectric element of the simultaneously driven piezoelectric element group, a method of assigning a complex phase difference that changes in a quadratic manner by imitating a concave lens-like converging rate, A method of allocating two phases (hereinafter, referred to as 0 phase and π phase) shifted by half a wavelength to simulate focusing like a Fresnel lens can be considered. The latter is an excellent method that can greatly simplify the drive circuit.
A driving method using only two phases, a phase and a π phase, was used.

FIGS. 2A and 2B are views for explaining the principle of the ultrasonic focusing method in the ink jet recording head shown in FIG. 1, wherein FIG. 2A shows a sub-scanning direction (a direction orthogonal to the array direction), and FIG. The state of the ultrasound collection in the main scanning direction is shown. As shown in FIG. 2A, the piezoelectric layer 102
Ultrasonic waves radiated from the acoustic lens (Fresnel lens)
Focuses in the ink in the sub-scanning direction so as to focus on the vicinity of the slit opening 109. Further, as shown in FIG. 2B, the ultrasonic wave radiated from the piezoelectric layer 102 passes through the acoustic lens layer 105 and is focused in the ink in the main scanning direction by driving based on the Fresnel cycle theory. In this manner, a large pressure is generated by the ultrasonic waves focused near the slit opening 109, and thus ink droplets are ejected.

(Driving Method of Inkjet Recording Apparatus) FIG.
(A) to (d) schematically show an operation in which four adjacent piezoelectric elements of the piezoelectric element array 2 are simultaneously driven as one piezoelectric element group to concentrate an ultrasonic beam at one point. It is a thing. This is an operation in a case where the image points for one line are formed by dividing the image into at least 1/4 lines or more, and the individual electrode layers 103a, 103b, 103c,
A driving voltage is applied to 103d, 103e, 103f, 103g, and 103h while shifting in the main scanning direction by a linear scanning operation.

In FIG. 3A, a predetermined burst voltage is applied to the inner two individual electrode layers 103c and 103d among the grouped individual electrode layers 103b, 103c, 103d and 103e, and the outer two
Each of the two individual electrode layers 103a and 103e has
By applying a burst voltage having a phase advanced from the phase of the burst voltage applied to 03c and 103d, ink droplets are ejected from the center of the piezoelectric element group, that is, directly above the individual electrodes 103c and 104d.

In FIG. 3B, a predetermined burst voltage is applied to the inner two individual electrode layers 103d and 103e of the next grouped individual electrode layers 103c, 103d, 103e and 103f, and the outer A burst voltage whose phase is advanced from the phase of the burst voltage applied to the inner two individual electrode layers 103d and 103e is applied to the individual electrode layers 103c and 103f, and ink droplets are ejected from immediately above between 103d and 103e. Let me.

In FIG. 3C, a predetermined burst voltage is applied to the inner two individual electrode layers 103e and 103f of the next grouped individual electrode layers 103d, 103e, 103f and 103g, and the outer two A burst voltage whose phase is advanced from the phase of the burst voltage applied to the inner two individual electrode layers 103e and 103f is applied to the individual electrode layers 103d and 103g.

In FIG. 3D, the individual electrode layers 103a,
103b, 103c, 103d, 103e, 103f, 103g, 103h are divided into groups of individual electrode layers 103a, 103b, 103c, 103d, and individual electrode layers 10
The operation in the case of dividing into three groups of 3e, 103f, 103g, and 103h and simultaneously driving these two groups to eject two ink droplets at a predetermined pitch is shown.

In this operation example, one piezoelectric element groove is formed by four piezoelectric elements in order to record one pixel.
Increasing the number of piezoelectric elements that make up one piezoelectric element group smoothes the wavefront of the ultrasonic beam concentrically focused and increases the energy density. The drive voltage applied to 101 can be reduced.

(Structural Example of Driving Means) Next, a structural example of the driving means 110 in FIG. 1 will be described. FIG.
FIG. 2 is a block diagram showing a configuration of a main part of FIG. In FIG. 4, a control unit 40 is a part that controls the timing of the system,
May have a CPU. The line memory 42 includes a control unit 40
, And writing and reading of image data are performed.

The drive data generator 43 generates drive data for driving the piezoelectric elements 48 of the piezoelectric element array 101 in FIG. 1 based on the image data sent from the line memory 42. Here, for the sake of simplicity, the piezoelectric elements 48 are individually shown as 48a, 48b, 48c,..., But can be considered to correspond to the individual electrodes 103 in FIGS. The details of the drive data generator 43 will be described later in detail with reference to FIG.

An output of a scanner (not shown) and image data sent from a transmission line are input to a line memory 42, and the timing is controlled by a control unit 40 to control the line memory 42.
Is written to. In this example, the image data is composed of 1-bit data per pixel. Line memory 42
For example, it has a capacity of 4960 bits and can store one line of image data of A4 paper size at a resolution of 600 dpi.

Of course, the image data may be multi-valued data such as 8 bits per pixel, and the line memory 42 at that time has a capacity corresponding to the number of bits.

The image data temporarily stored in the line memory 42 is sequentially read out and sent to the drive data generator 43. The drive data generation unit 43 generates a selection signal for driving the piezoelectric element 48.

(Operation of Driving Unit 110) Next, the operation of the driving unit 110 will be described with reference to the transfer timing of driving data and the driving timing chart of the piezoelectric element shown in FIG. Driving means 1
10 starts the operation at the rise of the horizontal synchronization signal HSYNC. The drive data generated by the drive data generation unit 43 is supplied to the input of the first-stage shift register element 44a of the shift register 44, and sequentially in synchronization with the clock SIFT CLOCK from the control unit 40, the next-stage shift register element 44b , 44c ・ ・ ・
Is forwarded to When all 4960 drive data are transferred to the shift register 44, the latch signal LA from the control unit 40
Drive data in the shift register 44 is taken into the latch 45 by TCHCLOCK.

Further, in the selector 46, the high-frequency signal generator 41 according to the drive data output from the latch 45.
SIGNAL ZERO, two kinds of high frequency signals with different phases from
Either the SIGNAL PAI or the ground signal GND is selectively output. The drive data generated by the drive data generator 43 includes these two types of high frequency signals SHIGNAL ZERO, SHIGN
This is data for controlling ON / OFF of driving of the piezoelectric element 48 by each of the AL PAIs, and is 1-bit data for one high-frequency signal. The drive data is output as 2-bit data by turning on / off two types of high-frequency signals. Therefore, the shift register 44 and the latch 45 corresponding to one piezoelectric element 48 are configured so as to form a set of two bits. The selection of the high-frequency signal in the selector 46 is performed based on a truth table as shown in Table 1.

[Table 1] The high-frequency signal output from the selector 46 is voltage-amplified by the driver 47 and then applied to the corresponding piezoelectric element 48. A voltage having an amplitude of substantially 10 to 30 V is applied to one piezoelectric element 48. In order to eject ink droplets suitable for a pixel density of about 600 dpi, the frequency of the high-frequency signal is selected to be about 50 MHz.

While the application of the high-frequency signal in the hearst shape to the piezoelectric element 48 is performed in this manner, the driving data for applying the second high-frequency signal is transferred to the shift register 44.
When the first high-frequency signal application period DRIVE1, that is, the first ink droplet discharge operation is completed, the second high-frequency signal application period DRIVE2 starts. Hereinafter, similarly, the application of the high-frequency signal is repeated, and the recording operation of one line is completed when the required number of times has been performed. FIG. 6 shows an example in which one line is printed by four ejection operations for simplicity.

(Regarding the Drive Data Generation Unit 43) FIG. 5 shows a schematic configuration of the drive data generation unit 43 in FIG. In FIG. 5, drive data string generation blocks 53 and 63 set data strings for driving a plurality of piezoelectric elements necessary for discharging one ink droplet by drive data string setting units 54 and 64. Are output via the drive data array buffers 55 and 65. For example, when one ink droplet is ejected by simultaneously driving four piezoelectric elements, the four drive data are converted into a set of data arrays. Set as The drive data string is composed of the two types of high-frequency signals SI having different phases described above.
2 to select GNAL ZERO, SIGNAL PAI and GND
Kinds are prepared.

That is, the drive data string generation blocks 53 and 6
3 generates three types of high-frequency signals SIGNAL ZERO, SIGNAL PAI, and two types of drive data strings ZERO-DATE corresponding to GND. These two drive data string generation blocks 53 and 63 can be realized by the same configuration. Drive data string setting unit 54, 64
Can be a simple switch configuration, RAM
It is also possible to use a ROM or a ROM.

The drive data string buffers 55 and 65 are buffers that take in the drive data strings from the drive data string setting units 54 and 64 and sequentially read out the data constituting the drive data strings one by one in time series. In the present embodiment, the drive data string buffers 55 and 65 are composed of parallel input / serial output shift registers, and the load signal LOAD CL
The drive data string is read from the drive data string setting units 54 and 64 by OCK, and the read signal READ CLOCK from the control unit 40 is read.
Thereby, one data of the driving data train is read.

The selectors 56 and 66 select the drive data sent from the drive data string buffers 55 and 65, respectively, according to the timing selection signal TIMING SELECT from the control unit 40, and send them to the AND circuits 57 and 67. AND circuits 57 and 67 are selectors
The logical product of the drive data 56 and 66 and the image data from the line memory 42 in FIG. 4 is sent to the shift register 44 in FIG. 4 as drive data DRIVE EDATA. Here, since it is necessary to make a plurality of drive data correspond to one pixel of image data, in this example, four read signals READ
After sending the logical values of the four drive data and one image data corresponding to CLOCK, the process proceeds to the image data processing for the next pixel. For this, line memory
A latch 52 is provided for holding one image data read out from 42 for a period of four readings.

In FIG. 5, the image data from the line memory 42 in FIG. 4 is configured to be input to the latch 52 via the quantization unit 51. Does not require that the quantization unit 51 function at all. However, when the image data input to the line memory 42 is multi-valued data such as 8 bits per pixel, as in the present embodiment, the quantization unit 51 performs, for example, a quaternary processing with an appropriate value. Is performed. Based on this multi-value processing, drive data strings are set in the drive data string setting units 54 and 64.

The data transmitted from the AND circuits 57 and 67 in this manner is drive data for driving a predetermined piezoelectric element, and is binary data for selecting the high-frequency signals SIGNAL ZERO and SIGNAL PAI. is there. High frequency signal SIGNAL
Similarly to the generation of the drive data ZERO-DATE for selecting ZERO, the drive data PAI-DATE for selecting the high-frequency signal SIGNAL PAI is also output. That is, 2-bit data is input to the shift register 44 in FIG.

(Operation of Drive Data Generation Unit 43) Next, the operation of the drive data generation unit 43 will be described in more detail with reference to a timing chart relating to generation and transfer of drive data shown in FIG. As shown in FIG. 7A, first, the drive data string setting unit 5 receives a load signal LOAD CLOCK from the control unit 40.
Drive data strings are taken into drive data string buffers 55 and 65 from 4,64. At this time, the image data IMAGE of the first pixel
DATE is read from the line memory 42 and temporarily stored in the latch 52. For the image data of the first pixel, 4
Drive data DRIVE DATE is read signal READ CLOCK
Is generated in synchronism. Next, the image data of the fifth pixel four pixels ahead of the image data of the first pixel is stored in the line memory 42.
, And four drive data are generated and transmitted for the image data of the fifth pixel. Hereinafter, similarly, image data shifted by four addresses is read from the line memory 42. That is, the drive data is set so that every fourth ink droplet is ejected at the position of the piezoelectric element.

When 4960 pieces of drive data are transferred in this way, as described earlier with reference to the timing chart of FIG. 6, the drive data is fetched into the latch 45 by the latch signal LACH CLOCK, and every four piezoelectric elements. A series of recording operations of ejecting ink droplets from the position are performed.

Since the ink droplets are ejected every four elements, the ejection position is shifted by one element when ejecting the next ink droplet. That is, as shown in FIG. 7B, the transfer clock SHIFT CLO
Transmission of CK is started, but for the first transfer clock, the timing selection signal TIMING SELE
CT is off, and the outputs of the selectors 56 and 66 in FIG. 5 output the non-drive data (here, the ground signal GN) without selecting the drive data train.
Send out D). This serves to shift the phase of the piezoelectric element used at the time of the previous ink droplet ejection by one,
This is for forcing the piezoelectric element corresponding to the extreme end to the non-drive state. After that, the timing selection signal TIMING SELE
CT is turned on, and a signal equal to or less than the load signal LOAD CLOCK is transmitted in the same manner as in FIG. At this time, the image data read from the line memory 42 is read every fourth pixel, such as the second pixel, the sixth pixel, the tenth pixel, the fourteenth pixel, and so on.

Similarly, at the time of the third ink droplet ejection, the relationship between the timing selection signal TIMING SELECT and the transfer clock SIFT CLOCK is set so that two elements from the end are not driven, as shown in FIG. 7C. Is set. Although not shown, the same operation is performed at the time of the fourth ink droplet ejection,
Discharge of all ink droplets for one line is completed, and discharge of the next line is performed by the same operation as the first line.

(Specific Example of Driving Data Sequence) A specific example of the driving data sequence when the four driving data necessary for simultaneously driving the four piezoelectric elements as described above are shown in Table 1 below. It is shown in FIG. Table 2 (a) shows the phase of the high-frequency signal selected in the arrangement order of the elements, and Table 2 (b)
The drive data sequence at that time is shown. In this example, the data sequence is PAI, ZERO, ZERO, and PAI in the order in which the piezoelectric elements 48 are arranged. Here, ZERO and PAI mean data for selecting high-frequency signals whose phases are different from each other by 180 °. The principle of ejecting ink droplets when such drive data is given is as described with reference to FIGS.

[Table 2] Further, Tables 3 to 5 show the number of simultaneously driven piezoelectric elements.
An example of a drive data sequence in the case of different numbers of (simultaneous drive elements) is also shown. Table 3 shows an example in which the number of simultaneously driven elements is eight, Table 4 shows an example in which the number of simultaneously driven elements is nine, and Table 5 shows an example in which the number of simultaneously driven elements is ten.

[Table 3]

[Table 4]

[Table 5] Next, a driving method when image information including ink droplet diameter information is input will be described with reference to FIG.

First, a method of controlling the ejection amount control element when ejecting ink droplets of the first particle diameter (ink ejection amount control drive 1) will be described. Of the plurality of piezoelectric elements forming the piezoelectric element array, the (m + 1) -th to (m + n) -th elements are a piezoelectric element group, and the m-th and (m + n) -th elements among them are ejection amount controlling elements. Each of the piezoelectric elements in this piezoelectric element group is driven by allocating a 0-phase or a π-phase based on the Fresnel zone theory according to Tables 6 (a) and 6 (b). That is, all the elements of the piezoelectric element group, including the ejection amount control elements, are simultaneously driven.

As for the ultrasonic waves generated from the respective piezoelectric elements, the ultrasonic waves in the main scanning direction are focused near the ink surface, and the ultrasonic waves in the sub-scanning direction are focused by the acoustic lens / acoustic matching layer 105 in FIG. Then, the ink 106 near the liquid surface is ejected as an ink droplet having the first particle diameter.

[Table 6] Next, a method of controlling the ejection amount control element when ejecting ink droplets of the second particle diameter (ink ejection amount control drive 2) will be described.

In the same piezoelectric element group as in (ink ejection amount control drive 1), a DC voltage is applied to the ejection amount control element, and the (m + 1) -th to (m + n-1) -th n-1 piezoelectric elements are subjected to Fresnel zone theory. Are assigned in accordance with Tables 7 (c) and 7 (d) at the phase of 0 phase or π phase based on

That is, at least one pair of elements (in this example, the (m + n) -th element and the m + n-th element, which are symmetrical with respect to the center position of the element array of the piezoelectric element group).
With respect to the + n-th piezoelectric element, the m-th element at a position symmetrical to the left and right with respect to the center position of the element array of the piezoelectric element group) is not driven at the same time, and is set to the non-driving state (grounded state). Drive means. As a result, the amount of generated ultrasonic energy is reduced, and the ejection amount of the ink droplet is reduced as compared with the “ink droplet ejection amount control drive 1”, so that a small ink droplet (an ink droplet having a second particle size) is formed. Is discharged.

[Table 7] Next, a method of controlling the ejection amount control element when ejecting ink droplets of the third particle diameter (ink ejection amount control drive 3) will be described.

In the same piezoelectric element group as (ink ejection amount control drive 1), the (m + 1) th to (m + n−1) th n−
One piezoelectric element is driven with a phase of 0 or π based on the Fresnel zone theory, and a high-frequency voltage is applied to the discharge control element at a phase opposite to the phase based on the Fresnel zone.
Assignment and simultaneous driving are performed according to Tables 8 (e) and 8 (f).

That is, at least one pair of elements (in this example, the (m + n) -th element and the m + n-th element, which are symmetrical with respect to the center position of the element arrangement of the piezoelectric element group).
+ N-th piezoelectric element, an adjustment drive for applying a drive signal having a phase opposite to the original phase to the m-th element at a position symmetrical with respect to the center position of the element array of the piezoelectric element group. This is a control method in which the element is used as a drive for reducing the energy amount of the sound wave at the focal point. Accordingly, the ejection amount of the ink droplet is reduced as compared with “ink droplet ejection amount control drive 1”. In particular, in the case of driving in which a drive signal having a phase opposite to the original phase is applied to cancel a part of the energy amount of the sound wave at the focal point and reduce the energy for ejection, the “ink droplet ejection amount” It is possible to discharge even smaller ink droplets (ink droplets of a third particle diameter) than in the case where the generated energy is simply reduced as in “Control Method 2”.

[Table 8] Next, a method of controlling the ejection amount control element when ejecting ink droplets of the fourth particle diameter (ink ejection amount control drive 4) will be described. M of the plurality of piezoelectric elements forming the piezoelectric element array
The (n-1) -th to (m + n + 1) -th n + 3 elements are taken as a piezoelectric element group, and the (m-1) -th and (m + n + 1) -th elements are taken as ejection amount control elements. Each of the piezoelectric elements in the piezoelectric element group is driven by allocating a 0-phase or a π-phase based on the Fresnel zone theory according to Tables 9 (a) and 9 (b). That is, all the elements of the piezoelectric element group, including the ejection amount control elements, are simultaneously driven.

As a result, the ink droplets (ink droplets having the fourth particle diameter) become large compared to [ink droplet ejection amount control drive 1].

[Table 9] The tone control of the image can be performed by selecting the ink droplet ejection amount control means 1 to 4 according to the information of the ink particle diameter and changing the image spot size.

Although the mechanism by which the particle size of the ink changes depending on the energy amount of the ultrasonic beam is not clear,
The following reasons are presumed.

FIG. 9 is a schematic diagram showing a state during ink ejection.

As shown in FIG. 9A, a meniscus 1 is formed on the ink liquid surface in the vicinity of the converging portion of the ultrasonic wave, and further, a neck is generated at the wavelength λ from the tip of the meniscus. As shown in FIG.
It is thought that this is because, when the energy amount of the ultrasonic beam increases, the width of the tip (shown by d in the figure) increases.

Hereinafter, specific examples and results based on “ink droplet ejection amount control driving 1 to 4” shown in Tables 6 to 9 will be described.

[0067]

EXAMPLE First, an ink jet recording apparatus as shown in FIG. 1 was prepared in the following manner.

For the piezoelectric layer 102, a titanate-based piezoelectric ceramic plate having a relative dielectric constant of 200 was used. Ti / Au laminated electrodes are formed on both sides of the piezoelectric ceramic plate by sputtering so that the thicknesses thereof become 0.05 μm and 0.3 μm, respectively, and then an electric field of 3 kV / mm is applied to perform polarization processing. Was. After that, the individual electrodes 103 are formed by etching,
The electrode width per element was 60 μm, the electrode interval was 26 μm, and the arrangement pitch was 86 μm. Also, the piezoelectric layer 10
The width of No. 2 in the sub-scanning direction was 5 mm. On the other hand, Ti / Au array-shaped individual electrodes are also provided on the support member 100 made of glass.
It was formed at intervals of μm. The arrayed individual electrodes 103 on the impression body layer 102 and the arrayed electrodes on the support member 100 were bonded with epoxy resin in a state where they were aligned, and pressure was applied so that both electrodes were conducted.

Next, the piezoelectric layer 102 is polished so as to have a thickness of 45 μm so that resonance can be obtained at about 50 MHz, and then the common electrodes 104 composed of Ti / Au laminated electrodes are each 0.05 μm thick by sputtering. It was formed to a thickness of 1 μm. At this time, the length of the electrode in the sub-scanning direction, that is, the aperture in the sub-scanning direction was 2.0 mm.

For the acoustic lens / acoustic matching layer 105 formed in the next step, 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 / s, and the density was 2.20 × 10 ³ kg / s.
s and a sound speed of 2.95 × 10 ³ m / s. This mixture is applied to the surface of the common electrode 104 and cured to a thickness of about 45 μm.
m. Then, a one-dimensional Fresnel lens was formed by inserting a groove having a depth of 1/2 wavelength (about 30 μm) parallel to the main scanning direction so that the focal length became a target value. Then, the ink liquid holding chamber 7 is attached so that the distance between the ultrasonic wave emitting surface and the liquid surface of the ink liquid 106 substantially coincides with the focal length of the acoustic lens 105, and wiring of the driving means 110 is performed. An ink jet recording head having the above configuration was completed. (First Embodiment) First, the inkjet recording head of FIG. 1 having a focal length of 2.5 mm and the number of elements of a piezoelectric element group driven at the same time of 16 was changed to the ink droplet ejection amount control drive shown in FIG. In accordance with [1], driving was performed with a burst signal having a driving frequency of 50 MHz, a voltage of 15 V, and a signal application time of 50 μsec.

The result of the printing and recording experiment at this time was a dot size diameter of 60 μm.

Next, the same ink jet recording head is
According to [ink droplet ejection amount control drive 2] shown in FIG. 8B, 14 piezoelectric elements were driven at a driving frequency of 50 MHz and a voltage of 1
Simultaneous driving was performed with a burst signal having a voltage of 5 V and a signal application time of 50 μsec.

As a result of the printing and recording experiment at this time, the pixel size was 50 μm in diameter.

Next, in accordance with [ink droplet ejection amount control drive 3] shown in FIG. 8C, the fourteen piezoelectric elements are simultaneously driven, and the elements at both ends adjacent to the simultaneously driven elements are originally applied. A drive signal having a phase opposite to the power phase was applied.
The driving conditions were a burst signal with a driving frequency of 50 MHz, a voltage of 15 V, and a signal application time of 50 μsec.

As a result of the print recording experiment at this time, the pixel size was 40 μm in diameter.

Further, in the same ink jet recording head, according to [ink droplet ejection amount control drive 4] shown in FIG.
A burst signal of 50 MHz and a voltage 15 V signal application time of 50 μsec was applied.

As a result of the printing and recording experiment at this time, the pixel size was 70 μm in diameter.

When a color photographic image was printed while selecting according to the above-mentioned four [ink droplet ejection amount control drives 1 to 4] ink particle size information, the gradation was higher than when no ink droplet control method was used. Was improved, and high-quality printing records were obtained. (Second Embodiment) In the second embodiment, ink ejection was confirmed using a piezoelectric element group of 32 elements as the basic number of elements. That is, the piezoelectric element groups were simultaneously driven according to Tables 10 to 12 below.

Further, in this embodiment, the acoustic lens of the ink jet recording head is changed to a lens having a focal length of 4.0 mm, and the ink level is adjusted to 4.0 mm from the piezoelectric element array by using an ink liquid holding chamber. Was.

According to Table 10, the first to 32nd 32 elements were set to 50 MHz, a voltage of 25 V, and a signal application time of 50.
When the ink droplets were ejected by simultaneous driving under the condition of μsec, the pixel size became 80 μm.

[Table 10] According to Table 11, the second to 31st 30 elements were simultaneously driven under the same conditions to eject ink droplets, and the dot size became 70 μm.

[Table 11] According to Table 12, the third to thirty-eighth elements were simultaneously driven under the same conditions to eject ink droplets, and the pixel size became 60 μm.

[Table 12] According to Table 13, the fourth to 29th 26 elements were simultaneously driven under the same conditions to eject ink droplets, and the pixel size became 50 μm.

[Table 13] When a color photographic image was printed while the above four driving conditions were selected in accordance with image information, gradation was improved as compared with the case where the ink droplet control method was not used, and high-quality print recording was possible.

As described above, according to the present embodiment, a group consisting of a sound wave generating element array in which a plurality of sound wave generating elements are arranged at a predetermined pitch and an adjacent local constant number of sound wave generating elements in the sound wave generating element array are simultaneously driven. Comprising a recording head having a driving means to perform, at least a part of the plurality of sound wave generating elements constituting the sound wave generating element array, as an ink droplet ejection amount control element,
By adjusting the driving conditions for the control element, the discharge amount control means for the ink droplets can be provided, so that the dot size on the recording paper can be changed and the gradation can be improved. Recording can be realized.

[0082]

As described above, according to the present invention, in an ink jet recording apparatus using ultrasonic waves, it is possible to easily control the particle diameter of ink droplets to be ejected,
As a result, it is possible to control the gradation of the image.

[Brief description of the drawings]

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

FIG. 2 is a view for explaining the principle of an ultrasonic convergence method in the ink jet recording head according to one embodiment of the present invention.

FIG. 3 is a diagram schematically illustrating an example of a case where an ultrasonic beam is focused on one point in an inkjet recording head according to an embodiment of the present invention.

FIG. 4 is a block diagram showing an element configuration of a driving unit of the inkjet recording head according to the embodiment of the present invention.

FIG. 5 is a schematic configuration diagram of a driving data generation unit of a driving unit of an inkjet recording head according to an embodiment of the present invention.

FIG. 6 is an explanatory diagram of an operation of a driving unit of the inkjet recording head according to the embodiment of the present invention.

FIG. 7 is an operation explanatory diagram of a drive data generation unit of a drive unit of the inkjet recording head according to one embodiment of the present invention.

FIG. 8 is a diagram for explaining an example of an ink droplet ejection amount control method according to an embodiment of the present invention.

FIG. 9 is a schematic diagram showing a state when ink droplets are ejected by the ink jet recording apparatus of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Meniscus 2 ... Ink droplet 40 ... Control part 41 ... High frequency signal generation part 42 ... Line memory 43 ... Drive data generation part 44 ... Shift register 45 ... Latch 46 ... Selector 47 ... Driver 48, 48a-c ... Piezoelectric element 51 ... Quantizer 52 ... Latch 53, 63 ... Drive data string generation block 54,64 ... Drive Data string setting unit 55, 65 ... Driving data string buffer 56, 66 ... Selector 57, 67 ... AND circuit 100 ... Glass plate 101 ... Piezoelectric element array 102 ... Piezoelectric layer 103 , 103a-h: individual electrodes (piezoelectric body side) 104: common electrode 105: acoustic lens 106: ink liquid 107: ink liquid holding chamber 108: slit plate 109 Slit openings (ink droplet ejection ports) 110 ... driving unit 111 ... bonding wire 112 ... the individual electrodes (glass plate side)

Claims (4)

[Claims] 1. An ink jet recording apparatus which radiates convergent ultrasonic waves toward ink and ejects ink near the convergence point of the convergent ultrasonic waves as ink droplets to perform recording on a recording medium. And driving means for simultaneously driving a piezoelectric element group consisting of a predetermined number of piezoelectric elements in the piezoelectric element array, wherein the driving means is symmetric with respect to a center position of the piezoelectric element group. Wherein at least one pair of piezoelectric elements at the position of (a) is an ejection amount control element, and the ejection amount control element has ejection amount control means for selecting driving / non-driving according to ink droplet diameter information. . 2. An ink jet recording apparatus according to claim 1, wherein said discharge amount control means is means for applying a DC voltage to said discharge amount control element when not being driven. 3. The discharge amount control means according to claim 1, wherein the discharge amount control means is a means for applying a high-frequency voltage having a phase for weakening a converging ultrasonic wave at the convergence point to the discharge amount control element when the element is not driven. Ink jet recording device. 4. An ink jet recording apparatus which radiates convergent ultrasonic waves toward ink and ejects ink near the convergence point of the convergent ultrasonic waves as ink droplets to perform recording on a recording medium. And a driving unit for simultaneously driving a piezoelectric element array composed of a predetermined number of piezoelectric elements in the piezoelectric element array, wherein the driving unit is simultaneously driven in accordance with ink droplet diameter information. An ink jet recording apparatus, comprising: an ejection amount control unit for changing the number of piezoelectric elements.