JP2003011362A - Ink jet printer and driving method for ink jet head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make unevenness in the density of an image sufficiently small to the extent of being negligible by sufficiently suppressing variation of ejection speed and the difference of ejection volume among nozzles due to difference of print pattern. SOLUTION: In an ink jet head 4, compliance ratio R, i.e., 'compliance of a piezoelectric member composing the sidewall between ink chambers/compliance of ink', is set so that the repeating pulse period 'Tf (unit: AL3)' of applying voltage satisfies following relation; 2.7R<2> -2.8R+3.9<Tf<3.0R<2> -3.2R+4.1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inkjet head having a plurality of ink chambers and a driving method thereof.

[0002]

2. Description of the Related Art A method of driving an ink jet head in which a predetermined voltage is applied to a polarized piezoelectric member forming an ink chamber and the piezoelectric member is displaced to eject ink is disclosed in, for example, Japanese Patent Laid-Open No. 4-369542. Etc.

In the ink jet head disclosed in the above publication, the ink chambers are separated by an electrostrictive member and are continuously arranged in the width direction of the substrate. Therefore, a voltage is applied to the electrode of the electrostrictive member forming the side wall of each ink chamber to deform the electrode, so that the ink is ejected from the nozzle when the pressure in the ink chamber is increased.

Further, Japanese Patent Application Laid-Open No. 60-157875 discloses a technique for varying the number of pulse voltages for generating small ink droplets according to the required dot size.

[0005]

However, in the technique disclosed in Japanese Unexamined Patent Publication No. 4-369542, the ink chambers are partitioned from each other by the electrostrictive member and are continuously provided in the width direction of the substrate. Therefore, pressure vibration due to the deformation of those electrostrictive members propagates to the other ink chambers, causing crosstalk between the ink chambers. As a result, it has been clarified by an experiment conducted by the present inventor that the ink ejection pressure in each ink chamber is distorted to cause an error in the ejected ink volume.

Further, in the technique disclosed in Japanese Patent Laid-Open No. 60-157875, the driving frequency for ejecting the ink forming one pixel becomes high, so that the driving frequency of the electrostrictive member also becomes high. It was also confirmed that there was a problem that the size of talk increased further.

When the ink chambers are driven, the degree of crosstalk between the adjacent ink chambers varies depending on whether the adjacent ink chambers are being driven. Therefore, the error in the ejected ink volume varies in various ways. Therefore, there is a problem that uneven printing occurs.

An object of the present invention is to sufficiently reduce variations in ejection speed between nozzles due to differences in printing patterns and differences in ejection volume between nozzles so that unevenness in image density can be sufficiently ignored. Is.

An object of the present invention is to make it possible to change the repetition period of the voltage applied to the ink jet head while suppressing the residual vibration of the side wall between the ink chambers.

An object of the present invention is to effectively reduce the residual pressure vibration of the side wall between the ink chambers by one driving of the ink chambers.

[0011]

The invention according to claim 1 has a plurality of ink chambers partitioned from each other by side walls formed of piezoelectric members, and electrodes are formed on the wall surfaces of the side walls. Then, by applying a voltage to the electrode to generate a shear mode displacement in the sidewall,
An inkjet head that ejects ink in the ink chamber from a nozzle to form pixels on a recording medium, and the voltage is applied so that the ink chambers that can be simultaneously driven are every two ink chambers. Equipped with an inkjet head driver for driving,
In the ink jet head, when the repetition pulse cycle of the applied voltage is “Tf (unit: AL3)” and the compliance ratio “compliance of the piezoelectric member on the side wall / compliance of the ink” is “R”, An inkjet printer in which the compliance ratio R is set such that the pulse period Tf is 2.7R ² -2.8R + 3.9 <Tf <3.0R ² -3.2R + 4.1 (1). .

Therefore, when an inkjet head having a large number of nozzles is used and printing is performed while moving the inkjet head relative to the recording medium,
By setting the compliance ratio R that satisfies the relationship of the equation (1), it is possible to reduce the variation in the ejection speed between the nozzles due to the difference in the print pattern and the difference in the ejection volume between the nozzles due to the difference in the print pattern. Therefore, the present inventor has found that the uneven density of the image can be reduced to a negligible level.

According to a second aspect of the present invention, there is provided a plurality of ink chambers that are partitioned from each other by side walls formed of a piezoelectric member, and electrodes are formed on the wall surfaces of the side walls.
By applying a voltage to the electrodes to generate a shear mode displacement on the side wall, an ink jet head that ejects ink in the ink chamber from a nozzle to form pixels on a recording medium, and an ink jet head that can be simultaneously driven An inkjet head driver that drives the inkjet head by applying the voltage so that every two ink chambers are provided, the inkjet head having a repetition pulse cycle of the applied voltage of “Tf”.
(Unit: AL3) "," when the compliance "compliance ratio is" R "of the compliance / the ink of the piezoelectric member of said side wall, said pulse period Tf is, ^Tf = 3.0R 2 -3.1R + 4 .0 (2) An inkjet printer in which the compliance ratio R is set to be (2).

Therefore, when an inkjet head having a large number of nozzles is used and printing is performed while moving the inkjet head relative to the recording medium,
By setting the compliance ratio R that satisfies the relationship of the equation (2), it is possible to sufficiently reduce the variation in the ejection speed between the nozzles due to the difference in the print pattern, and to reduce the difference in the ejection volume between the nozzles due to the difference in the print pattern. The present inventor has found that the density can be made sufficiently small, and thus the density unevenness of an image can be made sufficiently small to be ignored.

According to a third aspect of the present invention, in the ink jet printer according to the first or second aspect, the ink jet head driver has a repetitive pulse waveform of the applied voltage, which is a voltage pulse having opposite polarities and the both voltage pulses. It is assumed that the predetermined pause time is provided between them.

Therefore, the repetition cycle of the applied voltage can be changed while suppressing the residual vibration of the side wall between the ink chambers.

According to a fourth aspect of the present invention, in the ink jet printer according to the third aspect, the ink jet head driver sets the voltage pulse widths of opposite polarities to AL.

Therefore, it is possible to effectively reduce the residual pressure vibration of the side wall between the ink chambers due to one driving of the ink chambers.

According to a fifth aspect of the present invention, there is provided a plurality of ink chambers, which are partitioned from each other by side walls formed of a piezoelectric member, and electrodes are formed on the wall surfaces of the side walls. In addition, a voltage is applied so that every two ink chambers that can be driven at the same time are applied to each other to cause a shear mode displacement in the side wall, and the ink in the ink chamber is ejected from the nozzle to be recorded on the recording medium. When a pixel is formed in, a repetition pulse cycle of the applied voltage is “Tf (unit: AL3)”, and a compliance ratio “compliance of the piezoelectric member on the side wall / compliance of the ink” is “R”, the pulse period ^{Tf, 2.7R 2 -2.8R + 3.9 <} Tf <3.0R 2 -3.2R + 4.1 so that ... (1) And which is a driving method of an inkjet head.

Therefore, when an inkjet head having a large number of nozzles is used and printing is performed while moving the inkjet head relative to the recording medium,
By setting the compliance ratio R that satisfies the relationship of the equation (1), it is possible to reduce the variation in the ejection speed between the nozzles due to the difference in the print pattern and the difference in the ejection volume between the nozzles due to the difference in the print pattern. Therefore, the present inventor has found that the uneven density of the image can be reduced to a negligible level.

According to a sixth aspect of the present invention, there is provided a plurality of ink chambers, which are partitioned from each other by side walls formed of a piezoelectric member, and electrodes are formed on the wall surfaces of the side walls. In addition, by applying a voltage so that the ink chambers that can be simultaneously driven are every two ink chambers, a shear mode displacement is generated on the side wall,
The ink in the ink chamber is ejected from a nozzle to form pixels on a recording medium, and the repetition pulse cycle of the applied voltage is “Tf (unit: AL3)”, “compliance of piezoelectric member on the side wall / compliance of the ink”. When the compliance ratio which is “R” is “R”,
This is a method for driving an inkjet head in which the pulse period Tf is set to Tf = 3.0R ² -3.1R + 4.0 (2).

Therefore, when an inkjet head having a large number of nozzles is used and printing is performed while moving the inkjet head relative to the recording medium,
By setting the compliance ratio R that satisfies the relationship of the equation (2), it is possible to sufficiently reduce the variation in the ejection speed between the nozzles due to the difference in the print pattern, and to reduce the difference in the ejection volume between the nozzles due to the difference in the print pattern. The present inventor has found that the density can be made sufficiently small, and thus the density unevenness of an image can be made sufficiently small to be ignored.

According to a seventh aspect of the present invention, there is provided an ink jet head driving method according to the fifth or sixth aspect, wherein
The repetitive pulse waveform of the applied voltage is composed of voltage pulses having polarities opposite to each other and a predetermined pause time provided between the voltage pulses.

Therefore, the repetition cycle of the applied voltage can be changed while suppressing the residual vibration of the side wall between the ink chambers.

According to an eighth aspect of the present invention, in the ink jet head driving method according to the seventh aspect, the voltage pulse widths of opposite polarities are set to AL.

Therefore, it is possible to effectively reduce the residual pressure vibration of the side wall between the ink chambers due to one driving of the ink chambers.

[0027]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described.

FIG. 1 is a block diagram showing the electrical connection of the ink jet printer 1 according to this embodiment. As shown in FIG. 1, this inkjet printer 1
Is provided with a printer controller 2 which is a control device including a microcomputer or the like for performing various calculations and centrally controlling the entire inkjet printer 1.

Further, the printer controller 2 has a drive mechanism control circuit 3 for controlling various actuators (not shown) of the ink jet printer 1, an ink jet head driver 5 for driving the ink jet head 4, and a timing for ejecting ink by the ink jet head 4. An ink ejection timing control circuit 6 for controlling the print head and a print data transfer circuit 7 for transferring print data for printing with the inkjet head 4 to the inkjet head driver 5 are connected.

The printer controller 2 is connected to the ink jet printer 1 via a predetermined interface.
A host computer 8 such as a PC for driving the computer is connected.

FIG. 2 is a perspective view for explaining the construction of the ink jet head 4, and FIG. 3 is a partially enlarged view of FIG.
As shown in FIGS. 2 and 3, this inkjet head 4
Includes a substrate 12, and a piezoelectric member 12a is embedded in a part of the substrate 12. The piezoelectric member 12a is embedded in the tip of the substrate 12 so as to have a length of, for example, 1.2 mm (therefore, the effective flow path length is also 1.2 m).
m). The piezoelectric member 12a includes an upper piezoelectric substrate 16 and a lower piezoelectric substrate 17, which are polarized in opposite directions in the thickness direction, and are bonded to each other with an adhesive or the like.

On the upper surface of the piezoelectric member 12a, a plurality of grooves 12b having a predetermined size and depth are formed at a predetermined pitch. As an example, the groove 12b has a depth of 300 μm.
m and a width of 80 μm. And the groove 12b
Extends from the front end of the substrate 12 toward the rear end thereof, and the rear end portion thereof has an R-shaped groove bottom and reaches the upper surface of the substrate 12. As a result, in the length direction of the groove 12b, members other than the portion that operates as the actuator are made of a material other than the piezoelectric member 12a. The groove pitch of the grooves 12b is determined according to the print density of printing when printing is performed using the inkjet head 4. As an example, the groove pitch in the case of 150 dpi (dots / inch) is 170 μm. Further, an electrode is formed on the inner surface of each groove 12b, and a wiring 19 connected to the electrode is continuously formed on the upper surface of the substrate 12. Wiring 19
A terminal (not shown) is formed on the.

The nozzle plate 13 is fixed to the tip of the substrate 12 in which the piezoelectric member 12a is embedded by adhesion or the like.
Nozzles 20 for ejecting ink droplets are formed at positions of the nozzle plate 13 facing the respective grooves 12b. Each groove 12b is closed by the top plate 18 and the nozzle plate 13 to form the ink chamber 11.

4 (a) and 4 (b) are enlarged vertical cross-sectional views of the ink chamber 11 cut in a direction orthogonal to the lengthwise direction thereof, in which the basic operation of the ink chamber 11 is also shown. ing. Further, FIG. 5 shows a waveform diagram of the drive pulse voltage applied to each wiring 19 of the inkjet printer 1 in order to perform this basic operation.

First, as shown in FIG. 4A, since the piezoelectric member 12 is polarized in the direction of the arrow, the ink chamber 11B
When a positive voltage (a period from t1 to t2 in FIG. 5) is applied to
Ink chambers 11A and 11B, 11B and 11 of the piezoelectric member 12
The side walls 12B and 12C that separate C are deformed in the opposite directions to increase the volume of the ink chamber 11B.

Next, as shown in FIG.
As in (a), since the piezoelectric member 12 is polarized in the direction of the arrow, a negative voltage (t in FIG. 5) is applied to the central ink chamber 11B.
The period of 2 to t3), the side walls 12B and 12C are
The ink chambers 11B are deformed in the opposite directions to reduce the volume of the ink chambers 11B, and the ejection of the ink in the ink chambers 11B starts.
Thereafter, at time t3, the applied voltage returns to the original value, and the volume of the ink chamber 11B is initialized. The voltage application time is AL which is 1/2 of the pressure oscillation cycle of the ink chamber during the period from t1 to t2, and 2 A during the period from t2 to t3.
It is generally L.

Next, regarding the case where ink is ejected from a plurality of nozzles 20, a plurality of nozzles 20 continuous in FIG.
The waveform of the drive pulse voltage applied to each ink chamber 11 when ink is ejected from the above is shown. In FIG. 6, ink chambers 11A to 11G indicate the ink chambers 11 arranged in this order. As shown in FIG. 6, in this driving method, the ink chambers 11 that can be simultaneously driven are set every two ink chambers, and the driving timings of the ink chambers 11 adjacent to each other are sequentially shifted.

Of these, paying attention to the ink chamber 11 that can be driven simultaneously, an example of driving depending on the printing pattern will be described with reference to FIGS. 7 and 8. Note that FIG.
8 is a waveform diagram of a voltage applied to the ink chamber 11, and FIG. 8 shows a pressurizing operation of the ink chamber 11 corresponding to the nozzle 20 that ejects ink. Of the drive patterns, FIG. 7A shows a case where the ink chambers 11 every two ink chambers are simultaneously ejected, and FIG. Only the ink is ejected, and the drive voltage waveform when ink is not ejected from the nozzles 20 of the ink chambers 11A and 11G that can be simultaneously driven is shown.

At this time, paying attention to the ejection speed and ejection volume of the ink ejected from the nozzles of the ink chamber 11D, FIG.
It was found that there is a difference between the case of (a) and the case of FIG. 7 (b). This is the case of the drive pattern of FIG.
The deformation of each side wall 12A, 12B, ...
(A), but at this time, the ink chambers 11B and 11B
Since the pressures of C, 11E and 11F are equal, the sidewalls 12C,
Although there is no deformation of 12F, in the case of FIG.
As shown in (b), it can be seen that a pressure difference occurs between the ink chambers 11B and 11C, 11E and 11F on both sides of the side wall 12C and 12F, respectively, and this side wall 12 causes a pressure difference.
C and 12F will be deformed, and the ink chamber 11
The nozzles 2 of the ink chambers 11C and 11E where the pressure of D is adjacent
0 and the ink chamber 11
The pressure oscillation cycle of D is also affected by the time of this leakage, and the ink chamber 11D is different between the case of FIG. 7A and the case of FIG. 7B.
This is because the discharge pressure of is different.

As shown in FIG. 9, the time during which the ink chamber 11 is deformed in the expanding direction is Pre, and the ink chamber 11 is
When Post is the time during which is deformed in the contraction direction, a period Pre in which the speed of a steady ink droplet (the speed changes up to several drops) is fastest is represented by a unit of “AL”.

However, because of the above-mentioned reason, the value of "AL" varies depending on the driving pattern of each ink chamber 11, so in this specification, two ink chambers that can be simultaneously driven as shown in FIG. 7A. AL will be referred to as AL3 when 3 ink chambers are simultaneously driven, and AL will be referred to as AL1 when 1 ink chamber is driven as shown in FIG. 7B. That is, as shown in FIG. 9, when a drive waveform having a ratio of "Pre: Post = 1: 3" every two nozzles is continuously applied, AL3 is used.

By the way, conventionally, as a gradation printing method for changing the size of a printing dot, Japanese Patent Laid-Open No. 60-157875.
There is a technique disclosed in the publication. This is because the pulse voltage for generating small droplets is repeatedly applied to the inkjet head several times according to the required dot size, and printing
It forms a pixel. When such a technique is applied to the inkjet head 4 having the above-mentioned configuration, during the repeated small droplet discharge operation, the repeated small droplet discharge is overlapped with the residual pressure due to the small droplet discharge operation performed before that. Therefore, the ejection pressure of the ink when the nozzles 20 that can be driven at the same time are driven and when the nozzles 20 that can be driven at the same time are not driven repeatedly, the pulse voltage is repeated due to the difference in the attenuation of the residual pressure wave and the difference in the pressure oscillation cycle. The difference is even larger than when there is no.

Further, as shown in FIG. 10, the inkjet head 4 and the paper P move relative to each other, whereby the inkjet head 4 scans the paper P to form an image of one page. Alternatively, when solid printing (denoted by reference numeral 21) of the same density is performed over one sheet P feeding operation, for example, three nozzles located at the end of the array of nozzles 20 and the other nozzles 20.
The difference between the print dot diameter and the print dot diameter causes a density difference between the print seam during the feeding operation and the other portion.

Further, in the case where the ink jet printer 1 has a device configuration in which a plurality of ink jet heads 4 are alternately displaced so that the nozzles 20 are aligned in one direction of the printable area, as shown in FIG. Similarly, a density difference occurs between the print seam between the inkjet heads 4 and other portions. This is because when the influence of the crosstalk as described above is likely to occur in the nozzles 20 located on the end side of the nozzles 20 of each inkjet head 4 in the parallel direction, this influence is easily noticeable as print density unevenness (1 When printing is performed using the individual inkjet heads 4, even if the print density at both end portions of the nozzle 20 in the parallel direction differs from the print density at the central portion, it is not conspicuous.

Therefore, in the drive system according to the embodiment of the present invention, the ink chambers that can be simultaneously driven are set every two ink chambers, and the ejection timings of the ink chambers adjacent to each other are sequentially shifted, so that all the ink chambers are ejected. The three-division driving method is used for driving. That is, one line of printing is formed by ejecting ink by driving three times.

Further, it is a system in which one pixel for printing is formed by continuously applying a driving voltage waveform capable of generating small droplets a plurality of times. That is, as shown in FIG. 12, the waveform for generating small droplets is repeated at the same interval Tf.

The waveform of the drive pulse voltage in one operation is as shown in FIG. That is, voltages of opposite polarities are applied in one operation, and each period is T
1, T3, and a rest period T2 is inserted between T1 and T3. Then, "T1 = T2 = T3 = AL3 (for example, =
2.3 μs) ”, when the nozzles 20 that can be simultaneously driven are driven, that is, when a large number of nozzles that are continuous such as solid printing are driven, the residual pressure vibration in one driving is effectively reduced. In addition, the ink chamber 11
Since the time Tr for maintaining the state of not deforming is provided between the repetition cycles Tf and Tf, it is possible to change the repetition cycle Tf while suppressing the residual vibration.

The relationship between the repetition period Tf and the ejection volume ratio due to the difference in drive pattern is obtained as shown in the graph of FIG. Note that the repetition cycle Tf in FIG. 14 has AL3 as a unit, and the difference in drive pattern is
This is the difference between the case where the ink chambers that can be simultaneously driven are driven simultaneously for every two ink chambers and the case where only three ink chambers are driven, and the ejection volume ratio is such that the waveform for generating small droplets is repeated. When “(1 ejection chamber driving ejection volume)
/ (Every 2 ink chambers, ejection volume when 3 ink chambers are simultaneously driven) ". Further, as described above, the difference in the ejection volume due to the drive pattern is due to the influence of the pressure leakage to the adjacent nozzle 20. The time-dependent value of pressure leakage differs depending on the compliance ratio R, which is the ratio of the compliance of the ink to the compliance of the side wall that is the wall of the ink chamber 11, so a diagram is obtained for each compliance ratio R. It was

Assuming that the ink compliance is A, A = 1 / (bulk modulus) = 1 / ρc ² (ρ: ink density c: ink sound velocity (bulk)) Therefore, for example, ρ = 850 Kg / M ³ , C = 135
If 0 m / s, then A = 1.26 × 10 ⁻¹⁰ / Pa.

If the compliance of the side walls between the ink chambers 11 is B, then B = (strain area of the side walls between the ink chambers / pressure) / channel cross-sectional area = (ΔS / ΔP) / S Therefore, for example, , ΔS / ΔP = 3.03 × 10 ⁻¹⁸
If m ² / Pa and S = 300 × 80 × 10 ⁻¹² m ² , then B = 6.46 × 10 ⁻¹⁰ Pa ⁻¹ .

From the above compliances A and B, "R =
A / B ”is calculated.

In the above example, R = (1.26 × 10 ⁻¹⁰ Pa ⁻¹ ) / (6.46)
× ¹⁰ -10 ^{Pa -} a 1) = 0.2.

According to the results shown in FIG. 14, the ink ejection volume does not vary depending on the drive pattern of the ink jet head 4. In other words, the repetition cycle Tf is such that the Y-axis value is 1 in FIG. And the compliance ratio R can be obtained.

That is, from the result of FIG. 14, the relationship between the repetition ratio Tf (unit: AL3) in which the discharge volume does not vary depending on this drive pattern and the compliance ratio R is calculated as follows: Tf = 3R ² −3.14R + 4 .025, and by rounding the coefficient of this equation to two decimal places or less, Tf = 3.0R ² −3.1R + 4.0.

A graph showing the relationship between the repetition period Tf and the compliance ratio R is shown in FIG. In addition,
The same relationship holds when the ink ejection speed ratio is set to 1.

Next, in the above-mentioned apparatus for performing printing as shown in FIG. 10, the left and right sides (upper and lower sides in FIG. 10) of the print joint have the same density, and further, the density change is the largest with respect to the change in the ink ejection volume. The number of repetitions of the pulse waveform of the drive voltage is adjusted so that the density range becomes
When print samples with different f values were prepared and the print quality was observed subjectively, it was judged that the print seams were not noticeably conspicuous in terms of density. Of course, depending on the case, in the case of a print image using a normal multi-gradation, the repetition period Tf should be set so that the ejection volume ratio in FIG. 14 is within the range of 0.95 to 1.05. Revealed that they were generally satisfied. In the above printing evaluation in this case, a commercially available dedicated recording paper for an ink jet printer was used as a printing recording medium.

As described above, when printing a high quality image, for example, an image equivalent to a photograph, using the recording paper for exclusive use of the ink jet printer which is generally used, when the ink ejection volume ratio exceeds the above range. It was found that the print image quality became conspicuous with uneven density.

The ink ejection volume ratio is 0.95 to
The repetition period Tf of 1.05 is 2.75R ² -2.825R + 3.9075 <Tf <3.
R ² −3.24R + 4.095, which is 2.7R ² −2.8R + 3.9 <Tf <3.0R ² −
It becomes 3.2R + 4.1.

Therefore, it was found that the print seam can be made inconspicuous in the case described above with reference to FIG. 10 by setting the repetition period Tf so as to apply to this equation. FIG. 16 is a graph showing the range of the repetition cycle Tf.

[0060]

According to the first aspect of the invention, when the ink jet head having a large number of nozzles is used and printing is performed while the ink jet head is relatively moved with respect to the recording medium, the relation of the expression (1) is satisfied. By setting the compliance ratio R, it is possible to reduce the variation in the ejection speed between nozzles due to the difference in the print pattern, and to reduce the difference in the ejection volume between the nozzles due to the difference in the print pattern. It can be made small enough to be ignored.

According to a second aspect of the present invention, when an ink jet head having a large number of nozzles is used and printing is performed while moving the ink jet head relative to the recording medium, the compliance ratio satisfying the relationship of the expression (2) is satisfied. By setting R, it is possible to sufficiently reduce the variation in the ejection speed between the nozzles due to the difference in the print pattern, and it is possible to sufficiently reduce the difference in the ejection volume between the nozzles due to the difference in the print pattern. The unevenness can be made small enough to be ignored.

According to a third aspect of the present invention, in the ink jet printer according to the first or second aspect, the cycle of the applied voltage can be changed while suppressing the residual vibration of the side wall between the ink chambers.

According to a fourth aspect of the invention, in the ink jet printer according to the third aspect, it is possible to effectively reduce the residual pressure vibration of the side wall between the ink chambers due to one driving of the ink chambers.

According to a fifth aspect of the present invention, when an ink jet head having a large number of nozzles is used and printing is performed while moving the ink jet head relative to the recording medium, the compliance ratio satisfying the relationship of the expression (1) is satisfied. By setting R, it is possible to reduce the variation in the ejection speed between nozzles due to the difference in the print pattern, and to reduce the difference in the ejection volume between the nozzles due to the difference in the print pattern, so that the uneven density of the image can be ignored. The present inventor has found that it can be made as small as possible.

According to a sixth aspect of the present invention, when an ink jet head having a large number of nozzles is used and printing is performed while moving the ink jet head relative to the recording medium, the compliance ratio satisfying the relationship of the expression (2) is satisfied. By setting R, it is possible to sufficiently reduce the variation in the ejection speed between the nozzles due to the difference in the print pattern, and it is possible to sufficiently reduce the difference in the ejection volume between the nozzles due to the difference in the print pattern. The present inventor has found that the unevenness can be made small enough to be ignored.

According to a seventh aspect of the present invention, there is provided an ink jet head driving method according to the fifth or sixth aspect, wherein
The repetition cycle of the applied voltage can be changed while suppressing the residual vibration of the side wall between the ink chambers.

According to the eighth aspect of the present invention, in the ink jet head driving method according to the seventh aspect, it is possible to effectively reduce the residual pressure vibration of the side wall between the ink chambers due to one driving of the ink chambers. it can.

[Brief description of drawings]

FIG. 1 is a block diagram showing electrical connection of an inkjet printer according to an embodiment of the present invention.

FIG. 2 is an exploded perspective view of an inkjet head of the inkjet printer.

FIG. 3 is an enlarged view of the same portion.

FIG. 4 is an enlarged vertical cross-sectional view of the ink chamber of the inkjet head taken along a direction orthogonal to the length direction thereof.

FIG. 5 is a waveform diagram of a drive pulse voltage applied to the inkjet head.

FIG. 6 is a waveform diagram of a drive pulse voltage applied to each ink chamber when ink is ejected from a plurality of continuous nozzles in the inkjet head.

FIG. 7 is a waveform diagram of a drive pulse voltage applied to an ink chamber of the inkjet head.

FIG. 8 is an explanatory diagram illustrating a pressurizing operation of an ink chamber corresponding to a nozzle that ejects ink in the inkjet head.

FIG. 9 is an enlarged view of an ink chamber of the inkjet head,
It is explanatory drawing explaining a reduction operation.

FIG. 10 is an explanatory diagram illustrating a case in which the inkjet head scans the sheet to form a one-page image by the relative movement of the inkjet head and the sheet.

FIG. 11 is an explanatory diagram of an apparatus configuration in which a plurality of the inkjet heads are alternately arranged so that the nozzles are aligned in one direction in a printable area.

FIG. 12 is an explanatory diagram of a repetition frequency at which small droplets of ink are generated by the inkjet head.

FIG. 13 is an explanatory diagram of the same.

FIG. 14 is a graph illustrating the relationship between the ink ejection volume and the repetition frequency.

FIG. 15 is a graph illustrating a relationship between the ejection volume of the ink and the repetition frequency in the inkjet head.

FIG. 16 is the same graph.

[Explanation of symbols]

1 inkjet printer 4 inkjet head 5 inkjet head driver 11 ink chamber 20 nozzles

Claims (8)

[Claims] 1. A plurality of ink chambers that are partitioned from each other by side walls formed of piezoelectric members, electrodes are formed on the wall surfaces of the side walls, and the side walls are formed by applying a voltage to the electrodes. By causing a shear mode displacement in the ink jet head, the ink in the ink chamber is ejected from the nozzles to form pixels on the recording medium, and the ink chambers that can be driven at the same time are every two ink chambers. An inkjet head driver that drives the inkjet head by applying the voltage, wherein the inkjet head has a repetition pulse cycle of the applied voltage of “Tf (unit: AL3)” and “the piezoelectric member of the sidewall”. When the compliance ratio "Compliance / Compliance of the ink" is set to "R", Pulse period Tf ^{is, 2.7R 2 -2.8R + 3.9 <Tf} <3.0R 2 -3.2R + 4.1 ...... (1) and said compliance ratio inkjet printer sets the R so. 2. A plurality of ink chambers partitioned from each other by side walls formed of a piezoelectric member, electrodes are formed on the side walls of the side walls, and the side walls are formed by applying a voltage to the electrodes. By causing a shear mode displacement in the ink jet head, ink is ejected from the ink chambers from nozzles to form pixels on a recording medium, and at the same time, two ink chambers can be simultaneously driven. An inkjet head driver that drives the inkjet head by applying the voltage, wherein the inkjet head has a repetition pulse cycle of the applied voltage of “Tf (unit: AL3)” and “the piezoelectric member of the sidewall”. When the compliance ratio "Compliance / Compliance of the ink" is set to "R", Inkjet printer pulse period Tf has set the compliance ratio R so that ^{Tf = 3.0R 2 -3.1R + 4.0 ......} (2). 3. The inkjet head driver,
The inkjet printer according to claim 1 or 2, wherein the repeated pulse waveform of the applied voltage includes voltage pulses having polarities opposite to each other and a predetermined rest time provided between the voltage pulses. 4. The ink jet head driver,
The inkjet printer according to claim 3, wherein the voltage pulse widths having mutually opposite polarities are AL. 5. An ink jet head having a plurality of ink chambers partitioned from each other by a side wall formed of a piezoelectric member, and an electrode being formed on a wall surface of the side wall. By applying a voltage so that every two ink chambers are placed, a shear mode displacement is generated on the side wall, and ink in the ink chamber is ejected from a nozzle to form a pixel on a recording medium. The repeated pulse cycle of the applied voltage is "Tf (unit: A
L3) "," Compliance of the piezoelectric member on the side wall /
When the compliance ratio which is “compliance of the ink” is “R”, the pulse period Tf is 2.7R ² −2.8R + 3.9 <Tf <3.0R ² −3.2R + 4.1. 1) A method of driving an inkjet head, which is set as follows. 6. An ink jet head having a plurality of ink chambers partitioned from each other by a side wall formed of a piezoelectric member, and an electrode being formed on a wall surface of the side wall. By applying a voltage so that every two ink chambers are applied, a shear mode displacement is generated on the side wall, and the ink in the ink chamber is ejected from a nozzle to form a pixel on a recording medium. The repeated pulse cycle of the applied voltage is "Tf (unit: A
L3) "," Compliance of the piezoelectric member on the side wall /
When the compliance ratio which is “compliance of the ink” is “R”, the pulse cycle Tf is set to Tf = 3.0R ² −3.1R + 4.0 (2) Driving method. 7. A repetitive pulse waveform of the applied voltage,
7. The method for driving an inkjet head according to claim 5, wherein the voltage pulse has polarities opposite to each other and a predetermined rest time provided between the voltage pulses. 8. The voltage pulse widths of opposite polarities are set to AL.
The method of driving an inkjet head according to claim 7.