JP2007111965A - Driving method of inkjet head and inkjet recording apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve printing speed while suppressing generation of ink mist and air bubble entrainment from a nozzle. <P>SOLUTION: One ink droplet is discharged by: a first step of retracting an ink meniscus in a nozzle of an inkjet head into the inside of the inkjet head; a second step of advancing the ink meniscus to an outside of the inkjet head after the first step and injecting ink; and a third step of retracting the ink meniscus into the inside of the inkjet head after the second step. The time ratio of the second step to the start of the first step through to the end of the third step is set at 0.38 to 0.5. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an inkjet head driving method and an inkjet recording apparatus that eject ink by changing the volume of a pressure chamber in accordance with a drive signal.

  2. Description of the Related Art Piezoelectric ink jet heads that change the volume of a pressure chamber filled with ink by deformation of a piezoelectric actuator and eject ink are widely used. An ink jet head using a piezoelectric actuator can relatively easily control the ink meniscus, and therefore can perform gradation recording in which the size of dots printed on a printing medium is individually changed.

  In a recording apparatus using a piezoelectric inkjet head, the ink meniscus in the nozzle is retracted from the initial position and then the ink meniscus is advanced in the ejection stroke of one ink droplet, and the ink meniscus is moved forward from the initial position. A technique is widely used in which the ink droplets are ejected as ink droplets and then the ink meniscus is retracted again.

  Patent Document 1 discloses a technique for performing gradation recording using a shear mode type ink jet head. In order to perform the gradation recording, a plurality of ink droplets forming one pixel are continuously ejected to control the number of ejected ink droplets. In this technology, the inkjet head is driven in four parts, and the time from ejection of ink droplets from one nozzle to ejection of ink from that nozzle is taken as one printing cycle, and within a quarter of that printing cycle. It is necessary to eject four ink droplets. Therefore, as shown in FIG. 5, the time required for the ink droplet ejection process occupies most of the printing cycle.

  Patent Document 2 discloses that the ink meniscus retraction time before ink droplets are ejected and the ink after ink droplets are ejected by changing the waveform of the drive signal in the same manner as the drive signal disclosed in Patent Document 1. Changing the meniscus retraction time is disclosed. However, the time for which the ink meniscus advances, that is, the time for ejecting ink and the time required for the ejection stroke of one ink droplet are substantially constant.

JP 2004-42414 A JP 2004-82697 A

  The inventor has found that the techniques disclosed in Patent Documents 1 and 2 should be further improved as described below. In the following description, the time required for the ejection stroke of one ink droplet (hereinafter referred to as “ejection stroke time”) refers to the backward movement of the ink meniscus, the forward movement of the ink meniscus, and the subsequent ejection of ink. It is the sum of the time to move the ink meniscus backward.

  In the technique disclosed in Patent Document 1, the time during which ink droplets are ejected occupies most of the printing cycle. Therefore, in order to further shorten the printing cycle and improve the printing speed using this technique, it is necessary to shorten the discharge stroke time. In order to shorten the ejection stroke time, it is necessary to shorten the ink ejection time when the ratio of the ink ejection time to the ejection stroke time is constant as described in Patent Document 2.

  If the ink ejection time is simply shortened, the ink droplet ejection volume decreases. In order to maintain a desired ejection volume of ink droplets while shortening the ink ejection time, it is necessary to increase the ejection speed of the ink droplets or increase the nozzle opening diameter. However, when the discharge speed is increased, ink mist is liable to be generated and the print quality is impaired, and bubbles are easily caught from the nozzle, and the discharge stability is lowered. Therefore, there is a limit to a method for improving the printing speed by shortening the ink ejection time by increasing the ink droplet ejection speed.

  Therefore, in order to shorten the ink ejection time, the present inventor attempted to obtain ink droplets having a desired ejection volume while increasing the nozzle opening diameter and maintaining the ink droplet ejection speed at a low value. However, even when the opening diameter of the nozzle was increased, the discharge stability was lowered due to the entrainment of bubbles from the nozzle.

  As described above, with the technologies disclosed in Patent Documents 1 and 2, it has been found that when the printing speed is further increased, the ejection stability should be improved to a practical level.

  In order to solve the above problems, the present invention provides a nozzle that discharges ink, a pressure chamber that communicates with the nozzle, an ink supply unit that supplies ink to the pressure chamber, and a volume of the pressure chamber as a drive signal. In an ink jet head driving method in which an ink jet head having an actuator that is variable according to the drive signal is driven in accordance with the drive signal and ink is ejected from the nozzle, an ink meniscus in the nozzle is retracted into the ink jet head. 1 stroke, a second stroke in which the ink meniscus is advanced to the outside of the inkjet head after the first stroke, and ink is ejected after the second stroke, and the ink meniscus is moved into the interior of the inkjet head after the second stroke. One ink droplet is ejected by the third stroke that moves backward to the first stroke, Starting from the driving method of ink jet head is characterized in that setting the time ratio of the second stroke from 0.38 to 0.5 with respect to time to the end of the third stroke of.

  In the present invention, the ratio of the ink ejection time to the ejection stroke time is made larger than 1/3, thereby shortening the ejection stroke time without shortening the ink ejection time. Therefore, it is possible to maintain the ejection stability at a practical level while improving the printing speed as compared with the conventional method without increasing the ink droplet ejection speed or increasing the nozzle opening diameter.

  Embodiments of the present invention will be described below with reference to the drawings. First, the structure of the inkjet head 101 will be described. 1 and 2 are a longitudinal sectional view and a transverse sectional view of the inkjet head 101, respectively. Piezoelectric members 2 and 3 are embedded in the tip portion of the low dielectric constant substrate 1 so that the polarization directions are opposite to each other inward with respect to the plate thickness direction. A plurality of long grooves 6 are formed in parallel to each other at regular intervals in the piezoelectric members 2 and 3 and the portion of the substrate 1 behind the piezoelectric members 2 and 3 by cutting with a diamond cutter. The ink supply path 14 serving as an ink supply means is formed by adhering a top plate frame 4 and a top plate lid 5 having ink supply ports 15 on the substrate 1. A portion of each long groove 6 surrounded by the piezoelectric members 2 and 3 and the top frame 4 is a pressure chamber 7. Each of the piezoelectric members 2 and 3 is an actuator 13 that deforms and drives the pressure chamber 7. A nozzle plate 11 on which nozzles 10 for ejecting ink droplets are formed is fixed to the tip of each pressure chamber 7 with an adhesive. Electrodes 8 that are electrically independent from each other are formed on the side and bottom surfaces of the long groove 6 forming the pressure chamber 7 by electroless plating. The electrode 8 extends from the rear end of the pressure chamber 7 to the upper surface of the substrate 1 and is connected to a drive circuit described later. The electrode 8 is not limited to electroless plating, and can be formed by a method of forming a predetermined pattern by etching after forming an electrode material by sputtering or vacuum deposition. Here, the length L of the pressure chamber 7 is a portion surrounded by the rear end of the top plate frame 4, that is, the long groove 6 and the top plate frame 4 from the front end of the pressure chamber 7 as shown in FIG. 1.

  Next, the drive circuit will be described. FIG. 3 shows a block diagram of the drive circuit. The drive circuit is composed of drive signal generation means, drive signal selection means 24, image memory 25, and decoder 26 including a drive waveform memory 21, a D / A converter 22 and an amplifier 23. The drive waveform memory 21 stores waveform information of a drive signal ACT applied to a pressure chamber that ejects ink and a drive signal INA applied to a pressure chamber that does not eject ink. The waveform information of these drive signals ACT and INA is converted into analog drive signals by the D / A converter 22 respectively. Further, these drive signals are amplified by the amplifier 23 and then input to the drive signal selection means 24. The drive circuit may be provided with the drive signal selection means 24 after the D / A converter 22 and the amplifier 23 after that instead of the configuration of amplification after the D / A conversion.

Further, based on the gradation information of each pixel of the image recorded in the image memory 25, the decoder 26 generates an ON / OFF signal 27 for controlling ejection / non-ejection of ink droplets, and the ON / OFF signal 27 is used as a drive signal. It supplies to the selection means 24. In this embodiment, as shown in [Table 1], 8-level gradation recording can be performed by individually controlling the ejection / non-ejection of a maximum of four ink droplets per pixel. The discharge volume of the first drop is 6 pl, and the discharge volume of the second to fourth drops is 12 pl.

  FIG. 4 shows a circuit diagram of the drive signal selection means 24. The drive signal selection means 24 is composed of an analog switch connected to an electrode provided in each pressure chamber, and supplies an ACT signal or an INA signal by switching to each electrode. In this embodiment, drive signal selection means 24 for driving the ink-jet head into four parts is shown. For each pressure chamber, the drive signal selection means 24 selects the ACT signal by the analog switch 26 when the ON / OFF signal 27 is ON, and by the analog switch 26 when the ON / OFF signal 27 is OFF. The INA signal is selected, and the drive signals ACT 1 to 4 and INA 1 to 4 are distributed to the electrodes 8.

  The configuration of the drive signal selection unit 24 will be described by exemplifying a case where ink is ejected from the pressure chamber 7c and ink is not ejected from the pressure chamber 7g at the same operation timing. In the pressure chamber 7c, the ON / OFF signal 27c and the left and right ON / OFF signals 27a, 27b, and 27d are turned on, and the electrode 8c provided in the pressure chamber 7c for discharging ink and the left and right pressure chambers are provided. An ACT signal is supplied to the electrodes 8a, 8b and 8d. In the pressure chamber 7g, the ON / OFF signal 27g and the left and right ON / OFF signals 27e, 27f, and 27h are turned OFF, and the electrode 8g provided in the pressure chamber 7g that does not eject ink and the electrode provided in the left and right pressure chambers The INA signal is supplied to 8e, 8f, and 8h.

  Next, drive signals ACT1 to ACT1 and INA1 to INA4 supplied to the drive signal selection unit will be described. FIG. 5 shows ACT1 to ACT4 which are drive signals for ejecting ink and INA1 to 4 which are drive signals for not ejecting ink. Here, the cycle of ACT1 to ACT4 and INA1 to INA4 is Tc. Tc corresponds to a printing cycle of one pixel. That is, it is the time from the start of ejection of an ink droplet that forms one pixel from a certain nozzle until the next nozzle can eject the ink droplet. Moreover, ACT1-4 and INA1-4 differ in a phase only by the time-division time. Since the number of time divisions is 4 in this embodiment, the phases of ACT 1 to 4 and INA 1 to 4 are shifted by a time of Tc / 4. ACT1 to ACT4 are composed of three drive signals W1, W2 and W3, and INA is composed of three drive signals W3, W4 and W5. FIG. 6 shows enlarged drive signals W1 to W5. W1 to W5 are W1a, W2a, W3a, W4a, and W5a in a period for discharging a first drop having a volume of 6 pl, and W1b, W2b, W3b, and W4b are in a period for discharging a second drop having a volume of 12 pl. , W5b, and W1c, W2c, W3c, W4c, W5c, which are in the period for discharging the third drop having the volume of 12 pl, and W1d, W2d, W3d, W4d, which are also in the period for discharging the fourth drop having the volume of 12 pl. , W5d. For example, when 6 pl ink is ejected from the pressure chamber 7c, the ON / OFF signals 27a to 27d are turned ON in the third cycle, so that the pressure chamber 7a has W3a, the pressure chambers 7b and 7d have W2a, and the pressure chamber 7c. Is supplied with a drive signal W1a.

  Next, a method for generating waveforms of the drive signals W1 to W5 will be described. The waveforms of the drive signals W1 to W5 are based on virtual meniscus vibration (hereinafter referred to as virtual meniscus vibration) ignoring meniscus retreat due to ink ejection and response characteristics obtained from the meniscus vibration with respect to the actual drive signal of the inkjet head. , By calculating back the waveform of the drive signal.

  The virtual meniscus vibration is the meniscus vibration in the nozzle that occurs in the actual ejection operation of the inkjet head. The meniscus retreats due to the ink being ejected from the nozzle, the ink refilling action caused by the ink surface tension, etc. This is a meniscus vibration that is linear with respect to the drive signal, from which nonlinear components such as forward movement are removed. FIG. 7 shows the difference between actual meniscus vibration and virtual meniscus vibration. Such meniscus vibration can be considered to be an expansion of the amplitude of the meniscus vibration that occurs when a drive signal whose amplitude is reduced to the extent that ink is not ejected is applied to the inkjet head.

  Such virtual meniscus vibration is different from the meniscus vibration that occurs in the actual ejection operation of an inkjet head, but the ink droplet ejection such as the meniscus flow rate during ink ejection and the volume of ink pushed out of the nozzle It has important characteristics related to speed and discharge volume. In addition, the actual meniscus vibration is influenced by factors that are not related to the drive signal, such as an ink refill action, in addition to non-linear vibration, and there is a limit to controlling this by the drive signal. On the other hand, since the virtual meniscus vibration is not affected by factors unrelated to the drive signal such as nonlinear vibration and ink refilling action, the virtual meniscus vibration can be sufficiently reproduced by the drive signal. Therefore, by defining a desired virtual meniscus vibration and giving the actuator a drive signal for generating the desired virtual meniscus vibration, it is possible to obtain desirable characteristics regarding the ink droplet ejection speed, ejection volume, and the like.

  FIG. 8 shows an example of the displacement of virtual meniscus vibration (virtual meniscus displacement). X1 to X4 are virtual meniscus displacements of the nozzles for which the ACT signal is selected, and X5 to X8 are virtual meniscus displacements of the nozzles for which the INA signal is selected. The virtual meniscus displacement of the nozzle that ejects ink is X3. The displacement is shown on the basis of the nozzle surface, the displacement in the ink ejection direction is the upper side of the drawing, and the direction in which the meniscus is drawn into the nozzle is the lower side.

Hypothetical meniscus displacement X ₃ nozzles for ejecting ink, the first to fourth ink ejection stroke of each drop, the first step of retracting from the nozzle surface of the ink meniscus in the nozzle before ink ejection, ink jet Therefore, the ink meniscus has a second stroke in which the ink meniscus is advanced from the nozzle surface, and a third stroke in which the ink meniscus is retracted to the nozzle surface after ink ejection. The time of the first stroke, the time of the second stroke, and the time of the third stroke of the first drop are respectively indicated by t1a, t2a, and t3a. Also, the time of the first stroke, the time of the second stroke, and the time of the third stroke of the second to fourth drops are indicated by t1b, t2b, and t3b, respectively. In the first drop, the time from the start of the first stroke to the end of the third stroke, that is, the discharge stroke time is t1a + t2a + t3a, and the time of the second stroke is the ink ejection time t2a. In the second to fourth drops, the ejection stroke time is t1b + t2b + t3b, and the ink ejection time is t2b. In each drop, the ratio of the ejection time to the discharge stroke time is set to 0.38 to 0.5, preferably 0.43.

In this embodiment, the amplitudes of the virtual meniscus displacements X ₁ , X ₂ , X ₄ and X ₅ are set to −1/3 times the amplitude of the virtual meniscus displacement X ₃ , and the virtual meniscus displacements X ₆ , X ₇ and X ₈ amplitude is set to 1/9 times the amplitude of hypothetical meniscus displacement X _3. Other settings of the amplitude ratio of the virtual meniscus displacement are possible.

  The virtual meniscus vibration is defined by the number corresponding to the type of the drive signal waveform to be generated. In this embodiment, since there are a total of eight drive signals ACT1 to ACT4 which are drive signals for ejecting ink and INA1 to INA4 which are drive signals which do not eject ink, eight virtual meniscus vibrations are defined. Hereinafter, the number of defined virtual meniscus vibrations is represented by a variable n. In this embodiment, n = 8. For example, in the case of an inkjet head having a 1: 1 correspondence between the actuator and the pressure chamber, such as a Kaiser type inkjet head, n = 1. In that case, it is only necessary to define the virtual meniscus displacement of the nozzle that ejects ink.

  The response characteristic of the ink jet head can be obtained by giving a drive signal VT for response characteristic measurement to the ink jet head and measuring the vibration of the ink meniscus caused by the drive signal. As the drive signal VT for measuring the response characteristics, either a noise signal having many frequency components or a sine wave signal containing a single frequency component is considered appropriate, but here a noise signal is mainly used. The case will be described.

First, a noise signal VT having a voltage value randomly determined at an appropriate time interval dt in the same cycle as one printing cycle Tc is generated, and the noise signal VT is generated at intervals of n−1 pressure chambers. Apply to the pressure chamber of the inkjet head. The voltage of the pressure chamber not giving the noise signal VT is a constant voltage. For example, the noise signal VT is given to the electrodes 8a and 8i, and the voltages of the electrodes 8b to 8h, 8j and 8k are set to 0V. The voltage is applied in the same pattern for the other electrodes not given the reference numerals in FIG. In this state, the flow velocity waveform of the meniscus vibration of the number corresponding to n is measured. The flow velocity waveform of the meniscus vibration can be measured by irradiating the meniscus in the nozzle of the inkjet head with a laser beam using a commercially available laser Doppler vibrometer, for example, LV-1710 of Ono Sokki Co., Ltd. FIG. 9 shows the noise signal VT. Similarly, FIG. 9 shows an example of the flow velocity waveform of meniscus vibration in each nozzle caused by the noise signal VT. Velocity waveform of meniscus vibrations in nozzles noise signal VT is given is UT1, it is sequentially flow velocity waveform of the meniscus vibration in adjacent nozzles _{UT 2, UT 3,} a · · · UT _8.

The noise signal VT and the flow velocity waveform UT of the meniscus vibration are Fourier transformed using the equations [Equation 1] and [Equation 2], respectively, and converted into a voltage spectrum FVT and a flow velocity spectrum FUT, respectively.

  Here, m is the number of time-series flow velocity data observed with a laser Doppler vibrometer. If the sampling time of flow velocity data observed with a laser Doppler vibrometer is dt, m is a value of Tc / dt. The subscript i is an integer from 1 to n indicating the number of the pressure chamber. The subscript j is an integer from 1 to m indicating the jth data from the top in the time series data. The j-th data indicates data at time j × dt. The subscript k is an integer from 1 to m indicating the kth data from the top in the frequency series data. The k-th data indicates data of frequency (k−1) / Tc. I is an imaginary unit. The notation of the subscript described here will be used in the following description.

The voltage spectrum FVT _{i, k} represents the voltage amplitude and phase at the frequency (k−1) / Tc of the noise signal VT _i in the form of complex numbers. The flow velocity spectrum FUT _{i, k} represents the flow velocity amplitude and phase at the frequency (k−1) / Tc of the meniscus vibration flow velocity waveform UT _i in the form of complex numbers.

From the voltage spectrum FVT and the flow velocity spectrum FUT, the response characteristic R of the meniscus vibration caused by the drive signal is obtained from the equation [Equation 3].

R _{i, k} indicates in complex form the amplitude and phase of the flow velocity of the meniscus vibration generated in the i-th pressure chamber when a drive signal of frequency (k−1) / Tc is given to the first pressure chamber. ing. FIG. 10 shows the relationship between the frequency and the absolute value of the complex number and the relationship between the frequency and the phase number of the complex number of the frequency responses R _{1 to} R ₈ of each nozzle.

  Although the case where a noise waveform is obtained as the test drive signal VT has been described, a response characteristic R is obtained by measuring the amplitude and phase of flow velocity vibration at each frequency using a sine wave or cosine wave with a variable frequency as the test drive signal VT. Is also possible.

Next, a method for obtaining the waveform of the drive signal from the virtual meniscus displacement X and the response characteristic R will be described. First, a virtual meniscus flow velocity U corresponding to the virtual meniscus displacement X is obtained. The virtual meniscus flow velocity U is obtained by the mathematical formula [Equation 4].

Figure 11 illustrates a hypothetical meniscus flow velocity _U 1 ~U ₈ obtained by equation [Equation 4]. As shown in FIG. 11, the time of each stroke of the hypothetical meniscus displacement X ₃ so that the ink ejection speed and ink meniscus retraction time of each drop constant is adjusted.

Next, Fourier transformation of the virtual meniscus flow velocity U is performed using Equation [5] to obtain a flow velocity spectrum FU of the virtual meniscus flow velocity U.

The flow velocity spectrum FU _{i, k} represents the flow velocity amplitude and phase at the frequency (k−1) / Tc of the virtual meniscus flow velocity U _i in the form of complex numbers.

Next, the voltage spectrum FVA of the drive signal is obtained from the response characteristic R of the inkjet head and the flow velocity spectrum FU of the virtual meniscus vibration. When the response characteristic matrix [R] _k is expressed by the following equation (6), the voltage vector {FVA} _k is expressed by the following equation (7), and the flow velocity vector {FU} _k of the virtual meniscus vibration is expressed by the following equation (8): 9], the voltage vector FVA _{k at the} frequency (k-1) / Tc is obtained.

The voltage spectrum FVA _{i, k} obtained by the equations [Equation 7] and [Equation 9] represents the voltage amplitude and phase at the frequency (k−1) / Tc of the drive signal VA _i in the form of complex numbers. In addition, the element in the a row and the b column of [R] _k obtained by the mathematical formula [Equation 6] is the a th for the voltage oscillation at the frequency (k−1) / Tc of the drive signal applied to the b th pressure chamber. The change in the amplitude and phase of the flow velocity of the meniscus vibration in the nozzle communicating with the pressure chamber is expressed in the form of a complex number. [R] _k ⁻¹ is an inverse matrix of [R] _k . The calculation of the inverse matrix can be performed by mathematical analysis software such as MATHEMATICA manufactured by WOLFRAM RESEARCH.

Next, the waveform of the drive signal VA is obtained by performing an inverse Fourier transform on the voltage spectrum FVA using Equation [10].

Here, Re [z] is a function for obtaining the real part a of the complex number z = a + bI. VA _{i, j} is a voltage value at time j × dt of the i-th pressure chamber of the drive signal VA for generating the virtual meniscus flow velocity U. M ′ is an integer that determines the upper limit of the frequency component of the drive signal VA. As m ′ is increased, the reproducibility of the virtual meniscus vibration is improved and the voltage amplitude of the drive signal VA is increased. When m ′ exceeds a certain value, the voltage amplitude of the drive signal VA increases significantly. Therefore, it is desirable to adjust the value of m ′ to a value slightly smaller than the value at which the voltage amplitude of the drive signal VA increases significantly.

An example of the drive signal VA obtained as described above is shown in FIG. The drive signal VA can be used as it is as a drive signal for the inkjet head. When the drive signal obtained by the above method is used as it is, the drive signal voltage change range is large and the drive circuit becomes expensive. In this embodiment, the drive signal voltage change range is narrowed to reduce the drive signal voltage range. The price was reduced. To narrow the range of voltage variation, determining the minimum value of the voltage of the drive signal VA ₁ to VA ₈ at each time, it subtracts the minimum value from each of the voltage of the drive signal VA ₁ to VA _8. The calculated drive signals VB _{1 to} VB ₈ are shown in FIG. By cutting the appropriate section of _VB 1 through Vb ₈ obtained in this manner, the drive signal W1~W5 is obtained.

  Subsequently, the operation and effect of the present embodiment will be described. In the ink jet recording apparatus having the above-described configuration, the inventor evaluated the ejection stability by changing the ratio of the opening diameter of the nozzle 10 on the ink ejection side and the ejection time to the ejection stroke time.

Specifically, the voltage of the drive signal is set so that the ejection volume is 42 pl by giving the drive signal of gradation 7 of [Table 1] to each of the inkjet heads having the nozzles having the opening diameters shown in [Table 2]. The amplitude was adjusted. Further, while maintaining the first drop ejection stroke time (t1a + t2a + t3a) and the second to fourth drop ejection stroke times (t1b + t2b + t3b) of the virtual meniscus vibration, the ink droplet ejection speed is 10 to 12 m / s. The ink ejection time t2a for the first drop and the ink ejection time t2b for the second to fourth drops were adjusted so that

  As a result of observing the ejected droplets with a strobe and a microscope under such conditions, the results shown in Table 2 were obtained. Here, x indicates a case where non-ejection due to bubble entrainment occurs at a frequency of about once within 5 minutes from the start of ink ejection. Δ indicates a case where non-ejection due to bubble entrainment occurs at a frequency of about once within 20 minutes from the start of ink ejection. ○ indicates the case where the frequency of non-ejection due to entrainment of bubbles is less than once every 20 minutes.

  From the results of [Table 2], by setting the ink ejection time / discharge stroke time within the range of 0.38 to 0.5, the nozzle opening diameter can be reduced while keeping the ink droplet discharge speed within an appropriate range. The effect of improving the discharge stability to a practical level was observed. When the ink ejection time / ejection stroke time was made larger than 0.5, the ejection stability tended to decrease. This is presumed that as a result of increasing the injection time while keeping the discharge stroke time constant, the time t1a, t3a, t1b, t3b for retracting the meniscus is shortened, and the retracting speed of the meniscus is increased so that bubbles are easily involved. Is done.

  The inventor also analyzed the voltage amplitude of the drive signal calculated for the virtual meniscus vibration with the ink ejection time / discharge stroke time being 0.43 while changing the length L of the pressure chamber 7. As a result, it has been found that there is a pressure chamber length L that minimizes the voltage amplitude of the drive signal. In the pressure chamber length L, the voltage applied to the actuator has a voltage waveform VC shown in FIG. A voltage change in the upward direction from the horizontal axis indicates a voltage change that expands the volume of the pressure chamber 7.

  The second to fourth drop waveforms VCb to VCd of the voltage waveform VC are the first voltage change that expands the pressure chamber 7 from the initial state, and the second voltage that contracts the pressure chamber 7 after the first voltage change. Change, a third voltage change that expands the pressure chamber 7 after the second voltage change, a fourth voltage change that contracts the pressure chamber 7 after the third voltage change, and after the fourth voltage change. And a fifth voltage change for expanding the pressure chamber 7. Further, in the waveforms VCb to VCd, the second voltage change is larger than the first voltage change, the third voltage change is smaller than the second voltage change, and the fourth voltage change is larger than the third voltage change. ing. By applying such a voltage change to the actuator 13 of the inkjet head 101, the ratio of the ejection time to the ejection stroke time can be made suitable, and as a result, the ejection stability can be further improved without reducing the printing speed. It can be seen that it can be improved.

1 is a longitudinal sectional view of an ink jet head according to an embodiment. FIG. 2 is a cross-sectional view of the ink jet head of the present embodiment. The block diagram of the drive circuit of a present Example. The circuit diagram of the drive signal selection means of a present Example. The figure which shows the waveform of the drive signal of a present Example. The figure which shows the detail of the waveform of the drive signal of a present Example. The figure explaining the difference between an actual meniscus vibration and a virtual meniscus vibration. The figure which shows the displacement waveform of the virtual meniscus vibration of a present Example. The figure which shows the waveform of the test drive signal of a present Example, and the waveform of the flow velocity vibration generate | occur | produced by a test drive signal. The figure which shows the response function of the inkjet head of a present Example. The figure which shows the flow-velocity waveform of the virtual meniscus vibration of a present Example. The figure which shows the waveform of the calculated drive signal of a present Example. The figure which shows the waveform which deform | transformed the waveform of the calculated drive signal of a present Example. The figure which shows the voltage waveform applied to an actuator by the drive signal of a present Example.

Explanation of symbols

7 Pressure chamber 8 Electrode 10 Nozzle 13 Actuator 24 Drive signal selection means 27 ON / OFF signal 101 Inkjet head t1 Meniscus retraction time t2 before ink ejection Ink ejection time t3 Meniscus retraction time after ink ejection

Claims (3)

An ink jet head comprising: a nozzle that ejects ink; a pressure chamber that communicates with the nozzle; ink supply means that supplies ink to the pressure chamber; and an actuator that varies the volume of the pressure chamber according to a drive signal. In a driving method of an inkjet head that is driven according to a driving signal and discharges ink from the nozzle,
A first stroke in which the ink meniscus in the nozzle is retracted to the inside of the inkjet head; and a second stroke in which the ink meniscus is advanced to the outside of the inkjet head after the first stroke to eject ink. One ink droplet is ejected by a third stroke in which the ink meniscus is retracted into the inkjet head after the second stroke;
A method for driving an ink-jet head, wherein a ratio of the time of the second stroke to the time from the start of the first stroke to the end of the third stroke is set to 0.38 to 0.5. An ink jet head comprising: a nozzle that ejects ink; a pressure chamber that communicates with the nozzle; ink supply means that supplies ink to the pressure chamber; and an actuator that varies the volume of the pressure chamber according to a drive signal; Drive signal generating means for measuring a response characteristic of meniscus flow velocity vibration in the nozzle with respect to a drive signal for driving the inkjet head, and generating a drive signal obtained by calculation based on the response characteristic; In the ink jet recording apparatus for discharging ink from the nozzle according to
The waveform of the drive signal includes a first stroke for retracting the ink meniscus in the nozzle to the inside of the inkjet head, and a second stroke for advancing the ink meniscus to the outside of the inkjet head after the first stroke. And a third stroke for retracting the ink meniscus into the inkjet head after the second stroke, and the second stroke relative to the time from the start of the first stroke to the end of the third stroke. An ink jet recording apparatus characterized in that the ratio of the stroke time is set to 0.38 to 0.5. An ink jet head comprising: a nozzle that ejects ink; a pressure chamber that communicates with the nozzle; ink supply means that supplies ink to the pressure chamber; and an actuator that varies the volume of the pressure chamber according to a drive signal; In the ink jet recording apparatus which has a drive signal generating means for generating a drive signal for driving the ink jet head, and discharges ink from the nozzles according to the drive signal.
The drive signal is a signal for ejecting one ink droplet, a first voltage change that expands the pressure chamber from an initial state, and a second voltage change that contracts the pressure chamber after the first voltage change; A third voltage change for expanding the pressure chamber after the second voltage change; a fourth voltage change for contracting the pressure chamber after the third voltage change; and a pressure chamber after the fourth voltage change. The second voltage change is larger than the first voltage change, the third voltage change is smaller than the second voltage change, and the fourth voltage change is applied to the actuator. An ink jet recording apparatus characterized in that the voltage change of is larger than the third voltage change.

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