JP2008168533A - Liquid ejection method and liquid ejection apparatus - Google Patents

Abstract

In a liquid discharge head in which liquid is discharged by increasing and decreasing the volume of an individual liquid chamber from the initial volume in order to perform liquid discharge, regardless of various conditions such as physical properties of the liquid and the head structure. Therefore, it is possible to realize appropriate driving capable of preventing the occurrence of the “swing” of the discharge.
The discharged liquid extends in a columnar shape, and a liquid column having a portion that becomes a droplet (main droplet) is formed at the tip in the discharge direction, and then divided at a portion on the discharge port side. At this time, the drive condition is determined based on the volume change so that the volume does not decrease after the appearance of the minimum value that appears after the maximum value of the volume appears until the liquid column is divided at the discharge port side. As a result, the liquid in the discharge port does not push the liquid column, so that the liquid column is not bent, which causes “swing”. In addition, by determining the driving condition based on the change in volume, it is possible to reliably suppress the occurrence of “swing” regardless of various conditions such as the physical properties of the liquid and the head structure.
[Selection] Figure 7

Description

  The present invention relates to a liquid discharge method and a liquid discharge device, and more particularly, a pressure that generates pressure as energy for discharging liquid from the discharge port by increasing or decreasing the volume, and a discharge port for discharging liquid and the discharge port. A liquid discharge head having a chamber is used. The present invention is not only a device for recording on a recording medium such as paper, cloth, leather, nonwoven fabric, and OHP plastic film, but also an apparatus for patterning and processing by attaching a liquid to a substrate, a plate material, a solid material, etc. Furthermore, it can also be applied to a coating apparatus or the like.

  As a liquid ejection head, a pressure plate is provided with a vibration plate in contact with the liquid, and the volume of the pressure chamber is increased or decreased by displacing the vibration plate by a piezoelectric element that is deformed in response to the application of voltage. There is a thing that discharges. The liquid ejected from the liquid ejection head having such a configuration is divided in the middle after extending in a columnar shape, whereby the separated liquid droplets reach a receptor such as a recording medium.

  In a liquid discharge head, for example, a liquid discharge head that discharges ink as a recording agent, it is an important issue that a preferable discharge performance of liquid is obtained in order to achieve high definition and high quality recording. ing.

  In order to realize high-quality recording or the like, a technique for landing droplets on a recording medium or the like with high accuracy is required. As one of the factors that hinder this, unnecessary liquid that adheres and accumulates on the discharge port formation surface, especially near the discharge port edge, obstructs the straight movement of the discharge droplets or liquid column, thereby deflecting the discharge direction. There is a phenomenon (called “yore”) that causes it to occur. For this, there is a technique for improving by appropriately selecting the wettability and shape of the discharge port forming surface.

  However, another cause of “flickering” is the bending of the liquid column due to the fact that the liquid velocity in the discharge port becomes higher than the protruding velocity of the liquid column. That is, when the liquid in the discharge port pushes the liquid column, the liquid column is bent, and the flying direction of the liquid droplets separated therefrom is deflected. This “swing” cannot be solved by a configuration that prevents the liquid from adhering to the vicinity of the discharge port edge.

  Here, for example, Patent Document 1 discloses a technique for miniaturizing ink droplets (discharging 1 pl microdroplets) as a technique for obtaining preferable ejection performance. Although the essential discharge port dimensions are not specified in Patent Document 1, the same Table 1 is also described in Patent Document 2 which is the same applicant and the same inventor, and is described in Patent Document 2. From the numerical value, the discharge port diameter used in Patent Document 1 is estimated to be 20 μm.

  In Patent Document 1 and Patent Document 2, a drive waveform to be input to an actuator (piezoelectric element) in order to discharge a fine ink droplet is defined based on the natural period of the actuator. The technique disclosed in Patent Document 3 is cited as a method for calculating the natural period of the actuator.

  However, the method disclosed in Patent Document 3 is questionable when applied to the calculation of the natural period of an ink-jet head containing liquid, in addition to calculating the Helmholtz period of an electric circuit. This is because arbitrary parameters representing the structure of the head (such as shape characteristics and dimensions) and the physical properties of the liquid (such as viscosity) are introduced into the natural period calculation. And there is no uniform standard for applying these parameters. In this way, the natural period calculation method is not theoretically independent of the parameters to be considered, so that the natural period calculation method in a specific case is accurate for all inkjet heads with different shapes. There is no guarantee to calculate. Further, Patent Document 1 and Patent Document 2 do not have a description regarding measurement in which calculation accuracy is confirmed, but if there is a measurement method for confirming in the first place, there is no need for the above calculation. That is, the techniques disclosed in Patent Document 1 and Patent Document 2 can be applied only to an inkjet head that is subject to calculation of the natural period.

  On the other hand, Patent Document 4 discloses a technique related to a measuring apparatus that evaluates the time between discharge speed peaks as a natural period. At this time, a trapezoidal drive voltage waveform is applied to the piezoelectric element.

  However, there is no reason why the drive voltage waveform must be a trapezoidal waveform, nor is it defined by JIS or other industrial standards. Therefore, the present inventors use a rectangular wave that discharges a droplet by increasing and decreasing the volume of the pressure chamber, and when applying a potential change that increases the volume, and when applying a potential change that contracts The change in the discharge speed was arranged by changing the time of the difference. Here, the inventors apply a step-like voltage to a liquid discharge head using a so-called bender type piezoelectric element, and measure the displacement of the electrode surface formed on the piezoelectric film layer bonded to the diaphragm with a laser beam. Measured by the Doppler method and earnestly studied. When both the piezoelectric film layer and the electrode layer are thin, it can be interpreted that the out-of-plane displacement of the electrode surface is almost equal to the out-of-plane displacement of the diaphragm. It is thought that the vibration cycle of the entire head system can be observed.

  As a result, the period of vibration evaluated from the out-of-plane displacement of the electrode of the piezoelectric element by the laser Doppler method and the period evaluated from the time between the discharge speed peaks as in the method disclosed in Patent Document 4 are almost the same. (However, a trapezoidal wave is used in Patent Document 4).

Next, it was examined whether or not the period t _H evaluated from the out-of-plane displacement of the electrode of the piezoelectric element by the laser Doppler method has universality. That is, the period evaluated from the out-of-plane displacement of the electrode was arranged by changing the gradient of the potential change that increases the pressure chamber volume.

FIG. 11 is an explanatory diagram of various potential changes at this time. In the potential changes from V _H to V _L , potential changes of a, b, and c (inclination decreases in this order) are shown. 12A, 12B, and 12C show response curves of out-of-plane displacement from the initial position of the electrodes of the piezoelectric element with respect to potential changes a, b, and c, respectively. As is clear from these figures, it was confirmed that the period t _H evaluated from the out-of-plane displacement of the electrode becomes longer as the gradient of the potential change becomes milder (t _Hc > t _Hb > t _Ha ). That is, it was confirmed that the evaluated cycle t _H changes depending on the shape of the voltage waveform to be input.

JP 2001-246746 A JP 2002-19105 A U.S. Pat. No. 4,697,193 JP 2003-202261 A Japanese Patent Laid-Open No. 10-193877

  As described above, the inventors of the present invention have disclosed that the discharge amount control achieved by the input of the drive voltage waveform defined based on the natural period as disclosed in Patent Document 1 and Patent Document 2 is limited. It is only effective. In addition, both the method of evaluating the natural period of the system from the out-of-plane displacement of the electrode by the laser Doppler method, and the method disclosed in Patent Document 4, the waveforms defined in the globally unified standard were standardized. Unless measured by a method, the same result will not be obtained by anyone. Currently, there is an ambiguous “natural period” described in each of the above-mentioned patent documents. Therefore, the present inventors have used the criteria for determining the drive waveform to achieve the miniaturization of the ejected droplets. The idea that introducing the natural period itself is inappropriate in the first place.

  In addition, the above-mentioned “swing” due to the bending of the liquid column is caused by the fact that the speed of the liquid in the discharge port is larger than the protruding speed of the liquid column. It belongs to the category of performance and depends on the structure of the head and the physical properties of the liquid. Therefore, as in the case of the discharge amount control, it is inappropriate to introduce a natural period as a reference for determining a drive waveform for appropriately suppressing the occurrence of “twist”, and this cannot be a universal solution.

  Accordingly, an object of the present invention is to realize driving of a liquid discharge head capable of realizing good discharge performance without “swing” based on a universal guideline. Here, it is conceivable that the liquid discharge head is applied not only to the recording apparatus but also to various fields such as a patterning apparatus and a coating apparatus, and liquids having various physical properties and various head structures are used. Therefore, the present invention is preferable in providing an appropriate and universal guide for driving control of the liquid discharge head and expanding the application field.

Therefore, the present invention uses a liquid discharge head comprising a discharge port for discharging a liquid, an individual liquid chamber communicating with the discharge port, and volume control means for increasing or decreasing the volume of the individual liquid chamber, By driving the volume control means, the volume is increased from the initial volume and then decreased, whereby the liquid extending in a columnar shape from the discharge port is separated on the discharge port side to form droplets, A liquid ejection method for causing droplets to reach a medium,
In the time transition of displacement in the direction perpendicular to the surface on which the volume control means is formed, the volume control means is columnar from the discharge port after the appearance of the minimum displacement value that appears after the maximum displacement value appears. The volume control means is driven so that the displacement does not decrease during the period from when the liquid extending to the distance is separated to form droplets.

In addition, the present invention includes an ejection port for ejecting liquid, an individual liquid chamber communicating with the ejection port, volume control means for increasing or decreasing the volume of the individual liquid chamber, and a diaphragm. The means includes a piezoelectric film and an electrode, and by inputting a signal to the electrode and deforming the piezoelectric film, the diaphragm is displaced, and the volume is increased from the initial volume and then decreased. A liquid discharge apparatus that separates liquid extending in a columnar shape from the discharge port on the discharge port side to form a droplet, and causes the droplet to reach a medium,
In the time transition of the displacement in the direction perpendicular to the diaphragm surface on which the volume control means is formed, the discharge port after the appearance of the minimum displacement value that appears after the maximum displacement value appears. And a means for driving the volume control means so that the displacement does not decrease during the period from when the liquid extending in a columnar shape is separated to form droplets.

  According to the present invention, the volume is not reduced after the minimum value appears after the maximum value of the out-of-plane displacement on the surface of the volume control means appears until the liquid column is divided at the outlet side. The driving conditions are determined based on the change in volume. As a result, the liquid in the discharge port does not push the liquid column, so that the liquid column is not bent, and the occurrence of “warping” due to this can be prevented. In addition, by determining the driving conditions based on the change in volume, it becomes possible to reliably suppress the occurrence of “flickering” regardless of the physical properties of the liquid actually existing in the individual liquid chamber and various conditions such as the head structure. .

  Hereinafter, the present invention will be described in detail with reference to the drawings.

1. Basic concept of the present invention The present inventors have determined that the general guidelines for realizing preferable discharge performance through the various experiments and examinations described above are not general periods but are more general from other viewpoints. We considered that the mechanism should be discussed.

  Here, there is a range in which the input voltage and the displacement amount operate almost linearly in the piezoelectric element that is a mechanical drive source that causes the volume of the individual liquid chamber to increase or decrease. Noted that existing liquid ejection methods are based on this premise.

  However, Patent Document 5 shows that the displacement of the actuator that is a mechanical drive source does not become zero even if the drive voltage is returned to zero with respect to FIG. Similarly, FIG. 4 also shows that the displacement of the actuator has a larger absolute value of the voltage, the absolute value of the voltage is smaller than when the preceding pulsed drive waveform is added, and when the subsequent stepped drive waveform voltage is added. Is shown to be larger.

  That is, in the piezoelectric element, when the voltage is applied statically or when the voltage is changed to some extent with respect to the time axis, the amount of displacement becomes almost linear with respect to the applied voltage. However, when a driving voltage waveform that changes within a time width of about several tens of μs is input in order to eject liquid, it is known that there is no similarity between the driving voltage waveform and the amount of displacement. Teaches.

  As described above, in a liquid ejection head that utilizes deformation or deflection of a piezoelectric element, the voltage change does not necessarily coincide with the displacement of the actuator or the diaphragm 4. Further, even if the voltage is kept constant, the diaphragm may be displaced depending on how the voltage is changed so far. Therefore, it is not appropriate to introduce a natural period as a reference for determining a drive waveform, and direct and general-purpose control of discharge performance (discharge amount and discharge speed) with the drive waveform determined as such. It can be seen that it is difficult and inadequate to determine the general conditions and causality.

  The movement of the liquid is caused by the increase / decrease of the volume of the individual liquid chamber accompanying the input of the driving waveform. However, the response characteristic of the volume increase / decrease with respect to the input of the driving waveform varies depending on various properties such as the physical properties of the liquid actually existing in the individual liquid chamber and the head structure. Therefore, even if the drive waveform is defined based on the natural period under limited conditions, the liquid discharge performance or liquid behavior (liquid column generation, droplet separation, meniscus state near the discharge port, etc.) It cannot be a universal solution to control

  On the other hand, when the volume of the individual liquid chamber is increased from the initial volume, the liquid near the discharge port is always drawn inward, and the volume of the individual liquid chamber is decreased from the initial volume. During the operation, the liquid near the discharge port is always pushed outward.

Therefore, the present inventors have come to consider that as an index for controlling the discharge performance and the liquid behavior, attention should be paid not to the natural period but to the change in the volume of the individual liquid chamber. And
To increase the volume from the initial volume and then reduce the return to the initial volume so that liquid discharge is performed by shifting the out-of-plane displacement of the surface of the volume control means over time; and
-In order to prevent the out-of-plane displacement from decreasing after the minimum value appears after the maximum value appears, at the time until the liquid column breaks on the time transition curve of the out-of-plane displacement according to this process,
To achieve the intended purpose.

  In the following embodiments, the volume is first increased and then the actuator is driven so as to decrease the volume, thereby ejecting droplets. Here, “increase” means that the volume increases from the initial volume of the pressure chamber before the start of driving, and “decrease” means that the increasing volume changes toward the initial volume. I shall say that.

2. Embodiment of Liquid Ejecting Apparatus and Head FIG. 1 is a schematic perspective view showing an ink jet recording apparatus as an example of a liquid ejecting apparatus to which the present invention can be applied. The recording medium P inserted into the liquid ejection device is conveyed to the recordable area of the liquid ejection head unit 100 by the feed rollers 107, 108, 109, and 110. The liquid discharge head unit 100 is supported by a guide shaft 102 so as to be movable along the extending direction (main scanning direction). Then, the belt 104 laid on the pulleys 105 and 106 is moved by driving the motor 103, and the liquid discharge head unit 100 reciprocally scans the recording area. The scanning direction (A direction) of the liquid discharge head unit 100 is the main scanning direction, and the transport direction (B direction) of the recording medium P is the sub-scanning direction.

  The liquid discharge head unit 100 is equipped with a liquid discharge head 103 for discharging ink droplets of a plurality of colors, and an ink tank 101 for supplying ink to each liquid discharge head 103. The inks of a plurality of colors in the liquid ejection device of this example are four colors of black (Bk), cyan (C), magenta (M), and yellow (Y). The position of each color is not particularly limited, and the type and number of color tones (color and density) to be used are not limited.

  In the case of this example, the ink tanks of the respective color inks (Bk, C, M, Y) of black, cyan, magenta, and yellow are all replaceable independently. The liquid ejection head unit 100 includes a group of liquid ejection heads that eject liquid droplets of Bk, C, M, and Y, an ink tank for Bk 101B, an ink tank for C 101C, an ink tank for M, and ink for Y. A tank 101Y is mounted. Each ink tank is connected to a corresponding liquid discharge head, and supplies ink into an individual liquid chamber communicating with the discharge port of the liquid discharge head. In addition to this example, for example, an ink tank for each color and a liquid discharge head may be integrated so as not to be separated. Alternatively, only the liquid discharge head may be mounted on the liquid discharge head unit, and ink may be supplied from an ink tank provided at a fixed portion of the apparatus via a flexible tube or the like.

  A recovery system unit 112 is disposed below one end (right end in the figure) of the main scanning region where the liquid discharge head unit 100 can move. The recovery system unit 112 caps the discharge port forming surface of the liquid discharge head, and wipes off the cap or the discharge port forming surface for protecting or performing suction recovery during non-recording operations. It can have a wiper blade or the like.

  2 and 3 are configuration examples of a liquid discharge head applicable to the present invention, and respectively show a schematic front view and a cross-sectional view taken along the line C-C as viewed from the discharge port forming surface side.

  The liquid discharge head of this example supplies ink by communicating with an orifice plate 1 provided with a plurality of discharge ports 2 for discharging ink, a plurality of individual liquid chambers 3 corresponding to the respective discharge ports, and these in common. And a base body 6 on which walls defining the common liquid chamber 11 are arranged. The individual liquid chamber 3 communicates with the discharge port 2 via the communication path 7.

  A displaceable diaphragm 4 is provided on a part of the side surface of the individual liquid chamber 3, and an actuator 5 including a piezoelectric film and electrodes, which are volume control means of the individual liquid chamber, is disposed on the diaphragm 4. Yes. By applying a drive voltage signal to the actuator 5 corresponding to the recording information, the diaphragm 4 is displaced, and the volume of the individual liquid chamber 3 is changed, so that droplets can be discharged from the discharge port 2. It is. The actuator 5 is deformed in the thickness direction so as to increase the volume of the individual liquid chamber when the drive voltage applied thereto decreases, and to decrease the volume of the individual liquid chamber when the drive voltage increases. It shall be.

  The length of the individual liquid chamber of the head in which the present invention is suitably implemented is 2000 μm or more and 12000 μm or less, and the discharge port diameter is 20 μm or more and 50 μm or less. In addition, the actuator 5 (upper electrode, piezoelectric film, lower electrode) and diaphragm 4 each preferably have a thickness of 10 μm or less in order to facilitate deformation of the actuator 5 itself. More preferably, the diaphragm is 3 μm or more and 6 μm or less, and a thin film shape of 10 μm or less is good even when the diaphragm and the actuator are combined. In the case of such a thin film actuator, the time transition δ (t) of the displacement of the diaphragm, which serves as an index indicating the increase or decrease of the volume of the individual liquid chamber, is expressed by the displacement (surface) External displacement) can be approximated or substituted. This displacement refers to a displacement in a direction perpendicular to the surface on which the diaphragm is formed, and can be measured by, for example, a laser Doppler velocimeter. Using such a head, liquid discharge is suitably performed by performing deformation of the piezoelectric film, that is, displacement of the vibration plate that responds to bending so that the volume change of the individual liquid chamber shown in FIG. 5 occurs.

  FIG. 4 shows a configuration example of the drive unit of the actuator 5. The actuator 5 is connected to the drive circuit 51 via an electrode wiring for supplying electric power. The drive circuit 51 can operate the actuator 5 with a drive waveform defined by the drive waveform setting unit 53 in accordance with drive data (data for determining the presence or absence of ejection) corresponding to the recording information.

  The drive waveform setting unit 53 sets a drive waveform such that a time transition (time transition of out-of-plane displacement of the diaphragm) of the volume increase / decrease of the individual liquid chamber causing a preferable liquid behavior occurs.

3. Examples Hereinafter, specific examples and comparative examples of driving modes and effects of the liquid discharge head according to the present invention will be described.

3.1 Example First, the liquid discharge head shown in FIGS. 2 and 3 was produced. Here, the discharge port was a round hole having a diameter of 30 μm, the length (lateral dimension in FIG. 3) of the individual liquid chamber 3 was 6000 μm, and the width (dimension in the direction orthogonal to the drawing in FIG. 3) was 100 μm. The actuator 5 has a thickness of 3 μm, and the diaphragm 4 has a thickness of 5 μm.

The liquid discharge head utilizes deformation (extension / contraction) of a piezoelectric element as an actuator, and the volume of the individual liquid chamber is determined by displacement (out-of-plane displacement) in a direction perpendicular to the surface of a diaphragm fixed to the piezoelectric element. It is the form which makes increase / decrease of. In such a head, the volume of liquid to be excluded / flowed by deformation of the vibration plate 4 (control liquid amount V _CON ) is determined by the length of the individual liquid chamber, the width of the individual liquid chamber, and the vibration plate displacement. It is determined by the time transition δ (t). The control liquid amount V _CON is approximately proportional to these three products. Accordingly, the same effect can be obtained in a configuration in which the length of the individual liquid chamber is halved and the width is doubled.

Next, a liquid was supplied to the liquid discharge head to perform a discharge operation. Here, a cyan ink having a density of 1.0 × 10 ³ kg / m ³ , a viscosity of 3.3 × 10 ⁻³ Pa · s, and a surface tension of 3.3 × 10 ⁻² N / m was used as the liquid.

  Here, since the discharge port diameter is as large as 30 μm, even if the discharge operation is performed by simply reducing the volume of the individual liquid chamber from a state where the meniscus is static, only a large droplet of 28 pl or more can be discharged. Therefore, a thin liquid column is formed in order to discharge small droplets in the order of 10 pl from the discharge port having such a large diameter.

  FIGS. 5A to 5D are explanatory diagrams of the specific method. First, the meniscus was once retracted (FIG. 5A), and pressure was applied to the center bottom of the meniscus so that a raised portion was formed at this portion (FIG. 5B). This may be achieved by executing a process of increasing the volume of the individual liquid chamber from the initial volume (hereinafter referred to as expansion process) and then a process of decreasing (hereinafter referred to as contraction process). That is, the state shown in FIG. 5B can be realized by applying pressure from the pressure chamber side to the meniscus drawn into a substantially parabolic curved surface by the expansion process. This is because a high-pressure portion is inevitably generated at the center bottom of the meniscus in response to the pressurization, and only this portion can be raised. This is the same reason that the highest pressure part is formed at the tip of the flying rocket.

  After this, the shrinking process is further continued to control the size (thickness and length) of the thin liquid column to be generated, and more precise droplet discharge can be realized (FIG. 5C). , (D)).

At this time, as shown in FIG. 5 (c), "according" does not occur due to the bending of the liquid column by greater than the projection velocity v ₂ velocity v ₁ of the liquid column of fluid in the discharge ports (liquid) We have intensively studied to realize the discharge state. As a solution, if the liquid column generation process is controlled so that v ₁ <v ₂ , the liquid in the discharge port does not push the liquid column, so that the liquid column is not bent. However, it is difficult to measure the velocity v ₁ of the liquid hidden in the discharge port, and the control effect cannot be verified. Therefore, in this embodiment, when the liquid column protruding from the discharge port is cut on the side close to the discharge port, control is performed so that v ₁ and v ₂ have opposite direction components. Here, when the diaphragm 4 is displaced in the direction of decreasing the volume of the individual liquid chamber, the liquid in the discharge port flows toward the outside and when displaced in the direction of increasing the volume of the individual liquid chamber. Flows toward the individual liquid chamber. Therefore, as a method for grasping the direction of the velocity v ₁ described above, it is decided whether or not the volume of the individual liquid chamber is increasing.

That is, in this example, the time transition δ (t) of the measured displacement of the electrode of the piezoelectric element appears after the maximum value of the displacement curve appears until the time t _B when the liquid column division on the discharge port side is observed. After the minimum value appears, there is no diaphragm displacement that reduces the volume. And after the appearance of the minimum value by the time t _B when the liquid column division is observed, the diaphragm displacement that reduces the volume does not occur, that is, the liquid in the discharge port does not flow in the same direction as the protruding liquid column. The actuator 5 is controlled.

  FIG. 6 is a diagram in which the time transition of the out-of-plane displacement amount of the electrode of the piezoelectric element during the control of the actuator 5 is observed. Here, the measurement position was the central position of the individual liquid chamber. The actuator 5 was controlled so that such a time transition occurred, and the liquid discharge state was observed using a CCD camera and strobe light synchronized with ink discharge.

  7A to 7L are diagrams showing the observation results. As shown in these figures, the liquid column was not bent, and no “twist” caused by it was generated. Also. The traveling direction of the satellite did not deviate from the traveling direction of the main droplet, and the main droplet and the satellite were merged, and finally discharge without the satellite could be realized.

The reason why the satellite has caught up with the main droplet is considered to be as follows. First, after the time t _B when the liquid column division on the discharge port side is observed, the liquid column is drawn to the main droplet side by the surface tension, thereby increasing the speed of the liquid column division portion in the discharge direction. Until the speed of the main droplet was exceeded, the actuator was controlled so as not to generate a new divided portion in the liquid column. Here, the larger the time difference between the time t _B at which the liquid column division at the discharge port side is observed and the time at which another new division occurs, the longer the pulling period due to the surface tension, the higher the speed. To increase. Second, when the liquid column portion (FIG. 7 (f)) formed by the divided portion generated on the discharge port side and the newly generated divided portion becomes a substantially spherical satellite due to the surface tension. This is because the actuator was controlled so that the velocity in the ejection direction ((h) in the figure) exceeded the velocity of the main droplet.

FIG. 8 shows the waveform of the drive voltage applied to obtain the time transition of the out-of-plane displacement as shown in FIG. This basically consists of the following waveform parts. That is,
A waveform portion that changes from the initial voltage V _H to the voltage V _L to increase the volume of the individual liquid chamber,
The waveform portion held at voltage _VL ,
A waveform portion that changes to a voltage V _H to return the volume to the initial volume, and a waveform portion that is held at the initial voltage V _H ,
It is.

  In this embodiment, the driving voltage waveform is used to prevent the liquid column from being bent. However, it should be noted here that the setting of the driving waveform based on the natural period is not necessary unless the waveform is set at the beginning. There is no. To the last, the volume increase / decrease of the individual liquid chamber, which is a universal reference for preventing the bending of the liquid column, more specifically, the time transition of the out-of-plane displacement amount of the piezoelectric element electrode, which has a strong correlation with this, will occur. In addition, the drive waveform is selected and set. That is, with respect to the basic waveform as shown in FIG. 8, the voltage, the inclination and shape of each waveform portion, and the like can be appropriately determined in light of preferable discharge performance and liquid behavior.

3.2 Comparative Example In the comparative example, the same droplet ejection head and liquid as in the example were used, while the drive waveform was changed to increase the ejection speed. As a result, the liquid column was bent.

  FIG. 9 is a diagram of the time transition of the out-of-plane displacement amount of the electrodes of the piezoelectric element at this time. FIGS. 10A to 10E are views showing the results of observing the liquid discharge state in the same manner as in the first embodiment.

In the comparative example, the time course of the displacement of the electrodes of the piezoelectric element [delta] (t), the liquid column interrupted at the discharge port side is observed (FIG. 10 (c)) in up to the time t _B, the maximum value appearing in the displacement curve after the minimum appearance appearing later, it was observed diaphragm displacement to reduce the volume of the individual liquid chamber (p _c in FIG. _9). In response to this, the meniscus raised from the discharge port side pushes the end of the liquid column in the discharge direction (FIGS. 10A and 10B), and the central axis of the tip of the raised meniscus and the center of the liquid column It was confirmed that the axis was displaced (FIGS. 11C and 11D). This is considered to be the main cause of warping. That is, in the comparative example, since the conditions arranged in the example were not satisfied, the warp occurred.

4). Others In the above example, the case where the present invention is applied to the liquid ejecting apparatus and the head in the form of the ink jet recording apparatus has been described. However, the present invention is preferably applicable not only to the recording apparatus but also to various liquid ejecting apparatuses such as a patterning apparatus and a coating apparatus. It is. Suitable and universal liquid ejection head drive that can achieve finer ejection droplets without reducing the diameter of the ejection port, as liquids with various physical properties and various head structures are used depending on the device This is because a control guideline can be given.

1 is a schematic perspective view showing an ink jet recording apparatus as an example of a liquid ejection apparatus to which the present invention can be applied. FIG. 2 is a configuration example of a liquid discharge head applicable to the present invention, and shows a schematic front view seen from the discharge port forming surface side. 2 is a configuration example of a liquid discharge head applicable to the present invention, and shows a cross-sectional view taken along the line CC of FIG. It is a block diagram which shows the structural example of the drive part of an actuator (piezoelectric element). (A)-(d) is explanatory drawing of the liquid discharge state in an Example. It is a diagram which shows the time transition of the out-of-plane displacement amount of the electrode of the piezoelectric element in an Example. (A)-(l) is a figure which shows the observation result of the liquid discharge state in an Example. It is a figure which shows the example of the basic waveform of the drive voltage applied in order to obtain the time transition of an out-of-plane displacement amount like FIG. It is a diagram which shows the time transition of the out-of-plane displacement amount of the electrode of the piezoelectric element in a comparative example. It is a figure which shows the observation result of the liquid discharge state in a comparative example. In order to investigate whether or not the natural period of the liquid discharge head evaluated from the out-of-plane displacement of the electrodes of the piezoelectric element has universality, a state in which the gradient of the potential change that increases the volume of the individual liquid chamber is changed is shown. It is explanatory drawing. (A)-(c) is explanatory drawing for demonstrating the difference in the response curve of an out-of-plane displacement by the difference in inclination shown in FIG.

Explanation of symbols

2 Discharge port 3 Individual liquid chamber 4 Vibration plate 5 Volume control means (actuator)

Claims (3)

The volume control means is driven using a liquid discharge head comprising a discharge port for discharging liquid, an individual liquid chamber communicating with the discharge port, and a volume control means for increasing or decreasing the volume of the individual liquid chamber. Thus, by increasing the volume from the initial volume and then decreasing, the liquid extending in a columnar shape from the discharge port is separated on the discharge port side to form a droplet, and the droplet reaches the medium A liquid ejection method comprising:
In the time transition of displacement in the direction perpendicular to the surface on which the volume control means is formed, the volume control means is columnar from the discharge port after the appearance of the minimum displacement value that appears after the maximum displacement value appears. The volume control means is driven so that the displacement does not decrease during the period from when the liquid that has been separated into two separates to form droplets.   The volume control means includes a piezoelectric film and an electrode. When the piezoelectric film is deformed, a diaphragm formed corresponding to the individual liquid chamber is displaced, and the volume of the individual liquid chamber is increased or decreased. The liquid ejection method according to claim 1, wherein: A discharge port for discharging a liquid; an individual liquid chamber communicating with the discharge port; volume control means for increasing or decreasing the volume of the individual liquid chamber; and a diaphragm. The volume control means includes a piezoelectric film and an electrode. And by deforming the piezoelectric film by inputting a signal to the electrode, the diaphragm is displaced, and the volume is increased from the initial volume and then decreased, so that the discharge port has a columnar shape. A liquid discharge apparatus that separates the extended liquid at the discharge port side to form droplets and causes the droplets to reach a medium,
In the time transition of the displacement in the direction perpendicular to the diaphragm surface on which the volume control means is formed, the discharge port after the appearance of the minimum displacement value that appears after the maximum displacement value appears. A liquid ejection apparatus comprising means for driving the volume control means so that the displacement does not decrease during a period from when the liquid extending in a columnar shape is separated to form a droplet.

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