阅读说明：本技术 液滴喷出头的驱动方法 (Method for driving liquid droplet ejection head ) 是由 佐佐木淳 仓持升平 于 2019-02-22 设计创作，主要内容包括：一种液滴喷出头的驱动方法,该液滴喷出头具备：喷头,用于喷出液滴；压力产生室,能够在内部贮留液体,且与喷头连通；以及压力赋予机构,使压力产生室内的容积扩大或者缩小来使内压变化,在液滴喷出头的驱动方法中,为了很好地防止卫星液滴(从主滴分离的液滴的喷落)而具有：第1工序,通过压力赋予机构使压力产生室的容积扩大；第2工序,在第1工序之后通过压力赋予机构使压力产生室的容积缩小来使压力产生室内的液体从喷头喷出；以及第3工序,从第2工序经过0.4～1.55AL(AL是压力产生室的音响的共振周期的1/2)后通过压力赋予机构使压力产生室的容积扩大。(A method of driving a liquid droplet ejection head, the liquid droplet ejection head comprising: a head for ejecting liquid droplets; a pressure generating chamber capable of storing liquid therein and communicating with the head; and a pressure applying mechanism for changing an internal pressure by expanding or contracting a volume in the pressure generating chamber, wherein the droplet discharge head driving method includes, in order to favorably prevent satellite droplets (droplet landing separated from the main droplet): a step 1 of expanding the volume of a pressure generation chamber by a pressure applying mechanism; a 2 nd step of ejecting the liquid in the pressure generation chamber from the head by reducing the volume of the pressure generation chamber by the pressure applying mechanism after the 1 st step; and a 3 rd step of expanding the volume of the pressure generating chamber by the pressure applying mechanism after 0.4 to 1.55AL (AL is 1/2 of the resonance period of the sound of the pressure generating chamber) has passed from the 2 nd step.)

1. A method of driving a liquid droplet ejection head, the liquid droplet ejection head comprising: a head for ejecting liquid droplets; a pressure generating chamber capable of storing liquid therein and communicating with the head; and a pressure applying mechanism for changing an internal pressure by expanding or contracting a volume in the pressure generating chamber, the method for driving the liquid droplet ejection head including:

a first step of expanding the volume of the pressure generation chamber by the pressure applying mechanism;

a 2 nd step of, after the 1 st step, reducing the volume of the pressure generation chamber by the pressure application mechanism to discharge the liquid in the pressure generation chamber from the head; and

and a 3 rd step of expanding the volume of the pressure generating chamber by the pressure applying mechanism after 0.4 to 1.55AL (AL is 1/2 showing the resonance period of the sound of the pressure generating chamber) has passed from the 2 nd step.

2. A method of driving a liquid droplet ejection head according to claim 1,

the process interval from the 2 nd step to the 3 rd step is 0.4 to 1.1 AL.

3. A method of driving a liquid droplet ejection head according to claim 1,

the process interval from the 2 nd step to the 3 rd step is 0.4 to 0.9 AL.

4. A method of driving a liquid droplet ejection head according to claim 1, 2, or 3,

the process interval from the 1 st step to the 2 nd step is 0.7 to 1.3 AL.

5. A method of driving a liquid droplet ejection head according to any one of claims 1 to 4, comprising:

a 4 th step of eliminating vibration in the pressure generation chamber by reducing the volume of the pressure generation chamber by the pressure applying mechanism after 2.75 to 3.25AL has passed from the 2 nd step; and

and a 5 th step of eliminating vibration in the pressure generating chamber by expanding the volume of the pressure generating chamber by the pressure applying mechanism after 0.75 to 1.25AL has passed from the 4 th step.

6. A method of driving a liquid droplet ejection head according to any one of claims 1 to 5,

the volume of the pressure generating chamber when the pressure generating chamber is reduced in the 2 nd step is smaller than the volume before the pressure generating chamber is enlarged in the 1 st step, and the volume of the pressure generating chamber when the pressure generating chamber is enlarged in the 3 rd step is substantially the same as the volume before the pressure generating chamber is enlarged in the 1 st step.

7. A method of driving a liquid droplet ejection head according to any one of claims 1 to 6,

the pressure applying means is driven by applying a voltage to change the volume in the pressure generating chamber, and is configured to apply different pressures to the pressure generating chamber by applying different voltages, and when the voltage applied to the pressure applying means in the step 1 is V1(V), the voltage applied to the pressure applying means in the step 2 is V2(V), and the voltage applied to the pressure applying means in the step 3 is V3(V), V2 < V3 < V1 are provided.

8. A method of driving a liquid droplet ejection head according to any one of claims 1 to 7,

the pressure applying mechanism is a piezoelectric element.

9. A method of driving a liquid droplet ejection head according to claim 8,

the piezoelectric element is deformed in a shear mode by applying an electric field.

10. A method of driving a liquid droplet ejection head,

when discharging a plurality of droplets continuously, the final discharge of the plurality of droplets is performed by the method of driving the liquid droplet discharge head according to any one of claims 1 to 9.

11. A method of driving a liquid droplet ejection head according to any one of claims 1 to 10,

the method further includes a preliminary step of reducing the volume of the pressure generation chamber by the pressure applying mechanism, prior to the step 1.

12. A method of driving a liquid droplet ejection head according to any one of claims 1 to 11,

the drive waveform applied to the pressure applying mechanism to change the volume of the pressure generating chamber is a rectangular wave.

13. A method of driving a liquid droplet ejection head according to any one of claims 1 to 11,

the drive waveform applied to the pressure applying mechanism to change the volume of the pressure generating chamber is a triangular wave.

14. A method of driving a liquid droplet ejection head according to any one of claims 1 to 13, wherein the liquid is ink.

Technical Field

The present invention relates to a method of driving a liquid droplet ejection head that ejects liquid droplets from a head, and more particularly, to a method of driving a liquid droplet ejection head that can favorably prevent satellite liquid droplets (the landing of liquid droplets separated from main droplets).

Background

A droplet discharge head that discharges droplets from a head, such as an ink jet recording head that forms an image using minute ink droplets, discharges the droplets from the head by applying pressure to a pressure generating chamber, and discharges the droplets onto a recording medium.

In this liquid droplet ejection head, for example, as shown in fig. 10, a drive pulse composed of a rectangular wave shown in fig. 11 is applied to the piezoelectric elements S, S constituting the partition walls on both sides of the pressure generation chamber a. The drive waveform is a drive waveform (hereinafter referred to as "DRR waveform") of a DRR (Draw-Release-reinforcement) method composed of a rectangular wave. The first rise of the driving pulse (the 1 st step P1) causes the piezoelectric elements S, S to deform outward, thereby expanding the volume of the pressure generation chamber a. This generates a negative pressure on the ink in the pressure generation chamber a, and the ink flows in. At the same time, the pressure rises from both ends of the pressure generating chamber a, the sound wave propagates toward the center of the pressure generating chamber a, and thereafter, the sound wave reaches the opposite ends, and the pressure inside the pressure generating chamber a becomes positive.

If the drive pulse is lowered so that the potential 0 passes after a predetermined time has elapsed from the first rise of the drive pulse to deform the piezoelectric elements S, S in opposite directions (step 2P 2), the piezoelectric elements S, S pass through the neutral position from the expanded position to reduce the volume of the pressure generation chamber a. Then, as shown in fig. 10 (a), a positive pressure is generated in the pressure generation chamber a. Accordingly, the meniscus in the head 3 generated by filling a part of the ink in the pressure generation chamber a moves in the direction of being pushed out from the head 3, and the ink column 100 is ejected from the head 3.

After this state is maintained for a predetermined time, if the potential is raised and returned to 0 (step 3P 3), as shown in fig. 11, the piezoelectric element S, S returns from the contracted position to the neutral position, the volume of the pressure generation chamber is expanded, the meniscus is sucked, and the rear end of the ejected ink column 100 is sucked back, so that the ink column 100 is separated from the meniscus and flies as a droplet 101, as shown in fig. 10 (b).

The time (from the 2 nd step P2 to the 3 rd step P3) for keeping the ink column 100 ejected from the head 3 while reducing the volume of the pressure generating chamber a is generally set to 2AL in the past, but patent document 1 describes that the volume is set to 3.5 to 4.4AL as shown in fig. 11. "AL" refers to 1/2 indicating the resonance period of the sound of the pressure generating chamber.

In the ink jet recording apparatus described in patent document 1, the high frequency driving is enabled by setting the time for which the ink column 100 is kept ejected after the 2 nd step P2 to 3.5 to 4.4 AL.

Documents of the prior art

Patent document

Patent document 1 Japanese patent No. 4432426

Disclosure of Invention

Problems to be solved by the invention

In the conventional inkjet recording apparatus as described above, when droplets separated from the main droplets, called satellites, are generated during ink ejection, the droplets are ejected onto the recording medium, which causes deterioration of image quality. In order to reliably prevent deterioration of image quality, it is required to prevent satellite droplets in an inkjet recording apparatus.

Accordingly, an object of the present invention is to provide a method of driving a droplet discharge head capable of suitably preventing satellite droplets (droplet landing separated from main droplets).

Other problems of the present invention will be apparent from the following description.

Means for solving the problems

The above problems are solved by the following inventions.

1. A method of driving a liquid droplet ejection head, the liquid droplet ejection head comprising: a head for ejecting liquid droplets; a pressure generating chamber capable of storing liquid therein and communicating with the head; and a pressure applying mechanism for changing an internal pressure by expanding or contracting a volume in the pressure generating chamber, the method for driving the liquid droplet ejection head including:

a first step of expanding the volume of the pressure generation chamber by the pressure applying mechanism;

a 2 nd step of, after the 1 st step, reducing the volume of the pressure generation chamber by the pressure application mechanism to discharge the liquid in the pressure generation chamber from the head; and

and a 3 rd step of expanding the volume of the pressure generating chamber by the pressure applying mechanism after 0.4 to 1.55AL (AL is 1/2 showing the resonance period of the sound of the pressure generating chamber) has passed from the 2 nd step.

2. The method of driving a liquid droplet ejection head as described in the above 1,

the process interval from the 2 nd step to the 3 rd step is 0.4 to 1.1 AL.

3. The method of driving a liquid droplet ejection head as described in the above 1,

the process interval from the 2 nd step to the 3 rd step is 0.4 to 0.9 AL.

4. The method of driving a liquid droplet ejection head according to 1, 2 or 3 above,

the process interval from the 1 st step to the 2 nd step is 0.7 to 1.3 AL.

5. The method of driving a liquid droplet ejection head according to any one of the above 1 to 4, comprising:

a 4 th step of eliminating vibration in the pressure generation chamber by reducing the volume of the pressure generation chamber by the pressure applying mechanism after 2.75 to 3.25AL has passed from the 2 nd step; and

and a 5 th step of eliminating vibration in the pressure generating chamber by expanding the volume of the pressure generating chamber by the pressure applying mechanism after 0.75 to 1.25AL has passed from the 4 th step.

6. The method of driving a liquid droplet ejecting head according to any of the above 1 to 5,

the volume of the pressure generating chamber when the pressure generating chamber is reduced in the 2 nd step is smaller than the volume before the pressure generating chamber is enlarged in the 1 st step, and the volume of the pressure generating chamber when the pressure generating chamber is enlarged in the 3 rd step is substantially the same as the volume before the pressure generating chamber is enlarged in the 1 st step.

7. The method of driving a liquid droplet ejecting head according to any of the above 1 to 6,

the pressure applying means is driven by applying a voltage to change the volume in the pressure generating chamber, and is configured to apply different pressures to the pressure generating chamber by applying different voltages, and when the voltage applied to the pressure applying means in the step 1 is V1(V), the voltage applied to the pressure applying means in the step 2 is V2(V), and the voltage applied to the pressure applying means in the step 3 is V3(V), V2 < V3 < V1 are provided.

8. The method of driving a liquid droplet ejecting head according to any of the above 1 to 7,

the pressure applying mechanism is a piezoelectric element.

9. The method of driving a liquid droplet ejection head as described in the above 8,

the piezoelectric element is deformed in a shear mode by application of an electric field.

10. A method of driving a liquid droplet ejection head,

when discharging a plurality of droplets continuously, the final discharge of the plurality of droplets is performed by the method for driving a liquid droplet discharge head according to any one of the above 1 to 9.

11. The method of driving a liquid droplet ejecting head according to any of the above 1 to 10,

the method further includes a preliminary step of reducing the volume of the pressure generation chamber by the pressure applying mechanism, prior to the step 1.

12. The method of driving a liquid droplet ejecting head according to any of the above 1 to 11,

the drive waveform applied to the pressure applying mechanism to change the volume of the pressure generating chamber is a rectangular wave.

13. The method of driving a liquid droplet ejecting head according to any of the above 1 to 11,

the drive waveform applied to the pressure applying mechanism to change the volume of the pressure generating chamber is a triangular wave.

14. The method of driving a liquid droplet ejecting head according to any of the above 1 to 13,

the liquid is an ink.

Effects of the invention

According to the present invention, it is possible to provide a method of driving a droplet discharge head capable of suitably preventing satellite droplets (the landing of droplets separated from main droplets).

Drawings

Fig. 1 is a perspective view showing one embodiment of a liquid droplet ejection head to which the present invention is applied.

Fig. 2 (a) to (c) are sectional views showing the operation of the droplet ejection head.

Fig. 3 is a diagram showing drive waveforms for realizing a method of driving the droplet ejection head according to embodiment 1.

Fig. 4 is a diagram showing a change in ejection pressure according to the method of driving the droplet ejection head according to embodiment 1.

Fig. 5 (a) to (E) are diagrams showing a meniscus and a droplet discharge in a head according to the method for driving a droplet discharge head of embodiment 1, and fig. 5 (a) to (E) are diagrams showing a meniscus and a droplet discharge in a head according to the method for driving a conventional droplet discharge head.

Fig. 6 is a graph showing reverberation extrusion pressure generated due to the driving waveform shown in fig. 3.

Fig. 7 is a diagram showing drive waveforms for realizing the method of driving the liquid droplet ejection head according to embodiment 2.

Fig. 8 is a diagram showing drive waveforms for realizing a method of driving the droplet ejection head according to embodiment 3.

Fig. 9 is a graph showing the relationship between the droplet velocity and the satellite droplet length as an embodiment of the present invention.

Fig. 10 (a) and (b) are explanatory views showing a state of droplet discharge by a conventional driving method.

Fig. 11 is a diagram showing a drive waveform in a conventional drive method.

Detailed Description

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[ 1 st embodiment ]

Fig. 1 is a perspective view showing one embodiment of a liquid droplet ejection head to which the present invention is applied.

Fig. 2 (a) to (c) are sectional views showing the operation of the droplet ejection head.

As shown in fig. 1 and 2, the method of driving the liquid droplet ejection head according to the present invention can be applied to any type of liquid droplet ejection head as long as the liquid droplet ejection head includes the head 3 for ejecting the liquid droplet, the pressure generation chamber a that can store the liquid therein and communicates with the head 3, and the pressure applying mechanism that changes the internal pressure of the pressure generation chamber a.

In the following description, a case will be described in which the present invention is applied to an ink jet recording head H of a shear mode type which includes a piezoelectric element S as a pressure applying mechanism for expanding or contracting a volume in a pressure generating chamber a to change an internal force, and which uses ink as a liquid filled in the pressure generating chamber a, and in which the piezoelectric element S is deformed in a shear mode (shear mode) by applying an electric field.

As shown in fig. 1, the droplet discharge head H is configured to: a shower plate 1 is attached to the front end surface of the channel base material 2, and a flow divider member 4 is attached to the rear end surface of the channel base material 2. A plurality of heads 3 for ejecting ink droplets are provided in the head plate 1.

As shown in fig. 1 and 2, the channel substrate 2 is provided with a plurality of pressure generating chambers a. The pressure generating chambers a are arranged in parallel with a piezoelectric element S as a partition wall interposed therebetween. The pressure generating chambers a and the piezoelectric elements S are alternately arranged in parallel, so that one piezoelectric element S is shared between two adjacent pressure generating chambers a of the one piezoelectric element S.

One end of each pressure generation chamber a in the longitudinal direction communicates with the head 3. The liquid droplet ejection head H of the present embodiment is a liquid droplet ejection head that performs so-called "independent driving" in which ejection channels communicating with the heads 3 and dummy channels (also referred to as non-ejection channels) in which the heads 3 are not provided are alternately arranged in parallel as the pressure generation chambers a. However, the present invention is not limited to this, and a droplet discharge head that performs so-called "3-cycle driving" in which all the ink channels are divided into 3 groups and the adjacent ink channels are controlled in a time-sharing manner may be used.

The piezoelectric element S is composed of an upper wall portion S1 and a lower wall portion S2, and the upper wall portion S1 and the lower wall portion S2 are composed of a piezoelectric material whose polarization directions are opposite to each other. The piezoelectric material is not particularly limited, and for example, PZT (lead zirconate titanate) or the like can be used.

The flow divider member 4 attached to the rear end surface of the channel base material 2 has a flow divider 41 as an internal space. The flow divider 41 communicates with the other end of each pressure generation chamber a in the longitudinal direction. The flow diverter 41 communicates with an ink tank, not shown, via an ink tube 42.

The ink supplied from the ink tank is supplied from the flow divider 41 to the pressure generation chambers a. Each pressure generating chamber a forms a flow path connecting the flow divider 41 and the head 3. Each pressure generating chamber a forms an individual flow path corresponding to each head 3. A meniscus due to the ink is formed in the head 3.

Electrodes Q1, Q2, Q3, and Q4 are formed on the surface of the piezoelectric element S constituting each pressure generation chamber a. The electrodes Q1, Q2, Q3, and Q4 are connected to a drive signal generating unit 50, and the drive signal generating unit 50 supplies a drive signal for driving the piezoelectric element S to discharge ink in the pressure generating chamber a.

In fig. 2, arrows attached to the piezoelectric element S indicate the polarization directions of the upper wall portion S1 and the lower wall portion S2. In this manner, the polarization directions of the upper wall portion S1 and the lower wall portion S2 made of a piezoelectric material can be arranged in opposite directions to each other. The piezoelectric element S is driven by applying a voltage to change the volume in the pressure generation chamber a, and is configured to be capable of applying different pressures to the pressure generation chamber a by applying different voltages.

When no drive signal is applied to any of the electrodes Q1, Q2, Q3, and Q4, no deformation occurs in any of the piezoelectric elements S, as shown in fig. 2 (a). In this state, if the electrodes Q1 and Q4 located on the far side from the pressure generation chamber a are grounded and a drive signal (+ V) is applied to the electrodes Q2 and Q3 facing the inside of the pressure generation chamber a, an electric field in a direction perpendicular to the polarization direction of the piezoelectric element S, S is generated, and as shown in fig. 2 (b), the piezoelectric elements S, S are shear-deformed at the joint surface between the upper wall portion S1 and the lower wall portion S2, and are deformed toward the outside of the pressure generation chamber a. This deformation expands the volume of the pressure generation chamber a, and negative pressure is generated in the pressure generation chamber a, so that ink flows from the flow divider 41 into the pressure generation chamber a.

When the potentials of the electrodes Q2 and Q3 are returned to 0 from this state, the piezoelectric element S, S returns from the expanded position shown in fig. 2 (b) to the neutral position shown in fig. 2 (a), and applies pressure to the ink in the pressure generation chamber a.

In this state, if a drive signal (-V) is applied to the electrodes Q2, Q3 facing the inside of the pressure generation chamber a, an electric field in a direction perpendicular to the polarization direction of the piezoelectric element S, S is generated, and as shown in fig. 2 (c), the piezoelectric elements S, S are deformed toward the inside of the pressure generation chamber a. This deformation reduces the volume of the pressure generation chamber a, and a positive pressure is generated in the pressure generation chamber a, whereby ink is ejected from the head 3 corresponding to the pressure generation chamber a. By the series of operations of the piezoelectric element S, S based on the drive signal, an ink droplet is separated from the meniscus in the head 3 communicating with the pressure generation chamber a, and the ink droplet is ejected from the head 3.

Fig. 3 is a diagram showing drive waveforms for realizing a method of driving the droplet ejection head according to embodiment 1.

Fig. 4 is a diagram showing a change in ejection pressure according to the method of driving the droplet ejection head according to embodiment 1.

Fig. 5 (a) to (E) are diagrams showing a meniscus and a droplet discharge in a head according to the method for driving a droplet discharge head of embodiment 1, and fig. 5 (a) to (E) are diagrams showing a meniscus and a droplet discharge in a head according to the method for driving a conventional droplet discharge head.

(1 st Process P1)

The drive waveforms in this embodiment are: in the initial state shown in fig. 2 (a), the first rising pulse is applied as the 1 st step P1 as shown in fig. 3 (P1). In the 1 st step P1, for example, the electrodes Q1 and Q4 located on the far side from the pressure generation chamber a are grounded, and a + V potential is applied to the electrodes Q2 and Q3 located on the near side from the pressure generation chamber a, whereby the volume of the pressure generation chamber a is expanded by the piezoelectric element S, S.

At this time, an electric field is generated in a direction perpendicular to the polarization direction of the piezoelectric element S, S constituting the partition walls on both sides of the pressure generation chamber a. Then, as shown in fig. 2 (b), the piezoelectric elements S, S are deformed outward, and the volume of the pressure generation chamber a is expanded (strained). The ink is introduced into the pressure generation chamber a by the volume expansion of the pressure generation chamber a.

Since the pressure in the pressure generation chamber a is repeatedly inverted at 1AL cycles at process intervals at which the drive waveform does not change as shown in fig. 4, if the process intervals are continued for 1AL, the meniscus M sucked in returns to the front end surface of the head 3 on the droplet ejection side (hereinafter, the front end surface of the head 3 on the droplet ejection side is referred to as the "return position of the meniscus M") as shown in fig. 5a, and the pressure of the ink is inverted to a positive pressure. At this timing, if the expanded pressure generation chamber a is returned to the original neutral state (Release), a high pressure is applied to the ink in the pressure generation chamber a. Further, as shown in fig. 4, the ink pressure in the head 3 changes with a slight delay with respect to the change in the drive waveform, and the change in the meniscus M is more delayed.

Further, "AL" is 1/2 of the resonance cycle of the sound of the pressure generation chamber as described above. The AL is determined as the following time: when the velocity of an ink droplet ejected by applying a voltage pulse of a rectangular wave to the piezoelectric element S is measured and the process interval of the rectangular wave is changed by keeping the voltage value of the rectangular wave constant, the flight velocity of the ink droplet is maximized. The process interval is defined as: from 10% of the voltage start to rise or start to fall, until the next step starts.

In the present embodiment, a rectangular wave is used, and the rectangular wave is a waveform in which the rise time and the fall time of the voltage between 10% and 90% are both preferably within 1/2 of AL, and more preferably within 1/4. In the present invention, the rectangular wave is not limited, and a triangular wave may be used. In the case of using a triangular wave, the pressure fluctuation in the pressure generation chamber may be a waveform having a fluctuation similar to that in the case of using a rectangular wave.

(step 2P 2)

After the 1 st step, as shown in fig. 2 (c) and 3 (P2), a falling pulse (-V) is applied as the 2 nd step P2. In the 2 nd step P2, the volume of the pressure generation chamber a is reduced by the piezoelectric element S, S, and the liquid in the pressure generation chamber a is discharged from the head.

The process interval from the 1 st step P1 to the 2 nd step P2 is preferably 0.7 to 1.3 AL. This is because the negative pressure wave generated by the expansion of the volume of the pressure generation chamber a applied in the 1 st step P1 is inverted at 1AL to become a positive pressure wave, and the positive pressure wave generated by the reduction of the volume in the 2 nd step P2 is superimposed on the negative pressure wave, so that the ink ejection pressure becomes high.

In the 2 nd step P2, the volume of the pressure generation chamber a is reduced, and as shown in fig. 4, a higher pressure (force) is applied to the ink, and as shown in fig. 5B, the ink column 10 is ejected from the head 3.

In the present specification, the term "ink column" refers to ink that is ejected from the head 3 at the tip and has a trailing end that is continuous with the meniscus in the head 3 and is not yet separated from the meniscus, and the term "droplet" refers to ink that has a trailing end of the ink column completely separated from the meniscus in the head 3.

(3 rd step P3)

After the process interval of 0.4 to 1.55AL has elapsed from the 2 nd process P2, the piezoelectric element S, S is returned to the neutral position as the 3 rd process P3 as shown in fig. 2 (a) and 3 (P3). In the 3 rd step P3, the volume of the pressure generation chamber a is expanded by the piezoelectric element S from the previous state of reduction.

In the 3 rd step P3, the vibration (reverberation vibration) in the pressure generation chamber a is amplified. When the process interval from the 2 nd process P2 to the 3 rd process P3 is set to 1AL, the reverberation vibration is most amplified.

When 1AL has passed from the 2 nd step P2, the pressure of the ink is reversed to a negative pressure as shown in fig. 4, and therefore a thin waist portion is formed at the base of the discharged ink column 10 as shown in fig. 5 (C). If the negative pressure becomes maximum after 0.5AL, the meniscus M is sucked to the deepest position in the opposite direction to the head 3, and the meniscus M appears conspicuously.

If 0.5AL is passed, the pressure reverses to become positive and the meniscus M moves towards the recovery position. As shown in fig. 4 and 5 (D), since reverberation becomes larger than a conventional drive waveform in the 3 rd step P3, the meniscus M is pushed out from the head 3 together with the waisted portion by the squeezing out of the reverberation.

If further time elapses, the meniscus M returns to the return position as shown in fig. 4 and fig. 5 (E). The meniscus M drawn into the deep inside of the head 3 is rapidly moved toward the return position by the capillary force of the ink in accordance with the positive ink pressure. At the moment when the meniscus M returns to the recovery position, the ink column 10 has not yet separated from the meniscus M, and its tail 10b is connected to the meniscus M.

The meniscus M recedes from the head 3 in the direction opposite to the droplet ejection direction, and the ink column 10 ejected from the head 3 in the above-described 2 nd step P2 separates from the meniscus M and is ejected from the head 3 as a droplet. At this time, the distance from the leading end of the droplet to the tail 10b separated from the meniscus M is shorter than the conventional drive waveform, and thus satellite droplets (the landing of droplets separated from the main droplet) can be prevented well.

As described above, in the present embodiment, the DRR waveform is used, and after the process interval of 0.4 to 1.55AL has passed from the 2 nd process P2, the 3 rd process P3 is performed, and the 3 rd process P3 expands the volume of the pressure generation chamber a, thereby amplifying the vibration (reverberation vibration) in the pressure generation chamber a. The present inventors confirmed the following: it is effective to prevent satellite droplets by performing suction (3 rd step P3) after ink suction (1 st step P1) and extrusion (2 nd step P2) to impart pressure that amplifies the phase of vibration (reverberation vibration) in the pressure generating chamber, thereby promoting droplet break-off.

The process interval from the 2 nd step P2 to the 3 rd step P3 is also preferably 0.4 to 1.1 AL. In this case, the reverberation vibration is amplified as compared with the conventional drive waveform, and the droplet break-off is promoted, so that the satellite droplet can be prevented favorably.

Further, the process interval from the 2 nd process P2 to the 3 rd process P3 is preferably 0.4 to 0.9 AL. In this case, the reverberation vibration is amplified as compared with the conventional drive waveform, and the droplet break-off is promoted, so that the satellite droplet can be prevented favorably.

In the above description, it is preferable that the volume U1 of the pressure generation chamber a when expanded by the 1 st step P1 is larger than the volume before the pressure generation chamber a is expanded by the 1 st step P1, the volume U2 of the pressure generation chamber a when contracted by the 2 nd step P2 is smaller than the volume before the pressure generation chamber a is expanded by the 1 st step, and the volume U3 of the pressure generation chamber a when expanded by the 3 rd step is substantially the same as the volume before the pressure generation chamber a is expanded by the 1 st step.

As shown in fig. 3, when the voltage applied to the piezoelectric element S in the first step P1 is V3(V), the voltage applied to the piezoelectric element S in the first step P1 is V1(V), the voltage applied to the piezoelectric element S in the second step P2 is V2(V), and the voltage applied to the piezoelectric element S in the third step P3 is V3(V), V2 < V3 < V1 is preferable. This results in a volume U2 < volume U3 < volume U1. The voltage V3 in the initial state is not limited to 0, and the voltages V1, V2, and V3 are voltages having voltage differences.

(for preventing satellite drip)

As described above, according to the drive waveform of the embodiment, by amplifying the reverberation vibration, the satellite can be prevented well. The following describes the effects of the present invention as compared with conventional drive waveforms.

In the conventional driving waveform, as shown in fig. 4 and (a) to (C) of fig. 5, the pressure fluctuation in the pressure generation chamber a and the behavior of the ink from the 1 st step P1 to the 2 nd step P2 are the same as those in the above-described embodiments shown in (a) to (C) of fig. 5.

When 1.5AL has passed from the 2 nd step P2, the negative pressure becomes maximum as shown in fig. 4 and (C) of fig. 5, the meniscus M is sucked to the deepest position in the direction opposite to the head 3, and the meniscus M appears conspicuously.

When 0.5AL (2 AL process interval from the 2 nd process P2) has elapsed, the pressure is inverted to a positive pressure in the conventional drive waveform, and the meniscus M moves toward the return position, as shown in fig. 4 and 5 (d). At this time, as the 3 rd step P3 of expanding the volume of the pressure generation chamber a, the partition wall S is returned to the neutral position, and the volume of the pressure generation chamber a is expanded from the previous state of reduction. In the 3 rd step P3, the vibration (reverberation vibration) in the pressure generating chamber a is cancelled, and the meniscus M returns to the return position.

At the moment when the meniscus M returns to the recovery position, the ink column 10 has not yet separated from the meniscus M, and its tail 10b is connected to the meniscus M. Then, in the conventional driving waveform, as shown in fig. 5 (e), the ink column 10 ejected from the head 3 is separated from the meniscus M and ejected as a droplet from the head 3.

At this time, the distance from the leading end of the droplet to the tail 10b separated from the meniscus M is longer than the drive waveform of the above-described embodiment shown in fig. 5 (E), and satellite droplets are not sufficiently prevented. In the drive waveform of the embodiment, the droplet break off is promoted, and therefore the distance from the leading end portion of the droplet to the trailing portion 10b is short, and satellite droplets are prevented well.

Fig. 6 is a graph showing reverberation extrusion pressure generated due to the driving waveform shown in fig. 3.

In the drive waveforms of the above-described embodiments, as shown in fig. 6, the following relationship exists between the process interval (horizontal axis) from the 2 nd process P2 to the 3 rd process P3 and the extrusion pressure (vertical axis) of the meniscus M by the reverberation after the 3 rd process P3: the extrusion pressure is positive at a process interval of 0.4 to 1.55AL, and is maximum at a process interval of 1 AL.

When the process interval from the 2 nd process P2 to the 3 rd process P3 is set to 0.4 to 1.1AL or 0.4 to 0.9AL, the reverberation vibration is sufficiently amplified to promote the droplet break-off and to prevent the satellite droplets satisfactorily.

[ 2 nd embodiment ]

Fig. 7 is a diagram showing drive waveforms for realizing the method of driving the liquid droplet ejection head according to embodiment 2.

As shown in fig. 7, the drive waveform of the present embodiment is added with a cancellation waveform for canceling the reverberation vibration after the 3 rd step P3. The cancel waveform includes a 4 th step P4 of reducing the volume of the pressure generating chamber A by the piezoelectric element S after 2.75 to 3.25AL from the 2 nd step P2, and a 5 th step P5 of expanding and restoring the volume of the pressure generating chamber A by the piezoelectric element S after 0.75 to 1.25AL from the 4 th step P4.

The voltage applied to the piezoelectric element S in the 4 th step P4 is preferably equal to the voltage V2 applied in the 2 nd step P2. The voltage applied to the piezoelectric element S in the 5 th step P5 is preferably equal to the voltage V3 (initial potential) applied in the 3 rd step P3.

The cancellation waveform cancels the vibration (reverberation vibration) in the pressure generation chamber a, and enables the next droplet discharge to be performed properly.

When the same pixel is formed by performing droplet discharge subsequent to the previous droplet discharge, it is preferable to perform a preliminary step Pp of reducing the volume of the pressure generation chamber a by the piezoelectric element S before the 1 st step P1. The process interval from the preliminary process Pp to the 1 st process P1 is, for example, 0.3 AL. The voltage applied to the piezoelectric element S in the preliminary step Pp is preferably equal to the voltage V2 applied in the 2 nd step P2.

By adding this preliminary step Pp, the flying speed of the droplets ejected in the 2 nd step P2 can be increased, and the deviation from the ejection position of the droplets ejected before can be prevented.

[ 3 rd embodiment ]

Fig. 8 is a diagram showing drive waveforms for realizing a method of driving the droplet ejection head according to embodiment 3.

As shown in fig. 8, the drive waveform of the present embodiment is a drive waveform in the case where the multi-drop ejection is continuously performed. The last ejection among the multiple-droplet ejection is performed using the drive waveform of the above-described embodiment.

The ejection of the 1 st droplet is a waveform in which 2 droplets are ejected continuously and merged in air and then ejected. The ejection of the 2 nd and 3 rd droplets is a conventional DRR waveform. The ejection of the 4 th droplet is the drive waveform of the above-described embodiments 1 and 2. The numerical values in fig. 8 represent the process intervals as coefficients of AL.

In this manner, by performing the final discharge in the case of performing the multi-droplet discharge continuously using the drive waveform of the above-described embodiment, it is possible to favorably prevent satellite droplets from being generated in the final discharge, which is a problem in particular.

[ concerning ink ]

In each of the above embodiments, the liquid to be ejected is ink, but not limited to ink, and the capillary permeation rate of the liquid is expressed by {2 · (capillary radius) · (surface tension) · cos (contact angle) }/{8 · (tube length) }. Capillary penetration speed is greatly affected by the viscosity and surface tension of the liquid. For example, when a liquid having a surface tension of 40dyne/cm and a viscosity of 2cp is compared with a liquid having a surface tension of 28dyne/cm and a viscosity of 10cp, the capillary permeation rate of the liquid of the latter is reduced to 1/10 of the liquid of the former at the same capillary radius and the same tube length.

Therefore, the recovery timing of the meniscus M to the recovery position differs depending on the viscosity of the liquid, and the recovery of the meniscus M becomes late in a liquid having a high viscosity, whereas the recovery of the meniscus M becomes early in a liquid having a low viscosity. Similarly, the recovery timing of the meniscus M to the recovery position differs depending on the surface tension of the liquid, and the recovery of the meniscus M becomes later in a liquid having a low surface tension, whereas the recovery of the meniscus M becomes earlier in a liquid having a high surface tension.

As described above, if the timing of the meniscus M returning to the return position differs due to differences in the viscosity and surface tension of the liquid, it is conceivable that: after 0.4 to 1.55AL from the 2 nd step P2, the 3 rd step P3 is executed, and thereafter the meniscus M is substantially restored to the restoration position earlier or later. If the recovery of the meniscus M to the recovery position becomes early or late, there is a fear that the meniscus M cannot be squeezed out well by the reverberation vibration.

Therefore, the driving method of the present invention exerts a significant effect when the viscosity of the discharged liquid is 5cp or more and 15cp or less and the surface tension of the liquid is 20dyne/cm or more and 30dyne/cm or less.

[ concerning the embodiments ]

In the above embodiments, the pressure applying mechanism is constituted by the piezoelectric element S. The driving method of the present invention is preferable because the timing of decreasing the pressure in the pressure generation chamber can be easily controlled when the pressure applying means is constituted by the piezoelectric element S.

In each embodiment, a drive waveform of a rectangular wave is applied to the piezoelectric element. The use of the rectangular wave is preferable because the start timing of the 3 rd step P3 can be easily set to the timing at which the meniscus M returns to the return position, and the 3 rd step P3 generates a strong negative pressure, which can easily separate droplets.

In the above embodiment, the shear mode piezoelectric element S that deforms in the shear mode by applying an electric field is used as the pressure applying means. The shear mode piezoelectric element is preferable because the rectangular wave drive waveform shown in fig. 3 can be used more effectively, the drive voltage can be reduced, and more effective driving can be performed. However, the present invention is not limited to these, and for example, piezoelectric elements of other forms such as a single-plate type piezoelectric actuator and a longitudinal vibration type multilayer piezoelectric element may be used. Other pressure applying mechanisms such as an electromechanical conversion element using electrostatic force or magnetic force, an electrothermal conversion element for applying pressure using boiling phenomenon, and the like may be used.

In the above description, an ink jet recording head for performing image recording is used as the liquid droplet ejection head, but the present invention is not limited thereto, and the present invention can be applied to any liquid droplet ejection head provided with a head for ejecting liquid droplets, a pressure generation chamber communicating with the head, and a pressure applying mechanism for changing the pressure in the pressure generation chamber.

Examples

Fig. 9 is a graph showing the relationship between the droplet velocity and the satellite droplet length as an embodiment of the present invention.

In the recording head using the shear mode with the head pitch of 180dpi and the ejection droplet amount of 14pl, the process interval from the 1 st process P1 to the 2 nd process P2 was set to 1AL by the DRR waveform, and as shown in fig. 9, the process interval from the 2 nd process P2 to the 3 rd process P3 was (1)0.5AL, (2)2AL, and (3)4AL, and droplets were ejected by driving. The relationship between the droplet velocity (m/s) at this time (horizontal axis) and the satellite droplet length (mm) (vertical axis) was confirmed.

As shown in fig. 9, in (1) (example in which the process interval from the 2 nd process P2 to the 3 rd process P3 was set to 0.5 AL), the generation of satellites was not confirmed until the droplet velocity was 6.0 m/s. In (2) (comparative example in which the process interval from the 2 nd process P2 to the 3 rd process P3 was set to 2 AL), the generation of satellite droplets was confirmed if the droplet velocity exceeded 5.0 m/s. In (3) (comparative example in which the process interval from the 2 nd process P2 to the 3 rd process P3 was set to 4 AL), although the generation of satellites was not confirmed until the droplet velocity was 6.0m/s, the length of satellites generated when the droplet velocity exceeded 6.0m/s was longer than that of (1). In (1), satellite droplets occur if the droplet velocity is 6.0m/s or more, but the length thereof is suppressed to be shorter than that in (3).

Description of reference numerals:

1 shower nozzle plate

2-channel substrate

3 spray head

4 diverter element

41 shunt

42 ink tube

10 ink column

10b tail part

50

H recording head

A pressure generating chamber

S piezoelectric element (spacing wall)

Q1 electrode

Q2 electrode

Q3 electrode

Q4 electrode

M meniscus

P1 Process 1

P2 Process 2

P3 Process No. 3