JP4670838B2 - Ink droplet ejection device - Google Patents

Description

  The present invention relates to an ink droplet ejecting apparatus including a plurality of ink channels having nozzles.

  Various types of ink droplet ejecting apparatuses have been proposed. One of them is a shear mode ink droplet ejecting apparatus. FIGS. 1 and 2 are examples of the ink droplet ejecting apparatus described in Patent Document 1. It is a figure which shows an example. In FIG. 1, 1 is an ink tube, 2 is a nozzle forming member, 3 is a nozzle, 4 is an ink meniscus formed by ink, S is a side wall as an electromechanical conversion means, 6 is a cover plate, 7 is an ink supply port, Reference numeral 8 denotes a substrate. As shown in FIG. 2, the ink channel A that is an ink flow path is formed by the side wall S, the cover plate 6, and the substrate 8. The nozzles are formed in each ink channel, but are omitted in a part of FIG.

FIG. 1 shows a cross-sectional view of one ink channel having one nozzle. In an actual shear mode ink droplet ejecting apparatus H, as shown in FIG. 8, a plurality of ink channels A, that is, A1, A2,... An separated by a plurality of side walls S, that is, S1, S2,. One end of each of the ink channels A1, A2,... An is connected to a nozzle 3 formed on the nozzle forming member 2, and the other end is connected to an ink tank (not shown) by an ink tube 1 through a supply port 7. The nozzle 3 is formed with an ink meniscus 4 made of ink. For example, electrodes Q1 and Q2 formed in close contact with the side wall S1 and electrodes Q3 and Q4 formed in close contact with the side wall S2 are provided. Similarly, electrodes are formed in close contact with each side wall. As shown in FIG. 2B, for example, the electrode Q1 is connected to the ground, and the first pulse P ₁ having a peak value V1, a width J and a positive voltage as shown in FIG. A drive pulse P ₀ consisting of a high voltage V _{2, a} second pulse P _{2 having} a width R and a negative voltage, and a period E of zero voltage is applied. Driving pulse P ₀ in FIG. 7 is the absolute value of the voltage V1 and V2 are equal. Similarly, to connect the electrode Q4 to ground, the application of a driving pulse P ₀ to the electrodes Q3, flies ink droplets from the nozzle 3 by the operation described below. As shown in FIG. 7A, the horizontal axis is time, the vertical axis is the drive pulse voltage, and it is half the reciprocal of the acoustic resonance frequency of the ink channels A1, A2,. When (1/2) is AL (time), normally, in the drive pulse P ₀ , the width J of the first pulse P ₁ is substantially equal to AL, and the width R of the subsequent second pulse P ₂ is substantially equal. It is equal to 2AL, and the width of the period E of the zero (ground) voltage is configured to be substantially equal to an integral multiple of AL (for example, 1AL). With such a configuration of the driving pulse P ₀ , the ink channels A 1, A 2,... Operate efficiently, and the ink flying speed is maximized. AL corresponds to the length of the ink channel.

The side walls S1, S2,... Are composed of side walls S1a, S2a,... And S1b, S2b,... Made of two piezoelectric materials having different polarization directions as indicated by arrows in FIG. In addition, an actuator that operates by being deformed by applying a drive pulse is configured. If when the drive pulses to the electrodes Q2 and Q3 is not applied but not the sidewalls S1, S2 is modified as in FIG. 2 (a), the first pulse P ₁ is applied to the electrode Q2 and Q3, the polarization direction of the piezoelectric material As shown in FIG. 2B, an electric field in a direction perpendicular to the side wall is generated, both side walls S1a and S1b are deformed in the joint surface of the side walls, and the side walls S2a and S2b are similarly deformed in the opposite direction. The side walls S1a and S1b and the side walls S2a and S2b are deformed outward from each other, and in this example, the volume of the ink channel A1 is enlarged. Next, as shown in FIG. 2 (c), followed by the second pulse P ₂ by the sidewall S1a, S 1 b and S2a, S2b are deformed in opposite directions, the volume of the ink channel A1 is rapidly reduced, the ink The pressure in channel A1 changes. By this operation, the ink meniscus 4 in the nozzle 3 is changed by a part of the ink filling the ink channel A1, and the ink droplet is ejected from the nozzle 3. Similarly, each ink channel operates by applying a drive pulse to eject ink droplets.

  When the side walls S1 and S2 of the ink channel A1 are deformed as described above, the adjacent ink channel A2 is affected. For example, normally, for example, A1, A4, A7. A method of driving A2, A5, A8,... Is performed in the next cycle.

The ink droplet flight utilizes acoustic resonance (hereinafter referred to as resonance) of the ink channel, and first expands the ink channel volume by the first pulse P ₁ having a positive voltage, and then the ink channel by the second pulse P ₂ . A method of reducing the volume and causing ink droplets to fly is used. That is, the width J of the first pulse P ₁ is set to AL which is a half (1/2) of the resonance period of the ink channels A1, A2,..., And the width R of the second pulse P ₂ is set to 2AL. Increasing the ink flight efficiency is achieved by making the length of the zero period E substantially equal to an integral multiple of AL.

  Further, the amount of ink in the nozzle 3 and the ink channels A1, A2,... Decreases due to the flying of the ink droplets, but the decrease in the ink amount is reduced from the ink supply port 7 to the ink channel by the capillary force of the nozzle 3 and the ink. Ink is supplied to A1, A2,. In this way, after the first ink droplets fly, the ink is replenished before the second ink droplets fly, and the ink meniscus returns to the state when the original ink is not flying (stationary state). The next ink is ejected stably.

As described above, the ink flies to form an image, but in order to form a gradation image and a high density image in detail, a drive pulse is continuously applied to one ink channel a plurality of times, By flying ink droplets and combining the ink droplets before they land on the recording paper, that is, during the flight, and forming one pixel at the time of landing, the dots that fill the pixels are expanded or one pixel is formed. A method of forming a high-quality image by forming a gradation or a high density pixel by landing a plurality of ink droplets is used.
Japanese Patent Application Laid-Open No. 10-272771

  When the plurality of ink droplets combine to form one pixel during the flight, the plurality of individual ink droplets are sub-drop SD, and the plurality of sub-drops SD combine to form the ink droplet. Will be written as Super Drop UD.

As described above, in order to form a super drop UD by combining a plurality of sub-drops SD during flight, basically, the second sub-drop SD2 flies faster than the speed at which the first first sub-drop SD1 flies. It is difficult to unite during the flight unless the speed is high. Therefore, it is necessary to sequentially increase the speed to the third sub-drop SD3... SDn. However, when the first pulse P ₁ , the second pulse P ₂ , and the drive pulse P ₀ having the zero period E (length 1 AL) as a basic unit are driven, each sub-drop tends to fly separately. There is a problem that it is difficult to combine sub-drops during flight, and it becomes unstable to form a super-drop. In addition, there is a problem that a plurality of ink droplets forming one pixel lands separately from each other and the pixel is disturbed.

Therefore, as shown in FIG. 7 (b), the negative voltage value of the positive voltage values + V1 and the second pulse P ₁₂ of the first pulse P ₁₁ of the driving pulse P ₀₁ for jetting the first sub-drop SD1 -V1 in comparison, the voltage + V2 of the first pulse P ₁₂ of the driving pulse P ₀₂ for jetting the second sub-drop SD2, the values of the voltage -V2 of a second pulse P _22, respectively + V2> + V1, -V2 Drive with a voltage value having a large absolute value so that <-V1. Then, the second sub-drop SD2 flies at a higher speed than the first sub-drop SD1, and merges during the flight. Similarly, the third sub-drops SD3... SDn are sequentially driven with a voltage having a large absolute value, thereby combining the sub-drops during flight to form a super drop.

  However, this method requires a voltage circuit that changes in an analog manner, and the drive circuit becomes complicated and expensive, and the control of the drive pulse is also complicated.

  The present invention solves the above-described problems and reliably combines the sub-drops during flight without complicating the drive circuit or complicating the control, thereby forming the desired super drop. An object is to provide an apparatus.

The object of the present invention is achieved by the invention described below.
1.
The volume of the ink channel is enlarged with respect to the electro-mechanical conversion means of the ink droplet ejecting apparatus having an ink channel, an electric / mechanical conversion means for changing the volume of the ink channel, and a nozzle for ejecting ink. Ink droplet that causes the ink droplet to fly by applying a first pulse, a second pulse that reduces the volume of the ink channel following the first pulse, and a driving pulse consisting of a period of zero voltage following the second pulse. An injection device,
The drive pulse is applied to one of the ink channels continuously, with the width of the first pulse being substantially the AL of the ink channel (one-half of the acoustic resonance period), whereby the nozzle High density by ejecting multiple ink droplets continuously so that the flying speed of the ink droplets ejected later is faster than the flying velocity of the ink droplets ejected first, and combining these ink droplets during the flight In the ink droplet ejecting apparatus for forming the image of
An ink droplet ejecting apparatus that satisfies all of the following conditions (1) to (4):
(1) The width of the second pulse is (5/3) AL . (2) The period of the drive pulse is substantially four times the AL. (3) The drive pulse applied continuously 1. The voltage of the first pulse is substantially equal to each other (4) The voltage of the second pulse of the drive pulse applied continuously is substantially equal to each other.
2. The ink droplet ejecting apparatus according to 1, wherein a period of the zero voltage is (4/3) AL and a width of the second pulse is (5/3) AL.
3.
3. The ink droplet ejecting apparatus according to 1 or 2, wherein the three ink droplets are ejected in succession by the three drive pulses applied in succession.

  According to the invention described in the claims, a plurality of driving pulses are continuously applied to the actuator, and a plurality of sub-drops are continuously ejected from the nozzle, thereby forming a super drop and forming a high density image. In such a case, formation of a super drop by combining sub-drops during flight is performed stably, and an image with high image quality can be formed. Further, even when one pixel is formed on a recording material by a plurality of sub-drops, it is possible to form a high-quality image by performing controlled pixel formation.

  In the present invention, by using two driving methods, a plurality of sub-drops can be continuously ejected to form a super drop and fly.

In the first method, the driving pulse P ₀ for flying the sub-drop SD is substantially longer than 3 times AL, which is a half of the acoustic resonance period, and substantially equal to an integral multiple of AL. In this method, the actuator is driven at an unequal cycle. The second method is a method of causing the sub-drop SD to fly by driving with a driving pulse P ₀ having a second pulse whose pulse width R is not substantially equal to an integral multiple of AL.

  One example of the mechanical configuration of the embodiment of the present invention is shown in FIGS. 1 and 2, and other examples are shown in FIGS. 3, 4, 5, and 6.

  FIG. 3 is a schematic diagram of an ink droplet ejecting apparatus. Parts that are the same as the parts shown in FIG.

  In FIG. 3, L is the length of the ink channel A, and the half AL of the acoustic resonance period of the ink channel A is expressed by AL≈L / AC. AC is the velocity of the pressure wave in the ink channel. Note that the length of the ink channel A does not exactly match the geometric length of FIG. 7B, but is the effective length of the ink channel A. ≒ in the above formula takes this meaning into consideration.

  The acoustic resonance period AL of the ink channel A is determined by applying a rectangular wave to the electrical / mechanical conversion means of the ink droplet ejecting apparatus, measuring the velocity of the ink droplet emitted, and making the rectangular wave voltage value constant. When the pulse width is changed, it is obtained as a pulse width that maximizes the droplet velocity.

  FIG. 4 shows the ink channel arrangement of the ink droplet ejection apparatus shown in FIG. 3 and the operation of each ink channel when a drive pulse is applied.

The ink channels A1, A2, A3,... Are formed with an air channel D formed as a gap therebetween, and electrodes Qa are formed on the side walls forming the ink channels A1, A2, A3,. An electrode Qd is formed on the side wall forming the channel D. Pulses P ₁ and P ₂ are applied to the electrode Qa by a drive circuit (not shown).

First, as shown in FIG. 4B, as a first step, a pulse P ₁ of positive voltage + V that expands the volume of the ink channels A1, A2, A3,... Is applied to the electrode Qa. Next, as shown in FIG. 5A, a negative voltage −V pulse P ₂ that reduces the volume of the ink channels A1, A2, A3,... Is applied to the electrode Qa.

In this way, by applying a drive pulse composed of the pulses P ₁ and P ₂ to the electrode Qa, ink droplets fly from the ink channels A1, A2, A3,.

6A and 6B show the voltages of the electrodes Qa and Qd in the driving of the ink channels A1, A2, A3,. As is apparent from FIGS. 6A and 6B, in this drive, a positive pulse P ₁ and a negative pulse P ₂ are applied to the electrode Qa.

  As an ink channel driving method, there is another method described below.

6C and 6D show the voltages of the electrodes Qa and Qd in the other method. In this method, as shown in FIGS. 6C and 6D, a positive voltage pulse P ₁ is applied to the electrode Qa. On the other hand, a positive voltage pulse P ₂ is applied to the electrode Qd by a drive circuit (not shown).

  The volume of the ink channels A1, A2, A3,... Is increased in the same manner as in the case shown in FIG. 6A, and the drive for reducing the volumes of the ink channels A1, A2, A3,. In the stage, as shown in FIG. 5B, by applying a + V positive voltage to the air channel electrode Qd, the same driving as in FIG. 5A in which a negative voltage is applied to the electrode Qa is performed. ing.

  The driving methods shown in FIGS. 5B and 6C and 6D are advantageous in circuit design in that they can be driven using positive voltage pulses.

(1) Embodiment 1
The first driving method will be described by taking an example in which one super drop UD is formed by two sub-drops SD1 and SD2. In this embodiment, as shown in FIGS. 9 and 10, the voltages of the drive pulses P _O1 , P ₀₂ , P ₀₃ for driving the sub-drops SD1, SD2, SD3 are substantially equal to each other. As is clear from the description, the super drop UD can be formed stably.

  FIG. 8 is a diagram showing the waveform of a drive pulse for forming and flying a super drop in the present invention in contrast to the basic waveform of a drive pulse for forming and flying a super drop UD. And the vertical axis represents the voltage of the drive pulse.

  As described above, the first pulse is a pulse that expands the volume of the ink channel A, the second pulse is a pulse that is applied subsequent to the first pulse and reduces the volume of the ink channel A, and the first pulse One pulse and the second pulse constitute a drive pulse.

As described above, the basic waveform of the drive pulse P ₀ is the first pulse P _{11 having} the width AL and the subsequent width when AL (time) is 1/2 of the reciprocal of the acoustic resonance frequency of the ink channel A. A driving pulse P ₀₁ having a length of 4AL comprising a second pulse P _{21 of} 2AL and a period E (length AL) of zero voltage, a first pulse P ₁₂ having a width AL, a second pulse P ₂₂ having a width 2AL and a length and a driving pulse P ₀₂ length 4AL consisting period E of the voltage zero AL continuously applied to the ink channels a and form a sub-drop SD1 and SD2.

  In the driving of the ink channel A by the driving pulse having such a basic waveform, it is difficult to reliably combine the second sub-drop SD2 with the first sub-drop SD1, and the inventor of the present invention stabilizes the super-drop. The drive method that can be formed is searched, the ink channel A is driven by changing the cycle of the sub-drop drive pulse around 4AL (integer multiple of AL), the sub-drop flight interval and the flight speed The relationship was measured. As an example of the result, the measurement result in the case of two subdrops is shown in FIG. In the experiment, the voltages of the first pulse and the second pulse of the drive pulse are made the same during each period.

  In FIG. 14, the horizontal axis represents the subdrop flight interval (μs) changed by changing the drive pulse period, and the vertical axis represents the flight speed of the first subdrop SD1 and the second subdrop SD2. It is measured. In FIG. 14, since AL is 4.8 μs, the point indicated by the arrow indicated by the horizontal axis “4AL” is 4AL = 19.2 μs, and in the region on the left side from this point, the second sub-drop is more than the first sub-drop SD1. It became clear that Drop SD2 flew at high speed. This indicates that the second sub-drop SD2 can fly at a higher speed when the cycle of the drive pulse is shorter than 4AL.

  It was also confirmed that the same effect can be obtained when the period of the drive pulse is shorter than 6AL.

According to the experimental results, as shown in FIG. 9, the driving pulse P ₀₁ has a length following the first pulse P ₁₁ having a width J of AL, followed by the second pulse P ₂₁ and the second pulse P ₂₁ having a width R of 2AL. is (3/4) was constructed by period E of the voltage zero AL, a drive pulse P ₀₁ for discharging a first sub-drop SD1, the driving pulse having the same configuration as the driving pulse P ₀₁ for discharging a second sub-drop SD2 thereby forming P ₀₂ and as drive pulses having respective widths [(4-1 / 4) AL], a super-drop UD1 subsequently provided period Ex voltage zero length 6 / 4AL the driving pulse P ₀₂ When forming the super drop UD1 in a period of 9 AL, the super drop was stably formed, and the best result was obtained. It should be noted that the period for forming one super drop UD1 may be a value other than 9AL.

When one super drop is formed by three sub-drops by this method, as shown in FIG. 10, drive pulses P ₀₁ , P ₀₂ , P in the period of (4-1 / 4) × AL. ₀₃ and 3 after the pulse continuously applied, and (4 + 3/4) when the period Ex zero voltage × AL has elapsed, applies the driving pulse P ₀₄ for forming two second super drops UD2. That is, one super drop UD1 is formed and flew in a period of 16AL.

  The period for forming the super drop UD varies depending on the setting of the suspension period Ex. The suspension period Ex can be (n + 3/4) AL, and one super drop is formed according to the suspension period Ex. The period is (12 + n) AL.

From the experimental results shown in FIG. 14, it is found that a good super drop is formed when the period of the drive pulse P ₀ forming the sub-drop is (2n + 1) AL <P ₀ period <2 (n + 1) AL. did.

(2) Embodiment 2
The second method will be described by taking an example in which one super drop UD is formed by three sub-drops SD1, SD2, and SD3. Also in this embodiment, as shown in FIG. 12 , the voltages of the driving pulses P ₀₁ , P ₀₂ , P ₀₃ for driving the sub-drops SD1, SD2, SD3 are made substantially equal to each other. As is clear from the description, the super drop UD can be formed stably.

  FIG. 11 shows basic waveforms of drive pulses forming the sub-drops SD1, SD2, and SD3.

In order to fly the sub-drop SD1, a first pulse P ₁₁ having a width J of AL, a second pulse P ₂₁ having a width R of 2AL, and a period E of zero voltage having a length AL following the second pulse P ₂₁ are used. A drive pulse P ₀₁ is applied. Similarly, in order to form a sub-drop SD2, SD3 flight and applies a driving pulse P ₀₁ configured similarly to the driving pulse P _02, P _03, respectively. The period of the drive pulses P ₀₁ , P ₀₂ and P ₀₃ is 4AL as shown in the figure. Then, by providing a period Ex voltage zero length 4AL after driving pulse P _03, the period for forming the first super-drop UD1 and 16AL.

  When the super drop was formed by the drive pulse shown in FIG. 11 and then caused to fly, the sub-drops SD1, SD2, and SD3 were not stably combined.

  The inventor of the present invention searches for a driving method capable of stably forming a super drop, drives the ink channel A by changing the width of the negative pulse of the driving pulse for discharging the sub-drop, The relationship of the flying speed of sub-drops was measured. The result is shown in FIG. 15 by taking as an example the case of flying three subdrops.

In FIG. 15, the horizontal axis represents the pulse width R (pulse width, μs) of the driving pulse P ₀ , and the vertical axis represents the flight speeds of the first sub-drop SD1, the second sub-drop SD2, and the third sub-drop SD3. . In FIG. 11, since AL is 4.8 μs, the point of the arrow indicated by “2AL” on the horizontal axis is 2AL = 9.6 μs. From this point in the left region, the second subdrop SD2 is more than the first subdrop SD1. It is clear that the third sub-drop SD3 flies faster than the second sub-drop SD2. In the experiment, the voltages of the first pulse and the second pulse of the drive pulse are made the same during each period. From the experimental results, as shown in FIG. 12, the width J of the first pulse _{P 11} of the driving pulse _{P 01} is in AL, shorter 2AL width R of the subsequent second pulse _{P 21} (an integral multiple of AL) (2 The best result was obtained when −1/3) × AL, and then the period E of zero voltage was (4/3) × AL. In this case, the period of the driving pulse _{P 01} is 4AL. The ejected sub-drop SD1, SD2, SD3, the period of forming a super-drop UD1, as illustrated, the period of the voltage zero length 4AL after driving pulse _{P 01, P 02, P 03} provided Ex It becomes 16AL by this.

  The suspension period Ex can be set to n × AL, and the period for forming one super drop can be set to (12 + n) AL corresponding to the suspension period Ex.

FIG. 13 shows an example in which one super drop is formed by two sub drops by the second method. In the case of the drive of FIG. 13, by applying the drive pulses P ₀₁ and P ₀₂ having the above 4AL period continuously for two pulses and providing the drive pulse P ₀₂ with a period Ex of zero voltage having a length of 1AL, One super drop UD1 is formed with 9AL. In this case as well, the period for forming one super drop UD1 can be set to a value other than 9AL.

Further, in the first and second embodiments, the absolute value of the voltage of the first pulse P ₁ is equal to the absolute value of the voltage of the second pulse P _2. However, the absolute value of the voltage of the first pulse P _{1 is} the same. It is also possible to set the absolute value of the voltage of the second pulse P ₂ so as not to be equal. Also in this case, it is desirable that the values of the first pulses P _1n of the continuous drive pulses are equal to each other.

FIG. 6 is a cross-sectional view of the ink channel of the ink droplet ejecting apparatus along the ink flow path. FIG. 4 is a cross-sectional view across an ink flow path of an ink channel of the ink droplet ejecting apparatus. It is a schematic diagram of an ink droplet ejecting apparatus. It is a figure which shows the arrangement | sequence of the ink channel of an ink droplet ejecting apparatus. It is a figure which shows the action | operation of an ink channel. It is a figure which shows a drive pulse. It is the figure which showed the waveform of the conventional drive pulse. It is a figure which shows the basic waveform of the drive pulse which forms a super drop. It is a figure which shows the waveform of the drive pulse in Embodiment 1 of this invention. It is a figure which shows the waveform of the drive pulse in Embodiment 1 of this invention. It is a figure which shows the basic waveform of the drive pulse which forms a super drop. It is a figure which shows the waveform of the drive pulse in Embodiment 2 of this invention. It is a figure which shows the waveform of the drive pulse in Embodiment 2 of this invention. It is a figure which shows the measurement result of flight of two subdrops. It is a figure which shows the measurement result of flight of three subdrops.

Explanation of symbols

1 ink tubes 3 nozzles 4 ink meniscus 7 ink supply port 8 substrate A, A1, A2 ink channels H drop ejection device P _0, P _01, P ₀₃ driving pulses _{P 1, P 11, P 12} , P 13, P 14 the first pulse _{P 2, P 21, P 22} , P 23 second pulse SD1, SD2 sub drop UD1, UD2 Super drop

Claims (3)

The volume of the ink channel is enlarged with respect to the electro-mechanical conversion means of the ink droplet ejecting apparatus having an ink channel, an electric / mechanical conversion means for changing the volume of the ink channel, and a nozzle for ejecting ink. Ink droplet that causes the ink droplet to fly by applying a first pulse, a second pulse that reduces the volume of the ink channel following the first pulse, and a driving pulse consisting of a period of zero voltage following the second pulse. An injection device,
The drive pulse is applied to one of the ink channels continuously, with the width of the first pulse being substantially the AL of the ink channel (one-half of the acoustic resonance period), whereby the nozzle High density by ejecting multiple ink droplets continuously so that the flying speed of the ink droplets ejected later is faster than the flying velocity of the ink droplets ejected first, and combining these ink droplets during the flight In the ink droplet ejecting apparatus for forming the image of
An ink droplet ejecting apparatus that satisfies all of the following conditions (1) to (4):
(1) The width of the second pulse is (5/3) AL . (2) The period of the drive pulse is substantially four times the AL. (3) The drive pulse applied continuously The voltages of the first pulses are substantially equal to each other. (4) The voltages of the second pulses of the drive pulses applied continuously are substantially equal to each other. 2. The ink droplet ejecting apparatus according to claim 1, wherein the period of the zero voltage is (4/3) AL and the width of the second pulse is (5/3) AL. 3. The ink droplet ejecting apparatus according to claim 1, wherein the three ink droplets are ejected in succession by the three drive pulses applied in succession.

Images