JP6624205B2 - INK JET RECORDING APPARATUS, INK JET HEAD DRIVING METHOD, AND DRIVE WAVEFORM DESIGN METHOD - Google Patents

Description

  The present invention relates to an inkjet recording apparatus, a method of driving an inkjet head, and a method of designing a drive waveform. More specifically, an inkjet head can be driven in a multi-drop manner by a drive waveform having high robustness to an AL value, and a high-quality image is formed. The present invention relates to an ink jet recording apparatus, a method of driving an ink jet head, and a method of designing a driving waveform.

  In recent years, in order to form an inkjet image having excellent gradation, the necessity of a multi-drop in which droplets of different liquid amounts are separated from one inkjet head has been increased.

  As a method of ejecting droplets of different liquid amounts from the same nozzle, a plurality of droplets are continuously ejected from the same nozzle by repeatedly applying the same drive pulse within one pixel period, and the same A method of landing in a pixel is known (Patent Document 1). By changing the number of drive pulses applied, the dot diameter of one pixel can be changed. However, this method has a problem that the longer the dot diameter of one pixel, the longer the driving cycle.

  On the other hand, as a multi-drop drive waveform, a first expansion pulse for expanding the volume of the pressure chamber for a certain time, a first deflation pulse for reducing the volume of the pressure chamber for a certain time, and a first expansion pulse for expanding the volume of the pressure chamber for a certain time. The applicant of the present application has proposed a drive pulse having two expansion pulses and a drive pulse of a second contraction pulse for contracting the volume of the pressure chamber for a predetermined time (patent document 2).

  When a drive pulse having this drive waveform is applied to the pressure generating means of the ink jet head, the volume of the pressure chamber fluctuates a plurality of times, so that two or more droplets are continuously ejected from the same nozzle. Then, the droplet diameter of one pixel can be increased without lengthening the driving cycle by uniting the droplets during flight or landing the droplets in the same pixel on the recording medium.

JP 2000-15803 A WO 2015/152185 JP 2001-328259 A

  The present inventor has further studied the driving waveform of the multi-drop method, and has found the following new problem.

  The pulse width of each drive pulse in the drive waveform is set based on the acoustic resonance period of the pressure wave specific to the pressure chamber of the ink jet head so that the ejection characteristics such as the liquid amount and the droplet velocity have the intended characteristics. You. Assuming that 1/2 of the acoustic resonance period is AL, the pulse width that determines the emission characteristics is defined by the AL value.

  However, in general, the ink jet head has a certain degree of variation in the shape of the pressure chamber due to the manufacturing method and the material. For this reason, AL values also vary among pressure chambers, nozzle rows, ink jet heads, and the like. Therefore, even if the pulse width is set to be uniform in order to achieve the intended ejection characteristics, the ejection characteristics vary due to the variation in the AL value of each pressure chamber, nozzle row, inkjet head, etc. There is. This variation in the ejection characteristics is more likely to cause the displacement of the landing position of the droplet as the distance (gap) between the nozzle surface and the recording medium is increased, that is, as the flying distance of the droplet is increased, and disturbs the image. Cause. In particular, in the case of a textile printing apparatus that forms an ink jet image on a fabric, the gap is larger than that of a general recording apparatus, and therefore, the influence of the variation in the ejection characteristics due to the variation in the AL value is greater.

  FIG. 15 shows that one droplet (small droplet: 7 pl) is discharged from each nozzle by applying a general driving pulse for discharging one droplet from the nozzle using the same inkjet head. In this case, droplets (medium droplets: 18 pl) are ejected from each nozzle and landed by continuously applying a multi-drop driving pulse described in Patent Document 2 and the general driving pulse described above. It is a figure which compared with the case where it did. The gap is 3 mm.

  In this case, the voltage value of the driving pulse applied to the inkjet head is adjusted so that the landing positions of the small droplets are aligned in a horizontal line. Therefore, while a small droplet naturally has almost no landing position deviation, a medium droplet has a landing deviation. The present inventors have conducted intensive studies on the cause, and have found that the driving pulse of the multi-drop method is unstable with respect to the variation of the AL value, and is likely to cause the variation of the injection characteristics.

  Generally, the displacement of the landing position of the medium droplet can be adjusted by the voltage value of the drive pulse of the medium droplet. However, since the ink jet head is common to the small droplet and the medium droplet, a constant voltage value has to be set regardless of the size of the droplet. For this reason, the driving pulse of the multi-drop method should have high robustness that can suppress the variation of the ejection characteristics even if the AL value varies among the pressure chambers, the nozzle rows, the inkjet heads, and the like. is necessary.

  Here, the robustness of the drive waveform will be described. 16 to 18 are explanatory diagrams illustrating robustness with respect to the AL value. (A) in each drawing shows an expansion pulse for expanding the volume of the pressure chamber of the inkjet head and a contraction pulse for contracting the volume of the pressure chamber, and each of the driving waveforms for discharging one droplet from the nozzle. FIG. 4B is a graph showing an example, FIG. 4B is a graph showing a change in a droplet speed with respect to a variation in an AL value, and FIG. The meniscus vibration is positive when a positive pressure wave is generated in the pressure chamber (a direction protruding out of the nozzle), and negative when a negative pressure wave is generated (a direction that retracts into the nozzle). It becomes.

  Each of these drive waveforms causes a single droplet to be ejected from a nozzle by the fall of a contraction pulse synchronized with the fall of an expansion pulse. As shown in FIG. 16, when the pulse width of the expansion pulse is set to 1.0 AL, the pressure wave oscillation excited in the pressure chamber by the rising pulse P10 of the expansion pulse and the pressure wave oscillation excited by the falling pulse P20 in the pressure chamber. The phase of the pressure wave oscillation matches. Therefore, the discharge pressure can be efficiently applied to the liquid in the pressure chamber by the combined vibration of the pressure wave vibrations. In this case, since the peaks of the pressure wave vibrations coincide with each other, even if a phase shift occurs between the pressure wave vibrations due to a variation in the AL value, a change in the resultant vibration due to the phase shift is small. For this reason, the graph of the change in the droplet speed is flat. That is, since the change in the droplet speed with respect to the AL value becomes very insensitive, the robustness against the variation in the AL value is high. P30 is a rising pulse of the contraction pulse.

  On the other hand, as shown in FIGS. 17 and 18, when the pulse width of the expansion pulse for discharging the droplet is set to 0.5AL or 1.5AL, the pressure excited in the pressure chamber by the rising pulse P10 of the expansion pulse. The phase of the wave vibration does not match the phase of the pressure wave vibration excited into the pressure chamber by the falling pulse P20. The phase of the pressure wave vibration generated by the falling pulse P20 of the expansion pulse is earlier (leftward) in FIG. 17 and later in FIG. 18 than the phase of the pressure wave vibration generated by the rising pulse P10 of the expansion pulse. (To the right). As a result, the change in the synthetic vibration due to the variation in the AL value increases, and the graph of the change in the droplet velocity does not level off. FIG. 17 shows a downward-sloping graph, and the speed fluctuation has a negative correlation. In FIG. 18, the graph rises to the right, and the speed fluctuation has a positive correlation. In any case, since the change in the droplet speed with respect to the AL value is sensitive, the robustness to the variation in the AL value is reduced.

  As described above, by setting the pulse width of the expansion pulse for discharging a droplet to 1.0 AL, a drive waveform having high robustness with respect to the AL value can be obtained. However, this is the case where one droplet is discharged from the nozzle. In the case of the driving waveform of the multi-drop method as described in Patent Document 2, the volume of the pressure chamber is changed a plurality of times, and thus the overlap of the pressure wave vibrations excited in the pressure chamber becomes more complicated. Moreover, in the multi-drop method, since one pixel is formed by a plurality of droplets, the expansion pulse is not always set to 1.0 AL as in the case of discharging only one droplet. For this reason, even when the pulse width of the expansion pulse for discharging a droplet is not 1AL, it is desired that the inkjet head can be driven by a multi-drop method with a driving waveform having high robustness to the AL value.

  Note that Patent Document 3 discloses that the phases of pressure wave vibrations generated at each node of the drive waveform are matched with each other, but discharges minute droplets of 20 μm or less, and has high robustness against AL value. It does not disclose a driving waveform of the system.

  Therefore, an object of the present invention is to provide an ink jet recording apparatus which can drive an ink jet head by a multi-drop method with a driving waveform having high robustness to an AL value and can form a high quality image.

  Another object of the present invention is to provide a method of driving an ink jet head that can drive an ink jet head by a multi-drop method with a driving waveform having high robustness to an AL value and can form a high-quality image.

  It is still another object of the present invention to provide a drive waveform designing method capable of designing a multi-drop drive waveform having high robustness to an AL value.

  Other objects of the present invention will become apparent from the following description.

  The above object is achieved by the following inventions.

1. An ink jet head that varies the volume of the pressure chamber by driving the pressure generating means by applying a driving waveform, applies pressure to the liquid in the pressure chamber for discharge, and discharges a droplet from a nozzle;
A drive control unit that outputs the drive waveform to the pressure generating unit,
The drive control unit discharges the plurality of droplets from the nozzle by changing the volume of the pressure chamber a plurality of times, and a plurality of droplets for landing in the same pixel on the recording medium during flight. Outputting a driving waveform having a driving pulse;
At least one or more of the driving pulses for discharging the first droplet of the plurality of droplets are formed by changing the volume of the pressure chamber and causing two or more overlapping pressure waves in the pressure chamber. And the pressure wave vibration excited in the pressure chamber at the time of the first ejection of the droplet, and the pressure wave vibration excited in the pressure chamber by its pre-operation, the pressure wave in the pressure chamber When 1/2 of the acoustic resonance period is AL, the phase shift is from -0.6AL to 0.6AL,
At least one or more of the drive pulses for ejecting the subsequent second droplet ejects two or more overlapping pressure waves in the pressure chamber by changing the volume of the pressure chamber. A pressure wave vibration excited in the pressure chamber when the droplet is discharged, and a pressure wave vibration excited in the pressure chamber due to its pre-operation and remaining in the pressure chamber due to the first ejection of the droplet. The combined vibration of the reverberating pressure wave vibration and the ink jet recording apparatus having a phase shift in a direction opposite to the phase shift at the time of discharging the first droplet.
2. The drive waveform is synchronized with a first expansion pulse for expanding the volume of the pressure chamber for a certain period of time and the end of application of the first expansion pulse as the drive pulse for discharging the first droplet. And a first contraction pulse that is applied to contract the volume of the pressure chamber for a certain period of time,
The pulse width of the first expansion pulse is 0.4 AL or more and 0.8 AL or less or 1.2 AL or more and 1.6 AL or less,
2. The ink jet recording apparatus according to claim 1, wherein a pulse width of the first contraction pulse is 0.5AL.
3. The drive waveform has a second expansion pulse for expanding the volume of the pressure chamber for a certain period of time as the drive pulse for discharging the second droplet,
A combined vibration of the pressure wave vibration excited in the pressure chamber by the rising of the second expansion pulse and the reverberant pressure wave vibration remaining in the pressure chamber due to the first ejection of the droplet; When the pulse width of the first expansion pulse is 0.4 AL or more and 0.8 AL or less, the phase shift from the pressure wave vibration excited in the pressure chamber due to the fall of the expansion pulse is 0 AL or more and 1.5 AL or less. 3. The ink jet recording apparatus according to claim 2, wherein when the pulse width of the first expansion pulse is 1.2 AL or more and 1.6 AL or less, it is -0.5 AL or more and 0 AL or less.
4. The pulse width of the first expansion pulse is 0.4 AL or more and 0.8 AL or less,
4. The ink jet recording apparatus according to claim 3, wherein a pulse width of the second expansion pulse is larger than 1.2 AL and equal to or smaller than 1.9 AL.
5. The pulse width of the first expansion pulse is 1.2 AL or more and 1.6 AL or less,
4. The ink jet recording apparatus according to claim 3, wherein the pulse width of the second expansion pulse is 0.8 AL or more and 1.1 AL or less.
6. The driving waveform includes the third, fourth, or third pulse having a second contraction pulse for contracting the volume of the pressure chamber for a certain period of time after the second expansion pulse and canceling reverberation pressure wave vibration remaining in the pressure chamber. 6. The ink jet recording apparatus according to 5.
7. 7. The ink jet recording apparatus according to 6, wherein the second contraction pulse is applied in synchronization with the end of application of the second expansion pulse, and has a pulse width of 2AL.
8. 7. The ink jet recording apparatus according to claim 6, wherein the second contraction pulse is applied with a pause of 1AL after completion of the application of the second expansion pulse, and has a pulse width of 1AL.
9. The second contraction pulse is applied in synchronization with the end of the application of the second expansion pulse, has a pulse width of 0.5AL,
The drive waveform has a third contraction pulse having a pulse width of 1 AL which is applied after a pause of 0.5 AL after the application of the second contraction pulse is completed and contracts the volume of the pressure chamber for a certain period of time. 7. The ink jet recording apparatus according to the above item 6.
10. 10. The ink jet recording apparatus according to any one of 1 to 9, wherein the driving waveform is a rectangular wave.
11. The inkjet recording apparatus according to any one of 1 to 10, wherein the inkjet head is a shear mode type inkjet head in which the pressure generating unit is driven in a shear mode.
12. By driving the pressure generating means of the ink jet head by applying a driving waveform, the volume of the pressure chamber is changed a plurality of times, a pressure for discharging is applied to the liquid in the pressure chamber, and a plurality of droplets are discharged from the nozzle. A method of driving an ink jet head that causes a droplet to land in the same pixel on a recording medium during flight.
As the drive waveform, using a plurality of drive pulses for discharging the plurality of droplets from the nozzle by changing the volume of the pressure chamber a plurality of times,
At least one or more of the driving pulses for discharging the first droplet of the plurality of droplets are applied to the pressure chamber by changing the volume of the pressure chamber to form two or more overlapping pressure waves. And the pressure wave vibration excited in the pressure chamber at the time of the first ejection of the droplet and the pressure wave vibration excited in the pressure chamber by its pre-operation, the pressure in the pressure chamber When １ ／ of the acoustic resonance period of the wave is AL, it is assumed that there is a phase shift of −0.6 AL or more and 0.6 AL or less,
At least one or more of the drive pulses for discharging the subsequent second droplet is used to change the volume of the pressure chamber to excite two or more overlapping pressure waves in the pressure chamber. A pressure wave vibration excited in the pressure chamber at the time of ejection of the droplet, and a pressure wave vibration excited into the pressure chamber by a preliminary operation of the pressure droplet, and the pressure chamber caused by ejection of the first droplet. The combined vibration of the reverberant pressure wave vibrations remaining in the inkjet head is a method of driving an ink jet head in which a phase shift in a direction opposite to the phase shift at the time of discharging the first droplet is performed.
13. As a drive pulse for discharging the first droplet, a first expansion pulse for expanding the volume of the pressure chamber for a certain period of time, and a drive pulse applied in synchronization with the end of the application of the first expansion pulse, Using a first contraction pulse for contracting the volume of the pressure chamber for a certain time,
The pulse width of the first expansion pulse is 0.4 AL or more and 0.8 AL or less or 1.2 AL or more and 1.6 AL or less,
13. The ink jet head driving method according to the above item 12, wherein the pulse width of the first contraction pulse is 0.5AL.
14． As a drive pulse for discharging the second droplet, a second expansion pulse for expanding the volume of the pressure chamber for a certain period of time is used.
A combined vibration of the pressure wave vibration excited in the pressure chamber by the rising of the second expansion pulse and the reverberant pressure wave vibration remaining in the pressure chamber due to the first ejection of the droplet; When the pulse width of the first expansion pulse is 0.4 AL or more and 0.8 AL or less, the phase shift from the pressure wave vibration excited in the pressure chamber due to the fall of the expansion pulse is 0 AL or more and 1.5 AL or less. 14. The method of driving an ink jet head according to the item 13, wherein the pulse width of the first expansion pulse is -0.5 AL or more and 0 AL or less when the pulse width of the first expansion pulse is 1.2 AL or more and 1.6 AL or less.
15. The pulse width of the first expansion pulse is 0.4AL or more and 0.8AL or less,
15. The ink jet head driving device according to the item 14, wherein the pulse width of the second expansion pulse is set to be larger than 1.2 AL and equal to or smaller than 1.9 AL.
16. The pulse width of the first expansion pulse is set to 1.2 AL or more and 1.6 AL or less,
15. The inkjet head drive device according to the above 14, wherein the pulse width of the second expansion pulse is 0.8 AL or more and 1.1 AL or less.
17. As the driving waveform, after the second expansion pulse, a second contraction pulse is used which contracts the volume of the pressure chamber for a certain period of time and cancels reverberation pressure wave vibration excited in the pressure chamber. Or a method for driving an inkjet head according to item 16.
18. 18. The method of driving an ink jet head according to claim 17, wherein the second contraction pulse is applied in synchronization with the end of the application of the second expansion pulse to have a pulse width of 2AL.
19. 18. The ink jet head driving method according to claim 17, wherein the second contraction pulse has a pulse width of 1AL and is applied with a 1AL pause after completion of the application of the second expansion pulse.
20. The second contraction pulse has a pulse width of 0.5AL, and is applied in synchronization with the end of the application of the second expansion pulse.
As the drive waveform, a third contraction pulse having a pulse width of 1 AL for contracting the volume of the pressure chamber for a predetermined time is applied after a pause of 0.5 AL after the application of the second contraction pulse is completed. 18. The method for driving an inkjet head according to item 17.
21. 21. The method of driving an inkjet head according to any one of the items 12 to 20, wherein the drive waveform is a rectangular wave.
22. 22. The method of driving an inkjet head according to any one of the items 12 to 21, wherein a shear mode type inkjet head in which the pressure generating unit is driven in a shear mode is used as the inkjet head.
23. The pressure generating means is driven by applying the pressure to the pressure generating means of the ink jet head, and the volume of the pressure chamber is changed a plurality of times to discharge a plurality of droplets from the nozzle. A method for designing a drive waveform having a plurality of drive pulses for landing in a pixel,
At least one or more of the driving pulses for discharging the first droplet of the plurality of droplets are applied to the pressure chamber by changing the volume of the pressure chamber and two or more pressure waves overlapping the pressure chamber. And the pressure wave vibration excited in the pressure chamber at the time of the first ejection of the droplet and the pressure wave vibration excited in the pressure chamber by its pre-operation, the pressure in the pressure chamber When １ ／ of the acoustic resonance period of the wave is AL, it is assumed that there is a phase shift of −0.6 AL or more and 0.6 AL or less,
At least one or more of the drive pulses for discharging the subsequent second droplets are used to change the volume of the pressure chamber to excite two or more overlapping pressure waves in the pressure chamber. A pressure wave vibration excited into the pressure chamber at the time of ejection of the droplet, and a pressure wave vibration excited into the pressure chamber by a pre-operation of the pressure wave, and the pressure chamber due to ejection of the first droplet. The synthetic vibration of the reverberant pressure wave vibration remaining in the drive waveform designing method is assumed to have a phase shift in a direction opposite to the phase shift at the time of discharging the first droplet.

  According to the present invention, it is possible to provide an ink jet recording apparatus capable of driving an ink jet head by a multi-drop method with a driving waveform having high robustness to an AL value and forming a high quality image.

  Further, according to the present invention, it is possible to provide a driving method of an ink jet head which can drive an ink jet head by a multi-drop method with a driving waveform having high robustness to an AL value and can form a high quality image.

  Further, according to the present invention, it is possible to provide a driving waveform designing method capable of designing a multi-drop driving waveform having high robustness to the AL value.

1 is a schematic configuration diagram illustrating an embodiment of an inkjet recording apparatus according to the present invention. It is a figure which shows one Embodiment of an inkjet head, (a) is the perspective view which shows an external appearance in cross section, (b) is sectional drawing seen from the side. FIG. 3 is a diagram illustrating an embodiment of a multi-drop drive waveform as a drive waveform generated in a drive control unit. FIGS. 7A to 7C are diagrams for explaining the operation of the inkjet head when a drive waveform is applied. FIG. 3 is a conceptual diagram of droplets ejected from a nozzle when the drive waveform shown in FIG. 3 is applied. A graph showing the vibration speed of the pressure wave vibration excited in the pressure chamber when a drive waveform outside the present invention is applied, (a) showing the whole state, and (b) showing the state focused on the second shot. FIG. 7 is a graph showing a rate of change of a droplet speed with respect to an AL value in a driving waveform outside the present invention. A graph showing the vibration speed of the pressure wave vibration excited in the pressure chamber when the drive waveform according to the present invention is applied, (a) showing the whole state, and (b) showing the state focused on the second shot. FIG. 7 is a graph showing a rate of change of a droplet speed with respect to an AL value in a driving waveform according to the present invention. (A) is a graph showing the change rate of the droplet speed with respect to the AL value when the pulse width of the second expansion pulse is changed, and (b) shows the droplet amount and droplet speed of the combined droplet at that time. Graph (A) is a graph showing the rate of change of the droplet speed with respect to the AL value when the pulse width of the first expansion pulse is changed, and (b) shows the amount and speed of the combined droplet at that time. Graph FIG. 7 is a diagram for explaining another embodiment of the drive waveform in the present invention. FIG. 12 is a graph showing the rate of change of the droplet speed with respect to the AL value according to the drive waveform shown in FIG. FIG. 6 is a diagram for explaining still another embodiment of the drive waveform in the present invention. Diagram for explaining the state of landing position shift due to multi-drop drive waveforms (A)-(c) is explanatory drawing explaining the robustness with respect to AL value in the drive waveform which made the expansion pulse 1.0AL. (A)-(c) is an explanatory view for explaining robustness with respect to an AL value in a drive waveform with an expansion pulse of 0.5AL. (A)-(c) is an explanatory view for explaining robustness with respect to an AL value in a drive waveform with an expansion pulse of 1.5AL.

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

(Inkjet recording device)
FIG. 1 is a schematic configuration diagram showing one embodiment of an ink jet recording apparatus according to the present invention.

  In the inkjet recording apparatus 1, the transport mechanism 2 sandwiches a recording medium 7 made of paper, a plastic sheet, a cloth, or the like by a transport roller pair 22, and rotates the transport roller 21 by a transport motor 23 in the Y direction (sub-scanning) in the drawing. Direction). An inkjet head (hereinafter, simply referred to as a head) 3 is provided between the transport roller 21 and the transport roller pair 22. The head 3 is mounted on the carriage 5 such that the nozzle surface faces the recording surface 71 of the recording medium 7, and is electrically connected to the drive control unit 8 via the flexible cable 6.

  In the present invention, the distance (gap) between the nozzle surface of the head 3 and the recording surface 71 of the recording medium 7 is preferably 2 mm or more, and more preferably 3 mm or more. By increasing the gap, the flight distance of the droplet increases, and the variation in the ejection characteristics of the droplet becomes noticeable. Therefore, the effect of suppressing the variation in the ejection characteristics by applying the present invention described later becomes more remarkable. It is because it becomes possible to obtain.

  The carriage 5 is moved by a drive unit (not shown) along a guide rail 4 spanned across the width of the recording medium 7 in the XX ′ direction (main scanning direction) substantially orthogonal to the sub-scanning direction. ) Is provided so as to be able to reciprocate. The head 3 according to the present embodiment moves the recording surface 71 of the recording medium 7 in the main scanning direction with the reciprocating movement of the carriage 5, and in the course of this movement, ejects droplets from nozzles according to image data. , A scan type head for recording an ink jet image. However, in the inkjet recording apparatus of the present invention, the head 3 is not limited to the scan type. Although not shown, the head 3 is formed in a long shape across the width direction of the recording medium 7 or a plurality of small heads are arranged in a staggered manner, so that the head 3 is conveyed at a constant speed. A line type that performs recording with one pass may be used.

  2A and 2B are diagrams showing an embodiment of the head 3, wherein FIG. 2A is a perspective view showing the appearance in cross section, and FIG. 2B is a cross-sectional view seen from the side.

  In the head 3, a large number of narrow grooves 31 and partition walls 32 are arranged on the substrate 30 so as to be alternately arranged. A cover plate 33 is provided on the upper surface of the substrate 30 so as to cover over all the channels 31. The nozzle plate 34 is joined to the end surfaces of the substrate 30 and the cover plate 33. One end of each channel 31 communicates with the outside via a nozzle 341 formed in the nozzle plate 34.

  The other end of each channel 31 is formed so as to gradually become shallow with respect to the substrate 30. A common channel 331 common to each channel 31 is formed in the cover plate 33, and the other end of each channel 31 communicates with the common channel 331. The common channel 331 is closed by the plate 35. An ink supply port 351 is formed in the plate 35, and ink is supplied from the ink supply pipe 352 into the common flow channel 331 and each channel 31 via the ink supply port 351.

  The partition 32 is made of a piezoelectric element such as PZT. The partition 32 is formed by a piezoelectric element in which an upper wall portion 321 and a lower wall portion 322 are polarized in directions opposite to each other. However, the portion formed by the piezoelectric element in the partition 32 may be, for example, only the upper wall portion 321. Since the partition walls 32 and the channels 31 are alternately juxtaposed, one partition wall 32 is shared by the adjacent channels 31, 31.

  Drive electrodes (not shown in FIG. 2) are formed on the inner surface of the channel 31 from the wall surfaces of the partition walls 32, 32 to the bottom surface. When a drive waveform of a predetermined voltage is applied from the drive control unit 8 to each of the two drive electrodes arranged with the partition wall 32 interposed therebetween, the partition wall 32 is separated from the joint surface between the upper wall portion 321 and the lower wall portion 322 by a boundary. Shear deformation to change the volume of the channel 31 sandwiched between the two partition walls 32. That is, when the partitions 32, 32 are deformed away from each other, the volume of the channel 31 is expanded, and when the partitions 32, 32 are deformed toward each other, the volume of the channel 31 is contracted. As a result, a pressure wave is generated inside the channel 31, and a pressure for discharging is applied to the ink in the channel 31.

  The head 3 is a shear mode type head that discharges the ink in the channel 31 from the nozzle 341 by the partition wall 32 being subjected to shear deformation, and is a preferred embodiment of the present invention. The shear mode head can discharge droplets efficiently by using a rectangular wave described later as a driving waveform.

  In the head 3, the channel 31, which is surrounded by the substrate 30, the partition 32, the cover plate 33, and the nozzle plate 34, constitutes a pressure chamber in the present invention. Further, the partition wall 32 made of the piezoelectric element and the drive electrode on the surface thereof constitute the pressure generating means in the present invention.

  The drive control unit 8 generates a drive waveform for discharging the droplet from the nozzle 341. The generated drive waveform is output to the head 3 and applied to each drive electrode formed on each partition 32. By using a multi-drop driving waveform having high robustness described below as the driving waveform, a high-quality image can be formed by the multi-drop method.

(Configuration of drive waveform)
Next, the configuration of the driving waveform of the multi-drop method will be described.

  FIG. 3 is a diagram illustrating an embodiment of a multi-drop drive waveform as a drive waveform generated by the drive control unit 8.

  The driving waveform 100 is a driving waveform for forming a large liquid droplet having a large liquid amount by discharging at least two liquid droplets from the same nozzle 341 of the head 3 and uniting them during flight. This drive waveform 100 is constituted by a plurality of drive pulses for expanding and contracting the volume of the channel 31. Specifically, the drive waveform 100 includes a first expansion pulse P1 that expands the volume of the channel 31 and contracts after a certain time, and a first expansion pulse P2 that contracts the volume of the channel 31 and expands after a certain time. And a second expansion pulse P3 that expands the volume of the channel 31 and contracts it after a certain time, and a second contraction pulse P4 that contracts the volume of the channel 31 and expands it after a certain time. .

  The first expansion pulse P1 of the drive waveform 100 according to the present embodiment is a pulse that rises from the reference potential and falls to the reference potential after a fixed time (pulse width W1). The first contraction pulse P2 is a pulse that falls from the reference potential and rises to the reference potential after a fixed time (pulse width W2). The second expansion pulse P3 is a pulse that rises from the reference potential and falls to the reference potential after a fixed time (pulse width W3). The second contraction pulse P4 is a pulse that falls from the reference potential and rises to the reference potential after a fixed time (pulse width W4). Here, the reference potential is set to 0 potential, but is not particularly limited.

  The first contraction pulse P2 is synchronized with the fall of the first expansion pulse P1. That is, the first contraction pulse P2 falls continuously without a pause from the end of the fall of the first expansion pulse P1. Further, the second expansion pulse P3 is synchronized with the rising of the first contraction pulse P2. That is, the second expansion pulse P3 continuously rises without a pause from the end of the rise of the first contraction pulse P2. Further, the second contraction pulse P4 is synchronized with the falling of the second expansion pulse P3. That is, the second contraction pulse P4 continuously rises without a pause from the end of the fall of the second expansion pulse P3.

  Next, the operation of the head 3 when the drive waveform 100 is applied will be described with reference to FIG. FIG. 4 shows a part of a cross section of the head 3 cut in a direction orthogonal to the length direction of the channel 31. Here, it is assumed that droplets are ejected from the central channel 31B in FIG. FIG. 5 is a conceptual diagram of droplets ejected from the nozzles when the drive waveform 100 is applied.

  First, from the neutral state of the partitions 32B and 32C shown in FIG. 4A, when the drive electrodes 36A and 36C are grounded and the first expansion pulse P1 of the drive waveform 100 is applied to the drive electrode 36B, the partition 32B , 32C are deformed outward as shown in FIG. 4 (b), and the volume of the channel 31B sandwiched between the partition walls 32B, 32C expands. As a result, a negative pressure wave is generated in the channel 31B, and the ink flows.

  When the application of the first expansion pulse P1 ends after a certain time, the volume of the channel 31B contracts from the expanded state, and the partition walls 32B and 32C return to the neutral state shown in FIG. When the first contraction pulse P2 is continuously applied without a pause after the completion of the application of the first expansion pulse P1, the volume of the channel 31B is suddenly changed to the contracted state shown in FIG. 4C. At this time, pressure is applied to the ink in the channel 31B, the ink is pushed out from the nozzle 341 and the first droplet is ejected.

  When the application of the first contraction pulse P2 ends after a predetermined time, the volume of the channel 31B expands from the contracted state, and the partition walls 32B and 32C return to the neutral state shown in FIG. After the application of the first contraction pulse P2, if the second expansion pulse P3 is continuously applied without a pause, the volume of the channel 31B is suddenly changed to the expanded state shown in FIG. A negative pressure wave is generated in 31. For this reason, the tail of the first droplet ejected earlier is pulled, and the droplet speed is suppressed. Further, the ink flows again due to the negative pressure wave generated in the channel 31B.

  When the application of the second expansion pulse P3 ends after a certain time, the volume of the channel 31B contracts from the expanded state, and the partition walls 32B and 32C return to the neutral state shown in FIG. After the application of the second expansion pulse P3, if the second contraction pulse P4 is continuously applied without a pause, the volume of the channel 31B will be in a contracted state shown in FIG. 4C at a stretch. At this time, a large pressure was applied to the ink in the channel 31B, and the ink was further extruded following the first droplet ejected by the first expansion pulse P1 and the first contraction pulse P2, and was eventually extruded. The second droplet having a high speed is discharged after the ink is broken.

  As shown in FIG. 5, the droplet ejected by the drive waveform 100 follows the first droplet D1 having a low droplet velocity by the first expansion pulse P1 and the first contraction pulse P2, A second droplet D2 having a high droplet speed is formed by the second expansion pulse P3 and the second contraction pulse P4. At the beginning of the ejection, the droplet D1 and the droplet D2 are in a continuous form. However, since the speed of the droplet D2 is sufficiently higher than that of the droplet D1, they are united during the flight immediately after the ejection. And land as one large droplet D.

  When the application of the second contraction pulse P4 ends after a predetermined time, the volume of the channel 31B expands from the contracted state, and the partition walls 32B and 32C return to the neutral state in FIG. The second contraction pulse P4 is a drive pulse for canceling the reverberation pressure wave vibration remaining in the channel 31B by the pre-operation (application of the first expansion pulse P1 to the second expansion pulse P3). As a result, the influence of reverberation pressure wave vibration on the subsequent droplet discharge operation can be suppressed, and the driving frequency can be improved. Therefore, the second contraction pulse P4 is preferably provided in the present invention.

  Each of the drive pulses P1 to P4 of the drive waveform 100 is constituted by a pulse having a positive (+ Von) or negative (-Voff) voltage value for expanding and contracting the volume of the channel 31 by changing the polarity. In this case, the voltage value + Von of the first expansion pulse P1 and the second expansion pulse P3 and the voltage value −Voff of the first contraction pulse P2 and the second contraction pulse P4 have the same value (| + Von | = | −Voff |). Since the voltage value can be made common, the circuit configuration of the drive control unit 8 can be simplified.

(Drive waveform design method)
Next, a design method for setting the pulse widths W1 to W4 of the respective drive pulses P1 to P4 of the drive waveform 100 will be described.

  First, before describing the present invention, as an example outside the present invention in which a design with high robustness is not performed, the pulse width of the drive waveform 100 is set to W1 = 0.6AL, W2 = 0.5AL, W3 = 1AL, W4 = 2AL will be described.

  FIG. 6 is a graph showing the vibration speed of the pressure wave vibration excited in the channel 31 when the driving waveform is applied. (A) shows the whole state, and (b) shows the state focused on the second shot. FIG. 7 is a graph showing the rate of change of the droplet speed with respect to the AL value according to the drive waveform.

  0.6 AL after the start of application of the first expansion pulse P1, the first contraction pulse P2 is applied, and when the first droplet is ejected, the pressure excited by the fall of the first contraction pulse P2 The phase of the wave vibration Pv2 is shifted earlier than the phase of the pressure wave vibration Pv1 excited by the rising (preliminary operation) of the first expansion pulse P1. At this time, the rate of change in velocity with respect to the AL value of the first droplet drops to the right similarly to the case of FIG. 17 and has a negative correlation.

  It should be noted that the pressure wave vibration Pv1 indicates only the pressure wave vibration excited in the channel 31 at the time of discharging the droplet, when the droplet is not discharged in the driving cycle before the discharging of the droplet. However, when droplet ejection is performed in a driving cycle before the droplet ejection, a combined oscillation with the pressure wave oscillation (residual pressure wave oscillation or the like) excited in the channel 31 by the previous droplet ejection is generated. Point.

  When the second expansion pulse P3 having a width of 1AL is applied 0.5AL after 0.5AL from the start of application of the first contraction pulse P2, the second expansion pulse P3 falls and the second droplet is ejected. 6B, the composite vibration Pvc of the pressure wave vibrations Pv1 and Pv2 and the pressure wave vibration Pv3 excited by the rise of the second expansion pulse P3 is the most negative (the inside of the channel 31 is as shown in FIG. 6B). (Most negative pressure). For this reason, the phase of the pressure wave vibration (second pressure wave vibration) Pv4 excited by the fall of the second expansion pulse P3 is shifted earlier than the phase of the synthetic vibration Pvc. At this time, the rate of change of the velocity of the second droplet with respect to the AL value also falls to the right similarly to the case of FIG. 17 and has a negative correlation.

  As a result, the velocity of the combined droplet of the first droplet and the second droplet has a rate of velocity change falling to the right as shown in FIG. Therefore, the drive waveform designed in this way has low robustness against variations in the AL value.

  Here, if the pulse width W1 of the first expansion pulse P1 in the drive waveform 100 remains unchanged at the 0.6 AL width, it is necessary to increase the robustness by adjusting the pulse width W3 of the second expansion pulse P3. . As a technique for adjusting the pulse width, the present inventor focused on the phase shift of the pressure wave vibration excited in the channel 31. As described above, the change in the droplet velocity with respect to the AL value has a positive or negative correlation depending on the mode of the phase shift of the pressure wave oscillation. The drive waveform of the above design has a negative correlation in both the first shot and the second shot. For this reason, if the AL value varies to the minus side from the design value, the first and second droplet speeds are both higher than the design value, and the combined droplet speed is further increased. Conversely, when the AL value varies to the plus side from the design value, the drop speed of the combined drops further decreases. That is, it is considered that the robustness of the drive waveform of the above design is low due to the strengthening of the negative correlation between the first shot and the second shot.

  Therefore, the present invention sets the pulse width W3 of the second expansion pulse P3 to a pulse width having an inverse correlation (positive correlation) complementary to the first correlation (negative correlation). By configuring, robustness is enhanced.

  As an example of the design having high robustness, a case where the pulse width of the drive waveform 100 is set to W1 = 0.6 AL, W2 = 0.5 AL, W3 = 1.6 AL, and W4 = 2AL will be described.

  FIG. 8 is a graph showing the vibration speed of the pressure wave vibration excited in the channel 31 when the above-mentioned drive waveform is applied. (A) shows the whole state, and (b) shows the state focused on the second shot. FIG. 9 is a graph showing the rate of change of the droplet speed with respect to the AL value according to the drive waveform.

  This is the same as above until the first droplet ejection by the first expansion pulse P1. Here, when a second expansion pulse P3 having a width of 1.6 AL is applied after 0.5 AL from the start of application of the first contraction pulse P2, the second expansion pulse P3 falls and the second shot is generated. As shown in FIG. 8B, the timing at which the droplet is discharged is a timing when the synthetic vibration Pvc is on the way to the positive peak. For this reason, the phase of the pressure wave vibration (second pressure wave vibration) Pv4 excited by the fall of the second expansion pulse P3 is opposite to the pressure wave vibration (first pressure wave vibration) Pv2. It has a phase shift in the direction, and is shifted in a direction slower than the phase of the synthetic vibration Pvc. At this time, the rate of change of the velocity of the second droplet with respect to the AL value rises to the right, and has a positive correlation that is inversely correlated with the first droplet. That is, the first shot and the second shot have a complementary relationship.

  As a result, the rate of change in velocity with respect to the AL value of the combined droplet of the first droplet and the second droplet is substantially flat as shown in FIG. Therefore, the driving waveform in this case has high robustness against the variation of the AL value.

  In the above example, W1 = 0.6AL, W2 = 0.5AL, and W3 = 1.6AL are set, but the pulse width W1 of the first expansion pulse P1 has a positive correlation or a negative correlation. , The pulse width W3 of the second expansion pulse P3 is set to have an inverse correlation. This makes it possible to design a driving waveform 100 having high robustness.

  In the present invention, the phase of the pressure wave vibration excited in the channel 31 when the first droplet is ejected does not match the phase of the pressure wave vibration excited in the channel 31 by the pre-operation. And a phase shift of −0.6 AL or more and 0.6 AL or less. Outside of this range, it is difficult to stably eject the first droplet.

  The pulse width W1 of the first expansion pulse P1 is not limited to 0.6 AL, and the same effect can be obtained if the pulse width is 0.4 AL or more and 0.8 AL or less or 1.2 AL or more and 1.6 AL or less. Confirmed by the inventor.

  Specifically, the pulse width W1 of the first expansion pulse P1 in the drive waveform 100 determines the liquid volume of the combined droplets. Therefore, when the liquid volume is set to be small, W1 = 0.4AL to 0.8AL, It is preferable that W2 = 0.5AL, and when a large amount of liquid is set, it is preferable that W1 = 1.2AL to 1.6AL and W2 = 0.5AL.

  When W1 = 0.4AL or more and 0.8AL or less and W2 = 0.5, the pulse width W3 of the second expansion pulse P3 is determined by the pressure wave vibration generated by the fall of the second expansion pulse P3 (two pulses). It is preferable that the phase shift of the eye pressure wave vibration) Pv4 with respect to the combined vibration Pvc is set to be 0 AL or more and 1.5 AL or less. Thereby, when the liquid amount is set to be relatively small, it is possible to obtain a driving waveform with higher robustness.

  Here, in FIG. 10A, the pulse width W1 of the first expansion pulse P1 is kept at 0.6AL, and the pulse width W3 of the second expansion pulse P3 is set to 1.0AL, 1.2AL, 1.4AL. 5 shows the rate of change of the droplet velocity with respect to the AL value when changing to 1.6 AL, 1.8 AL, and 2.0 AL. FIG. 10B shows the amount and speed of the combined drops at that time.

  As described above, when the pulse width W1 of the first expansion pulse P1 is set to 0.6AL, as the pulse width W3 of the second expansion pulse P3 changes, the gradient of the speed change rate graph also changes. Here, assuming that a range (± 10%) of 90% to 110% with respect to the target speed (100%) is an allowable value, the pulse width W3 of the second expansion pulse P3 exceeds 1. It can be seen that by setting it to 9AL or less, the slope of the graph becomes almost flat and falls within the range of the allowable value. Therefore, when the number of droplets is set to be small, a driving waveform having high robustness can be obtained. In this range, the second shot has a positive correlation with respect to the first negative correlation, and the first shot and the second shot have a complementary relationship with each other. In this range, the droplet amount and the droplet speed become substantially constant, and the variation in the ejection characteristics is suppressed.

  When W1 = 1.2AL or more and 1.6AL or less and W2 = 0.5, the pulse width W3 of the second expansion pulse P3 is determined by the pressure wave vibration ( It is preferable that the phase shift of the second pressure wave vibration) Pv4 with respect to the combined vibration Pvc is set to be −0.5 AL or more and 0 AL or less. Thereby, when the liquid amount is set to be relatively large, it is possible to obtain a driving waveform with higher robustness.

  Here, FIG. 11A shows that the pulse width W3 of the second expansion pulse P3 is 1.0AL and the pulse width W1 of the first expansion pulse P1 is 0.6AL, 0.8AL, 1.0AL, 1AL. 10 shows the rate of change of the velocity of the droplet with respect to the AL value when changing to .2AL, 1.6AL, and 1.8AL. FIG. 11B shows the amount and speed of the combined drops at that time.

  As described above, when the pulse width W3 of the second expansion pulse P3 is set to 1.0AL, as the pulse width W1 of the first expansion pulse P1 changes, the gradient of the speed change rate graph also changes. Here, assuming that a range (± 10%) of 90% to 110% with respect to the target speed (100%) is an allowable value, the pulse width W1 of the first expansion pulse P1 is 1.2 AL or more and 1.6 AL or less. By doing so, it can be seen that the slope of the graph is almost flat and falls within the range of the allowable value, and a driving waveform with high robustness can be obtained. In this range, the second shot has a negative correlation with respect to the first positive correlation, and the first shot and the second shot have a complementary relationship with each other.

  In addition, in this range, the droplet amount and the droplet speed increase as the pulse width W1 increases, and it can be seen that the droplet amount can be set to be large.

  The inventor has confirmed that the pulse width W3 of the second expansion pulse P3 at this time is not limited to 1.0 AL, and the same effect can be obtained if the pulse width is 0.8 AL or more and 1.1 AL or less. .

  By the way, in order to set the liquid amount and the droplet speed to desired values, there are cases where the pulse width W3 of the second expansion pulse P3 is not satisfied simply by setting the value to ensure the robustness. In this case, as shown in FIG. 12, after a pause time W5 having a width of 1AL is set from the fall of the second expansion pulse P3, a drive waveform 200 having a configuration in which a second contraction pulse P4 of W4 = 1AL is applied. It is preferred to use As a result, the discharge pressure generated by the falling of the second expansion pulse P3 can be reduced by the provision of the pause time W5.

  Here, the rate of change in velocity with respect to the AL value of the droplet when the drive waveform 200 set to W1 = 0.6AL, W2 = 0.5AL, W3 = 1.4AL, W4 = 1AL, and W5 = 1AL is shown. The graph is shown in FIG. It can be seen that the rate of change of the speed is almost flat, and the robustness is improved.

  It is also preferable that the drive waveform has the configuration shown in FIG. The drive waveform 300 has a third contraction pulse P5 for contracting the volume of the channel 31 at a fixed pause time W6 after the application of the second contraction pulse P4 is completed.

  The second contraction pulse P4 is synchronized with the falling of the second expansion pulse P3. That is, the second contraction pulse P4 continuously falls without a pause time from the end of the fall of the second expansion pulse P3. Then, the pulse width W4 of the second contraction pulse P4 is set to 0.5AL, and after the pause time W6 is set to 0.5AL, the third contraction pulse P5 having the pulse width W7 of 1AL is set. The reverberation pressure wave vibration in the channel 31 after the droplet is discharged can be more effectively canceled, and the droplet discharge of the multi-drop method can be continuously and stably performed.

  Each of the driving waveforms 100, 200, and 300 described above is constituted by a rectangular wave. In particular, the shear mode type head 3 easily controls the phase of the pressure wave vibration generated in the channel 31 in response to the application of the driving waveform composed of a rectangular wave. It is preferred to use waves. Further, since a rectangular wave can be easily created by using a simple digital circuit, the circuit configuration can be simplified as compared with a case where a trapezoidal wave having a ramp wave is used. Note that a rectangular wave refers to a waveform in which both the rise time and the fall time between 10% and 90% of the voltage are within 1/2, preferably 1/4 of AL.

  In addition, in the driving waveforms 100, 200, and 300 described above, a plurality of droplets are continuously ejected from the same nozzle 341 and the plurality of droplets are united during flight. The invention can be similarly applied to the case where the ink droplets land on the same pixel on the recording medium 7.

(Driving method of inkjet head)
The head 3 is driven by the drive waveform 100, 200 or 300 output from the drive control unit 8 to form an ink jet image on the recording medium 7. By setting the pulse width of each drive pulse of the drive waveforms 100, 200, and 300 as described above, multi-drop driving with high robustness to the AL value can be realized. Can be formed.

1: inkjet recording device 2: transport mechanism 21: transport roller 22: transport roller pair 23: transport motor 3: inkjet head 30: substrate 31: channel (pressure chamber)
32: partition wall (pressure generating means)
321: Upper wall part 322: Lower wall part 33: Cover plate 331: Common flow path 34: Nozzle plate 341: Nozzle 35: Plate 351: Ink supply port 352: Ink supply pipe 4: Guide rail 5: Carriage 6: Flexible cable 7: recording medium 71: recording surface 8: drive control unit 100, 200, 300: drive waveform D: droplet D1: first droplet D2: second droplet P1: first expansion pulse P2: First contraction pulse P3: Second contraction pulse P4: Second contraction pulse P5: Third contraction pulse Pv1 to Pv4: Pressure wave vibration Pvc: Synthetic vibration W1: Pulse width of first expansion pulse W2: No. 1 pulse width of the contraction pulse W3: pulse width of the second expansion pulse W4: pulse width of the second contraction pulse W5: pause time W6: pause time W7: third contraction Pulse of pulse width

Claims (23)

An ink jet head that varies the volume of the pressure chamber by driving the pressure generating means by applying a driving waveform, applies pressure to the liquid in the pressure chamber for discharge, and discharges a droplet from a nozzle;
A drive control unit that outputs the drive waveform to the pressure generating unit,
The drive control unit discharges the plurality of droplets from the nozzle by changing the volume of the pressure chamber a plurality of times, and a plurality of droplets for landing in the same pixel on the recording medium during flight. Outputting a driving waveform having a driving pulse;
At least one or more of the driving pulses for discharging the first droplet of the plurality of droplets are formed by changing the volume of the pressure chamber and causing two or more overlapping pressure waves in the pressure chamber. And the pressure wave vibration excited in the pressure chamber at the time of the first ejection of the droplet, and the pressure wave vibration excited in the pressure chamber by its pre-operation, the pressure wave in the pressure chamber When 1/2 of the acoustic resonance period is AL, the phase shift is from -0.6AL to 0.6AL,
At least one or more of the drive pulses for ejecting the subsequent second droplet ejects two or more overlapping pressure waves in the pressure chamber by changing the volume of the pressure chamber. A pressure wave vibration excited in the pressure chamber when the droplet is discharged, and a pressure wave vibration excited in the pressure chamber due to its pre-operation and remaining in the pressure chamber due to the first ejection of the droplet. The combined vibration of the reverberating pressure wave vibration and the ink jet recording apparatus having a phase shift in a direction opposite to the phase shift at the time of discharging the first droplet. The drive waveform is synchronized with a first expansion pulse for expanding the volume of the pressure chamber for a certain period of time and the end of application of the first expansion pulse as the drive pulse for discharging the first droplet. And a first contraction pulse that is applied to contract the volume of the pressure chamber for a certain period of time,
The pulse width of the first expansion pulse is 0.4 AL or more and 0.8 AL or less or 1.2 AL or more and 1.6 AL or less,
2. The ink jet recording apparatus according to claim 1, wherein a pulse width of the first contraction pulse is 0.5AL. The drive waveform has a second expansion pulse for expanding the volume of the pressure chamber for a certain period of time as the drive pulse for discharging the second droplet,
A combined vibration of the pressure wave vibration excited in the pressure chamber by the rising of the second expansion pulse and the reverberant pressure wave vibration remaining in the pressure chamber due to the first ejection of the droplet; When the pulse width of the first expansion pulse is 0.4 AL or more and 0.8 AL or less, the phase shift from the pressure wave vibration excited in the pressure chamber due to the fall of the expansion pulse is 0 AL or more and 1.5 AL or less. 3. The ink jet recording apparatus according to claim 2, wherein when the pulse width of the first expansion pulse is 1.2 AL or more and 1.6 AL or less, it is -0.5 AL or more and 0 AL or less. The pulse width of the first expansion pulse is 0.4 AL or more and 0.8 AL or less,
4. The ink jet recording apparatus according to claim 3, wherein a pulse width of the second expansion pulse is greater than 1.2 AL and equal to or less than 1.9 AL. The pulse width of the first expansion pulse is 1.2 AL or more and 1.6 AL or less,
4. The ink jet recording apparatus according to claim 3, wherein the pulse width of the second expansion pulse is 0.8 AL or more and 1.1 AL or less.   5. The driving waveform according to claim 3, wherein after the second expansion pulse, a second contraction pulse for contracting the volume of the pressure chamber for a certain period of time and canceling reverberant pressure wave vibration remaining in the pressure chamber is provided. Or the inkjet recording apparatus according to 5.   The ink jet recording apparatus according to claim 6, wherein the second contraction pulse is applied in synchronization with the end of the application of the second expansion pulse, and has a pulse width of 2AL.   7. The ink jet recording apparatus according to claim 6, wherein the second contraction pulse is applied with a pause of 1AL after the application of the second expansion pulse is completed, and has a pulse width of 1AL. The second contraction pulse is applied in synchronization with the end of the application of the second expansion pulse, has a pulse width of 0.5AL,
The drive waveform has a third contraction pulse having a pulse width of 1 AL which is applied after a pause of 0.5 AL after the application of the second contraction pulse is completed and contracts the volume of the pressure chamber for a certain period of time. An ink jet recording apparatus according to claim 6.   The inkjet recording apparatus according to claim 1, wherein the drive waveform is a rectangular wave.   The inkjet recording apparatus according to any one of claims 1 to 10, wherein the inkjet head is a shear mode type inkjet head in which the pressure generating unit is driven in a shear mode. By driving the pressure generating means of the ink jet head by applying a driving waveform, the volume of the pressure chamber is changed a plurality of times, a pressure for discharging is applied to the liquid in the pressure chamber, and a plurality of droplets are discharged from the nozzle. A method of driving an ink jet head that causes a droplet to land in the same pixel on a recording medium during flight.
As the drive waveform, using a plurality of drive pulses for discharging the plurality of droplets from the nozzle by changing the volume of the pressure chamber a plurality of times,
At least one or more of the driving pulses for discharging the first droplet of the plurality of droplets are applied to the pressure chamber by changing the volume of the pressure chamber to form two or more overlapping pressure waves. And the pressure wave vibration excited in the pressure chamber at the time of the first ejection of the droplet and the pressure wave vibration excited in the pressure chamber by its pre-operation, the pressure in the pressure chamber When １ ／ of the acoustic resonance period of the wave is AL, it is assumed that there is a phase shift of −0.6 AL or more and 0.6 AL or less,
At least one or more of the drive pulses for discharging the subsequent second droplet is used to change the volume of the pressure chamber to excite two or more overlapping pressure waves in the pressure chamber. A pressure wave vibration excited in the pressure chamber at the time of ejection of the droplet, and a pressure wave vibration excited into the pressure chamber by a preliminary operation of the pressure droplet, and the pressure chamber caused by ejection of the first droplet. The combined vibration of the reverberant pressure wave vibrations remaining in the inkjet head is a method of driving an ink jet head in which a phase shift in a direction opposite to the phase shift at the time of discharging the first droplet is performed. As a drive pulse for discharging the first droplet, a first expansion pulse for expanding the volume of the pressure chamber for a certain period of time, and a drive pulse applied in synchronization with the end of the application of the first expansion pulse, Using a first contraction pulse for contracting the volume of the pressure chamber for a certain time,
The pulse width of the first expansion pulse is 0.4 AL or more and 0.8 AL or less or 1.2 AL or more and 1.6 AL or less,
The method according to claim 12, wherein a pulse width of the first contraction pulse is 0.5AL. As a drive pulse for discharging the second droplet, a second expansion pulse for expanding the volume of the pressure chamber for a certain period of time is used.
A combined vibration of the pressure wave vibration excited in the pressure chamber by the rising of the second expansion pulse and the reverberant pressure wave vibration remaining in the pressure chamber due to the first ejection of the droplet; When the pulse width of the first expansion pulse is 0.4 AL or more and 0.8 AL or less, the phase shift from the pressure wave vibration excited in the pressure chamber due to the fall of the expansion pulse is 0 AL or more and 1.5 AL or less. 14. The method according to claim 13, wherein when the pulse width of the first expansion pulse is not less than 1.2 AL and not more than 1.6 AL, the pulse width is not less than -0.5 AL and not more than 0 AL. The pulse width of the first expansion pulse is 0.4AL or more and 0.8AL or less,
15. The ink jet head driving device according to claim 14, wherein a pulse width of the second expansion pulse is set to be larger than 1.2 AL and equal to or smaller than 1.9 AL. The pulse width of the first expansion pulse is set to 1.2 AL or more and 1.6 AL or less,
The driving apparatus of an ink jet head according to claim 14, wherein a pulse width of the second expansion pulse is set to 0.8 AL or more and 1.1 AL or less.   15. The method according to claim 14, wherein, after the second expansion pulse, a second contraction pulse that contracts the volume of the pressure chamber for a predetermined time and cancels reverberation pressure wave vibration excited in the pressure chamber is used as the drive waveform. 17. The method for driving an inkjet head according to 15 or 16.   The method according to claim 17, wherein the second contraction pulse is applied in synchronization with the end of the application of the second expansion pulse to have a pulse width of 2AL.   The method according to claim 17, wherein the second contraction pulse has a pulse width of 1AL, and is applied after a pause of 1AL after the application of the second expansion pulse is completed. The second contraction pulse has a pulse width of 0.5AL, and is applied in synchronization with the end of the application of the second expansion pulse;
A third contraction pulse having a pulse width of 1 AL for contracting the volume of the pressure chamber for a predetermined time as the driving waveform is applied after a pause of 0.5 AL after the application of the second contraction pulse is completed. Item 18. A method for driving an inkjet head according to Item 17.   21. The method according to claim 12, wherein the driving waveform is a rectangular wave.   22. The method of driving an ink jet head according to claim 12, wherein a shear mode ink jet head in which the pressure generating means drives in a shear mode is used as the ink jet head. By applying pressure to the pressure generating means of the ink jet head, the pressure generating means is driven, the volume of the pressure chamber is changed a plurality of times, and a plurality of droplets are ejected from the nozzles. A method for designing a drive waveform having a plurality of drive pulses for landing in a pixel,
At least one or more of the driving pulses for discharging the first droplet of the plurality of droplets are applied to the pressure chamber by changing the volume of the pressure chamber to form two or more overlapping pressure waves. And the pressure wave vibration excited in the pressure chamber at the time of the first ejection of the droplet and the pressure wave vibration excited in the pressure chamber by its pre-operation, the pressure in the pressure chamber When １ ／ of the acoustic resonance period of the wave is AL, it is assumed that there is a phase shift of −0.6 AL or more and 0.6 AL or less,
At least one or more of the drive pulses for discharging the subsequent second droplet is used to change the volume of the pressure chamber to excite two or more overlapping pressure waves in the pressure chamber. A pressure wave vibration excited in the pressure chamber at the time of ejection of the droplet, and a pressure wave vibration excited into the pressure chamber by a preliminary operation of the pressure droplet, and the pressure chamber caused by ejection of the first droplet. The synthetic vibration of the reverberant pressure wave vibration remaining in the drive waveform designing method is assumed to have a phase shift in a direction opposite to the phase shift at the time of discharging the first droplet.

Images