JP6497384B2 - Ink jet head driving method and ink jet recording apparatus - Google Patents

Description

  The present invention relates to an ink-jet head driving method and an ink-jet recording apparatus, and more specifically, even if a plurality of droplets are ejected within one pixel period to form a large dot on a medium, the generation of satellites can be suppressed. The present invention relates to an inkjet head driving method and an inkjet recording apparatus.

  When droplets are ejected from the nozzles of an inkjet head to form a large dot on the medium, multiple droplets are ejected from the same nozzle within one pixel period and merged during flight or overlap on the medium A method of landing is known. According to this method, light and shade can be expressed by selecting the number of droplets to be ejected within one pixel period, so that it is also used for gradation expression.

  Conventional techniques for ejecting a plurality of droplets from the same nozzle within one pixel period include those described in Patent Documents 1 to 3.

  In Patent Document 1, when applying one or more initial drive pulses according to gradation before the final drive pulse applied within one pixel period, the voltage value of each pulse is made constant, By making the application time longer or shorter than the final drive pulse, the droplet velocity discharged by each pulse is made the same, and the droplet velocity by the initial drive pulse is made slower than the droplet velocity by the final drive pulse. It is described that.

  In Patent Document 2, when one or more drive pulses corresponding to gradations are applied within one pixel period, the voltage value of each drive pulse is made constant, and final driving is performed with the maximum gradation waveform and other gradation waveforms. It is described that the pulse output timings are made to coincide with each other and a pause period of a predetermined interval is provided between pixel periods.

  In Patent Document 3, a plurality of ejection pulse signals and one auxiliary pulse signal for suppressing ink meniscus vibration are generated within one pixel period, and the number of ejection pulse signals is selected according to the gradation. It is described to do. Each discharge pulse signal has a constant voltage value, but the later the discharge pulse signal, the longer the pulse time interval approaches the natural period of the actuator, and the longer the droplet discharged later. The droplet velocity is increased so that a plurality of droplets are united during flight.

  Patent Document 4 discloses that a portion of the second drive signal is selected within a period of one pixel from a series of drive waveforms including drive signals having different first to third drive signals, and droplets are ejected. Then, the gradation expression is performed by selecting the first and third drive signal portions and discharging the middle droplet, and selecting the first to third drive signal portions and discharging the large droplet. Is described.

JP 2007-118278 A JP 2008-93950 A JP 2001-146011 A JP 2007-105936 A

  When a plurality of droplets are ejected within one pixel period to form as large a dot as possible on the medium, it is necessary to eject as many droplets as possible from the same nozzle within one pixel period.

  However, as the droplet volume increases, and when the droplet volume is large, satellite generation becomes a problem as the droplet velocity increases. The satellite is a small droplet (splash) that is formed as a secondary component behind the droplet (main droplet) ejected from the nozzle, which may cause a reduction in image quality.

  In Patent Documents 1 and 3, the droplet amounts of a plurality of droplets ejected from the same nozzle within one pixel period are the same. For this reason, if small droplets are continuously ejected, satellites can be suppressed, but the formation of large dots requires a large number of droplets to be ejected within one pixel period, resulting in reduced productivity. In addition, when large droplets are continuously ejected, the last ejected droplet is also a large droplet, and thus there is a problem that many satellites are generated by the final ejected droplet.

  Patent Document 2 aims to reduce the influence of residual vibration by putting a pause interval of a predetermined interval between pixel periods, but it is not sufficient for suppressing the occurrence of satellites.

  In Patent Document 4, there is no mention of suppressing the generation of satellites.

  As a result of intensive studies on a method for forming a dot as large as possible on a medium by ejecting a plurality of droplets within one pixel period, the present inventor combined a relatively large droplet and a relatively small droplet. In addition, by devising the relationship between the droplet velocities and the timing for ejecting relatively small droplets, it has been found that large dots can be formed on the medium and the generation of satellites can be suppressed. It came to.

  Further, the present inventors have found that the generation of satellites can be similarly suppressed when gradation expression is performed by changing the number of droplets discharged within one pixel period.

  That is, according to the present invention, even when a plurality of liquid droplets are ejected within one pixel period to form a large dot on a medium, the generation of satellites can be suppressed while suppressing a decrease in productivity and high quality. It is an object of the present invention to provide an ink jet head driving method and an ink jet recording apparatus that can perform image recording.

  In addition, the present invention can suppress the generation of satellites while suppressing a decrease in productivity when performing gradation expression by changing the number of droplets to be ejected within one pixel period. It is an object of the present invention to provide an inkjet head driving method and an inkjet recording apparatus that can perform image recording.

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

  In order to achieve at least one of the above-described objects, an inkjet head driving method reflecting one aspect of the present invention has the following configuration.

1.
In a driving method of an ink jet head that applies a pressure for discharging to a liquid in a pressure chamber by applying a driving signal to a pressure generating means, and discharges a droplet from a nozzle.
The drive signal includes at least two types of drive signals: a first drive signal for ejecting droplets and a second drive signal for ejecting large droplets at a relatively lower speed than the first drive signal. Including
In one pixel cycle, N second driving signals are applied, and at least lastly, the first driving signal is applied, whereby droplets are ejected from the same nozzle, and the liquid is discharged on the medium. is intended to form a pixel by dots of droplets, and wherein N is Ri 1 or more integer der,
The pressure generating means expands or contracts the volume of the pressure chamber by driving,
The first drive signal and the second drive signal include an expansion pulse that expands the volume of the pressure chamber and contracts after a certain time, and a contraction pulse that contracts the volume of the pressure chamber and expands after a certain time. Each of the first drive signal and the second drive signal applied to the pressure generating means corresponding to the same nozzle has a constant wave height of the expansion pulse, and the same The height of the contraction pulse of each of the first drive signal and the second drive signal applied to the pressure generating means corresponding to the nozzle is constant,
The second drive signal includes a first expansion pulse including the expansion pulse, a first contraction pulse including the contraction pulse, a second expansion pulse including the expansion pulse, and the contraction pulse in time series order. A second contraction pulse consisting of
The pulse width of the first expansion pulse in the second drive signal is 0.4 AL or more and 2.0 AL or less (where AL is 1/2 of the acoustic resonance period of the pressure wave in the pressure chamber),
The pulse width of the first contraction pulse is 0.4 AL or more and 0.7 AL or less,
The pulse width of the second expansion pulse is 0.8 AL or more and 1.2 AL or less,
The pulse width of the second contraction pulse driving method of ink jet head is characterized in der Rukoto more 2.2AL less 1.8AL.
2.
It said first drive signal, and the expansion pulse and the contraction pulse driving method of the one ink-jet head, wherein a and a pause period that connects between the expansion pulse and the contraction pulse.
3.
The pulse width of the expansion pulse in the first drive signal is not less than 0.8 AL and not more than 1.2 AL (where AL is 1/2 of the acoustic resonance period of the pressure wave in the pressure chamber),
The pulse width of the contraction pulse is 1.8 AL or more and 2.2 AL or less,
3. The method of driving an ink-jet head according to 2 , wherein the pause period is 1/4 AL or less.
4).
In a driving method of an ink jet head that applies a pressure for discharging to a liquid in a pressure chamber by applying a driving signal to a pressure generating means, and discharges a droplet from a nozzle.
The drive signal includes at least two types of drive signals: a first drive signal for ejecting droplets and a second drive signal for ejecting large droplets at a relatively lower speed than the first drive signal. Including
In one pixel cycle, N second driving signals are applied, and at least lastly, the first driving signal is applied, whereby droplets are ejected from the same nozzle, and the liquid is discharged on the medium. An ink jet head that forms pixels by dots made of droplets, and changes the N by an integer of 0 or more according to image data to create dots of different sizes on the medium, thereby expressing gradation Driving method ,
The distance between the nozzle surface of the inkjet head and the medium is L, the droplet velocity by the first drive signal is VA, the droplet amount is MA, the droplet velocity by the second drive signal is VB, When the drop volume is MB,
In the case of N ≧ 3, at least to the position away from the nozzle by (L × MA × VA) / (MB × VB), the droplet by the first driving signal and the second driving just before the droplet A method of driving an ink jet head, wherein a droplet formed by a signal does not form a combined droplet .
5).
5. The method of driving an inkjet head according to 1 or 4 , wherein a diameter of a droplet ejected by the first driving signal is smaller than a diameter of the nozzle.
6).
6. The method of driving an ink jet head according to 1, 4, or 5 , wherein a diameter of a droplet ejected by the second driving signal is larger than a diameter of the nozzle.
7).
7. The inkjet according to any one of 1 to 4 , wherein TA ≧ TB, where TA is a driving cycle of the first driving signal and TB is a driving cycle of the second driving signal. Head drive method.
8).
MA × 1.5 ≦ MB, where MA is the amount of droplets ejected by the first drive signal, and MB is the amount of droplets ejected by the second drive signal. The method of driving an ink jet head according to any one of the above items 1 , 4 to 7, wherein :
9.
The pressure generating means expands or contracts the volume of the pressure chamber by driving,
The first drive signal and the second drive signal include an expansion pulse that expands the volume of the pressure chamber and contracts after a certain time, and a contraction pulse that contracts the volume of the pressure chamber and expands after a certain time. Each of the first drive signal and the second drive signal applied to the pressure generating means corresponding to the same nozzle has a constant wave height of the expansion pulse, and the same Any of 4 to 8 above, wherein the height of the contraction pulse of each of the first drive signal and the second drive signal applied to the pressure generating means corresponding to the nozzle is constant. The inkjet head driving method described.
10.
10. The inkjet head driving method according to claim 9, wherein the first drive signal includes the expansion pulse, the contraction pulse, and a pause period connecting the expansion pulse and the contraction pulse.
11.
The pulse width of the expansion pulse in the first drive signal is not less than 0.8 AL and not more than 1.2 AL (where AL is 1/2 of the acoustic resonance period of the pressure wave in the pressure chamber),
The pulse width of the contraction pulse is 1.8 AL or more and 2.2 AL or less,
11. The method of driving an inkjet head according to 10 , wherein the pause period is ¼ AL or less.
12
The second drive signal includes a first expansion pulse including the expansion pulse, a first contraction pulse including the contraction pulse, a second expansion pulse including the expansion pulse, and the contraction pulse in time series order. A method for driving an ink-jet head according to the above-mentioned 9, 10 or 11 , characterized by comprising: a second contraction pulse comprising:
13.
The pulse width of the first expansion pulse in the second drive signal is 0.4 AL or more and 2.0 AL or less (where AL is 1/2 of the acoustic resonance period of the pressure wave in the pressure chamber),
The pulse width of the first contraction pulse is 0.4 AL or more and 0.7 AL or less,
The pulse width of the second expansion pulse is 0.8 AL or more and 1.2 AL or less,
13. The inkjet head driving method according to item 12, wherein a pulse width of the second contraction pulse is 1.8 AL or more and 2.2 AL or less.
14
When N ≧ 2, the first expansion pulses of the N second drive signals applied in one pixel period have different pulse widths, respectively . The inkjet head drive method according to any one of the above.
15.
15. The method of driving an ink jet head according to 14 , wherein the first expansion pulse is applied in the order of short pulse width within one pixel period.
16.
16. The method of driving an ink jet head according to any one of 1 to 15 , wherein each of the first drive signal and the second drive signal is a rectangular wave.
17.
Any of the above 1 to 16 , wherein the first drive signal is a drive signal for forming the smallest droplet among a plurality of drive signals arranged in time series within one pixel period. A method for driving an ink jet head according to claim 1.
18.
An inkjet head that applies a pressure for ejection to the liquid in the pressure chamber by driving the pressure generating means, and ejects droplets from the nozzle;
In an inkjet recording apparatus comprising: a drive control unit that outputs a drive signal for driving the pressure generation unit;
The drive signal includes at least two types of drive signals: a first drive signal for ejecting droplets and a second drive signal for ejecting large droplets at a relatively lower speed than the first drive signal. Including
The drive control means discharges droplets from the same nozzle by applying the N second drive signals and applying the first drive signal at the end at least in one pixel period. , which forms a pixel by dots of the droplets on the medium, and the N is Ri 1 or more integer der,
The pressure generating means expands or contracts the volume of the pressure chamber by driving,
The first drive signal and the second drive signal include an expansion pulse that expands the volume of the pressure chamber and contracts after a certain time, and a contraction pulse that contracts the volume of the pressure chamber and expands after a certain time. Each of the first drive signal and the second drive signal applied to the pressure generating means corresponding to the same nozzle has a constant wave height of the expansion pulse, and the same The height of the contraction pulse of each of the first drive signal and the second drive signal applied to the pressure generating means corresponding to the nozzle is constant,
The second drive signal includes a first expansion pulse composed of the expansion pulse, a first contraction pulse composed of the contraction pulse, a second expansion pulse composed of the expansion pulse, and a first expansion pulse composed of the contraction pulse. Two contraction pulses,
The pulse width of the first expansion pulse in the second drive signal is 0.4 AL or more and 2.0 AL or less (where AL is 1/2 of the acoustic resonance period of the pressure wave in the pressure chamber),
The pulse width of the first contraction pulse is 0.4 AL or more and 0.7 AL or less,
The pulse width of the second expansion pulse is 0.8 AL or more and 1.2 AL or less,
The pulse width of the second contraction pulse jet recording apparatus characterized der Rukoto more 2.2AL less 1.8AL.
19.
19. The inkjet recording apparatus according to claim 18, wherein the first drive signal includes the expansion pulse, the contraction pulse, and a pause period connecting the expansion pulse and the contraction pulse.
20.
The pulse width of the expansion pulse in the first drive signal is not less than 0.8 AL and not more than 1.2 AL (where AL is 1/2 of the acoustic resonance period of the pressure wave in the pressure chamber),
The pulse width of the contraction pulse is 1.8 AL or more and 2.2 AL or less,
20. The inkjet recording apparatus as described in 19 above, wherein the pause period is ¼ AL or less.
21.
An inkjet head that applies a pressure for ejection to the liquid in the pressure chamber by driving the pressure generating means, and ejects droplets from the nozzle;
In an inkjet recording apparatus comprising: a drive control unit that outputs a drive signal for driving the pressure generation unit;
The drive signal includes at least two types of drive signals: a first drive signal for ejecting droplets and a second drive signal for ejecting large droplets at a relatively lower speed than the first drive signal. Including
The drive control means discharges droplets from the same nozzle by applying the N second drive signals and applying the first drive signal at the end at least in one pixel period. The pixel is formed by dots formed of the droplets on the medium, and the N is changed by an integer of 0 or more according to the image data to create dots of different sizes on the medium. There line the tone representation,
The distance between the nozzle surface of the inkjet head and the medium is L, the droplet velocity by the first drive signal is VA, the droplet amount is MA, the droplet velocity by the second drive signal is VB, When the drop volume is MB,
In the case of N ≧ 3, at least to the position away from the nozzle by (L × MA × VA) / (MB × VB), the droplet by the first driving signal and the second driving just before the droplet An ink jet recording apparatus, wherein a droplet formed by a signal does not form a combined droplet .
22.
22. The inkjet recording apparatus according to item 18 or 21 , wherein a diameter of a droplet ejected by the first drive signal is smaller than a diameter of the nozzle.
23.
23. The ink jet recording apparatus according to claim 18 , wherein a diameter of a droplet ejected by the second drive signal is larger than a diameter of the nozzle.
24.
24. The inkjet according to any one of 18, 21 to 23 , wherein TA ≧ TB, where TA is a driving cycle of the first driving signal and TB is a driving cycle of the second driving signal. Recording device.
25.
MA × 1.5 ≦ MB, where MA is the amount of droplets ejected by the first drive signal, and MB is the amount of droplets ejected by the second drive signal. 25. The ink jet recording apparatus according to any one of the above items 18, 21 to 24 .
26.
The pressure generating means expands or contracts the volume of the pressure chamber by driving,
The first drive signal and the second drive signal include an expansion pulse that expands the volume of the pressure chamber and contracts after a certain time, and a contraction pulse that contracts the volume of the pressure chamber and expands after a certain time. Each of the first drive signal and the second drive signal applied to the pressure generating means corresponding to the same nozzle has a constant wave height of the expansion pulse, and the same Any one of the items 21 to 25 , wherein the heights of the contraction pulses of the first driving signal and the second driving signal applied to the pressure generating unit corresponding to the nozzle are constant. The ink jet recording apparatus described.
27.
27. The ink jet recording apparatus according to claim 26, wherein the first drive signal includes the expansion pulse, the contraction pulse, and a pause period connecting the expansion pulse and the contraction pulse.
28.
The pulse width of the expansion pulse in the first drive signal is not less than 0.8 AL and not more than 1.2 AL (where AL is 1/2 of the acoustic resonance period of the pressure wave in the pressure chamber),
The pulse width of the contraction pulse is 1.8 AL or more and 2.2 AL or less,
28. The inkjet recording apparatus as described in 27 above, wherein the pause period is ¼ AL or less.
29.
The second drive signal includes a first expansion pulse composed of the expansion pulse, a first contraction pulse composed of the contraction pulse, a second expansion pulse composed of the expansion pulse, and a first expansion pulse composed of the contraction pulse. 29. The inkjet recording apparatus according to 26 , 27, or 28 , comprising two contraction pulses.
30.
The pulse width of the first expansion pulse in the second drive signal is 0.4 AL or more and 2.0 AL or less (where AL is 1/2 of the acoustic resonance period of the pressure wave in the pressure chamber),
The pulse width of the first contraction pulse is 0.4 AL or more and 0.7 AL or less,
The pulse width of the second expansion pulse is 0.8 AL or more and 1.2 AL or less,
30. The ink jet recording apparatus according to 29, wherein a pulse width of the second contraction pulse is 1.8 AL or more and 2.2 AL or less.
31.
When N ≧ 2, the first expansion pulses of the N second drive signals applied in one pixel period have different pulse widths, respectively . An ink jet recording apparatus according to any one of the above.
32.
32. The ink jet recording apparatus according to 31 above, wherein the first expansion pulse is applied in ascending order of pulse width within one pixel period.
33.
33. The ink jet recording apparatus according to any one of 18 to 32 , wherein each of the first drive signal and the second drive signal is a rectangular wave.
34.
Any of the above-mentioned 18 to 33 , wherein the first drive signal is a drive signal for forming the smallest droplet among a plurality of drive signals arranged in time series within one pixel period. An ink jet recording apparatus according to claim 1.

  In the example of the first drive signal PA, a pause period PWA3 for maintaining a reference potential for a certain period is provided between the end of the expansion pulse Pa1 and the start of the contraction pulse Pa2. This is due to the relationship with the second drive signal PB, which will be described later, and avoids the droplet velocity from becoming too fast due to a sudden change in the volume of the channel 31 from the expanded state due to the expansion pulse Pa1 to the contracted state due to the contraction pulse Pa2. This is in order to avoid an excessive increase in the amount of discharged liquid droplets. By adjusting the length of the pause period PWA3, the speed and the amount of liquid droplets ejected by the application of the first drive signal PA can be adjusted to the droplets ejected by the second drive signal PB described later. Therefore, it can be easily adjusted. For this reason, this pause period PWA3 is preferably provided in the first drive signal PA.

  In the present invention, it is only necessary to always apply one first drive signal PA at least at the end of one pixel period T. Therefore, it prevents any one or more first drive signals PA from being applied in addition to the second drive signal PB before the first drive signal PA applied last in one pixel period T. It is not a thing. At this time, the first drive signal PA may be applied first in one pixel period T. In this case, for example, the pause period PWA3 of the first drive signal PA to be applied first is set as follows. It is preferable to improve the landing elasticity by setting the first drive signal PA to be applied last longer than the pause period PWA3 so that the speed of the first ejected droplet is decreased.

  The first drive signal PA is preferably a drive signal for forming the smallest droplet among a plurality of drive signals arranged in time series within one pixel period T. As a result, the effect of suppressing satellites can be further enhanced, and landing position deviation can also be suppressed.

  Furthermore, the first drive signal PA is a drive for forming a droplet having the smallest droplet speed and a fast droplet velocity among the plurality of drive signals arranged in time series within one pixel period T. The signal is preferable from the viewpoint of further enhancing the satellite suppressing effect and the landing position shift suppressing effect.

  The first drive signal PA is preferably a rectangular wave. That is, as shown in the drawing, the expansion pulse Pa1 and the contraction pulse Pa2 are both composed of rectangular waves. The shear mode type head 3 shown in the present embodiment can generate pressure waves with the same phase in response to the application of a drive signal composed of a rectangular wave. The drive voltage can be kept low. In general, a voltage is always applied to the head 3 regardless of whether it is ejected or not. Therefore, a low driving voltage is important for suppressing heat generation of the head 3 and ejecting droplets stably.

  In addition, since the rectangular wave can be easily generated by using a simple digital circuit, the circuit configuration can be simplified as compared with the case of using a trapezoidal wave having an inclined wave.

  The pulse width PWA1 of the expansion pulse Pa1 is preferably 0.8 AL to 1.2 AL, and the pulse width PWA2 of the contraction pulse Pa2 is preferably 1.8 AL to 2.2 AL. As a result, the droplets can be discharged efficiently. If the pause period PWA3 is too long, it becomes difficult to eject a droplet having a high droplet velocity relative to the droplet by the second drive signal PB, and the ejection efficiency is greatly reduced. It is preferable to adjust at / 4AL or less.

  Here, “AL” is an abbreviation for “Acoustic Length”, which is ½ of the acoustic resonance period of the pressure wave in the channel 31. AL measures the flying speed of a droplet discharged when a rectangular wave driving signal is applied to the driving electrode, and changes the pulse width of the rectangular wave while keeping the rectangular wave voltage value constant. It is determined as the pulse width that maximizes the droplet flight speed.

  A pulse is a rectangular wave having a constant voltage peak value. When 0V is 0% and a peak voltage is 100%, the pulse width is 10% of the voltage from 0V and the peak voltage. It is defined as the time between 10% of the falling edge.

  Furthermore, a rectangular wave refers to a waveform in which both the rise time and fall time between 10% and 90% of the voltage are within ½, preferably within ¼ of AL.

  Next, the configuration of the second drive signal PB will be described.

  Examples of the second drive signal PB include a first expansion pulse Pb1 that expands the volume of the channel 31 and contracts after a certain time, and a first contraction pulse Pb2 that contracts the volume of the channel 31 and expands after a certain time. And a second expansion pulse Pb3 that expands the volume of the channel 31 and contracts after a certain time, and a second contraction pulse Pb4 that contracts the volume of the channel 31 and expands after a certain time. .

  In the example shown in FIG. 4B, the first expansion pulse Pb1 is a pulse that rises from the reference potential and falls to the reference potential after a certain time. The first contraction pulse Pb2 is a pulse that falls from the reference potential and rises to the reference potential after a certain time. The second expansion pulse Pb3 is a pulse that rises from the reference potential and falls to the reference potential after a certain time. The second contraction pulse Pb4 is a pulse that falls from the reference potential and rises to the reference potential after a certain time. Here, the reference potential is set to 0 potential, but is not particularly limited.

  The drive voltage values (+ Von) of the first expansion pulse Pb1 and the second expansion pulse Pb3 and the drive voltage values (−Voff) of the first contraction pulse Pb2 and the second contraction pulse Pb4 are | Von |: | Voff | = 2: 1 is set.

  The first contraction pulse Pb2 continuously falls without any rest period from the end of the fall of the first expansion pulse Pb1. In addition, the second expansion pulse Pb3 rises continuously without any rest period from the end of the rise of the first contraction pulse Pb2. Furthermore, the second contraction pulse Pb4 falls continuously without any rest period from the end of the fall of the second expansion pulse Pb3.

  The second drive signal PB is also preferably a rectangular wave for the same reason as the first drive signal PA. As shown in the figure, the first expansion pulse Pb1, the first contraction pulse Pb2, the second expansion pulse Pb3, and the second contraction pulse Pb4 are composed of rectangular waves.

  In the second drive signal PB, the pulse width PWB1 of the first expansion pulse Pb1 is 0.4 AL or more and 2.0 AL or less, the pulse width PWB2 of the first contraction pulse Pb2 is 0.4 AL or more and 0.7 AL or less, the second The pulse width PWB3 of the expansion pulse Pb3 is preferably 0.8 AL or more and 1.2 AL or less, and the pulse width PWB4 of the second contraction pulse Pb4 is preferably 1.8 AL or more and 2.2 AL or less. As a result, large droplets can be ejected in a short driving cycle, and the droplet velocity can be suppressed. Accordingly, it is possible to eject a droplet having a large droplet amount at a relatively low speed as compared with the droplet based on the first drive signal PA.

  In addition, from the viewpoint of reducing the influence of satellites existing between a plurality of droplets, the rest period T1 is preferably 2AL or less, suppressing the influence of pressure wave reverberation vibration in the channel 31 after droplet discharge, From the viewpoint of stabilizing the subsequent droplet discharge, the pause period T2 is preferably 1.5 AL or more.

  Next, the ejection operation of the head 3 when the first drive signal PA and the second drive signal PB shown in FIG. 4 are applied will be described with reference to FIG. FIG. 5 shows a part of a cross section obtained by cutting the head 3 in a direction orthogonal to the length direction of the channel 31. Here, it is assumed that droplets are ejected from the center channel 31B in FIG. Further, FIG. 6 shows a conceptual diagram of droplets ejected when the first drive signal PA and the second drive signal PB are applied.

  First, the ejection operation using the first drive signal PA will be described.

  As shown in FIG. 5A, when no drive signal is applied to any of the drive electrodes 36A, 36B, 36C in the adjacent channels 31A, 31B, 31C, the partition walls 32A, 32B, 32C, 32D are deformed. Do not neutral. Then, when the drive electrodes 36A and 36C are grounded and the expansion pulse Pa1 in the first drive signal PA is applied to the drive electrode 36B, an electric field in a direction perpendicular to the polarization direction of the piezoelectric elements constituting the partition walls 32B and 32C is generated. . As a result, the partition walls 32B and 32C bend and deform toward each other as shown in FIG. 5B, and the volume of the channel 31B expands (Draw). As a result, negative pressure is generated in the channel 31B, and ink flows.

  Since the pressure in the channel 31B is reversed every 1 AL, if the expansion pulse Pa1 is maintained for a period of 0.8 AL or more and 1.2 AL or less, the channel 31B changes to a positive pressure. When the application of the expansion pulse Pa1 is finished at this timing and returned to the reference potential, the partition walls 32B and 32C return to the neutral state shown in FIG. 5A (Release). At this time, a large pressure is applied to the ink in the channel 31 </ b> B, and the ink moves in the direction pushed out from the nozzle 341.

  When the contraction pulse Pa2 is applied to the drive electrode 36B after maintaining the neutral state for the rest period PWA3, the partition walls 32B and 32C are bent and deformed inward toward each other as shown in FIG. Contracts (Reinforce). As a result, more pressure is applied to the ink in the channel 31B, and the ink moved in the direction pushed out from the nozzle 341 is further pushed out. Thereafter, the extruded ink is cut off and one droplet 100 is ejected as shown in FIG.

  The droplet 100 is a small droplet having a smaller droplet amount than a droplet by a second drive signal PB described later. When the droplet 100 is ejected, satellites are not generated or are suppressed to a very small amount even when they are generated.

  The contraction state caused by the contraction pulse Pa2 is restored when the pressure in the channel 31B changes to positive after 1.8A or more and 2.2AL or less have passed. As a result, the partition walls 32B and 32C return to the neutral state in FIG.

  Next, an ejection operation using the second drive signal PB will be described.

  When the drive electrodes 36A and 36C are grounded and the first expansion pulse Pb1 in the second drive signal PB is applied to the drive electrode 36B from the neutral state shown in FIG. 5A, the partition walls 32B and 32C become as shown in FIG. As shown in FIG. 5B, the channels 31B are expanded and deformed by bending toward each other. As a result, negative pressure is generated in the channel 31B, and ink flows.

  After the first expansion pulse Pb1 is maintained at 0.4 AL or more and 2.0 AL or less, application of the first expansion pulse Pb1 is finished. Thereby, the partition walls 32B and 32C contract from the expanded state and return to the neutral state. When the first contraction pulse Pb2 is subsequently applied without any rest period, the partition walls 32B and 32C immediately enter the contracted state shown in FIG. 5C through the neutral state. At this time, pressure is applied to the ink in the channel 31B, and the ink is pushed out from the nozzle 341 and ejected as a first droplet.

  The first contraction pulse Pb2 is maintained between 0.4 AL and 0.7 AL. Then, when the second expansion pulse Pb3 is applied without any rest period, the partition walls 32B and 32C expand from the contracted state and immediately enter the expanded state shown in FIG. Negative pressure is generated. For this reason, the speed of the first droplet ejected first is suppressed. As a result, negative pressure is generated in the channel 31B, and ink flows again.

  After the second expansion pulse Pb3 is maintained between 0.8 AL and 1.2 AL, the application ends when the inside of the channel 31B changes to a positive pressure. Then, when the second contraction pulse Pb4 is applied without any rest period, the partition walls 32B and 32C contract from the expanded state and immediately enter the contracted state shown in FIG. 5C through the neutral state. At this time, a large pressure is applied to the ink in the channel 31B, and the ink is further pushed out following the first droplet ejected by the first expansion pulse Pb1 and the first contraction pulse Pb2, and is eventually pushed out. The second ink droplet with a large droplet velocity is ejected.

  As shown in FIG. 6B, the droplet ejected by the second drive signal PB is the first one having a small droplet velocity ejected by the first expansion pulse Pb1 and the first contraction pulse Pb2. Subsequent to the first droplet 201, a second second droplet 202 having a high droplet velocity is formed by the second expansion pulse Pb3 and the second contraction pulse Pb4. For this reason, at the beginning of ejection, the first droplet 201 and the second droplet 202 become a droplet 200 that is continuous. The first droplet 201 and the second droplet 202 are integrated into a single large droplet 200 during the flight immediately after ejection.

  The droplet 200 is a large droplet having a larger droplet amount than the droplet 100 ejected by the first drive signal PA. However, since the first droplet 201 having a low droplet velocity and the second droplet 202 having a large droplet velocity are combined, compared with a case where one large droplet having the same droplet amount is ejected from the nozzle 341. The droplet velocity is reduced, and according to the present embodiment, the droplet velocity is lower than that of the droplet 100 ejected by the first drive signal PA. At this time, the droplet velocity of the droplet 100 ejected by the first drive signal PA is preferably adjusted to be smaller than the droplet velocity of the second droplet 202. The satellite amount of the droplet 200 depends on the droplet velocity of the second droplet 202, and the droplet velocity of the droplet 100 is adjusted to be smaller than the droplet velocity of the second droplet 202 by the second drive signal PB. Thus, the satellite amount of the droplet 100 can be suppressed.

  Note that the droplet velocity of the droplet 200 ejected by the second drive signal PB is a droplet velocity in a state where the first droplet 201 and the second droplet 202 are integrated.

  The contraction state by the second contraction pulse Pb4 is restored when the pressure in the channel 31B changes to positive after 1.8 AL or more and 2.2 AL or less has elapsed. As a result, the partition walls 32B and 32C expand from the contracted state and return to the neutral state.

  According to the driving method shown in FIG. 3, three large droplets 200 are output from the same nozzle 341 by first applying three second driving signals PB continuously in one pixel period T. Is discharged, and finally one first drive signal PA is applied, whereby one droplet 100 is discharged. Therefore, a pixel is formed on the medium 7 by dots composed of four droplets. It is formed.

  In the present embodiment, it is assumed that a 6 pl (picoliter) droplet 100 is ejected by the first drive signal PA and a 10 pl droplet 200 is ejected by the second drive signal PB. Therefore, in FIG. 3, a large dot composed of a total of 36 pl droplets in one pixel period T can be formed on the medium 7.

  If only four first drive signals PA are applied continuously, even if satellites can be suppressed, only dots composed of a total of 24 pl droplets can be formed. Further, in order to form dots composed of 36 pl droplets, it is necessary to apply six first drive signals PA in one pixel period T, so productivity is lowered. In addition, if only the second drive signal PB is continuously applied, the last ejected droplet is also a large droplet, so there is a concern about the generation of satellites. However, as in the present invention, one or more second drive signals PB are applied within one pixel period T, and at the end of a plurality of drive signals arranged in time series within the one pixel period T. Although the first drive signal PA is always applied, a large dot can be formed on the medium 7, but the droplet 100 consisting of the smallest droplet is always discharged at the end, thereby suppressing the decrease in productivity. However, the generation of satellites is suppressed.

  In general, a large droplet can also be ejected by using a drive signal having a DRR (Draw-Release-Reinforce) waveform similar to the first drive signal PA and increasing its pulse width. However, in this case, since the drive signal has a long period, many droplets cannot be ejected within a limited time within one pixel period T. However, since the second drive signal PB can eject a relatively low-speed large droplet 200 in a short cycle, more droplets are ejected within a limited time within one pixel cycle T. Accordingly, a pixel composed of large dots can be formed on the medium 7 accordingly.

  The deformation of the partition wall 32 occurs due to a voltage difference between two drive electrodes provided so as to sandwich the partition wall 32. Therefore, when ejection is performed from the channel 31B shown in FIG. 5 by the first drive signal PA, as shown in FIG. 7A, the + Von expansion pulse Pa1 is applied to the drive electrode 36B in the channel 31B as the ejection channel. Can be driven in the same manner by applying + Voff contraction pulse Pa2 to the drive electrodes 36A and 36C of the adjacent channels 31A and 31C.

  Similarly, when ejection is performed by the second drive signal PB from the channel 31B shown in FIG. 5, as shown in FIG. 7B, + Von is applied to the drive electrode 36B in the channel 31B as the ejection channel. A first expansion pulse Pb1 and a second expansion pulse Pb3 are applied, and a + Voff first contraction pulse Pb2 and a second contraction pulse Pb4 are applied to the drive electrodes 36A and 36C of the adjacent channels 31A and 31C. Can be driven similarly.

  When the first drive signal PA and the second drive signal PB shown in FIGS. 7A and 7B are used, each drive signal can be configured with only a positive voltage, and thus the configuration of the drive control unit 8 is simplified. be able to.

  In the present invention, it is preferable that the diameter of the droplet 100 ejected by the first drive signal PA is smaller than the diameter of the nozzle 341. By making the droplet 100 smaller in diameter than the nozzle 341, the satellite suppression effect can be further enhanced.

  Here, the diameter of the nozzle refers to the diameter when the shape of the opening at the tip of the discharge direction of the nozzle is circular, and when not, it is the diameter of the circle when the area of the opening is replaced with the same circle. .

  The diameter of the droplet refers to the diameter when the droplet is spherical, and when the droplet is not spherical, the diameter of the sphere when the volume is replaced with the same sphere.

  On the other hand, it is preferable that the diameter of the droplet 200 ejected by the second drive signal PB is larger than the diameter of the nozzle 341. By making the droplet 200 larger in diameter than the diameter of the nozzle 341, it is possible to form as large a dot as possible on the medium 7.

  The diameter of the droplet 200 ejected by the second drive signal PB is a diameter in a state where the first droplet 201 and the second droplet 202 are integrated into one large droplet. .

  Of course, the diameter of the droplet 100 ejected by the first drive signal PA is smaller than the diameter of the nozzle 341, and the diameter of the droplet 200 ejected by the second drive signal PB is larger than the diameter of the nozzle 341. It is more preferable that it is large.

  Further, when the droplet amount of the droplet 100 ejected by the first drive signal PA is MA and the droplet amount of the droplet 200 ejected by the second drive signal PB is MB, MA × 1.5. It is preferable that ≦ MB. Thereby, it is possible to form pixels composed of as large dots as possible on the medium 7 while effectively suppressing satellites.

  By the way, in general, in the shear mode type head 3 in which the partition wall 32 is shared by the adjacent channels 31, when one channel 31 is driven for ejection, the adjacent channels 31, 31 cannot perform ejection. . For this reason, it is known to use an independent drive type head in which ejection channels for ejecting droplets and dummy channels for not ejecting droplets are alternately arranged. When the head 3 is such an independent drive type head, there is a possibility that the discharge channel may discharge in all the pixel periods T, and therefore the pixel period T for forming pixels may be continuous.

  At this time, the drive cycle TA of the first drive signal PA and the drive cycle TB of the second drive signal PB within one pixel cycle T are used for expressing the gradation described later on the medium 7 while suppressing satellites. TA = TB can be set, but TA ≧ TB is preferable. Since the large droplet 200 by the second drive signal PB is relatively slow, by setting TA ≧ TB, for example, when it is desired to form a dot as large as possible at the time of dark gradation, one pixel cycle T A large number of large droplets 200 by the second drive signal PB can be produced in a short time at a high speed.

  Further, as shown in FIG. 3, the respective expansion pulses (expansion pulse Pa1, first pulse) of the first drive signal PA and the second drive signal PB applied to the drive electrodes of the channel 31 corresponding to the same nozzle 341. The expansion pulse Pb1 and the second expansion pulse Pb3) have a constant wave height, and the first drive signal PA and the second drive signal applied to the drive electrodes of the channel 31 corresponding to the same nozzle 341. It is preferable that each PB contraction pulse (contraction pulse Pa2, first contraction pulse Pb2, second contraction pulse Pb4) also has a constant wave height. Since the voltage value of the expansion pulse and the voltage value of the contraction pulse of the drive signals PA and PB can be made constant, the configuration of the drive control unit 8 can be further simplified.

  When the number N of second drive signals PB applied within one pixel period T is N ≧ 2, the droplets 200 ejected by each second drive signal PB may have the same speed, It may be a different speed.

  FIG. 8 shows, as an example, when N = 3 shown in FIG. 3, the droplets 100 and 200 when the droplets 200 ejected from the same nozzle 341 by the plurality of second drive signals PB have the same speed. The plan view of the flying state with the passage of time and the dots D formed on the medium 7 thereby.

  When each droplet 200 is set to the same speed, as shown in FIG. 8A, the three droplets 200 ejected continuously within one pixel period T fly at a constant velocity. When the final droplet 100 is ejected by the first drive signal PA, the droplet 100 catches up and coalesces because it is faster than the droplet 200 ejected immediately before. Further, since the discharged droplets are subjected to air resistance during the flight and decelerate, the combined droplets further catch up with the immediately preceding droplet 200 and coalesce, so that all the droplets 100 and 200 during the flight. Unite. As a result, a pixel composed of dots D by one droplet shown in FIG. 8B is formed on the medium 7. Since all the droplets 100 and 200 land after coalescence, it is possible to form highly accurate dots D with no landing position deviation.

  Further, the droplet velocity of the droplet 200 by the second drive signal PB can be adjusted by the pulse width PWB1 of the first expansion pulse Pb1. Therefore, when the droplet velocity of the droplet 200 ejected by each second drive signal PB is made different, this can be done by adjusting the pulse width PWB1 of the first expansion pulse Pb1. In the present embodiment, as a preferable range of the pulse width PWB1, a range of 0.4 AL or more and 2.0 AL or less is illustrated, and thus the length of the pulse width PWB1 is adjusted within this range.

  At this time, it is preferable to apply the second drive signal PB in order of decreasing pulse width PWB1 of the first expansion pulse Pb1 within one pixel period T. Since each droplet 200 ejected thereby has a higher speed as the droplet 200 ejected later, it is effective when the droplets 200 are surely united during flight.

  FIG. 9 shows, as an example, when N = 3 shown in FIG. 3, each droplet 200 ejected from the same nozzle 341 by a plurality of second drive signals PB is about as fast as the droplet 200 ejected later. 3 is a plan view of the flying state of the droplets 100 and 200 with the passage of time and the dots D formed on the medium 7 by the time when the droplets are made faster.

  In this case, as shown in FIG. 9A, three droplets 200 continuously ejected within one pixel period T are united during flight to form a unitary droplet, and finally the first All the droplets 100 and 200 are united during flight by catching up and uniting the final droplet 100 by the drive signal PA. As a result, the dot D by one droplet shown in FIG. 9B is formed on the medium 7. Also in this case, since all the droplets 100 and 200 land after coalescence, it is possible to form highly accurate dots D with no landing position deviation.

  On the other hand, within one pixel period T, the second drive signal PB can be applied in the order of increasing pulse width PWB1 of the first expansion pulse Pb1 of the second drive signal PB, that is, in order of increasing droplet velocity.

  FIG. 10 shows, as an example, when N = 3 shown in FIG. 3, each droplet 200 ejected from the same nozzle 341 by a plurality of second drive signals PB is about as fast as the droplet 200 ejected earlier. 3 is a plan view of the flying state of the droplets 100 and 200 with the passage of time and the dots D formed on the medium 7 by the time when the droplets are made faster.

  In this case, as shown in FIG. 10A, the droplet 100 by the first drive signal PA is combined with the droplet 200 discharged immediately before to form a combined droplet, as shown in FIG. As shown in b), a pixel composed of one dot D in which a plurality of dots overlap on the medium 7 is formed. This is because the energy of the last discharged droplet 100 is lost at an early stage after discharge.

  As will be described later, the dot D as shown in FIG. 10B is used in a case where gradation expression is performed by changing the droplet amount (number of droplets) discharged within one pixel period T. Although there is a concern that the landing position slightly shifts every time, the image quality is not greatly affected. In addition, there is no effect in applications where only a large dot is used to increase the coating amount as in the case of recording a solid image.

  Next, a case where gradation expression is performed in the present invention will be described.

  In the present invention, gradation representation is performed by applying N second drive signals PB within one pixel period T, and applying the first drive signal PA at least last, from the same nozzle 341. A droplet is ejected to form a pixel composed of a droplet on the medium 7, and the number N of second drive signals PB applied is changed by an integer of 0 or more according to image data. This can be done by creating dots of different sizes on the media 7 and forming pixels with dots of various sizes on the media 7.

  As a result, even when gradation expression is performed by changing the number of droplets to be ejected within one pixel period T, it is possible to suppress the occurrence of satellites and suppress the landing position deviation while suppressing the decrease in productivity. The inkjet head 3 driving method and the inkjet recording apparatus 1 that can perform high-quality image recording can be provided. Further, since it is only necessary to change the number N of second drive signals PB applied within one pixel period T, gradation can be expressed easily.

  FIG. 11 shows an example of a driving method according to the present invention in the case where gradation expression is performed using the first driving signal PA and the second driving signal PB described above. Here, by changing the number of second drive signals PB applied within one pixel period T from 0 (N = 0) to a maximum of 4 (N = 4), Level 0 (minimum gradation) to Level 5 In this example, six levels of gradation (maximum gradation) are expressed. Level 0 is when no drive signal is applied.

  Each drive signal group expressing gradations of Level 1 to Level 5 can be stored in advance in the drive control unit 8 in association with each gradation. The drive control unit 8 selects a desired gradation in accordance with the image data, and applies it to the head 3 by calling a corresponding drive signal group.

  When performing gradation expression, except for Level 0 where no drive signal is applied, Level 1 to Level 5 include those that do not apply the second drive signal PB (N = 0), but Level 1 to Level 5 In any gradation, the first drive signal PA is always applied at the end of one pixel period T. For this reason, the satellite is suppressed as described above in any gradation of Level 1 to Level 5. Note that the first drive signal PA to be applied last is applied so as to be at the same timing within one pixel period T in any gradation of Level 1 to Level 5.

  Here, it is also assumed that a 6 pl droplet 100 is ejected by the first drive signal PA and a 10 pl droplet 200 is ejected by the second drive signal PB. Therefore, Level 1 = 6 pl, Level 2 = 16 pl, Level 3 = 26 pl, Level 4 = 36 pl, Level 5 = 46 pl, and a wide gradation can be expressed while ensuring the minimum liquid amount (6 pl) by the first drive signal PA. .

By the way, when the gradation expression is performed by changing the number of droplets ejected in one pixel period T in this way, the landing position deviation for each gradation becomes a problem. This is because the droplet velocity changes depending on the timing at which the discharged droplets merge. In particular, when the droplet 100 ejected by the first drive signal PA and the droplet 200 ejected by the second drive signal PB come together during flight, the energy of the droplet 100 is lost, and the liquid Affects drop speed. This is because the droplet 200 is relatively larger than the droplet 100. Therefore, there is a possibility that the landing position is slightly different between the case where only one droplet 100 is ejected and the case where a plurality of droplets 200 are ejected in addition to the droplet 100.

  When the droplet velocity of the droplet 100 by the first drive signal PA is VA, the droplet amount is MA, the droplet velocity of the droplet 200 by the second drive signal PB is VB, and the droplet amount is MB. The effect of the temporary break depends on the ratio of the momentum of the large droplet to the small droplet (MA × VA) / (MB × VB), and the impact on the landing is the gap to the media 7 (the nozzle surface of the head 3) Depends on the distance L between the surface of the media 7. Further, when the number N of the second drive signals PB increases and N ≧ 3, the final number of coalescence tends to increase, so that the problem of landing position deviation becomes more significant than others.

  Therefore, when the number N of second drive signals PB applied within one pixel period T is N ≧ 3, at least the position away from the nozzle by (MA × VA) / (MB × VB) × L. The droplet 100 by the first drive signal PA applied at the end of one pixel period T and the droplet 200 by the second drive signal PB applied immediately before the droplet do not form a combined droplet. Is preferred. That is, the droplet 100 and the droplet 200 are merged after passing a position (MA × VA) / (MB × VB) × L away from the nozzle, or land on the medium 7 so as to overlap.

  Thereby, landing position deviation for each gradation can be suppressed. Further, since it is not necessary to increase the speed of the last droplet 100 discharged in one pixel period T more than necessary, the generation of satellites can be further suppressed.

  In the above description, the head 3 is exemplified by shearing the partition wall 32 between the adjacent channels 31, 31, but the upper wall or lower wall of the channel is a pressure generating means configured by a piezoelectric element such as PZT, The upper wall or the lower wall may be subjected to shear deformation.

  In addition, the ink jet head in the present invention is not limited to the shear mode type. For example, an ink jet of a type in which one wall surface of a pressure chamber is formed by a vibration plate, and the vibration plate is vibrated by a pressure generating means constituted by a piezoelectric element such as PZT, and pressure for ejection is applied to ink in the pressure chamber. It may be a head.

  Examples of the present invention will be described below, but the present invention is not limited to these examples.

Example 1
A shear mode type ink jet head (nozzle diameter = 24 μm, AL = 3.7 μs) shown in FIG. 2 was prepared. As the ink, UV curable ink was used at 40 ° C. The viscosity of the ink at this time was 0.01 Pa · s. Inkjet paper was used for the media, and the gap L between the media surface and the nozzle surface was 1.5 mm.

  The first driving waveform PA having the rectangular wave shown in FIG. 4A is used as the first driving waveform, and the second driving waveform PB having the rectangular wave shown in FIG. 4B is used as the second driving waveform. . Each pulse width and driving cycle were as follows.

<First drive waveform PA>
The pulse width PWA1 of the expansion pulse Pa1 = 3.7 μs (1AL)
Pulse width PWA2 of contraction pulse Pa2 = 7.4 μs (2AL)
Drive cycle TA = 26μs (7AL)
A pause period PWA3 of 0.5 μs (1/4 AL or less) was provided between the expansion pulse Pa1 and the contraction pulse Pa2.

<Second drive waveform PB>
Pulse width PWB1 of the first expansion pulse Pb1 = 2.4 μs (0.65 AL)
Pulse width PWB2 of the first contraction pulse Pb2 = 1.8 μs (0.5 AL)
Pulse width PWB3 of the second expansion pulse Pb3 = 3.7 μs (1AL)
Pulse width PWB4 of second contraction pulse Pb4 = 7.4 μs (2AL)
Drive cycle TB = 18.5μs (5AL)

  The reference potential of the first drive signal PA and the second drive signal PB is 0 potential, the voltage value (| Von |) of the expansion pulses (Pa1, Pb1, Pb3) is 11V, and the contraction pulses (Pa2, Pb2, Pb4). Voltage value (| Voff |) of 5.5V was constant.

  As in FIG. 3, the number N of the second drive signals PB in one pixel period T is set to N = 3, and finally, one first drive signal PA is applied, and three large droplets and 1 Small droplets were continuously discharged.

  The droplet speed of the droplets ejected by the first drive signal PA is 6 m / s, and the droplet velocities of the three droplets ejected by the second drive signal PB are all the same at 5 m / s. It was. The droplet amount of one droplet ejected by the first drive signal PA is 6 pl (diameter 22.5 μm), and the droplet amount of three droplets ejected by the second drive signal PB is Each of them was 10 pl (diameter 26.5 μm).

  When satellites are generated in the ejected droplets, splashes resulting from the satellite droplets are formed around the dots. Therefore, the dots on the media were observed with a microscope, and the state of satellite generation was evaluated according to the following criteria. The results are shown in Table 1.

A: No satellite is generated.
○: Slight satellites are generated, but the image quality is not affected at all.
Δ: A level at which the image quality is slightly affected by the satellite.
×: Many satellites are generated and the image quality is affected.

  In addition, the dots formed on the medium were observed with a microscope, and the occurrence of landing position deviation was evaluated according to the following criteria. The results are shown in Table 1.

(Double-circle): There was no landing position shift | offset | difference at all and the highly accurate pixel was formed.
○: The landing position is slightly shifted, but the image quality is not affected at all.
Δ: There is a landing position shift, and the image quality is slightly affected.
×: A level at which a large landing position shift occurs and the image quality is affected.

(Comparative Example 1)
As shown in FIG. 12A, the first drive signal PA is not applied within one pixel period T, and only the second drive signal PB is continuously applied, and the same as in the first embodiment. Similarly, the occurrence of satellites and landing position deviation were evaluated. The results are shown in Table 1.

(Comparative Example 2)
As shown in FIG. 12B, the timing of applying the first drive signal PA within one pixel period T is incremented by one, and the second drive signal PB is finally applied. Similarly, the situation of satellite occurrence and the occurrence of landing position deviation were evaluated. The results are shown in Table 1.

(Comparative Example 3)
The same as in Example 1 except that the pause period PWA3 between the expansion pulse Pa1 and the contraction pulse Pa2 in the first drive signal PA is 1.2 μs (1/4 AL or more). The state of occurrence of deviation was evaluated.

  At this time, the last droplet ejected is a droplet (6 pl) smaller than the droplet ejected by the second drive signal PB as in the first embodiment, but the pause period PWA3 is set longer. As a result, the droplet velocity became 4.5 m / s, which was slower than the droplets ejected by the second drive signal PB. The results are shown in Table 1.

(Example 2)
By setting the pulse PWA1 of the expansion pulse Pa1 in the first drive signal PA to 5.6 μs (1.5 AL) and the pulse width PWA of the contraction pulse Pa2 to 11.2 μs (3 AL), 1 according to the first drive signal PA The droplet volume of each droplet was 8 pl (diameter 25 μm), and was the same as in Example 1 except that the droplet diameter was larger than the nozzle diameter (24 μm). Similarly, the satellite generation status and landing position deviation The occurrence situation was evaluated. The results are shown in Table 1.

(Example 3)
By setting each pulse width PWB1 of the first expansion pulse Pb1 in the three second drive waveforms PB to 2.2 μs, 2.4 μs, and 2.6 μs in the order in which they are applied within one pixel period T, In the same manner as in Example 1 except that the droplet velocity was increased as the number of droplets increased, the satellite generation state and the landing position deviation generation state were similarly evaluated. The results are shown in Table 1.

  The droplet speeds of the droplets ejected by the three second drive signals PB were 4.5 m / s, 5.0 m / s, and 5.5 m / s in order. In addition, the droplet amounts of the droplets ejected by the three second drive signals PB were 9.5 pl (diameter 26 μm), 10 pl (diameter 26.5 μm), and 10.5 pl (diameter 26 μm) in this order. It was.

Example 4
By setting each pulse width PWB1 of the first expansion pulse Pb1 in the three second drive waveforms PB to 2.6 μs, 2.4 μs, and 2.2 μs in the order in which they are applied within one pixel period T, In the same manner as in Example 1 except that the droplet velocity was decreased as the number of droplets increased, the satellite generation state and the landing position deviation generation state were similarly evaluated. The results are shown in Table 1.

  Note that the droplet velocities of the droplets ejected by the three second drive signals PB were 5.5 m / s, 5.0 m / s, and 4.5 m / s in order. In addition, the droplet amounts of the droplets ejected by the three second drive signals PB were 10.5 pl (diameter 27 μm), 10 pl (diameter 26.5 μm), and 9.5 pl (diameter 26 μm) in this order. It was.

(Example 5)
In the third embodiment, when the number N of the second drive signals PB is N = 3, the maximum gradation is obtained, and the number N in one pixel period T is decreased by one to increase N = 2, N = 1, N Gradation driving using four levels with = 0 was performed, and an experiment for confirming the landing position deviation between gradations and the satellite of each gradation dot was performed. The results are shown in Table 1.

  In this embodiment, the droplet volume MA of the first drive signal PA = 6 pl, the droplet velocity VA = 6 m / s, and the droplet volume MB of the second drive signal PB = 10.5 pl. Since the droplet velocity VB = 5.5 m / s and the gap L between the media surface and the nozzle surface L = 1.5 mm, (L × MA × VA) / (MB × VB) is 0.94 mm. Become.

  As a result of observation by the droplet observation device, a droplet generated by the first drive signal PA applied at the end of one pixel period T and a droplet generated by the second drive signal PB applied immediately before the droplet are output from the nozzle. It was confirmed that a single drop was not formed at a position separated by 0.94 mm.

  The results of satellite and landing position deviation are shown in Table 1. In this example, no landing position deviation was observed between gradations, and a good image was obtained.

1: Inkjet recording apparatus 2: Transport mechanism 21: Transport roller 22: Transport roller pair 23: Transport motor 3: Inkjet head 30: Channel substrate 31: Channel 32: Partition wall 321: Upper wall portion 322: Lower wall portion 33: Cover substrate 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: Media 71: Recording surface 8: Drive control unit 100: Droplet 200: Droplet 201: Small liquid ball 202: Large liquid ball D: Dot PA: First drive signal Pa1: Expansion pulse Pa2: Contraction pulse PWA1, PWA2: Pulse width PWA3: Rest period PB: Second drive Signal Pb1: First expansion pulse Pb2: First contraction pulse Pb3: First 2 expansion pulses Pb4: second contraction pulses PWB1 to PWB4: pulse width T: pixel period TA: first drive signal drive period TB: second drive signal drive period T1, T2: pause period

Claims (34)

In a driving method of an ink jet head that applies a pressure for discharging to a liquid in a pressure chamber by applying a driving signal to a pressure generating means, and discharges a droplet from a nozzle.
The drive signal includes at least two types of drive signals: a first drive signal for ejecting droplets and a second drive signal for ejecting large droplets at a relatively lower speed than the first drive signal. Including
In one pixel cycle, N second driving signals are applied, and at least lastly, the first driving signal is applied, whereby droplets are ejected from the same nozzle, and the liquid is discharged on the medium. is intended to form a pixel by dots of droplets, and wherein N is Ri 1 or more integer der,
The pressure generating means expands or contracts the volume of the pressure chamber by driving,
The first drive signal and the second drive signal include an expansion pulse that expands the volume of the pressure chamber and contracts after a certain time, and a contraction pulse that contracts the volume of the pressure chamber and expands after a certain time. Each of the first drive signal and the second drive signal applied to the pressure generating means corresponding to the same nozzle has a constant wave height of the expansion pulse, and the same The height of the contraction pulse of each of the first drive signal and the second drive signal applied to the pressure generating means corresponding to the nozzle is constant,
The second drive signal includes a first expansion pulse including the expansion pulse, a first contraction pulse including the contraction pulse, a second expansion pulse including the expansion pulse, and the contraction pulse in time series order. A second contraction pulse consisting of
The pulse width of the first expansion pulse in the second drive signal is 0.4 AL or more and 2.0 AL or less (where AL is 1/2 of the acoustic resonance period of the pressure wave in the pressure chamber),
The pulse width of the first contraction pulse is 0.4 AL or more and 0.7 AL or less,
The pulse width of the second expansion pulse is 0.8 AL or more and 1.2 AL or less,
The pulse width of the second contraction pulse driving method of ink jet head is characterized in der Rukoto more 2.2AL less 1.8AL. It said first drive signal, and the expansion pulse and the contraction pulse driving method for an ink jet head according to claim 1, characterized in that it comprises a rest period that connects between the decreasing pulse and the expansion pulse . The pulse width of the expansion pulse in the first drive signal is not less than 0.8 AL and not more than 1.2 AL (where AL is 1/2 of the acoustic resonance period of the pressure wave in the pressure chamber),
The pulse width of the contraction pulse is 1.8 AL or more and 2.2 AL or less,
3. The ink jet head driving method according to claim 2 , wherein the pause period is 1/4 AL or less. In a driving method of an ink jet head that applies a pressure for discharging to a liquid in a pressure chamber by applying a driving signal to a pressure generating means, and discharges a droplet from a nozzle.
The drive signal includes at least two types of drive signals: a first drive signal for ejecting droplets and a second drive signal for ejecting large droplets at a relatively lower speed than the first drive signal. Including
In one pixel cycle, N second driving signals are applied, and at least lastly, the first driving signal is applied, whereby droplets are ejected from the same nozzle, and the liquid is discharged on the medium. An ink jet head that forms pixels by dots made of droplets, and changes the N by an integer of 0 or more according to image data to create dots of different sizes on the medium, thereby expressing gradation Driving method ,
The distance between the nozzle surface of the inkjet head and the medium is L, the droplet velocity by the first drive signal is VA, the droplet amount is MA, the droplet velocity by the second drive signal is VB, When the drop volume is MB,
In the case of N ≧ 3, at least to the position away from the nozzle by (L × MA × VA) / (MB × VB), the droplet by the first driving signal and the second driving just before the droplet A method of driving an ink jet head, wherein a droplet formed by a signal does not form a combined droplet . The first diameter of the droplets ejected by the drive signal, the drive method according to claim 1 or 4 ink jet head according to and smaller than the diameter of the nozzle. The driving method of the second diameter of the droplets ejected by the drive signal, the ink-jet head according to claim 1, 4 or 5, wherein greater than the diameter of the nozzle. Said first driving cycle of the drive signals TA, when the driving cycle of the second drive signal TB, according to any of claims 1,4～6, characterized in that the TA ≧ TB A method for driving an inkjet head. MA × 1.5 ≦ MB, where MA is the amount of droplets ejected by the first drive signal, and MB is the amount of droplets ejected by the second drive signal. The method for driving an ink-jet head according to claim 1, wherein the ink-jet head is driven. The pressure generating means expands or contracts the volume of the pressure chamber by driving,
The first drive signal and the second drive signal include an expansion pulse that expands the volume of the pressure chamber and contracts after a certain time, and a contraction pulse that contracts the volume of the pressure chamber and expands after a certain time. Each of the first drive signal and the second drive signal applied to the pressure generating means corresponding to the same nozzle has a constant wave height of the expansion pulse, and the same claim 4-8 in which each of the wave height of the contraction pulse of the first driving signal and the second drive signal applied to the pressure generation unit corresponding to the nozzles characterized in that it is a constant The method for driving an ink jet head according to claim 1. 10. The method of driving an ink jet head according to claim 9, wherein the first drive signal includes the expansion pulse, the contraction pulse, and a pause period connecting the expansion pulse and the contraction pulse. . The pulse width of the expansion pulse in the first drive signal is not less than 0.8 AL and not more than 1.2 AL (where AL is 1/2 of the acoustic resonance period of the pressure wave in the pressure chamber),
The pulse width of the contraction pulse is 1.8 AL or more and 2.2 AL or less,
The method of driving an inkjet head according to claim 10 , wherein the pause period is ¼ AL or less. The second drive signal includes a first expansion pulse including the expansion pulse, a first contraction pulse including the contraction pulse, a second expansion pulse including the expansion pulse, and the contraction pulse in time series order. 12. A method for driving an ink jet head according to claim 9, wherein the second contraction pulse comprises: The pulse width of the first expansion pulse in the second drive signal is 0.4 AL or more and 2.0 AL or less (where AL is 1/2 of the acoustic resonance period of the pressure wave in the pressure chamber),
The pulse width of the first contraction pulse is 0.4 AL or more and 0.7 AL or less,
The pulse width of the second expansion pulse is 0.8 AL or more and 1.2 AL or less,
13. The ink jet head driving method according to claim 12, wherein a pulse width of the second contraction pulse is 1.8 AL or more and 2.2 AL or less. When a N ≧ 2, the first expansion pulse of the N second drive signal applied to the one pixel period, claim pulse width respectively are different from each other 1～3,13 The inkjet head drive method according to any one of the above. The inkjet head driving method according to claim 14 , wherein the first expansion pulse is applied in order of decreasing pulse width within one pixel period. 16. The ink jet head driving method according to claim 1, wherein the first driving signal and the second driving signal are both rectangular waves. Said first drive signal, according to claim 1-16, characterized in that a driving signal for forming the smallest droplets among the plurality of driving signals arranged in time series within one pixel period The inkjet head drive method according to any one of the above. An inkjet head that applies a pressure for ejection to the liquid in the pressure chamber by driving the pressure generating means, and ejects droplets from the nozzle;
In an inkjet recording apparatus comprising: a drive control unit that outputs a drive signal for driving the pressure generation unit;
The drive signal includes at least two types of drive signals: a first drive signal for ejecting droplets and a second drive signal for ejecting large droplets at a relatively lower speed than the first drive signal. Including
The drive control means discharges droplets from the same nozzle by applying the N second drive signals and applying the first drive signal at the end at least in one pixel period. , which forms a pixel by dots of the droplets on the medium, and the N is Ri 1 or more integer der,
The pressure generating means expands or contracts the volume of the pressure chamber by driving,
The first drive signal and the second drive signal include an expansion pulse that expands the volume of the pressure chamber and contracts after a certain time, and a contraction pulse that contracts the volume of the pressure chamber and expands after a certain time. Each of the first drive signal and the second drive signal applied to the pressure generating means corresponding to the same nozzle has a constant wave height of the expansion pulse, and the same The height of the contraction pulse of each of the first drive signal and the second drive signal applied to the pressure generating means corresponding to the nozzle is constant,
The second drive signal includes a first expansion pulse composed of the expansion pulse, a first contraction pulse composed of the contraction pulse, a second expansion pulse composed of the expansion pulse, and a first expansion pulse composed of the contraction pulse. Two contraction pulses,
The pulse width of the first expansion pulse in the second drive signal is 0.4 AL or more and 2.0 AL or less (where AL is 1/2 of the acoustic resonance period of the pressure wave in the pressure chamber),
The pulse width of the first contraction pulse is 0.4 AL or more and 0.7 AL or less,
The pulse width of the second expansion pulse is 0.8 AL or more and 1.2 AL or less,
The pulse width of the second contraction pulse jet recording apparatus characterized der Rukoto more 2.2AL less 1.8AL. 19. The ink jet recording apparatus according to claim 18, wherein the first drive signal includes the expansion pulse, the contraction pulse, and a pause period connecting the expansion pulse and the contraction pulse. The pulse width of the expansion pulse in the first drive signal is not less than 0.8 AL and not more than 1.2 AL (where AL is 1/2 of the acoustic resonance period of the pressure wave in the pressure chamber),
The pulse width of the contraction pulse is 1.8 AL or more and 2.2 AL or less,
The inkjet recording apparatus according to claim 19 , wherein the pause period is ¼ AL or less. An inkjet head that applies a pressure for ejection to the liquid in the pressure chamber by driving the pressure generating means, and ejects droplets from the nozzle;
In an inkjet recording apparatus comprising: a drive control unit that outputs a drive signal for driving the pressure generation unit;
The drive signal includes at least two types of drive signals: a first drive signal for ejecting droplets and a second drive signal for ejecting large droplets at a relatively lower speed than the first drive signal. Including
The drive control means discharges droplets from the same nozzle by applying the N second drive signals and applying the first drive signal at the end at least in one pixel period. The pixel is formed by dots formed of the droplets on the medium, and the N is changed by an integer of 0 or more according to the image data to create dots of different sizes on the medium. There line the tone representation,
The distance between the nozzle surface of the inkjet head and the medium is L, the droplet velocity by the first drive signal is VA, the droplet amount is MA, the droplet velocity by the second drive signal is VB, When the drop volume is MB,
In the case of N ≧ 3, at least to the position away from the nozzle by (L × MA × VA) / (MB × VB), the droplet by the first driving signal and the second driving just before the droplet An ink jet recording apparatus, wherein a droplet formed by a signal does not form a combined droplet . The inkjet recording apparatus according to claim 18 or 21 , wherein a diameter of a droplet ejected by the first drive signal is smaller than a diameter of the nozzle. 23. The ink jet recording apparatus according to claim 18 , wherein a diameter of a droplet ejected by the second drive signal is larger than a diameter of the nozzle. The TA according to any one of claims 18, 21 to 23 , wherein TA ≧ TB, where TA is a driving cycle of the first driving signal and TB is a driving cycle of the second driving signal. Inkjet recording device. MA × 1.5 ≦ MB, where MA is the amount of droplets ejected by the first drive signal, and MB is the amount of droplets ejected by the second drive signal. 25. The ink jet recording apparatus according to any one of claims 18, 21 to 24 . The pressure generating means expands or contracts the volume of the pressure chamber by driving,
The first drive signal and the second drive signal include an expansion pulse that expands the volume of the pressure chamber and contracts after a certain time, and a contraction pulse that contracts the volume of the pressure chamber and expands after a certain time. Each of the first drive signal and the second drive signal applied to the pressure generating means corresponding to the same nozzle has a constant wave height of the expansion pulse, and the same any of claim 21 to 25 respectively of the wave height of the contraction pulse of the first driving signal and the second drive signal applied to the pressure generation unit corresponding to the nozzles characterized in that it is a constant 2. An ink jet recording apparatus according to 1. 27. The ink jet recording apparatus according to claim 26, wherein the first drive signal includes the expansion pulse, the contraction pulse, and a pause period connecting the expansion pulse and the contraction pulse. The pulse width of the expansion pulse in the first drive signal is not less than 0.8 AL and not more than 1.2 AL (where AL is 1/2 of the acoustic resonance period of the pressure wave in the pressure chamber),
The pulse width of the contraction pulse is 1.8 AL or more and 2.2 AL or less,
28. The inkjet recording apparatus according to claim 27 , wherein the pause period is 1/4 AL or less. The second drive signal includes a first expansion pulse composed of the expansion pulse, a first contraction pulse composed of the contraction pulse, a second expansion pulse composed of the expansion pulse, and a first expansion pulse composed of the contraction pulse. 29. The inkjet recording apparatus according to claim 26 , 27 or 28 , comprising two contraction pulses. The pulse width of the first expansion pulse in the second drive signal is 0.4 AL or more and 2.0 AL or less (where AL is 1/2 of the acoustic resonance period of the pressure wave in the pressure chamber),
The pulse width of the first contraction pulse is 0.4 AL or more and 0.7 AL or less,
The pulse width of the second expansion pulse is 0.8 AL or more and 1.2 AL or less,
30. The inkjet recording apparatus according to claim 29, wherein a pulse width of the second contraction pulse is not less than 1.8 AL and not more than 2.2 AL. The pulse width of each of the first expansion pulses of the N second drive signals applied within one pixel period when N ≧ 2 is different from each other. Any one of the inkjet recording apparatuses. 32. The ink jet recording apparatus according to claim 31 , wherein the first expansion pulse is applied in order of decreasing pulse width within one pixel period. Said first drive signal and second drive signal, the ink jet recording apparatus according to any one of claims 18 to 32, characterized in that both a square wave. Said first drive signal, the claims 18-33, characterized in that a driving signal for forming the smallest droplets among the plurality of driving signals arranged in time series within one pixel period An ink jet recording apparatus according to any one of the above.

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