WO2015152186A1 - Inkjet head driving method and inkjet printing apparatus - Google Patents

Abstract

The purpose of the present invention is to provide an inkjet head driving method and an inkjet printing apparatus that can suppress reduction of productivity while limiting occurrence of satellites and are capable of high quality image printing even when multiple droplets are discharged in a one-pixel period to form a large dot on the medium. The drive signal, when applying a discharging pressure on a liquid in a pressure chamber by applying the drive signal on a pressure-generating means to discharge droplets from a nozzle, comprises at least two kinds of drive signals, a first drive signal (PA) for discharging a droplet and a second drive signal (PB) for discharging a large droplet at a relatively slower speed than the first drive signal (PA). Pixels of dots obtained from droplets on a medium are formed by applying N of the second drive signals (PB) and applying the first drive signal (PA) at least at the end of a one-pixel period to discharge droplets from the same nozzle; N is an integer of at least 1.

Description

Ink jet head driving method and ink jet recording apparatus

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.

Conventionally, as a technique for discharging a plurality of droplets from the same nozzle within one pixel cycle, there are 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.

In Patent Document 4, a portion of the second drive signal is selected within a period of one pixel from a series of drive waveforms including different drive signals of the first to third drive signals, and droplets are ejected. Then, 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 forming as large a dot as possible on a medium by ejecting a plurality of droplets within one pixel cycle, it is necessary to eject as many droplets as possible from the same nozzle within one pixel cycle.

However, the generation of satellites becomes a problem as the droplet volume increases, and when the droplet volume increases, the faster the droplet velocity. 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 vibrations by setting a predetermined interval between pixel periods, but it is not sufficient to suppress the generation 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.

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. A method of driving an ink-jet head, wherein pixels are formed by dots formed of droplets, and the N is an integer of 1 or more.

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

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.

In order to achieve at least one of the above objects, an ink jet recording apparatus reflecting one aspect of the present invention has the following configuration.

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. An ink jet recording apparatus for forming pixels by dots made of the droplets on a medium, and wherein N is an integer of 1 or more.

In order to realize at least one of the objects described above, another inkjet recording apparatus reflecting one aspect of the present invention has the following configuration.

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. An ink jet recording apparatus that performs tonal expression.

1 is a schematic configuration diagram showing an example of an ink jet recording apparatus according to the present invention. It is a figure which shows an example 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 surface The figure explaining an example of the drive method of the inkjet head in this invention (A) is a figure explaining an example of a 1st drive signal, (b) is a figure explaining an example of a 2nd drive signal. (A)-(c) is a figure explaining the discharge operation | movement of an inkjet head. (A) is a conceptual diagram of a droplet ejected by a first drive signal, (b) is a conceptual diagram of a droplet ejected by a second drive signal. (A) is a figure explaining other examples of the 1st drive signal, (b) is a figure explaining other examples of the 2nd drive signal. (A) is a figure explaining an example of the flying state of a droplet, (b) is a figure which shows the dot formed on the medium by it (A) is a figure explaining another example of the flying state of a droplet, (b) is a figure which shows the dot formed on the medium by it (A) is a figure explaining another example of the flying state of a droplet, (b) is a figure which shows the dot formed on the medium by it The figure explaining an example of the drive method of the inkjet head in the case of performing gradation expression in this invention (A) is a diagram for explaining an example of a driving method in which only the second driving signal is applied within one pixel period, and (b) is an example of a driving method in which the timing of the first driving signal in FIG. 3 is varied. Illustration to explain

FIG. 1 is a schematic configuration diagram showing an example of an ink jet recording apparatus according to the present invention.

In the inkjet recording apparatus 1, the transport mechanism 2 sandwiches a medium 7 made of paper, a plastic sheet, a fabric, or the like by a pair of transport rollers 22, and rotates the transport roller 21 by a transport motor 23 in the Y direction (sub-scanning direction). ). An ink jet 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 so that the nozzle surface side faces the recording surface 71 of the medium 7, and is electrically connected to the drive control unit 8 constituting the drive control means in the present invention via the flexible cable 6. It is connected.

The carriage 5 is driven by a driving means (not shown) along the guide rail 4 spanned across the width direction of the medium 7, and is substantially perpendicular to the sub-scanning direction that is the conveyance direction of the medium 7. It is provided so that it can reciprocate in the 'direction (main scanning direction). As the carriage 5 reciprocates, the head 3 moves the recording surface 71 of the medium 7 in the main scanning direction, and in the course of this movement, ejects droplets from the nozzles according to the image data to record an inkjet image. .

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

In the head 3, 30 is a channel substrate. On the channel substrate 30, a large number of narrow groove-like channels 31 and partition walls 32 are arranged in parallel so as to be alternately arranged. A cover substrate 33 is provided on the upper surface of the channel substrate 30 so as to block all the channels 31 above. A nozzle plate 34 is bonded to the end surfaces of the channel substrate 30 and the cover substrate 33. One end of each channel 31 communicates with the outside through a nozzle 341 formed in the nozzle plate 34.

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

The partition wall 32 is made of a piezoelectric element such as PZT which is an electrical / mechanical conversion means. The partition wall 32 is an example in which an upper wall portion 321 and a lower wall portion 322 are formed of piezoelectric elements that are polarized in opposite directions. However, the portion formed by the piezoelectric element in the partition wall 32 may be only the upper wall portion 321, for example. Since the partition walls 32 and the channels 31 are alternately arranged in parallel, one partition wall 32 is shared by the adjacent channels 31 and 31.

On the inner surface of the channel 31, drive electrodes (not shown in FIG. 2) are formed from the wall surfaces of the partition walls 32, 32 to the bottom surface. When a drive signal having a predetermined voltage is applied from the drive control unit 8 to the two drive electrodes arranged with the partition wall 32 in between, the partition wall 32 is bordered on the joint surface between the upper wall portion 321 and the lower wall portion 322. Shear deformation. When two adjacent partition walls 32 and 32 are shear-deformed in opposite directions, the volume of the channel 31 sandwiched between the partition walls 32 and 32 expands or contracts, and a pressure wave is generated inside. As a result, pressure for ejection is applied to the ink in the channel 31.

This head 3 is a shear mode type head in which the ink in the channel 31 is ejected from the nozzle 341 when the partition wall 32 undergoes shear deformation, and is a preferred embodiment in the present invention. The channel 31 surrounded by the channel substrate 30, the partition wall 32, the cover substrate 33, and the nozzle plate 34 is an example of the pressure chamber in the present invention, and the partition wall 32 and the driving electrode on the surface thereof are an example of the pressure generating means in the present invention. is there.

The drive control unit 8 can generate a plurality of drive signals within one pixel period in order to enable a plurality of droplets to be ejected from the same nozzle 341 within one pixel period. The generated drive signal is output to the head 3 and applied to each drive electrode formed on the partition wall 32. One pixel cycle is a time interval for forming each pixel by dots by causing droplets ejected from a nozzle to land on a medium.

FIG. 3 is a diagram for explaining an example of a driving method for forming a large dot on the medium 7 by applying a plurality of driving signals within one pixel period in the present invention. Here, a plurality of drive signals applied within one pixel period T to the drive electrodes of the channel 31 corresponding to the nozzles 341 that discharge droplets are illustrated.

The plurality of drive signals in the present invention include at least two types of drive signals, the first drive signal PA and the second drive signal PB. The first drive signal PA and the second drive signal PB are signals in which the speed and the amount of droplets discharged are different. The droplets ejected by the second drive signal PB are relatively slower than the droplets ejected by the first drive signal PA, and the droplet amount is large.

The droplet velocity in the present invention is calculated by recognizing a droplet image by a droplet observation device and obtaining the elapsed time from ejection and the position coordinates where the droplet is present. Specifically, it is calculated from the distance at which the droplets fly for 50 μs from the position 500 μm away from the nozzle surface. The elapsed time from the ejection can be calculated by synchronizing the ejection signal of the inkjet head and the observation strobe. Further, the position coordinates of the droplet can be calculated by performing image processing on the flying image.

According to the ink jet head driving method of the present invention for forming a large dot, N second drive signals PB are applied within one pixel period T, and at least at the end of the one pixel period T, the second driving signal PB is applied. By applying one drive signal PA, a plurality of droplets are ejected from the same nozzle 341. At this time, by setting N to an integer equal to or greater than 1, a pixel composed of a plurality of droplets is formed on the medium 7. A plurality of droplets ejected from the same nozzle 341 within one pixel period T are united during flight, so that a pixel can be formed on the medium 7 by dots composed of one united droplet. In addition, a plurality of liquid droplets can be landed on the medium 7 so as to overlap each other, and a pixel can be formed by a dot composed of an aggregate of a plurality of dots.

Since the second drive signal PB is a drive signal for ejecting a relatively large droplet compared to the droplet generated by the first drive signal PA, one or more of the second drive signals PB are applied within one pixel period T. This mainly contributes to the formation of large dots. In addition, the droplets generated by the second drive signal PB are relatively slow compared to the droplets generated by the first drive signal PA, and the generated satellite is captured by the droplets discharged later within the same pixel period T. Therefore, it does not become a problem that degrades the image quality.

When a plurality of droplets are ejected within one pixel period T, satellites of the preceding droplet are captured by droplets ejected later within the same pixel period T, so from the viewpoint of image quality, one pixel period Satellites associated with the last ejected droplet in T are particularly problematic. According to the present invention, the first drive signal PA is always applied at the end of one pixel period T, and as a result, a relatively small droplet is ejected compared to the droplet generated by the second drive signal PB. Therefore, satellites are not generated or suppressed.

Therefore, even if a large dot is formed on the medium 7 by applying the first drive signal PA and the second drive signal PB within one pixel period T and ejecting a plurality of droplets, the productivity decreases. The inkjet head 3 driving method and the inkjet recording apparatus 1 that can suppress the generation of satellites and suppress high-quality image recording can be provided.

In FIG. 3, TA is a drive cycle of the first drive signal PA within one pixel cycle T, and TB is a drive cycle of the second drive signal PB within one pixel cycle T. Here, three (N = 3) second drive signals PB are applied within one pixel period T with a predetermined pause period T1 between the second drive signal PB and the subsequent drive signal, and one is applied last. In this example, a predetermined pause period T2 is provided between the end of application of the first drive signal PA and the start of the next one pixel period T.

Further, the number N of the second drive signals PB is an integer equal to or greater than 1, and is not limited to the three shown in the figure. A first drive signal PA is applied. For this reason, even if N is any value equal to or greater than 1, satellites are suppressed as described above. Although not shown, the first drive signal PA to be applied last is applied so as to have the same timing within one pixel period T regardless of N being any value of 1 or more.

Next, specific configurations of the first drive signal PA and the second drive signal PB will be described with reference to FIG. 4A shows the first drive signal PA, and FIG. 4B shows the second drive signal PB. However, the drive signals PA and PB shown in FIG. 4 are preferable examples in the present invention, and are not limited to those shown in the drawings.

First, the configuration of the first drive signal PA will be described.

The first drive signal PA has an expansion pulse Pa1 that expands the volume of the channel 31 and contracts after a certain time, and a contraction pulse Pa2 that contracts the volume of the channel 31 and expands after a certain time.

In the example shown in FIG. 4A, the expansion pulse Pa1 is a pulse that rises from the reference potential and falls to the reference potential after a certain time. The contraction pulse Pa2 is a pulse that falls from the reference potential and rises to the reference potential after a certain time. Although the reference potential is 0 potential here, it is not particularly limited.

The drive voltage value (+ Von) of the expansion pulse Pa1 and the drive voltage value (−Voff) of the contraction pulse Pa2 are set to | Von |: | Voff | = 2: 1.

In the example of the first drive signal PA, a pause period PWA3 for maintaining the 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 a gradient wave.

The pulse width PWA1 of the expansion pulse Pa1 is preferably 0.8 AL or more and 1.2 AL or less, and the pulse width PWA2 of the contraction pulse Pa2 is preferably 1.8 AL or more and 2.2 AL or less. 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”, and is 1/2 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, the rectangular wave refers to a waveform in which the rise time and fall time between 10% and 90% of the voltage are both 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 value (+ Von) of the first expansion pulse Pb1 and the second expansion pulse Pb3 and the drive voltage value (−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 falls continuously 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 by 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 turns 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 contracted state due to the contraction pulse Pa2 is restored when the pressure in the channel 31B turns positive after 1.8A or more and 2.2AL or less has passed. As a result, the partition walls 32B and 32C return to the neutral state in FIG.

Next, the 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 from 0.4 AL to 2.0 AL, the application of the first expansion pulse Pb1 is completed. 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 at 0.8 AL or more and 1.2 AL or less, 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 in succession, satellites can be suppressed, but only dots consisting 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 partition wall 32 is deformed by 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. .

Also, the diameter of the droplet refers to the diameter when the droplet is spherical, and when the droplet is not spherical, it is 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 each 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 in 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 the drive control unit 8 in association with each gradation in advance. 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.

Also, it is assumed here that 6 pl droplet 100 is ejected by the first drive signal PA and 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.

This makes it possible to suppress landing position deviation for each gradation. 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.

Hereinafter, examples of the present invention will be described, but the present invention is not limited to the 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 discharged 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 media 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.

Note that the droplet velocities 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 Contracted pulse Pb3: Second expanded pulse Pb4: Second contracted pulse PWB1 to PWB4: Pulse width T: Pixel period TA: Drive period of first drive signal TB: Drive period of second drive signal T1, T2: Rest period

Claims (32)

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. A method of driving an ink-jet head, wherein pixels are formed by dots formed of droplets, and the N is an integer of 1 or more.
2. 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.
3. 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 The ink jet head driving method according to claim 2, wherein a droplet formed by a signal does not form a combined droplet.
4. 4. The method of driving an ink jet head according to claim 1, wherein a diameter of a droplet ejected by the first driving signal is smaller than a diameter of the nozzle.
5. The method of driving an inkjet head according to any one of claims 1 to 4, wherein a diameter of a droplet ejected by the second drive signal is larger than a diameter of the nozzle.
6. 6. The ink jet head driving method according to claim 1, wherein TA ≧ TB, where TA is the driving period of the first driving signal and TB is the driving period of the second driving signal.
7. 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 any one of claims 1 to 6.
8. 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 inkjet head according to any one of claims 1 to 7, wherein the heights of the contraction pulses of the first drive signal and the second drive signal applied to the pressure generating unit corresponding to the nozzle are constant. Driving method.
9. The inkjet head driving method according to claim 8, wherein the first driving signal includes the expansion pulse, the contraction pulse, and a pause period connecting the expansion pulse and the contraction pulse.
10. 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 9, wherein the pause period is ¼ AL or less.
11. 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. The method of driving an ink jet head according to claim 8, comprising: a second contraction pulse comprising:
12. 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 method of driving an inkjet head according to claim 11, wherein a pulse width of the second contraction pulse is not less than 1.8 AL and not more than 2.2 AL.
13. 13. The inkjet head driving method according to claim 12, wherein when N ≧ 2, the first dilation pulses of the N second driving signals applied within one pixel period have different pulse widths.
14. The inkjet head driving method according to claim 13, wherein the first expansion pulse is applied in ascending order of pulse width within one pixel period.
15. 15. The ink jet head driving method according to claim 1, wherein the first driving signal and the second driving signal are both rectangular waves.
16. 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 inkjet head.
17. 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. An ink jet recording apparatus for forming pixels by dots made of the droplets on a medium, and wherein N is an integer of 1 or more.
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. 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. An ink jet recording apparatus that performs tonal expression.
19. 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 The ink jet recording apparatus according to claim 18, wherein a droplet formed by a signal does not form a combined droplet.
20. 20. The ink jet recording apparatus according to claim 17, 18 or 19, wherein a diameter of a droplet ejected by the first drive signal is smaller than a diameter of the nozzle.
21. 21. The ink jet recording apparatus according to claim 17, wherein a diameter of a droplet ejected by the second drive signal is larger than a diameter of the nozzle.
22. 22. The ink jet recording apparatus according to claim 17, wherein TA ≧ TB, where TA is the driving period of the first driving signal and TB is the driving period of the second driving signal.
23. 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 ink jet recording apparatus according to any one of claims 17 to 22.
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 The ink jet recording according to any one of claims 17 to 23, wherein the heights of the contraction pulses of the first drive signal and the second drive signal applied to the pressure generating means corresponding to the nozzle are constant. apparatus.
25. 25. The ink jet recording apparatus according to claim 24, wherein the first drive signal includes the expansion pulse, the contraction pulse, and a pause period connecting the expansion pulse and the contraction pulse.
26. 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 ink jet recording apparatus according to claim 25, wherein the pause period is ¼ AL or less.
27. 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. 27. The ink jet recording apparatus according to claim 24, 25 or 26, comprising two contraction pulses.
28. 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,
    28. The ink jet recording apparatus according to claim 27, wherein a pulse width of the second contraction pulse is not less than 1.8 AL and not more than 2.2 AL.
29. 29. The inkjet recording apparatus according to claim 28, wherein when N ≧ 2, the first dilation pulses of the N second drive signals applied within one pixel period have different pulse widths.
30. 30. The ink jet recording apparatus according to claim 29, wherein the first expansion pulse is applied in ascending order of pulse width within one pixel period.
31. The ink jet recording apparatus according to any one of claims 17 to 30, wherein each of the first drive signal and the second drive signal is a rectangular wave.
32. 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. Inkjet recording device.
    

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