JP2002086765A - Ink jet head and ink-jet recording apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably discharge ink drops which are to be discharged later and stably combine the ink drops in a method wherein three or more ink drops are combined during flying to be one ink drop before landing to a recording medium. SOLUTION: When three ink drops are to be discharged, discharge velocities v1-v3 of the first - the third ink drops to be discharged sequentially are set to satisfy v2<=v2<v3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an ink jet head and an ink jet recording apparatus.

[0002]

2. Description of the Related Art Conventionally, a plurality of ink droplets are ejected from the same nozzle of an inkjet head during one printing cycle.
An ink jet recording apparatus that forms one dot by using a plurality of ink droplets is known.

[0003] This type of ink jet recording apparatus is provided with an ink jet head for ejecting ink droplets, and relative moving means for relatively moving the ink jet head and recording paper. The ink jet head has a head body in which a pressure chamber and a nozzle for containing ink are formed,
An actuator for discharging ink in the pressure chamber from the nozzle and a drive signal supply unit for supplying a drive signal to the actuator are provided.

When the ink jet head and the recording paper are relatively moving by the relative moving means, the driving signal supplying means supplies one or more driving pulse signals during one printing cycle. The actuator operates in response to these drive signals, and causes one or more ink droplets to be ejected from the nozzle. The ink droplets thus ejected land on the recording paper in the order of ejection to form one ink dot. Then, a large number of such ink dots are aggregated on the recording paper to form a predetermined image on the recording paper. At this time, by adjusting the number of ink droplets ejected during one printing cycle, the density and size of the dots are adjusted, and so-called multi-tone printing is performed.

However, when high-speed printing is performed, a plurality of ink droplets ejected from the same nozzle land at mutually displaced positions on the recording paper because the moving speed of the relative movement between the ink jet head and the recording paper is high. It's easy to do. As a result, the ink dots become elliptical, and the print quality tends to deteriorate. Therefore, high-speed printing was difficult with the above-mentioned apparatus.

Therefore, as disclosed in Japanese Patent Publication No. 7-108568 and Japanese Patent Publication No. 6-55513,
By setting the ejection speed of the ink droplet ejected later to be greater than the ejection speed of the ink droplet ejected first, the two ink droplets ejected from the same nozzle are united before landing, forming one ink droplet. There has been proposed a method of causing the ball to land.

[0007]

However, in the method of ejecting a plurality of ink droplets while sequentially increasing the speed, it is relatively simple when there are two ink droplets, but it is possible to accurately apply three or more ink droplets. It was difficult to unite well. This is because, as the number of ink droplets increases, the ejection speed of the ink droplet ejected toward the end must be considerably increased, and it becomes difficult to stably eject the ink droplet. Therefore, it has been difficult to increase the number of coalesced ink droplets. However, from the viewpoint of high image quality, multi-tone printing performed by combining a plurality of ink droplets during flight is very important. Therefore, in order to achieve higher image quality in the future, a new technique for combining more ink droplets has been awaited.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an ink jet head and an ink jet recording apparatus which stably combine three or more ink droplets. .

[0009]

In order to achieve the above object, an ink jet head according to the present invention ejects at least first to third ink droplets from a nozzle in order and combines these ink droplets. An ink jet head that lands on a recording medium, the ejection speed v of the first ink droplet
1. The ejection speed v2 of the second ink droplet and the ejection speed v3 of the third ink droplet are such that v1 ≧ v2 or v2 ≧ v3.

This eliminates the necessity of sequentially ejecting the first to third ink droplets so as to increase the speed. Therefore, the second and third ink droplets are stably ejected, and the accuracy of uniting the first to third ink droplets is improved.

The ejection speeds v1 to v3 of the first to third ink droplets
May be v2 ≦ v1 <v3.

After the second ink droplet and the third ink droplet are combined to form a combined ink droplet, the combined ink droplet and the first ink droplet may be combined.

As a result, the third ink droplet catches up with the second ink droplet and coalesces, and the merged ink droplet catches up with the first ink droplet and further coalesces. As a result, the first to third ink droplets are obtained. Are landed on a recording medium as one ink droplet. Thus, the speed of the united ink droplets is
Since it is sufficient if the velocity is higher than the velocity of the ink droplet, it is not necessary to eject the first to third ink droplets in such a manner that the velocity sequentially increases. Therefore, the second and third ink droplets are ejected stably, and the accuracy of the combination of the first to third ink droplets is improved.

On the other hand, the ejection speed v1 of the first to third ink droplets
-V3 may be v1 <v3 <v2.

After the first ink droplet and the second ink droplet are combined to form a combined ink droplet, the combined ink droplet and the third ink droplet may be combined.

By this, the second ink droplet catches up with the first ink and coalesces, and the third ink droplet catches up with the coalesced ink droplet and further coalesces. As a result,
The first to third ink droplets land as a single ink droplet on a recording medium. As described above, since it is sufficient that the speed of the third ink droplet is higher than the speed of the united ink droplet, it is not necessary to eject the first to third ink droplets in order to increase the speed. Therefore, the second and third ink droplets are ejected stably, and the accuracy of the combination of the first to third ink droplets is improved.

Another ink-jet head according to the present invention is an ink-jet head which sequentially discharges at least first to fourth ink droplets from nozzles, combines these ink droplets, and lands on a recording medium. The ejection speed v1 of one ink droplet, the ejection speed v2 of the second ink droplet, the third
The ejection speed v3 of the ink droplet and the ejection speed v4 of the fourth ink droplet are defined as v1 ≧ v2 or v2 ≧ v3 or v
3 ≧ v4.

This eliminates the necessity of sequentially ejecting the first to fourth ink droplets so as to increase the speed. Therefore, the second to fourth ink droplets are stably ejected, and the first to fourth ink droplets are discharged.
-The accuracy of coalescence of the fourth ink droplet is improved.

The ejection speeds v1 to v4 of the first to fourth ink droplets
Are v1 <v2, v3 <v2, and v3 <v4
It may be.

The first ink droplet and the second ink droplet are combined to form a first combined ink droplet, while the third ink droplet and the fourth ink droplet are combined to form a second combined ink droplet.
The first united ink droplet and the second united ink droplet may be united.

As a result, the second ink droplet catches up with the first ink droplet and coalesces, and the first and second ink droplets become the first ink droplet.
It becomes a united ink drop. Further, the fourth ink droplet catches up with the third ink droplet and unites, and the third and fourth ink droplets become the second united ink droplet. At this time, the first united ink droplet may be generated before or after the second united ink droplet. Then, the second united ink droplet catches up with the first united ink droplet and unites, and as a result, the first to fourth ink droplets land as a single ink droplet on the recording medium. Therefore, it is not necessary to sequentially eject the first to fourth ink droplets so as to increase the speed.

Another ink jet head according to the present invention is a method for driving an ink jet head in which at least first to fifth ink droplets are sequentially discharged from nozzles, these ink droplets are united, and then landed on a recording medium. hand,
The ejection speed v1 of the first ink droplet, the ejection speed v2 of the second ink droplet, the ejection speed v3 of the third ink droplet, the ejection speed v4 of the fourth ink droplet, and the ejection speed v5 of the fifth ink droplet are represented by v1.
≧ v2, or v2 ≧ v3, or v3 ≧ v4, or v4 ≧ v5.

Thus, there is no need to eject the first to fifth ink droplets in such a manner that the ink droplets sequentially increase in speed. Therefore, the second to fifth ink droplets are stably ejected, and the first to fifth ink droplets are discharged.
The accuracy of coalescence of the fifth ink droplet is improved.

The ejection speeds v3 to v5 of the third to fifth ink droplets
May be v3> v4 and v4 <v5.

The first to third ink droplets are combined to form a first combined ink droplet, while the fourth ink droplet and the fifth ink droplet are combined to form a second combined ink droplet. The ink droplet and the second combined ink droplet may be combined.

As a result, the first to third ink droplets unite to form a first united ink droplet, while the fifth ink droplet catches up with the fourth ink droplet and unites to form a second united ink droplet. At this time, the first united ink droplet may be generated before or after the second united ink droplet. Thereafter, the second united ink droplet catches up with the first united ink droplet and unites, and as a result, the first to fifth ink droplets land as a single ink droplet on the recording medium. Therefore, the first to fifth
It is no longer necessary to eject ink droplets in such a manner that the ink droplets sequentially increase in speed.

The ink jet head has a pressure chamber for containing ink, a nozzle communicating with the pressure chamber, and a piezoelectric element, and applies a pressure to the ink in the pressure chamber by a piezoelectric effect of the piezoelectric element. The actuator may include an actuator that ejects ink droplets from the nozzles, and a drive signal supply unit that supplies a plurality of drive pulse signals having different amplitudes to the actuator.

Thus, the ejection speed of the ink droplet changes in accordance with the magnitude of the amplitude of the drive pulse signal. For example, a drive pulse having a small amplitude is supplied when discharging an ink droplet having a low discharge speed, and a drive pulse having a large amplitude is supplied when discharging an ink droplet having a high discharge speed. As a result, a plurality of ink droplets having different ejection speeds are ejected as described above.

The ink jet head has a pressure chamber for containing ink, a nozzle communicating with the pressure chamber, and a piezoelectric element. The piezoelectric element applies pressure to the ink in the pressure chamber by a piezoelectric effect of the piezoelectric element. An actuator for ejecting ink droplets from a nozzle, a pressurized waveform component for driving the actuator on the side that pressurizes the pressure chamber, and a depressurized waveform component for driving the actuator on the side that depressurizes the pressure chamber. And a drive signal supply means for supplying a plurality of drive pulse signals having different inclination angles of the pressurized waveform components.

Thus, the ejection speed of the ink droplet changes according to the magnitude of the inclination angle of the pressure waveform component. For example, a drive pulse with a small inclination angle of the pressurized waveform component is supplied when ejecting an ink droplet with a small ejection speed, and a drive pulse with a large inclination angle of the pressurized waveform component is ejected when an ink droplet with a large ejection speed is ejected. Supply. As a result, a plurality of ink droplets having different ejection speeds are ejected as described above.

The ink jet head has a pressure chamber for containing ink, a nozzle communicating with the pressure chamber, and a piezoelectric element. The piezoelectric element applies pressure to the ink in the pressure chamber by the piezoelectric effect of the piezoelectric element. The actuator may include an actuator that ejects ink droplets from the nozzles, and a drive signal supply unit that supplies a plurality of drive pulse signals having different pulse intervals to the actuator.

Thus, the ejection speed of the ink droplet changes according to the pulse interval. For example, when ejecting ink droplets having a high ejection speed, drive pulses are supplied at intervals close to the natural period of the actuator, and when ejecting ink droplets having a low ejection speed, drive pulses are applied at intervals greatly different from the natural period. Supply. As a result, a plurality of ink droplets having different ejection speeds are ejected as described above. Note that the natural period of the actuator referred to here is the natural period of the entire vibration system including the acoustic element (specifically, ink).

The ink-jet head has a pressure chamber for containing ink, a nozzle communicating with the pressure chamber, and a piezoelectric element. The piezoelectric element applies pressure to the ink in the pressure chamber by the piezoelectric effect of the piezoelectric element. The actuator may include an actuator that ejects ink droplets from the nozzles, and a drive signal supply unit that supplies a plurality of drive pulse signals having different pulse widths to the actuator.

As a result, the ejection speed of the ink droplet changes according to the pulse width. For example, when ejecting ink droplets having a high ejection speed, a drive pulse having a pulse width that is half or almost half of the natural period of the actuator is supplied. And a driving pulse having a pulse width that is significantly different from the above. As a result, a plurality of ink droplets having different ejection speeds are ejected as described above.

The ink jet head has a pressure chamber for accommodating ink, a nozzle communicating with the pressure chamber, and a piezoelectric element. The piezoelectric element applies pressure to the ink in the pressure chamber by a piezoelectric effect of the piezoelectric element. An actuator for discharging ink droplets from a nozzle; a pulse signal arranged at a predetermined reference interval to the actuator;
And a driving signal supply unit for supplying a driving pulse signal including a pulse signal arranged at double intervals.

Thus, the ejection speed of the ink droplet changes depending on whether the interval between the pulse signals is the reference interval or twice the reference interval. For example, a pulse signal is supplied at a reference interval when an ink droplet having a high ejection speed is ejected, and a pulse signal is supplied twice at a reference interval when an ink droplet having a low ejection speed is ejected so as not to apply a pulse signal for one pulse. Supply pulse signals at intervals. As a result, a plurality of ink droplets having different ejection speeds are ejected as described above.

The driving pulse signal may be a rectangular pulse signal.

[0038] Thus, since a rectangular pulse signal can be easily generated, a drive signal can be easily generated.

An ink jet recording apparatus according to the present invention includes any one of the above ink jet heads.

As a result, an ink jet recording apparatus that performs high-quality multi-tone recording can be obtained.

[0041]

Embodiments of the present invention will be described below with reference to the drawings.

<Embodiment 1> FIG. 1 shows a schematic configuration of an ink jet recording apparatus according to an embodiment. The ink jet recording apparatus includes an ink jet head 1 supported and fixed on a carriage 16. Carriage 1
6, a carriage motor 28 not shown in FIG.
(See FIG. 6). The carriage motor 28 guides the inkjet head 1 and the carriage 16 on a carriage shaft 17 extending in the main scanning direction (X direction shown in FIGS. 1 and 2), and reciprocates in that direction. It has become. The carriage 16, the carriage shaft 17, and the carriage motor 28 constitute a relative moving unit that relatively moves the inkjet head 1 and the recording paper 41.

The recording paper 41 is sandwiched between two transport rollers 42 which are driven to rotate by a transport motor 26 (not shown in FIG. 1) (see FIG. 6).
Further, the sheet is conveyed by the respective conveying rollers 42 in a sub-scanning direction (Y direction shown in FIGS. 1 and 2) perpendicular to the main scanning direction.

As shown in FIGS. 2 to 5, the ink-jet head 1 has a head body 40 having a plurality of pressure chambers 4 for accommodating ink and a plurality of nozzles 2 communicating with the respective pressure chambers 4. It has a plurality of actuators 10 for ejecting ink droplets from each nozzle 2 by applying pressure to the ink in each pressure chamber 4. The actuator 10 uses a so-called flexural vibration type piezoelectric element 13 as described later. The actuator 10 ejects ink droplets from the nozzles 2 and changes ink pressure into the pressure chambers 4 by pressure changes accompanying contraction and expansion of the pressure chambers 4. Is to be filled.

As shown in FIG. 2, the pressure chambers 4 are formed in a long groove shape inside the ink jet head 1 so as to extend in the main scanning direction X, and are arranged at predetermined intervals in the sub scanning direction Y. Have been. One end of the pressure chamber 4 (FIG. 2)
The nozzle 2 is formed at the right end of the drawing). The nozzles 2 are arranged on the lower surface of the ink jet head 1 so as to open at predetermined intervals in the sub-scanning direction Y. The other end of the pressure chamber 4 (the left end in FIG. 2)
Is connected to one end of an ink supply path 5, and the other end of each ink supply path 5 is connected to an ink supply chamber 3 provided to extend in the sub-scanning direction Y.

As shown in FIG. 3, the ink jet head 1 has a nozzle plate 6 in which the nozzles 2 are formed, a partition wall 7 for forming the pressure chamber 4 and the ink supply path 5, and an actuator 10 which are sequentially laminated. It is configured.
For example, a polyimide plate having a thickness of 20 μm can be used for the nozzle plate 6, and the partition wall 7 has a thickness of 280 μm.
m stainless steel laminate plate can be used.

As shown in exaggerated manner in FIGS. 4 and 5, the actuator 10 includes a diaphragm 11 provided in the pressure chamber 4.
And a thin-film piezoelectric element 13 for vibrating the diaphragm 11 and an individual electrode 14 are sequentially laminated. The diaphragm 11 is made of, for example, a chrome plate having a thickness of 2 μm.
It also has a function as a common electrode for applying a voltage to the piezoelectric element 13 together with the individual electrodes 14. Piezoelectric element 13
Are provided corresponding to the pressure chambers 4 and have a thickness of 3
An ultra-thin PZT (lead zirconate titanate) having a thickness of μm can be suitably used. The individual electrode 14 is made of a platinum plate having a thickness of 0.1 μm, and the entire thickness of the actuator 10 is about 5 μm. Note that an insulating layer 15 made of polyimide is embedded between the piezoelectric elements 13 and the individual electrodes 14 adjacent to each other.

Next, referring to the block diagram of FIG.
The control circuit 20 of the ink jet recording apparatus will be described. The control circuit 20 includes a main control unit 21 including a CPU.
And an RO storing routines for various data processing, etc.
M22, a RAM 23 for storing various data, etc .; driver circuits 25 and 27 for controlling the driving of a transport motor 26 and a carriage motor 28; a motor control circuit 24;
And a drive signal generation circuit 30 and a selection circuit 31. The actuator 10 is connected to each selection circuit 31. The drive signal generation circuit 30 is configured to generate a drive signal having a plurality of drive pulses within one printing cycle. The selection circuit 31 is configured to selectively input one or more drive pulses included in the drive signal to the actuator 10 when the inkjet head 1 is moving in the main scanning direction X together with the carriage 16. ing. Then, these drive signal generation circuits 3
The drive signal supply unit 32 that supplies a predetermined drive signal to the actuator 10 is configured by the 0 and the selection circuit 31.

The operation of the ink jet recording apparatus will be described. First, when the data receiving circuit 29 receives image data, the main control unit 21 controls the transport motor 26 and the carriage motor 28 via the motor control circuit 24 and the driver circuits 25 and 27 based on the processing routine stored in the ROM 22. Each of them is controlled, and the drive signal generation circuit 30 generates a drive signal having a plurality of drive pulses. Further, the main control section 21 outputs information of a drive pulse to be selected to the selection circuit 31 based on the image data. Then, the selection circuit 31 determines, based on the information,
One or more predetermined drive pulses are selected from the plurality of drive pulses and supplied to the actuator 10. Thus, one or more ink droplets are ejected from the nozzles 2 of the inkjet head 1 within one printing cycle.

Next, with reference to FIGS. 7 and 8, a description will be given of a drive signal and the behavior of ink droplets when three ink droplets are ejected from the nozzle 2 within one printing cycle. FIG.
As shown in (1), in the present embodiment, the drive signal supplied to the actuator 10 includes three trapezoidal waveform pulses P1 to P3 within one printing cycle. The first to third pulses P1 to P3 are signals for driving the actuator 10 so that the pressure chamber 4 is once depressurized and then pressurized.
In other words, the first to third pulses P1 to P3 are signals for ejecting ink droplets by causing the actuator 10 to perform a so-called pulling operation (pull-push operation). By these first to third pulses P1 to P3, first to third ink droplets are sequentially ejected from the nozzle 2. First
To amplitude of third pulse (potential difference from reference potential) V1 to V
3 is set to V2 ≦ V1 <V3. In general, the larger the amplitude, the higher the ejection speed of the ink droplets.
<V3.

Then, the first to third pulses P1 to P3
Is supplied, the first to third ink droplets Q1 to Q1
Q3 coalesces as shown in FIGS. 8 (a) to 8 (h). That is, first, the third ink droplet Q3 catches up with the second ink droplet Q2, and the second ink droplet Q2 and the third ink droplet Q3 are combined to form a combined ink droplet Q23 (FIGS. 8A to 8D).
reference). Next, the united ink droplet Q23 catches up with the first ink droplet Q1, and the united ink droplet Q23 and the first ink
Combine with 1. Thus, the first to third ink droplets Q1 to Q3 are united before landing, and one ink droplet Q123 is formed.
And land on the recording paper 41.

As described above, according to the present embodiment, the first to first embodiments are performed.
It is not necessary to eject the third ink droplets Q1 to Q3 so that the speed increases sequentially. Since the speed difference between the second ink droplet Q2 and the third ink droplet Q3 is large, both ink droplets Q2, Q
3 stably coalesces. As a result, the first to third ink droplets Q1 to Q3 stably combine before landing.

The above-described method of ejecting ink droplets can be realized by other drive signals. For example, utilizing the fact that the greater the inclination angle of the rising waveform of the pulse signal (in other words, the greater the inclination of the rising waveform), the higher the ejection speed of the ink droplet, as shown in FIG. Rising waveform of three pulses P1 to P3 (actuator 10
The ejection speeds v1 to v3 may be adjusted by adjusting the inclination angles α1 to α3 of the pressurized waveform components that drive. Specifically, the first to third pulses P1 to P3
The inclination angles α1 to α3 of the rising waveform of α2 ≦ α1 <
By setting α3, v2 ≦ v1 <v3 can be satisfied, and the above-described unification of ink droplets can be realized.

<Embodiment 2> Embodiment 2 also discharges three ink droplets Q1 to Q3 within one printing cycle and combines the ink droplets Q1 to Q3 before landing. But,
The second embodiment differs from the first embodiment in the order of merging of the ink droplets Q1 to Q3 and the waveform of the drive signal. FIG.
As shown in (1), the drive signal according to the present embodiment includes three pulses P1 to P3 having different pulse intervals. Generally, as the pulse interval is closer to the natural period (natural period of the entire vibration system including the acoustic element) t0 of the actuator 10, the ejection speed of the ink droplet is increased. Therefore, in the present embodiment, the pulse intervals t1 to t3 of the first to third pulses P1 to P3 are set.
3 is the ejection speed v1 of the first to third ink droplets Q1 to Q3.
t1 <t3 <t such that v3 satisfies v1 <v3 <v2.
2 ≦ t0 is set.

Here, the interval between the start of the fall of the first pulse P1 and the end of the rise is the first pulse interval t1, and the interval between the end of the rise of the first pulse P1 and the end of the rise of the second pulse. For the second pulse interval t2 and the second
The third pulse interval t3 is defined between the end of the rise of the pulse P2 and the end of the rise of the third pulse P3. However, the method of defining the pulse intervals t1 to t3 is not limited to the above method, and other methods are used. It is also possible to specify in.

By supplying the first to third pulses P1 to P3, the first to third ink droplets Q1 to Q3
Are combined as shown in FIGS. 11 (a) to 11 (h). That is, first, the second ink droplet Q2 catches up with the first ink droplet Q1, and the first ink droplet Q1 and the second ink droplet Q2 are merged into a merged ink droplet Q12 (FIGS. 11A to 11E).
reference). Next, the third ink droplet Q3 is combined with the united ink droplet Q12.
And the united ink droplet Q12 and the third ink droplet unite. Thus, the first to third ink droplets Q1 to Q
No. 3 is united before landing and lands on the recording paper 41 as one ink droplet Q123.

As described above, also in the present embodiment, the first
It is not necessary to sequentially eject the third to third ink droplets Q1 to Q3 so as to increase the speed. Since the speed difference between the first ink droplet Q1 and the second ink droplet Q2 is large, both ink droplets Q1,
Q2 stably coalesces. As a result, the first to third ink droplets Q1 to Q3 stably combine before landing.

The above-described method of ejecting ink droplets can be realized by other drive signals. For example, as in the first embodiment, by adjusting the amplitude or the inclination angle of the rising waveform, the ejection speeds v1 to v3 can be adjusted.
May be set to v1 <v3 <v2. Further, the pulse width of the pulse signal is half the value of the natural period t0 (if the damping vibration of the actuator 10 due to the previous pulse remains, the pulse width that maximizes the ejection speed is half the value of the natural period. In this case, the closer the value is to about half the value), the larger the discharge speed of the ink droplet becomes. As shown in FIG. 12, the pulse widths of the first to third pulses P1 to P3 are used. t1 ′ to t3 ′ is defined as t1 ′ <t
3 ′ <t2 ′ ≦ 0.5 × t0. Here, the pulse width is defined by the time from the falling start point to the rising start point, but the pulse width is defined by the time from the falling half value point to the rising half value point, or from the falling start point to the rising end point. It is also possible to specify the time.

<Embodiment 3> In Embodiment 3, four ink droplets Q1 to Q4 are ejected within one printing cycle, and these ink droplets Q1 to Q4 are united before landing.

As shown in FIG. 13, the drive signal according to the present embodiment has a waveform in which one pulse signal is omitted from a plurality of pulse signals arranged at a predetermined reference interval t. . Specifically, the first drive signal
Out of the fourth pulse, the first pulse P1 and the second pulse P2
, And between the third pulse P3 and the fourth pulse P4 are reference intervals t, respectively.
The interval from the pulse P3 is 2t, which is twice the reference interval.

When the second pulse P2 is supplied, the influence of the first pulse P1 (the effect of damped vibration) remains in the vibration system including the actuator 10, and the second pulse P2 ejected by the second pulse P2 The ejection speed v2 of the ink droplet Q2 is
The ejection speed v1 of the first ink droplet Q1 ejected by the first pulse P1 is higher than the ejection speed v1. Similarly, the fourth pulse P
Ejection speed v4 of the fourth ink droplet Q4 ejected by No. 4
Is the third ink droplet Q ejected by the third pulse P3
3 becomes higher than the discharge speed v3. However, since the interval between the second pulse P2 and the third pulse P3 is twice as long as the reference interval, when the third pulse P3 is supplied, the influence of the second pulse P2 does not remain much. Therefore, the third ink droplet Q3 is different from the second ink droplet Q2,
The third ink droplet Q3 is less affected by the previous pulse.
Is lower than the discharge speed v2 of the second ink droplet Q2. As a result, in the present embodiment, the first to fourth
The ejection speeds v1 to v4 of the ink droplets Q1 to Q4 are as follows: v1 <v2 v3 <v2 v3 <v4.

By supplying the first to fourth pulses P1 to P4, the first to fourth ink droplets Q1 to Q4
Are combined as shown in FIGS. 14 (a) to (h). That is, the second ink drop Q2 catches up with the first ink drop Q1, and the first ink drop Q1 and the second ink drop Q2 are combined into a first combined ink drop Q12, while the fourth ink drop Q4 is formed.
Catches up with the third ink droplet Q3, and the third ink droplet Q3 and the fourth ink droplet Q4 are merged into a second merged ink droplet Q34 (see FIGS. 14A to 14E). At this time, the first united ink droplet Q12 may be generated earlier than the second united ink droplet Q34, may be generated later, or may be generated simultaneously. Thereafter, the second united ink droplet Q34 catches up with the first united ink droplet Q12, and the first united ink droplet Q12
And the second united ink droplet Q34 are united to form one ink droplet Q1234 and land on the recording paper 41.

As described above, according to the present embodiment, the first to first embodiments
It is not necessary to eject the fourth ink droplets Q1 to Q4 so that the speed increases sequentially. Since v3 <v2, especially the third case is compared with the conventional case where v1 <v2 <v3 <v4.
In addition, it is possible to stably eject the fourth ink droplets Q3 and Q4.

The above-described method of ejecting ink droplets can be realized by other drive signals. For example, as in the first embodiment, the amplitude of the pulse signal may be adjusted, or the inclination angle of the rising waveform may be adjusted. Further, the pulse interval and the pulse width may be adjusted as in the second embodiment.

<Embodiment 4> In Embodiment 4, five ink droplets Q1 to Q5 are ejected within one printing cycle, and these ink droplets Q1 to Q5 are united before landing.

In the present embodiment, the fifth ink droplet Q5 is
Catches up with ink drop Q4 and coalesces, and the combined ink drop Q
45 is a combined ink drop Q of the first to third ink drops Q1 to Q3
The ejection speeds v3 to v5 of the third to fifth ink droplets Q3 to Q5 are set to satisfy v3> v4 v4 <v5 so as to catch up with the ink droplets 123 and to be further united.

Specifically, as shown in FIGS. 15A to 15I, the fifth ink droplet Q5 catches up with the fourth ink droplet Q4, and the fourth ink droplet Q4 and the fifth ink droplet Q5 are united. As a result, a second combined ink droplet Q45 is obtained (FIGS. 15A to 15E).
reference). On the other hand, the third ink droplet Q3 catches up with the second ink droplet Q2 and unites, and the united ink droplet Q23 further
The first to third ink droplets Q1 to Q3 form a first combined ink droplet Q123 by catching up with the ink droplet Q1 (see FIGS. 15F to 15H). Thereafter, the second united ink droplet Q45 catches up with the first united ink droplet Q123, and the first united ink droplet Q123 and the second united ink droplet Q45 are united to land on the recording paper 41 as one ink droplet Q12345. .

The ejection speeds v1 to v5 of the ink droplets Q1 to Q5
May be adjusted by adjusting the amplitude of the pulse of the drive signal, the inclination angle of the rising waveform, the pulse interval or the pulse width as in the first or second embodiment, and may be adjusted at the reference interval as in the third embodiment. The adjustment may be performed by supplying a drive signal including a pulse signal arranged in a line and a pulse signal arranged in an integer multiple of the reference interval. Further, other drive signals may be used.

<Other Embodiments> The First to Fourth Embodiments
In the above, the pulse signal included in the drive signal has a trapezoidal waveform, but the pulse signal included in the drive signal may be a rectangular pulse signal. The rectangular pulse signal can be easily generated simply by turning on / off the selection circuit 31 (see FIG. 6) between the first potential and the second potential. Therefore, if the drive signal is formed by only rectangular pulses, the drive signal need not be generated in advance, and the drive signal generation circuit 30 can be omitted. Therefore, the configuration of the control circuit 20 can be simplified, and the cost can be reduced.

[0070]

As described above, according to the present invention, it is not necessary to eject three or more ink droplets at a high speed in the order of ejection, so that the ink droplets ejected later are ejected stably. The ink droplets can be stably combined before landing. Therefore, printing or printing with excellent gradation can be executed with high accuracy, and advanced ink jet recording can be realized.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an ink jet recording apparatus according to an embodiment.

FIG. 2 is a partial plan view of the inkjet head.

FIG. 3 is a sectional view taken along line AA of FIG. 2;

FIG. 4 is a partial sectional view near an actuator.

FIG. 5 is a sectional view taken along line BB of FIG. 2;

FIG. 6 is a block diagram of a control circuit.

FIG. 7 is a waveform diagram of a drive signal.

FIGS. 8A to 8H are diagrams illustrating the behavior of ink droplets.

FIG. 9 is a waveform diagram of a drive signal.

FIG. 10 is a waveform diagram of a drive signal.

FIGS. 11A to 11H are diagrams illustrating the behavior of ink droplets.

FIG. 12 is a waveform diagram of a drive signal.

FIG. 13 is a waveform diagram of a drive signal.

14A to 14H are diagrams illustrating behavior of ink droplets.

FIGS. 15A to 15I are diagrams illustrating behavior of ink droplets.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ink jet head 2 Nozzle 4 Pressure chamber 10 Actuator 11 Vibration plate 13 Piezoelectric element 14 Individual electrode 20 Control circuit 40 Head main body 41 Recording paper

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2C056 EA04 EC07 EC42 ED01 FA04 FA10 2C057 AF39 AG12 AG44 AN01 AR08 BA04 BA14 CA01

Claims (18)

[Claims] 1. An ink jet head which sequentially discharges at least first to third ink droplets from a nozzle, combines these ink droplets, and lands on a recording medium. An inkjet head in which the ejection speed v2 of the second ink droplet and the ejection speed v3 of the third ink droplet satisfy v1 ≧ v2 or v2 ≧ v3. 2. The ink jet head according to claim 1, wherein v2 ≦ v1 <v3. 3. The ink jet head according to claim 1, wherein the second ink droplet and the third ink droplet are merged into a merged ink droplet, and then the merged ink droplet and the first ink droplet are merged. Inkjet head. 4. The ink jet head according to claim 1, wherein v1 <v3 <v2. 5. The ink jet head according to claim 1, wherein the first ink droplet and the second ink droplet are merged into a merged ink droplet, and then the merged ink droplet and the third ink droplet are merged. Inkjet head. 6. An ink jet head that sequentially discharges at least first to fourth ink droplets from nozzles, combines these ink droplets, and lands on a recording medium. The ejection speed v2 of the second ink droplet, the ejection speed v3 of the third ink droplet, and the ejection speed v4 of the fourth ink droplet are v1 ≧ v2, or v2 ≧ v3, or v3 ≧ v4.
Inkjet head. 7. The ink jet head according to claim 6, wherein v1 <v2 v3 <v2 v3 <v4. 8. The ink jet head according to claim 6, wherein the first ink droplet and the second ink droplet are combined to form a first combined ink droplet, while the third ink droplet and the fourth ink droplet are combined. An ink jet head that combines the first and second combined ink droplets into a second combined ink droplet. 9. An ink jet head that sequentially discharges at least first to fifth ink droplets from nozzles, combines these ink droplets, and lands on a recording medium, wherein the discharge speed v1 of the first ink droplet is The ejection speed v2 of the second ink droplet, the ejection speed v3 of the third ink droplet, the ejection speed v4 of the fourth ink droplet, and the ejection speed v5 of the fifth ink droplet are: v1 ≧ v2, or v2 ≧ v3, or v3 ≧ v
4, or an inkjet head satisfying v4 ≧ v5. 10. The ink jet head according to claim 9, wherein v3> v4 v4 <v5. 11. The ink jet head according to claim 9, wherein the first to third ink droplets are combined into a first combined ink droplet, while the fourth ink droplet and the fifth ink droplet are combined. An ink jet head for forming a second united ink droplet and then merging the first united ink droplet and the second united ink droplet. 12. The ink jet head according to claim 1, further comprising: a pressure chamber containing ink; a nozzle communicating with the pressure chamber; and a piezoelectric element. An actuator that applies pressure to ink in the pressure chamber by the piezoelectric effect to eject ink droplets from the nozzles; and a drive signal supply unit that supplies a plurality of drive pulse signals having different amplitudes to the actuator. Inkjet head. 13. The ink jet head according to claim 1, further comprising: a pressure chamber containing ink; a nozzle communicating with the pressure chamber; and a piezoelectric element. An actuator that applies pressure to the ink in the pressure chamber by the piezoelectric effect to eject ink droplets from the nozzles; and a pressure waveform component that drives the actuator to the side that presses the pressure chamber with respect to the actuator. An inkjet head comprising: a pressure-reducing waveform component for driving the actuator on a side for reducing the pressure in the pressure chamber; 14. The ink jet head according to claim 1, further comprising: a pressure chamber containing ink; a nozzle communicating with the pressure chamber; and a piezoelectric element. An actuator that applies pressure to ink in the pressure chamber by the piezoelectric effect to eject ink droplets from the nozzles; and a drive signal supply unit that supplies a plurality of drive pulse signals having different pulse intervals to the actuator. Inkjet head. 15. The ink jet head according to claim 1, further comprising: a pressure chamber containing ink; a nozzle communicating with the pressure chamber; and a piezoelectric element. An actuator that applies pressure to ink in the pressure chamber by the piezoelectric effect to eject ink droplets from the nozzles; and a drive signal supply unit that supplies a plurality of drive pulse signals having different pulse widths to the actuator. Inkjet head. 16. The ink jet head according to claim 1, further comprising: a pressure chamber containing ink; a nozzle communicating with the pressure chamber; and a piezoelectric element. An actuator that applies pressure to the ink in the pressure chamber by the piezoelectric effect to eject ink droplets from the nozzles; A driving signal supply unit for supplying a driving pulse signal including the pulse signal. 17. The ink jet head according to claim 14, wherein the drive pulse signal is a rectangular pulse signal. 18. An ink jet recording apparatus comprising the ink jet head according to claim 1.