JP2003175599A - Ink jet head and ink jet recording apparatus - Google Patents

Abstract

(57) [Problem] To increase the speed of printing in an ink jet head that ejects a plurality of ink droplets within one printing cycle, combines these ink droplets during flight, and lands on recording paper. SOLUTION: A first pulse P1, a second pulse P2, and a third pulse P2 are provided.
The pulse P3 and the fourth pulse P4 are applied at intervals equal to or shorter than the Helmholtz period of the head. The pulses P1 to P4 are set to resonate the meniscus vibration of the ink. Fall time t ₁ of the first pulse P1 is set below the Helmholtz period, the second to fourth pulse P2~P4
Fall time t ₂ ~t ₄ of is set in the following half cycle of the Helmholtz period. Fall time t ₁ of the first pulse P1 is set to be longer than the fall time t ₂ ~t ₄ of the second to fourth pulse P2 to P4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inkjet head and an inkjet recording apparatus.

[0002]

2. Description of the Related Art Conventionally, for so-called multi-gradation printing and the like, a plurality of ink droplets are ejected from one nozzle of an ink jet head within one printing cycle, and one ink dot is formed by these plurality of ink droplets. Inkjet recording devices are known.

In general, an ink jet head mounted on an ink jet recording apparatus of this type has a head body having a pressure chamber for accommodating ink and a nozzle communicating with the pressure chamber, and ejects ink droplets from the nozzle. An actuator that applies a pressure to the ink in the pressure chamber so as to perform the driving, and a drive signal supply unit that supplies a drive signal to the actuator are provided. In order to reduce the size of the head and the like, an actuator having a piezoelectric element is often used.

In the recording operation, first, the drive signal supply section supplies a drive signal containing one or more pulses during one printing cycle. Then, the actuator that receives the drive signal ejects the ink in the pressure chamber from the nozzle to eject the same number of ink droplets as the number of pulses. The ejected ink droplets land on the recording paper in the ejection order to form one ink dot. By accumulating a large number of such ink dots on the recording paper, a predetermined image or the like is formed on the recording paper. Here, the density and size of dots are adjusted by adjusting the number of ink droplets ejected in one printing cycle. As a result, so-called multi-tone printing is performed.

However, when high-speed printing is performed, the carriage speed of the ink jet head is high, so that a plurality of ink droplets ejected from the same nozzle easily land at positions displaced in the carriage direction. As a result, the ink dots become oblong in the carriage direction, and the image quality is likely to deteriorate.

Therefore, in order to enable high-speed printing, for example, as disclosed in Japanese Patent Laid-Open No. 8-336970, the ejection speed of ink droplets ejected later is faster than the ejection speed of ink droplets ejected first. It has been proposed that by increasing the size, two ink droplets ejected from the same nozzle are combined during flight to form one ink droplet and then landed.

The above-mentioned ink jet head is premised on applying a pulse signal with a period longer than the Helmholtz period of the head, and then changing the inclination angle of the rising waveform or the falling waveform of the pulse signal,
The focus is on the fact that the amount of ink meniscus drawn in the nozzle changes and the ejection speed of the ink droplet changes. In the above-mentioned inkjet head, the ejection speed of the ink droplet ejected later is made higher than the ejection speed of the ink droplet ejected before by adjusting the inclination angle of the rising waveform or the falling waveform of the pulse signal.

[0008]

However, in the above ink jet head, since the application period of each pulse signal is longer than the Helmholtz period, one printing period is necessarily longer than the Helmholtz period by several pulses. for that reason,
It was difficult to increase the driving frequency, and it was difficult to further increase the printing speed. Therefore, a new technology that enables higher-speed printing has been desired.

The present invention has been made in view of the above point, and an object of the present invention is to eject a plurality of ink droplets within one printing cycle and combine the ink droplets during flight, and In an ink jet type recording apparatus provided with it, it is intended to further speed up printing.

[0010]

An ink jet head according to the present invention includes a head body in which a nozzle and a pressure chamber communicating with the nozzle and filled with ink are formed, a piezoelectric element and a voltage applied to the piezoelectric element. An actuator having an applying electrode and applying a pressure to the ink in the pressure chamber by the piezoelectric effect of the piezoelectric element, and a signal for supplying the actuator with a drive signal including a plurality of pulse signals in one printing cycle. An inkjet head provided with a supply means, wherein the plurality of pulse signals are ejected in such a manner that the ink meniscus vibration caused by the subsequent pulse signal resonates with the ink meniscus vibration caused by the preceding pulse signal. Ink droplets are set to coalesce during flight, and the peak potential is changed from the reference potential in the first pulse signal. Potential change time in are those that are set longer than the potential variation time from the reference potential to peak potential after the pulse signal.

As a result, the latter pulse signal is applied in a relatively short time from the preceding pulse signal so that the meniscus vibration of the ink resonates, so that the time of one printing cycle can be shortened. . Therefore, the printing speed can be increased. The plurality of ink droplets ejected by the application of the pulse signal coalesce during the flight and become one ink droplet and land on the recording paper. Therefore, the ink dots do not become elliptical and the recording quality is improved. Since the potential change time of the first pulse signal is set longer than the potential change time of the subsequent pulse signal, the drawing speed of the ink meniscus in the nozzle by the first pulse signal is the drawing speed of the ink meniscus by the subsequent pulse signal. It becomes slower than the speed. Therefore, the ink droplets ejected by the first application of the pulse signal have a lower ejection speed than the ink droplets ejected by the subsequent application of the pulse signal. Therefore, the ink droplets ejected later easily catch up with the ink droplets ejected first, and it becomes easy to combine the plurality of ink droplets during flight. Therefore, stable flight of ink droplets can be obtained even if the time of one printing cycle is shortened. As a result, the quality of the recording is improved.

The potential change time from the reference potential to the peak potential in the first pulse signal may be set to be less than the Helmholtz cycle of the head.

As a result, the printing speed can be increased.

Further, the potential change time from the reference potential to the peak potential in the later pulse signal may be set to a half cycle or less of the Helmholtz cycle.

As a result, the ejection speed of the ink droplets after the coalescence is high, and the landing accuracy is improved.

An ink jet head according to the present invention has a head body in which a nozzle and a pressure chamber communicating with the nozzle and filled with ink are formed, a piezoelectric element and an electrode for applying a voltage to the piezoelectric element. And an actuator that applies pressure to the ink in the pressure chamber by the piezoelectric effect of the piezoelectric element, and a signal supply unit that supplies the actuator with a drive signal including a plurality of pulse signals within one printing cycle. In the inkjet head, the plurality of pulse signals are such that the ink meniscus vibration due to a later pulse signal resonates with the ink meniscus vibration due to a preceding pulse signal and a plurality of ink droplets ejected by these pulse signals are flying. The pulse signals are set so that the pressure in the pressure chamber is reduced by the reference potential. And a peak potential for driving a chute, and the plurality of pulse signals are a first pulse signal whose potential change time from the reference potential to the peak potential is equal to or less than a half cycle of the Helmholtz cycle of the head, and a peak from the reference potential. The second pulse signal includes a second pulse signal whose potential change time up to the potential is equal to or less than the Helmholtz cycle and longer than the potential change time of the first pulse signal.

As a result, the ink droplet ejected by the second pulse signal (hereinafter referred to as the second ink droplet) is ejected by the first pulse signal (hereinafter referred to as the first ink droplet).
Since the ejection speed is slower than that of ink droplets)
The ink droplets easily catch up with the second ink droplet and the ink droplets easily coalesce. Therefore, as described above, the printing speed can be increased and the recording quality can be improved.

An ink jet head according to the present invention has a head main body in which a nozzle and a pressure chamber communicating with the nozzle and filled with ink are formed, a piezoelectric element and an electrode for applying a voltage to the piezoelectric element. And an actuator that applies pressure to the ink in the pressure chamber by the piezoelectric effect of the piezoelectric element, and a signal supply unit that supplies the actuator with a drive signal including a plurality of pulse signals within one printing cycle. In the inkjet head, the plurality of pulse signals include two or more pulse signals having different pulse heights, and the ink meniscus vibration due to the subsequent pulse signal resonates with the ink meniscus vibration due to the preceding pulse signal. The plurality of ink droplets ejected by the pulse signal are set so as to be combined during flight.

As a result, an ink droplet ejected by a pulse signal having a low pulse height (hereinafter referred to as a second ink droplet) is an ink droplet ejected by a pulse signal having a high pulse height (hereinafter referred to as a first ink droplet). Since the ejection speed is slower than that of the first ink droplet, the first ink droplet easily catches up with the second ink droplet, and the ink droplets easily coalesce. Therefore, as described above, the printing speed can be increased and the recording quality can be improved.

In the ink jet head, it is preferable that the pulse height of the first pulse signal is set lower than the pulse height of the subsequent pulse signal.

As a result, the first ejected ink droplet has a lower ejection velocity than the later ejected ink droplet, and the combination of the first ejected ink droplet and the subsequent ink droplet is smooth and reliable. To be done.

Each of the pulse signals has a reference potential and a peak potential for driving the actuator so as to reduce the pressure in the pressure chamber. The peak potential of each pulse signal is the ground potential and has different pulse heights. The reference potentials of the pulse signals are preferably different from each other.

As a result, the peak potential of the pulse signal is shared as the ground potential. Therefore, the pulse height, which is the difference between the reference potential and the peak potential, is determined by the reference potential. Therefore, between the pulse signals, the difference in reference potential becomes the difference in pulse height. Since the reference potential can be easily adjusted, the pulse height can be easily adjusted, and an error in pulse height between pulse signals is less likely to occur.

The thickness of the piezoelectric element of the actuator may be set to 0.5 μm to 5 μm.

An ink jet recording apparatus according to the present invention comprises the ink jet head and a moving means for relatively moving the ink jet head and the recording medium.

As a result, it is possible to obtain a recording apparatus that records at high speed and with high quality.

[0027]

As described above, according to the present invention, since a plurality of pulse signals are applied so as to resonate the meniscus vibration of ink, the time of one printing cycle can be shortened and the printing speed can be increased. Can be realized.

Since the potential change time of the first pulse signal is set longer than the potential change time of the subsequent pulse signal, it becomes easy to combine a plurality of ink droplets during flight.

Since the potential change time of the second pulse signal is set longer than the potential change time of the first pulse signal,
The ink droplets ejected by the first pulse signal easily catch up with the ink droplets ejected by the second pulse signal.
Therefore, it becomes easy to combine a plurality of ink drops, and the stability of the combination is improved.

Further, since two or more pulse signals having different pulse heights are used, ink droplets ejected by a pulse signal having a high pulse height are ejected more than ink droplets ejected by a pulse signal having a low pulse height. The speed increases.
Therefore, it becomes easy to combine a plurality of ink drops, and the stability of the combination is improved.

Therefore, according to the present invention, further high speed printing is possible and high quality recording is facilitated.

[0032]

BEST MODE FOR CARRYING OUT THE INVENTION <Relationship Between Driving Signal and Ejection Performance>
Prior to the description of the embodiments of the present invention, the relationship between the drive signal and the ejection performance will be described.

FIG. 1 is a diagram showing the relationship between the waveform of the drive signal, the displacement of the actuator, and the state of the ink meniscus. The drive signal is a pulse signal P having a reference potential V0 and a peak potential V1. The peak potential V1 is a potential that drives the actuator so as to reduce the pressure chamber, in other words, a potential that drives the actuator so as to increase the volume of the pressure chamber. The main drive signal is a signal that decompresses the pressure chamber and then pressurizes it, and is a signal that pushes the ink meniscus once into the nozzle and then pushes it out (a signal of a so-called pull-push waveform). In the drive signals of FIG. 1 and FIGS. 2 to 4 to be described later, in order to utilize resonance, the time from the start of the potential drop waveform S1 of the pulse signal P to the start of the potential rise waveform S3 is equal to the Helmholtz cycle. It is set to half cycle. For comparison with the drive signals of FIGS. 2 to 4, the drive signal of FIG. 1 will be referred to as a basic signal below.

Here, the droplet amount of the ejected ink is influenced by the displacement amount of the actuator and the drawing amount of the meniscus, and between the difference between the displacement amount and the drawing amount and the droplet amount, There is a correlation. The ejection speed of the liquid droplets has a correlation with the displacement speed of the actuator (that is, the inclination of the actuator displacement curve in FIG. 1).

As shown in FIG. 2, when the slope of the potential drop waveform S1 of the pulse signal P is made gentle, the displacement amount of the actuator is reduced, but the pulling amount of the meniscus is also reduced. Therefore, the droplet amount m2 of the ejected ink is substantially equal to or slightly smaller than the droplet amount m1 of the ink ejected by the basic signal. On the other hand, since the displacement amount of the actuator has decreased, the inclination of the displacement curve becomes gentle. Therefore, the ejection speed v2 is lower than the ejection speed v1 of the ink ejected by the basic signal. That is, m2 ≦ m1 and v2 <v1.

As shown in FIG. 3, when the slope of the potential rising waveform S3 of the pulse signal P is made gentle so that the ejection speed becomes substantially equal to v2, the pulling-in amount of the meniscus is the same as that of the basic signal, but the actuator is The displacement amount of is slightly reduced. Therefore, the droplet amount m3 is smaller than m2. Also, because the displacement of the actuator has decreased,
The inclination of the displacement curve becomes gentle, and the ejection speed v3 becomes smaller than v1. That is, m3 <m2 ≦ m1, v3≈v
2 <v1.

As shown in FIG. 4, when the pulse height of the pulse signal P is slightly lowered so that the ejection speed becomes substantially equal to v2, the displacement amount of the actuator is reduced, but the retraction amount of the meniscus is smaller than that of the basic signal. Also decreases slightly. Therefore, the droplet amount m4 is smaller than m1 but larger than m3. In addition, since the displacement amount of the actuator is reduced, the inclination of the displacement curve becomes gentle, and the discharge speed v4 becomes
It becomes smaller than 1. That is, m3 <m4 <m1, v4
≈v3≈v2 <v1.

As described above, regarding the droplet amount, m3 <
The relationship of m2 ≦ m1 and m3 <m4 <m1 is found, and the relationship of ejection speed is v4≈v3≈v2 <v1.

Experiments were conducted to actually measure the discharge speed and the droplet amount using the drive signals shown in FIGS. FIG. 5 shows the measurement conditions and the measurement results. From this experiment, it was confirmed that the above relationship was correct.

<First Embodiment> An embodiment of the present invention will be described below with reference to the drawings.

FIG. 6 shows a schematic structure of a printer 20 as an ink jet recording apparatus. Printer 20
Includes an inkjet head 1 fixed to a carriage 16. The carriage 16 is provided with a carriage motor 28 (see FIG. 11) not shown in FIG. The carriage 16 is configured to be guided by a carriage shaft 28 extending in the main scanning direction (X direction shown in FIGS. 6 and 7) by a carriage motor 28 and reciprocate in that direction. Since the inkjet head 1 is mounted on the carriage 16, the inkjet head 1 also reciprocates in the main scanning direction X as the carriage 16 reciprocates. The carriage 16, the carriage shaft 17, and the carriage motor 28 constitute a moving unit that relatively moves the inkjet head 1 and the recording paper 41.

The recording paper 41 is rotatably driven by a conveyance motor 26 (see FIG. 11) which is not shown in FIG.
It is sandwiched between two conveyor rollers 42,
6 and each of the transport rollers 42 transport the sheet in the sub-scanning direction (Y direction shown in FIGS. 6 and 7) orthogonal to the main scanning direction X.

As shown in FIGS. 7 to 10, the ink jet head 1 includes a head body 40 having a plurality of pressure chambers 4 for containing ink and a plurality of nozzles 2 communicating with the pressure chambers 4, respectively. An actuator 10 that applies a pressure to the ink in each pressure chamber 4 is provided. The actuator 10 is a piezo-type actuator having a piezoelectric element 13, and is a so-called flexural vibration type actuator in which the vibration plate 11 fixed to the piezoelectric element 13 is flexibly deformed. The actuator 10 discharges ink droplets from the nozzle 2 and fills the pressure chamber 4 with ink due to the pressure change in the pressure chamber 4 due to the contraction and expansion of the pressure chamber 4.

As shown in FIG. 7, the pressure chambers 4 are formed inside the ink jet head 1 in the form of long grooves extending in the main scanning direction X, and are arranged at predetermined intervals in the sub scanning direction Y. There is. The nozzle 2 is provided at one end (the right end in FIG. 7) of the pressure chamber 4. Nozzle 2,2
Are provided on the lower surface of the inkjet head 1 so as to be opened at predetermined intervals in the sub-scanning direction Y. The other end of the pressure chamber 4 (the left end in FIG. 7) is
It is continuous with one end of the ink supply path 5. The other end of each ink supply path 5 has an ink supply chamber 3 extending in the sub-scanning direction Y.
In succession.

As shown in FIG. 8, in the ink jet head 1, a nozzle plate 6 having nozzles 2 formed therein, a partition wall 7 for partitioning and forming a pressure chamber 4 and an ink supply passage 5, and an actuator 10 are sequentially laminated. Is configured.
The nozzle plate 6 is made of a polyimide plate having a thickness of 20 μm, and the partition wall 7 is made of a stainless laminate plate of 480 μm thickness or a laminate plate of stainless steel and photosensitive glass.

As exaggeratedly shown in FIGS. 9 and 10, the actuator 10 includes a vibrating plate 11 for covering the pressure chamber 4, a thin film piezoelectric element 13 for vibrating the vibrating plate 11, and an individual electrode 14 which are sequentially laminated. Is configured. Diaphragm 11
Is a chrome plate with a thickness of 2 μm,
4 also has a function as a common electrode for applying a voltage to the piezoelectric element 13. The piezoelectric element 13 is provided corresponding to the pressure chamber 4 and has a thickness of 0.5 μm to 5 μm.
PZT (lead zircolate titanate) or the like can be preferably used. In this embodiment, the piezoelectric element 13 has a thickness of 3
It is set to μm. The individual electrode 14 has a thickness of 0.1 μm
Of the platinum plate, and the total thickness of the actuator 10 is about 5 μm. An insulating layer 15 made of polyimide is provided between the piezoelectric element 13 and the individual electrode 14 which are adjacent to each other.

Next, the control circuit 35 of the printer 20 will be described with reference to the block diagram of FIG. The control circuit 35 drives and controls the main control unit 21 including a CPU, the ROM 22 that stores routines for processing various data, the RAM 23 that stores various data, and the carry motor 26 and the carriage motor 28. Driver circuits 25, 27 and a motor control circuit 24, a data receiving circuit 29 for receiving print data, a drive signal generating circuit 30, and a selecting circuit 31. The actuator 10 is connected to the selection circuit 31. The drive signal generation circuit 30 generates a drive signal having a plurality of pulse signals within one printing cycle. The selection circuit 31 selectively inputs one or more drive pulses included in the drive signal to the actuator 10 while the inkjet head 1 is moving in the main scanning direction X together with the carriage 16. The drive signal generation circuit 30 and the selection circuit 31 constitute a signal supply means 32 for supplying a predetermined drive signal to the actuator 10.

Next, the operation of the printer 20 will be described. First, when image data is transmitted from the printer body (not shown) and the data receiving circuit 29 receives this image data, the main control unit 21 executes the motor control circuit 24 and the driver based on the processing routine stored in the ROM 22. The carriage motor 26 and the carriage motor 28 are respectively controlled via the circuits 25 and 27, and the drive signal generation circuit 30 is caused to generate a drive signal. Further, the main controller 21
Outputs information on the pulse signal to be selected to the selection circuit 31 based on the image data. Then, the selection circuit 31 selects a predetermined one or more drive pulses from the plurality of drive pulses based on the above information and supplies the selected drive pulse to the actuator 10. For example, when ejecting one ink droplet within one printing cycle, one pulse signal is selected, and when ejecting two ink droplets, two pulse signals are selected. As a result, one or more ink droplets are ejected from the nozzle 2 of the inkjet head 1 within one printing cycle.

The pulse intervals of the plurality of pulse signals applied within one printing cycle are set to be equal to or less than the Helmholtz cycle of the ink jet head 1. The Helmholtz cycle here means not only the ink but also the actuator 1
Natural period (resonance period) of the entire vibration system including the effect of 0
Say. Further, the plurality of pulse signals are set so that the plurality of ink droplets ejected by the application of these pulse signals coalesce during flight. The plurality of pulse signals are set such that the falling time of the falling waveform of the first pulse signal is longer than the falling time of the falling waveform of the subsequent pulse signal.

Next, with reference to FIG. 12, a case will be described in which four ink droplets are ejected from the nozzle 2 within one printing cycle T. Here, the drive signal supplied to the actuator 10 includes four trapezoidal wave pulses P1 to P4, that is, a first pulse P1, a second pulse P2, a third pulse P3, and a fourth pulse P4. Each pulse P1
P4 is a pulse signal that drives the actuator 10 so as to depressurize the pressure chamber 4 and then pressurize it. In other words, P4 ejects ink droplets by causing the actuator 10 to perform a pull-push operation (so-called pull-push operation). It is a signal to make.

The first to fourth pulses P1 to P4 are arranged in such an order that the pulse interval gradually approaches the Helmholtz cycle (however, the pulse intervals of some adjacent pulses may be equal. The order should be closer to the Helmholtz cycle). However, the pulse intervals of the first to fourth pulses P1 to P4 are not limited to the above intervals as long as the first to fourth ink droplets ejected by these pulses can be combined during flight. .

The fall time t ₁ of the fall waveform P11 of the first pulse P1 is set to be less than the Helmholtz cycle. The falling time t ₂ of the falling waveform P21 of the second pulse P2 and the falling waveform P of the third pulse P3
31 fall time t _3, and the fall time t ₄ of the falling waveform P41 of the fourth pulse P4 are both set to less than half the value of the Helmholtz period (half period).

By the way, in the conventional ink jet head disclosed in the above-mentioned Japanese Patent Laid-Open No. 8-336970, a plurality of pulses expand the pressure chamber for a time longer than the Helmholtz cycle, and the meniscus of the ink is introduced into the nozzle. I was withdrawn. Since the pull-in time is longer than the Helmholtz cycle, the resonance of the meniscus vibration does not occur, and the displacement of the actuator does not change even if the pull-in time is changed. In other words, the conventional inkjet head adjusts the liquid amount and the ejection speed of the ink droplet only by adjusting the pulling-in amount of the meniscus without changing the displacement of the actuator.

On the other hand, in this embodiment, resonance of ink meniscus vibration is used. In particular,
By pulling in the meniscus in a time shorter than the Helmholtz cycle and adjusting the fall time of the pulse, both the pulling-in amount of the meniscus and the displacement of the actuator are adjusted. In this embodiment, since the pull-in time (pulse fall time) is shorter than the Helmholtz cycle, the displacement of the actuator can be changed depending on the pull-in time. Therefore, the longer the pull-in time, the smaller the displacement of the actuator. for that reason,
When ejecting an ink droplet having a slow ejection speed, the displacement of the actuator is reduced by lengthening the pull-in time. In this case, the appropriate amount of ink droplets is also slightly reduced.

When the drive signal is supplied to the actuator 10, first, the first ink droplet is ejected by the first pulse P1. Then, the second pulse P2 is applied, and the resonance of the ink meniscus vibration causes the second ink droplet to be ejected at an ejection speed v2 higher than the ejection speed v1 of the first ink droplet. Further, the third pulse P3 is applied, and the resonance of the ink meniscus vibration causes the third ink droplet to be ejected at the ejection speed v3 that is equal to or higher than the ejection speed v2 of the second ink droplet. Then, the fourth pulse P4 is further applied, and the resonance of the ink meniscus vibration causes the fourth ink droplet to be ejected at the ejection speed v4 that is equal to or higher than the ejection speed v3 of the third ink droplet. That is, v1 <v2 ≦ v3 ≦ v4.

The first to fourth ink droplets ejected by the first to fourth pulses P1 to P4 coalesce into one ink droplet during flight and land on the recording paper 41 to form a single ink dot. Form. As a result, even in the case of high-speed printing, good ink dots are formed without the ink dots becoming oblong.

The term "coalescence of ink droplets" as used herein means not only the case where completely separated ink droplets are integrated in the air but also the presence of each ink droplet although some of them are connected. It also includes a case in which the ink droplets that are divided into visible portions are integrated to the extent that the existence of each ink droplet is unknown.

As described above, according to the present embodiment, since a plurality of pulse signals are continuously applied so that the ink meniscus vibration resonates, a plurality of inks for forming a combined ink drop is formed. Drops can be ejected in a short time. Therefore, the driving frequency can be improved and high-speed printing can be realized.

[0059] Since the fall time t ₁ of the first pulse P1 and longer than the fall time t ₂ ~t ₄ of the second to fourth pulse P2 to P4, the first ink droplet ejected by the first pulse P1 Discharge speed v1 of the second to fourth pulse P2
.About.P4, the ejection speeds v2 to v4 of the second to fourth ink droplets ejected can be made smaller.

Since the ejection speed of the first ink droplet is low as described above, even if the ejection speed v3 of the third ink droplet is equal to the ejection speed v2 of the second ink droplet, the second ink droplet and the first ink droplet Combined ink droplets, which are formed by coalescing with ink droplets,
The ejection speed is lower than that of the third ink droplet. for that reason,
The third ink droplet easily merges with the merged ink droplet. Similarly, the fourth ink droplet is also likely to combine with the combined ink droplet formed by combining the first to third ink droplets.

Therefore, according to the present embodiment, it becomes easy to combine a plurality of ink drops during flight, and a good single dot can be formed on the recording paper 41 by the combined ink drops. Therefore, high quality recording can be performed.

The pulse signals P1 to P of the above embodiment are
Although 4 is a signal that causes the actuator 10 to perform a pull-push operation, the pulse signals P1 to P4 may be signals that cause the actuator 10 to perform a push-pull operation (push-pull operation).

The number of pulses included in one printing cycle is not limited to 4, and may be 2 or 3, or 5 or more.

-Examples- Next, examples will be described. In this embodiment, the reference potential _VH , the negative pressure potential _VL , and the first to fourth pulses P1 to P4.
The fall times t _{1 to} t ₄ of each of these are set to the values shown in Table 1, respectively. In this embodiment, the Helmholtz cycle is 8
μs.

[0065]

[Table 1]

When the first to fourth pulses P1 to P4 are applied, the first to fourth ink droplets coalesce during flight and become one ink droplet on the recording paper at an ejection speed of about 8 m / s. It landed. As a result, a single good ink dot was formed on the recording paper.

<Embodiment 2> In Embodiment 1, among the plurality of pulse signals applied in one printing cycle, the falling time t ₁ of the first pulse P1 is changed to the subsequent pulses P2 to P2.
No. ₄ fall time t _{2 to} t ₄ . On the other hand, as shown in FIG.
The fall time t ₂ of the second pulse P2 is made longer than the fall times t ₁ , t ₃ , t ₄ of the other pulses P1, P3, P4.

The drive signals of this embodiment are the pulse signals P1 to P4 for ejecting the first to fourth inks, and the auxiliary pulse signal P for driving the actuator to the extent that ink is not ejected.
5 and 5. The auxiliary pulse signal P5 suppresses residual vibration of the actuator or suppresses an increase in ink viscosity in the nozzle.

The pulse signals P1 to P4 are combined such that the ink meniscus vibration due to the subsequent pulse signal resonates with the ink meniscus vibration due to the preceding pulse signal, and a plurality of ink droplets ejected by these pulse signals coalesce during flight. Is set to. Further, the pulse signals P1 and P
The falling times t ₁ , t ₃ , and t ₄ of P3 and P4 are set to be half or less of the Helmholtz cycle. On the other hand, the fall time t ₂ of the second pulse signal P2 is equal to or less than the Helmholtz cycle and is set longer than any of the fall times t ₁ , t ₃ , and t ₄ . In the present embodiment, the first pulse signal P1, the third pulse signal P3, and the fourth pulse signal P4 correspond to the “first pulse signal” in the present invention, and the second pulse signal P2 is It corresponds to the "second pulse signal".

In this embodiment, the amount of the second ink droplet ejected by the second pulse P2 does not change so much, but the ejection speed becomes relatively small. Therefore, the third ink droplet ejected by the third pulse P3 easily catches up with the second ink droplet, and the stability of coalescence of these ink droplets is improved. Since the resonance is used in the present embodiment, the ejection speed of the fourth ink droplet ejected by the fourth pulse P4 is increased, and the fourth ink droplet catches up with the ink droplet after being combined. Finally, all the first to fourth ink droplets will be combined.

Also in this embodiment, the number of pulses included in one printing cycle is not limited to 4, and may be 2 or 3, or 5 or more. The pulse whose fall time is longer than other pulses (the “second pulse” in the present invention) is not limited to the second pulse, and may be the third pulse or later. In addition, the number of the above-mentioned pulse (= “second pulse”) included in one printing cycle is not limited to 1 and may be 2
It may be more than.

<Third Embodiment> In the third embodiment, the ejection speed is reduced by decreasing the pulse height, instead of decreasing the ejection speed by lengthening the pulse fall time.

[0073] driving signals shown in FIG. 14 is made from the first to third pulses P1 to P3, the pulse height V _H2 -V _L of the first pulse P1 and the second pulse P2, pulse height of a subsequent pulse P3 The height is set lower than V _H1 -V _L. Note that, like the first pulse P1 and the second pulse P2 of the present embodiment, the value of the reference potential may differ before and after the pulse depending on the pulse. Here, the pulse height is the smaller of the difference between the reference potential and the peak potential at the start of the fall of the falling waveform and the difference between the reference potential and the peak potential after the end of the rise of the rising waveform. Shall be said.

The first to third pulses P1 to P3 are such that the ink meniscus vibration caused by the subsequent pulse signal resonates with the ink meniscus vibration caused by the preceding pulse signal, and a plurality of ink droplets ejected by these pulse signals are generated. It is set to coalesce during flight.

According to the drive signal, the ejection speeds of the first ink droplet and the second ink droplet are reduced, and the third ink droplet easily catches up with the first ink droplet and the second ink droplet. Therefore, the stability of the combination of the first to third ink droplets can be improved. Also, of the multiple ink drops,
Since the ejection speed of the ink droplets ejected toward the beginning is reduced, it is possible to smoothly and reliably combine the ink droplets with the subsequent ink droplets. Therefore, the stability of the coalescence can be further improved.

The number of pulses included in one printing cycle is not limited to 3, and may be 2 or 4 or more.

For example, like the drive signal shown in FIG.
It may include four pulse signals P1 to P4. Further, the auxiliary pulse signal P5 for driving the actuator to the extent that ink is not ejected may be included. The auxiliary pulse signal P5 suppresses residual vibration of the actuator or suppresses an increase in ink viscosity in the nozzle.
Also in the above drive signal, the pulse heights V _H2 -V _L of the first pulse P1 and the second pulse P2 are
It is set lower than the pulse heights V _H1 -V _{L of} P3 and P4. Therefore, the stability of the coalescence of the ink droplets can also be improved by the drive signal.

As a method of changing the pulse height,
The reference potential V_HValue of peak potential while keeping V constant_LStrange
It can also be turned into. However, depending on the configuration of the drive circuit
Peak voltage V_LCan be set to ground potential (GND)
Since it is preferable, in such a case, the peak potential V_LTo
Reference potential V while keeping constant (= ground potential)_HThe value of
Preferably. As shown in Fig. 16 (a), grounding
Potential V other than potential_L1After reaching the peak potential, raise the potential
An error is likely to occur when the temperature is raised, and the value of the reference potential V _H= V
_L1This is because + ΔV easily becomes unstable. Against this
Then, as shown in FIG. 16B, the peak potential V_LGround
If the potential, the value of the reference potential V_H2= ΔV is easy to stabilize
This makes it easier to adjust the peak height accurately.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship among a waveform of a drive signal, an actuator displacement, and a meniscus state.

FIG. 2 is a diagram showing a relationship between a waveform of a drive signal, actuator displacement, and a meniscus state.

FIG. 3 is a diagram showing a relationship between a waveform of a drive signal, actuator displacement, and a meniscus state.

FIG. 4 is a diagram showing a relationship between a waveform of a drive signal, actuator displacement, and a meniscus state.

5A and 5B are diagrams showing a result of a confirmation experiment for examining a relationship between a drive signal and ejection performance, FIG. 5A is a waveform diagram showing definition of parameters, and FIG. 5B is a table showing measurement conditions and measurement results. Is.

FIG. 6 is a schematic configuration diagram of a printer according to an embodiment.

FIG. 7 is a partial plan view of an inkjet head.

8 is a cross-sectional view taken along the line AA of FIG.

FIG. 9 is a partial cross-sectional view near the actuator.

10 is a sectional view taken along line BB of FIG.

FIG. 11 is a block diagram of a control circuit.

FIG. 12 is a waveform diagram of a drive signal according to the first embodiment.

FIG. 13 is a waveform diagram of a drive signal according to the second embodiment.

FIG. 14 is a waveform diagram of a drive signal according to the third embodiment.

FIG. 15 is a waveform diagram of a drive signal according to the third embodiment.

FIG. 16 is a waveform diagram of a drive signal according to the third embodiment.

[Explanation of symbols]

1 inkjet head 2 nozzles 3 ink supply chamber 4 Pressure chamber 10 actuators 11 diaphragm 13 Piezoelectric element 14 individual electrodes 20 Printer (inkjet recording device) 32 signal supply means 35 Control circuit 40 head body 41 Recording paper (recording medium) P1 to P4 pulse signal

Continued front page    (72) Inventor Koji Matsuo             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. (72) Inventor Masafumi Tomita             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. (72) Inventor, Shoji Oyama             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. (72) Inventor Masaichiro Tachikawa             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. F-term (reference) 2C057 AF02 AM17 AM22 AR04 AR08                       BA03 BA14

Claims (9)

[Claims] 1. A head body having a nozzle and a pressure chamber communicating with the nozzle and filled with ink, a piezoelectric element, and an electrode for applying a voltage to the piezoelectric element. An ink jet head comprising: an actuator that applies pressure to ink in the pressure chamber by a piezoelectric effect; and a signal supply unit that supplies a drive signal including a plurality of pulse signals to the actuator in one printing cycle, The plurality of pulse signals are set so that the ink meniscus vibration caused by the subsequent pulse signal resonates with the ink meniscus vibration caused by the preceding pulse signal, and the plurality of ink droplets ejected by these pulse signals coalesce during flight. The potential change time from the reference potential to the peak potential in the first pulse signal is Ink jet head is set to be longer than the potential variation time to peak potential from position. 2. The inkjet head according to claim 1, wherein the potential change time from the reference potential to the peak potential in the first pulse signal is set to be equal to or less than the Helmholtz cycle of the head. 3. The inkjet head according to claim 1, wherein a potential change time from a reference potential to a peak potential in a subsequent pulse signal is set to a half cycle or less of a Helmholtz cycle of the head. head. 4. A head main body having a nozzle and a pressure chamber communicating with the nozzle and filled with ink, a piezoelectric element, and an electrode for applying a voltage to the piezoelectric element. An inkjet head comprising: an actuator that applies a pressure to ink in the pressure chamber by a piezoelectric effect; and a signal supply unit that supplies a drive signal including a plurality of pulse signals in one printing cycle to the actuator, The plurality of pulse signals are set so that the ink meniscus vibration caused by the subsequent pulse signal resonates with the ink meniscus vibration caused by the preceding pulse signal, and the plurality of ink droplets ejected by these pulse signals coalesce during flight. Each of the pulse signals includes a reference potential and a peak potential that drives an actuator to reduce the pressure in the pressure chamber. A plurality of pulse signals, the first pulse signal whose potential change time from the reference potential to the peak potential is equal to or less than a half cycle of the Helmholtz cycle of the head, and the potential change time from the reference potential to the peak potential. An ink jet head including a second pulse signal that is equal to or less than the Helmholtz period and is longer than the potential change time of the first pulse signal. 5. A head body having a nozzle and a pressure chamber communicating with the nozzle and filled with ink, a piezoelectric element, and an electrode for applying a voltage to the piezoelectric element. An inkjet head comprising: an actuator that applies a pressure to ink in the pressure chamber by a piezoelectric effect; and a signal supply unit that supplies a drive signal including a plurality of pulse signals in one printing cycle to the actuator, The plurality of pulse signals include two or more pulse signals having different pulse heights, and the ink meniscus vibration due to the subsequent pulse signal is ejected so as to resonate with the ink meniscus vibration due to the preceding pulse signal. An inkjet head that is set so that multiple ink droplets coalesce during flight. 6. The inkjet head according to claim 5, wherein the pulse height of the first pulse signal is set lower than the pulse height of the subsequent pulse signal. 7. The inkjet head according to claim 5, wherein each of the pulse signals has a reference potential and a peak potential for driving an actuator to reduce the pressure in the pressure chamber. The peak potential of the signal is the ground potential, and the reference potentials of the pulse signals with different pulse heights are different from each other. 8. The ink jet head according to claim 1, wherein the piezoelectric element of the actuator has a thickness of 0.5 μm to 5 μm.
Inkjet head set to. 9. An inkjet recording apparatus comprising: the inkjet head according to claim 1; and a moving unit that relatively moves the inkjet head and a recording medium.