JP2967739B2 - Method and apparatus for driving ink jet print head - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for driving an ink-jet printhead, and more particularly to a method and apparatus for driving a drop-on-demand ink-jet printhead which discharges ink by converting an electric signal into mechanical energy.

[0001]

2. Description of the Related Art A conventional method of driving an ink jet print head of this type is used for driving a drop-on-demand type print head using a piezoelectric element.

A print head receives a piezoelectric element for converting an electric signal into mechanical energy, a vibration plate for transmitting the pressure of the piezoelectric element to a pressure chamber, a nozzle for discharging ink, and ink from a common ink chamber. The pressure chamber communicates with the nozzle and is pressurized by a piezoelectric element. The piezoelectric element is configured to pressurize the pressure chamber when a voltage in the same direction as the polarization direction is applied.

Next, the operation will be described. FIG. 14 shows a waveform of an electric signal applied to drive the piezoelectric element. First, a voltage in the same direction as the polarization direction is raised to the drive voltage V31 for a certain time T31, this voltage V31 is maintained for a certain time T32, and the potential becomes 0 for a certain time T33.
Is returned to. When this drive voltage is applied to the piezoelectric element,
The piezoelectric element expands, and as a result, the pressure inside the pressure chamber increases, and ink is ejected.

The driving method described above (hereinafter referred to as a pushing method) is most commonly used.
A driving method capable of ejecting small ink droplets and efficiently driving a piezoelectric element is disclosed in Japanese Patent Laid-Open No. 63-9485.
No. 0 publication.

FIG. 15 shows a driving waveform disclosed in Japanese Patent Application Laid-Open No. 63-94850.

First, a voltage V21 in the direction opposite to the polarization direction is applied for a certain time T21, then a voltage V22 in the same direction as the polarization direction is applied for a certain time T22, and thereafter the potential is gradually returned to zero. Therefore, first, the reverse voltage V2
When 1 is added, the piezoelectric element contracts, and as a result, the pressure inside the pressure chamber becomes negative, and ink is drawn from the common ink chamber into the pressure chamber. Thereafter, when a voltage V22 in the same direction as the polarization direction is applied for a certain time T22, the piezoelectric element expands, and as a result, the pressure in the pressure chamber increases, and ink is ejected. With this driving method, a smaller ink droplet can be ejected (hereinafter referred to as a pulling method), and a large expansion and contraction of the piezoelectric element can be obtained by the amount of driving in the reverse direction, thereby enabling efficient ink ejection. It is.

[0007]

In the prior art of the above-described pulling method, since the drive waveform is abruptly changed in voltage, the ringing of the piezoelectric element becomes large, and this ringing adversely affects the meniscus vibration, resulting in a stable operation. A large amount of meniscus retraction cannot be obtained.

In the prior art, since the voltage applied to the piezoelectric element is gradually discharged from V22 in the driving waveform shown in FIG. 15, it becomes difficult to control the minimum amount of the ink droplet by the timing of the start of the discharge. The appropriate amount greatly depends on the natural period of the pressure wave inside the pressure chamber, and the influence of variations during manufacturing and the like increases.

This is because when the drive waveform is suddenly changed from V21 to V22 before the discharge, a strong pressure wave is generated from the piezoelectric element, reaches the nozzle inside the pressure chamber, and is reflected by the nozzle. The wave repeats back and forth inside the pressure chamber until the wave becomes strong and attenuates and disappears. This period is the natural period of the natural vibration of the pressure wave in the ink inside the pressure chamber. The natural period T is T = 2 W / C, where W is the length of the pressure chamber and C is the sound speed transmitted through the ink. It is proportional to the room size.

When the voltage to be applied to the piezoelectric element is gradually discharged from V22, no negative pressure wave is applied to the ink chamber, and the ink droplet has a positive pressure wave generated by the change from V21 to V22. By reaching the nozzle, and the negative pressure wave due to the nozzle reaching the nozzle after a lapse of T / 2 time,
Since the ink is cut off from the nozzle and becomes an ink droplet, the minimum amount of the ink droplet greatly depends on the natural period T of the pressure wave inside the pressure chamber.

Further, since the natural period T is proportional to the size of the pressure chamber, the influence of variations at the time of manufacturing becomes large.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method of driving an ink jet print head which can prevent ringing of a piezoelectric element and can discharge ink stably with little meniscus vibration.

It is another object of the present invention to provide a method of driving an ink jet print head in which the influence of variations during manufacturing is small and the control is reliable by the timing of starting discharge.

It is another object of the present invention to provide a method of driving an ink jet print head in which input driving energy can be used efficiently for ink ejection.

Another object of the present invention is to extend the range of controlling the size of the ink droplet to be ejected,
It is an object of the present invention to provide a method of driving an ink jet print head capable of discharging smaller ink droplets and enabling printing with excellent gradation.

[0016]

In order to achieve the above object, the present invention provides a pressure chamber (FIG. 1) by applying an electric signal to a piezoelectric element (101 in FIG. 1) to drive the piezoelectric element (101 in FIG. 1). 105) by changing the volume of the nozzle (FIG. 1)
104), a piezoelectric element (1 in FIG. 1) is used to drive an ink jet print head that ejects ink droplets from the piezoelectric element.
The maximum value of the absolute value of the voltage change rate of the electric signal applied to the piezoelectric element (01) is equal to or less than a predetermined value for suppressing ringing of the piezoelectric element (101 in FIG. 1).

The maximum value of the absolute value of the voltage change rate of the electric signal applied to the piezoelectric element (101 in FIG. 1) is determined by the voltage at the maximum displacement of the piezoelectric element (101 in FIG. 1).
101) is less than or equal to the value obtained by dividing by 80% of the mechanical natural period.

As a result, ringing of the piezoelectric element 101 can be prevented, and stable ink discharge with less meniscus vibration can be performed.

Also, according to the present invention, the driving waveform when the potential of the piezoelectric element 101 is returned to 0 after the inside of the pressure chamber 105 is pressurized and the ink is ejected, the potential is changed at a constant rate until the potential becomes 0. It is a drive waveform to be changed.

Thus, the influence of variations during manufacturing is small, and the minimum amount of ink droplets can be reliably controlled by the timing of the start of discharge after the ejection of ink droplets.

Further, according to the present invention, the driving waveform applied to the piezoelectric element 101 is such that the piezoelectric element 101 is driven in the direction of reducing the pressure inside the pressure chamber 105 from the state of potential 0,
A drive waveform for driving the piezoelectric element 101 so as to pressurize the inside and eject ink, and the voltage changes at a constant rate from a state of potential 0 to a predetermined voltage in a direction of reducing the pressure inside the pressure chamber. This is a driving waveform that changes the voltage in a direction to pressurize the inside of the pressure chamber immediately after reaching.

Thus, the voltage change of the drive waveform applied to the piezoelectric element 101 to make the pressure chamber 105 a negative pressure is minimized, the pressure wave inside the pressure chamber 105 is weakened, and the vibration of the meniscus is reduced. And can be less affected by manufacturing variations.

Further, according to the present invention, after the driving of the piezoelectric element 101 in the direction of reducing the pressure inside the pressure chamber 105 is started, the inside of the pressure chamber 105 is applied after a half of the natural period of the pressure wave inside the pressure chamber 105. The driving of the piezoelectric element 101 is started in the direction of pressing.

Thus, although the driving of the piezoelectric element 101 is moderated and relaxed as described above, the piezoelectric element 1
01, a negative pressure wave is generated, and reaches the nozzle 104 after a lapse of a half of the natural period. Subsequently, a positive pressure wave is generated due to ink elasticity and wave reflection. The element 101 will be driven.
Therefore, the operation becomes stable, and the ink jet head can be driven efficiently.

Further, according to the present invention, when the ink droplet amount is increased in accordance with the range of the ink droplet amount to be controlled, the inside of the pressure chamber 105 is pressurized from the state where the potential of the piezoelectric element 101 is 0 to discharge ink. When the piezoelectric element 101 is driven to reduce the amount of ink droplets as described above, the piezoelectric element 101 is driven in a direction to reduce the pressure inside the pressure chamber 105, and then the pressure chamber 1
05 so that the piezoelectric element 10
1 is driven.

In this way, when a large ink droplet is ejected, it is possible to use a pressing method, and to broaden the range of controlling the ink droplet size and to eject a larger ink droplet than when using only the pulling method.

Also, according to the present invention, after the piezoelectric element 101 is driven in a direction to reduce the pressure inside the pressure chamber 105,
The piezoelectric element 101 is driven in a direction to pressurize the inside, and after the pressurization, the piezoelectric element 101 is moved in a direction to reduce the pressure inside the pressure chamber 105.
In the driving method for driving the piezoelectric element 101, the pressure inside the pressure chamber 105 after the pressurization starts when the driving of the piezoelectric element 101 is started in the direction to pressurize the inside of the pressure chamber 105 according to the range of the ink droplet amount to be controlled. The time until the start of the decompression to start driving the piezoelectric element 101 in the direction in which the pressure is reduced is changed.

Thus, the range in which the ink droplet size is controlled can be widened, smaller ink droplets can be ejected, and printing with excellent gradation can be performed.

[0029]

Next, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a drive waveform generating circuit 1 for generating a drive signal for driving a print head and a piezoelectric element according to the present invention.
11 is shown. In particular, the print head is shown in a sectional view showing an example of its structure. The print head includes a piezoelectric element 101 for converting an electric signal into mechanical energy, a signal line 102 for sending an electric signal to the piezoelectric element 101, a vibration plate 103 for transmitting the pressure of the piezoelectric element 101 to the inside of the pressure chamber 105, A nozzle 104 for discharging ink, and a pressure chamber 105 for internally transmitting pressurized energy given to the ink by the diaphragm 103 to the nozzle 104
And the pressure chamber 1 from the common ink chamber 106 into the pressure chamber 105.
And a supply path 107 for supplying ink to the ink cartridge 05. Further, a driving waveform generating circuit 111 for generating a driving waveform for driving the piezoelectric element 101 is connected to the signal line 102, and a switching circuit 112 for selecting whether to drive the piezoelectric element is connected to the external electrode 108.

Next, the operation will be described.

FIG. 2 shows a driving waveform according to the embodiment of the present invention, which is a driving waveform generated by the driving waveform generating circuit 111 of FIG.

In the figure, first, a voltage in the direction opposite to the polarization direction is raised to a drive voltage V11 for a certain time T11, and this voltage V11 is maintained for a certain time T12. Thereafter, the voltage is decreased at a predetermined time T13, and a voltage in the same direction as the polarization direction is applied, and the voltage is increased to the drive voltage V12. Then, the voltage V12 is maintained for the fixed time T14, and the voltage is returned to 0 at the fixed time T15.

According to the signal waveform of FIG. 2, when the switching circuit 112 is ON, when the voltage V11 in the reverse direction is applied, the piezoelectric element 101 contracts.
05 has a negative pressure, and the ink is
06 to the pressure chamber 105. Nozzle 10
4, the negative pressure wave from the piezoelectric element 101
By reaching 4, the meniscus retreats. FIG. 3 shows the state of the print head at this time.

Next, when a voltage in the same direction as the polarization direction is applied to the piezoelectric element 101, the piezoelectric element 101 expands. As a result, the pressure inside the pressure chamber 105 increases, and ink is ejected. FIG. 4 shows the state of the print head at this time.

When the voltage is returned to 0 at a certain time T15, the ejected ink flows from the common ink chamber 106 through the supply path 107 into the pressure chamber 105, and the meniscus is ejected from the nozzle 104 by the ink droplet ejection. After retreating, the ink is supplied from the common ink chamber 106 to the pressure chamber 10.
5 returns to the original state by flowing into the inside.

Here, the ringing of the piezoelectric element 101 can be prevented by making the gradient of the voltage change during the times T11, T13 and T15 smaller than the voltage change rate at which ringing of the piezoelectric element 101 occurs. .

Specifically, assuming that the mechanical natural period of the piezoelectric element 101 is Tf and the voltage at which the piezoelectric element 101 reaches the maximum displacement is Vmax, the gradient of the voltage change is Vmax.
/0.8 Tf. Thereby, the piezoelectric element 1
Since it is known from experience that the ringing of 01 is almost eliminated, the adverse effect of the ringing of the piezoelectric element 101 can be suppressed.

FIG. 5 is a diagram showing a meniscus in the nozzle 104 when driven by this driving waveform.

FIG. 6 is a diagram showing a vibrating state of the meniscus when the gradient of the voltage change of the drive waveform is sharp.

FIG. 5 does not show the vibration at the time of meniscus retreat as shown in FIG. When the gradient of the voltage change of the drive waveform is made sharp, the ringing of the piezoelectric element 101 becomes large, and the residual vibration occurs. Therefore, the residual vibration of the piezoelectric element 101 affects the vibration of the meniscus, and FIG. It induces the vibration during meniscus retreat as seen. As a result, slight variations in driving and structural variations such as the length of the piezoelectric element 101 affect the ink ejection amount and the ink droplet speed, and the ink droplet ejection tends to become unstable.

This also relates to the ejection of ink droplets and the return of the meniscus, and it is necessary to drive the piezoelectric element 101 so as to suppress ringing of the piezoelectric element 101.

When the piezoelectric element 101 is driven, a pressure wave is generated, reaches the nozzle 104 inside the pressure chamber 105, reflects off the nozzle 104, returns to the pressure chamber 1 until it attenuates and disappears.
The waves repeat back and forth inside 05. This cycle is pressure chamber 1
It takes about half the time of the natural period T of the pressure wave inside the 05. Therefore, when the positive drive is performed and then the negative drive is performed, if the piezoelectric element 101 is driven in accordance with this wave,
Is efficiently transmitted to the ink, and the ink droplet becomes large. If the ink droplet is driven without adjusting to this wave, the piezoelectric element 10
The driving of No. 1 is not efficiently transmitted to the ink, and the ink droplet becomes small for the driving energy.

From such a viewpoint, it is possible to weaken the pressure wave inside the pressure chamber 105 and to reduce the vibration of the meniscus by making the voltage change of the drive waveform as small as possible.
Further, it is preferable because it is hard to be affected by manufacturing variations and the like.

FIG. 7 shows a driving waveform when the voltage change rate applied to the piezoelectric element 101 to make the pressure chamber 105 have a negative pressure is minimized. With such a drive waveform, the piezoelectric element 10
By driving 1, the meniscus is most stabilized.

In the driving waveform shown in FIG.
The electric signal applied to 1 is defined as T, where T is the natural period of the natural vibration of the pressure wave in the ink inside the pressure chamber. First, a time T / 2 after the voltage in the direction opposite to the polarization direction is raised,
A voltage in the same direction as the polarization direction rises.

For this reason, although the driving of the piezoelectric element 101 is moderated and relaxed, the pressure wave reciprocating in the pressure chamber 105 is not completely eliminated. / 2 after reaching the nozzle 104, and subsequently a positive pressure wave is generated due to the elasticity of the ink and the reflection of the wave. By driving the piezoelectric element 101 in accordance with this wave, a stable operation is achieved. Can be driven efficiently.

In the drive waveform of the present invention, the meniscus vibration can be suppressed by making the rise and fall of the voltage in the drive waveform gentle as described above.
The drive of the piezoelectric element 101 is efficiently transmitted to the ink, and the influence on the ink droplet ejection due to the deviation of the drive timing and the structural variation such as the length of the piezoelectric element 101 is prevented.

When a voltage in the direction opposite to the polarization direction is applied, the piezoelectric element 101 contracts gradually when the applied voltage is increased from 0, but expands when the applied voltage exceeds a predetermined voltage. It is desirable that V11 be lower than this voltage from the viewpoint of efficiency.

Further, when a voltage in the same direction as the polarization direction is applied, the piezoelectric element 101 does not expand any more at Vmax or more, so it is desirable to set V12 to Vmax or less from the viewpoint of efficiency.

Since the driving method described above is a so-called pulling method, a small ink droplet can be ejected. However, a pushing method is advantageous for a large ink droplet.
Therefore, the voltage V11 in the direction opposite to the polarization direction is made variable, V11 is set according to the ink droplet, and when a large ink droplet is ejected, the voltage for the time of T11 + T12 is set to 0 as shown in FIG. At time T13, the voltage rises to a voltage V12 in the same direction as the polarization direction, and this voltage V12 is maintained for a certain time T14, and becomes zero at a certain time T15.
In the case where a small ink droplet is ejected, the driving waveform shown in FIG. 2 may be used. Thus, first, the ink droplets are controlled by changing V12. However, when a larger ink droplet is required, V11 is reduced to 0, and the range in which the ink droplet amount can be controlled so as to eject a large ink droplet is expanded. be able to.

The control for obtaining smaller ink droplets can be realized by the following method.

FIG. 9 is a diagram schematically showing the flow velocity at the tip of the nozzle 104. What is indicated by a broken line in FIG.
The time from when a voltage is applied in the same direction as the polarization to when the applied voltage starts to drop is T / 2 or more,
The solid line is the case of the driving waveform of the present invention in which the time from when a voltage is applied in the same direction as the polarization to when the applied voltage starts dropping is T / 2 or less. Since the ink ejection amount is proportional to the area of the hatched portion in FIG. 9, ejecting a small ink droplet is equivalent to reducing this area.

In the conventional driving waveform shown in FIG. 15, when the voltage applied to the piezoelectric element 101 is gradually discharged from V22 and no negative pressure wave is applied, a positive pressure wave reaches the nozzle 104, thereby causing a negative pressure wave. Pressure wave of the nozzle 104
Is reached, the ink becomes a droplet and the nozzle 104
The time from when the positive pressure wave reaches the nozzle 104 is after a lapse of T / 2 after the positive pressure wave reaches the nozzle 104. Therefore, the minimum ink droplet amount is determined by the length of the pressure chamber 105, and cannot be reduced any further.

FIG. 10 shows driving waveforms for controlling the ink droplets to obtain smaller ink droplets.

As shown in FIG. 10, the voltage applied to the piezoelectric element 101 is increased from V11 to V13, a positive pressure wave is applied to the pressure chamber, and then the voltage is decreased from V13 at a constant rate until the potential becomes zero. As a result, a negative pressure wave is applied to the pressure chamber, and the time T13 is changed from the start of pressurizing the pressure chamber 105 to the start of depressurization, so that T / 2
By doing the following, small ink droplets can be ejected.

However, the actual control of the ink droplets is as follows.
First, it is performed by changing the voltage of V13 of this waveform, and when it is necessary to obtain a smaller ink droplet, T1 is used.
3 is set short. If it is necessary to obtain a large ink droplet, T13 can be set longer.

Here, when the meniscus is retracted, the driving waveform of the piezoelectric element is made gentle as described above, so that the meniscus vibration is reduced and small ink droplets can be stably ejected.

Although the voltage is not held at V13 for a fixed time in FIG. 10, the voltage can be held at V13 for a fixed time by increasing the start-up time.

The print head driving method described above presupposes a print head in which the lamination direction of the piezoelectric elements 101 is perpendicular to the diaphragm, but the print head in which the lamination direction is parallel to the diaphragm. Can be similarly implemented.

FIG. 11 shows an example of the driving waveform generating circuit 111 for generating the driving waveform as described above.

The drive waveform generation circuit 111 is configured to output signals from Tr1 to T
r6 is connected as shown, the collectors of Tr2 and Tr5 are connected via two diodes, C1 is connected between the connection point of the two diodes and 0V, and the bases of Tr3 and Tr6 are connected to Tr2 and Tr5, respectively. Connect the collector, Tr
3 is a circuit that connects the emitters of the transistors 3 and 6 to each other to serve as an output terminal. The emitter of Tr2 is connected to V1 via a variable resistor RA.
1 and the emitter of Tr5 is connected to V12 via a variable resistor RB.

Next, the operation of the waveform generation circuit 111 will be described.

FIGS. 12A and 12B show the drive waveform generation circuit 11.
An example of a signal input to 1 is shown, and C is a signal waveform output from the drive waveform generation circuit 111 by the signals A and B. When both the signal A and the signal B are 0V, Tr1 to Tr
3 is turned on, Tr4 to Tr6 are turned off, a current starts flowing out from C1, and the voltage of the signal C falls linearly according to the voltage of C1, and when it reaches V11, it is held at V11 thereafter. Signal A and signal B are both 5
In the case of V, Tr1 to Tr3 are turned off and Tr4 to T
r6 is turned on, and a current flows as in C1,
The voltage of the signal C rises linearly according to the voltage of C1, and when it reaches V12, it is thereafter held at V12. When the signal A is set to 5V and the signal B is set to 0V, the outflow and inflow of current to C1 is stopped, and the voltage of the signal C is maintained. Therefore, an output like a waveform C is obtained for A and B in FIG.

In order to set the output to 0 V, C
A circuit for connecting 1 to 0 V may be added.

Further, RA and RB are variable resistors whose resistance values change according to the signal input. The resistance values are set by inputting the RA setting signal and the RB setting signal, respectively.
Can be controlled.

Further, any type of device can be used as long as the current flowing into C1 can be controlled without using a variable resistor whose resistance value changes according to a signal input.

FIG. 13 is a sectional view of a print head in which the lamination direction of the piezoelectric elements 101 is parallel to the diaphragm.

When driving such a print head, first, a potential is applied to the piezoelectric element 101 in the same direction as the polarization direction to reduce the pressure inside the pressure chamber 105 to a negative pressure. , The potential inside the pressure chamber 105 is increased by applying a potential in the direction opposite to the polarization direction, and finally, the potential of the piezoelectric element 101 is returned to zero.

[0070]

As described above, the present invention has an effect that the ringing of the piezoelectric element 101 is prevented, and the ink can be stably ejected with less meniscus vibration.

Further, there is an effect that the input driving energy can be efficiently used for ink ejection.

Further, it is possible to discharge smaller ink droplets, and it is possible to perform printing with excellent gradation.

Further, it is possible to stably control the size of the ink droplet to be ejected and to perform stable gradation printing.

[Brief description of the drawings]

FIG. 1 shows a cross-sectional view of an example of a printhead according to the present invention, and shows a drive waveform generation circuit and a switching circuit connected to piezoelectric elements of the printhead.

FIG. 2 is a diagram of a driving waveform according to the present invention.

FIG. 3 is a cross-sectional view of the print head of FIG. 1 when a piezoelectric element is contracted.

FIG. 4 is a cross-sectional view of the print head of FIG. 1 when a piezoelectric element is extended.

FIG. 5 is a diagram showing a vibration model of a meniscus in a nozzle according to the present invention.

6 shows a steep gradient of the voltage change of the drive waveform of FIG. 5,
It is a figure which shows the vibration state of the meniscus in the case of making it rectangular.

FIG. 7 is an example of a driving waveform according to the present invention, which is a driving waveform when a large ink droplet is ejected.

FIG. 8 is a diagram schematically illustrating the flow velocity at the nozzle tip according to the present invention.

FIG. 9 is an example of a driving waveform according to the present invention, which is a driving waveform when a small ink droplet is ejected.

FIG. 10 is an example of a driving waveform according to the present invention, which is the most stable driving waveform of the meniscus when the meniscus retreats.

FIG. 11 is an example of a circuit diagram of the drive waveform generation circuit of FIG. 1;

FIG. 12 is a waveform chart showing an operation of the drive waveform generation circuit of FIG. 11; A and B are waveform diagrams of signals A and B input to the drive waveform generation circuit, and C is a waveform diagram output from the drive waveform generation circuit by signals A and B.

FIG. 13 is a cross-sectional view of another example of the print head according to the present invention.

FIG. 14 is an example of a conventional drive waveform.

FIG. 15 is another example of a conventional driving waveform.

[Explanation of symbols]

 Reference Signs List 101 piezoelectric element 102 signal line 103 diaphragm 104 nozzle 105 pressure chamber 106 common ink chamber 107 ink supply path 108 external electrode 109 internal electrode 110 nozzle plate 111 drive waveform generation circuit 112 switching circuit

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B41J 2/045 B41J 2/055 B41J 2/205

Claims (8)

(57) [Claims] 1. A method of driving an ink-jet printhead in which an electric signal is applied to a piezoelectric element to drive the piezoelectric element, thereby changing the volume of the pressure chamber and ejecting ink droplets from a communicating nozzle. A method of driving an ink jet print head, wherein a maximum value of an absolute value of a voltage change rate of an applied electric signal is equal to or less than a predetermined value for suppressing ringing of a piezoelectric element. 2. The maximum value of the absolute value of the voltage change rate of an electric signal applied to the piezoelectric element is equal to or less than a value obtained by dividing the voltage at the maximum displacement of the piezoelectric element by a value of 80% of the mechanical natural period of the piezoelectric element. 2. The method for driving an ink jet print head according to claim 1, wherein: 3. A drive waveform for returning the potential of the piezoelectric element to 0 after the ink is ejected by pressurizing the inside of the pressure chamber is a drive waveform for changing the potential at a constant rate until the potential becomes 0. 2. The method for driving an ink jet print head according to claim 1, wherein: 4. A driving waveform applied to the piezoelectric element has a potential of zero.
A driving waveform for driving the piezoelectric element to drive the piezoelectric element in a direction to reduce the pressure in the pressure chamber from the state, and then pressurize the pressure chamber and discharge ink.
Changing the voltage at a constant rate of change from the state of potential 0 to a predetermined voltage in the direction of reducing the pressure inside the pressure chamber,
2. The method according to claim 1, wherein the driving waveform changes the voltage in a direction to pressurize the inside of the pressure chamber immediately after the arrival. 5. A method according to claim 5, wherein after starting driving of the piezoelectric element in a direction to reduce the pressure inside the pressure chamber, a half of a natural period of a pressure wave in the pressure chamber is started, and then the piezoelectric element is pressed in a direction to pressurize the inside of the pressure chamber. 2. The method according to claim 1, wherein the driving is started. 6. The method according to claim 1, wherein when the ink droplet volume is increased in accordance with the range of the ink droplet volume to be controlled, the piezoelectric element is configured to pressurize the inside of the pressure chamber from a state where the potential of the piezoelectric element is zero to discharge ink. When the ink droplet amount is reduced, the piezoelectric element is driven in such a manner that the piezoelectric element is driven in a direction to reduce the pressure in the pressure chamber, and then the piezoelectric element is driven so as to pressurize the pressure chamber and discharge ink. The method for driving an ink jet print head according to claim 1. 7. A piezoelectric element is driven in a direction to depressurize the inside of the pressure chamber, and then a piezoelectric element is driven in a direction to pressurize the inside of the pressure chamber. In the driving method, the pressure in the pressure chamber after the pressurization is reduced from the start of the pressurization to start driving the piezoelectric element in the direction to pressurize the inside of the pressure chamber according to the range of the ink droplet amount to be controlled. 2. The method according to claim 1, wherein the time until the start of decompression to start driving the piezoelectric element is changed in the direction in which the piezoelectric element is driven. 8. A piezoelectric element, a pressure chamber, and a nozzle communicating with the pressure chamber, wherein a volume of the pressure chamber changes by applying an electric signal to the piezoelectric element to drive the piezoelectric element. An ink jet print head that ejects ink droplets, and a drive waveform generation circuit that generates an electric signal whose maximum value of the absolute value of the voltage change rate is equal to or less than a predetermined value that suppresses ringing of the piezoelectric element. Drive unit for inkjet print head.