JP2002316414A - Ink jet recorder and method of driving ink jet nozzle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem wherein there are variations in an electromechanical conversion characteristic of each piezoelectric element, a coupling property between the piezoelectric element and a diaphragm and a mechanical position relationship therebetween so that ejection speeds of ink drops ejected from a plurality of nozzles are varied and the variation in the ejection speed of the ink drop causes an error of an arrival position of the ink drop when the ink drop is ejected while a print head is moved at a constant speed. SOLUTION: In a plurality of driving circuits provided respectively corresponding to the plurality of piezoelectric elements, electric charge quantities at charge and discharge times for the piezoelectric element are controlled based on time periods in which a plus current source for charging and a minus current source for discharging connected to the piezoelectric elements. Alternatively, the electric charge quantities are controlled based on the current values of the plus current source for charging and the minus current source for discharging.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric ink jet recording apparatus, which controls a nozzle driving waveform to correct the variation of the electromechanical conversion characteristics of each piezoelectric element, and makes the ink droplet ejection speed uniform. More specifically, the present invention relates to an ink jet recording apparatus having an ink jetting technique for improving the landing position accuracy.

[0002]

2. Description of the Related Art Conventionally, an apparatus for ejecting ink using a piezoelectric element has been used in an ink jet printer or the like, and FIG. 8A shows an example thereof. A piezo element is provided in the ink chamber 11 as a piezoelectric element 1 via a diaphragm 13, and a side surface of the piezoelectric element 1 opposite to the diaphragm 13 is fixed by a back plate 10. A nozzle 12 for ejecting ink droplets is provided on a surface of the ink chamber 11 facing the diaphragm 13. Further, the ink chamber 11 has a manifold 15 for temporarily storing ink supplied from an ink tank (not shown).
Are connected to each other via an ink flow path 14. In addition, the heater 17 provided adjacent to the manifold 15 heats the ink in the hot-melt ink jet recording apparatus.
It is for melting. Here, the piezoelectric element 1 is shown in FIG.
When the lamination type is used as in 1, the amount of contraction and expansion of the diaphragm 13 can be increased, so that energy-efficient driving can be performed.

A driving circuit 9 operates to drive the piezoelectric element 1 in response to a print command from a host computer (not shown).

On the other hand, a conventional pulse voltage control means is shown in FIG.
Shown in In FIG. 9, reference numeral 18 denotes a piezoelectric element driving circuit;
Is a signal generating circuit. When a pulse signal 20 shown in FIG. 10 is applied to point B while a constant DC voltage is applied as a piezoelectric element driving voltage to point A, the potential of the piezoelectric element 1 changes as shown in a waveform 21. This causes the piezoelectric element 1 to deform. In the ink jet head having such a configuration, the driving circuit 9 applies the voltage 2 shown in FIG.
When 1 is applied, the piezoelectric element 1 is deformed and the diaphragm 13a shown in FIG. 8B is bent, so that the volume of the ink chamber 11 increases, and ink is supplied via the ink flow path 14 and the manifold 15. Is done. Next, when the piezoelectric element applied voltage 21 is de-energized, the piezoelectric element 1 is restored, so that the diaphragm 13 is restored and the ink in the ink chamber 11 is compressed, so that the ink droplet 16 is ejected from the nozzle 12. I do. Note that the drive circuit in FIG. 9 corresponds to the drive circuit 9 in FIG. In FIG. 9, the piezoelectric element drive circuit 18
Although only two circuits are shown, a plurality of circuits are provided so as to correspond to the number of piezoelectric elements 1 on a one-to-one basis.

When ejecting ink droplets, a pulse signal 20 from a signal generating circuit 19 is supplied to the piezoelectric element driving circuit 18.
, The pulse voltage 21 is applied to the piezoelectric element 1 by turning on and off the DC voltage V1 at the point A, thereby deforming the diaphragm 13. On the other hand, when the ink droplet is not ejected, the pulse signal 2
Control is performed so that 0 is not generated.

[0006]

In the above-described conventional piezoelectric print head, a uniform electric potential is applied to each piezoelectric element, the electric potential of the piezoelectric element is changed by a driving circuit, the piezoelectric element is deformed, and ink droplets are formed. I was spraying. However, the electrical / mechanical conversion characteristics of the piezoelectric elements corresponding to a plurality of nozzles have variations, and it is extremely difficult to correspond each time.
In addition, there are variations in the degree of coupling between the piezoelectric element and the diaphragm and in the mechanical positional relationship, and there is a limit in terms of accuracy in correcting such variations. Therefore, the ejection speed of the ink droplet ejected from the plurality of nozzles has been varied. In some cases, the above-described variation may be superimposed to generate a composite variation. When an ink jet print head having such a variation is slid at a constant speed and ink droplets are ejected in the process, the variation in the landing position of the ink droplet on the inkjet recording material is affected, and the image quality of the inkjet recording is deteriorated. That was a problem. Another problem is that the yield when the variation with respect to the jetting liquid speed in manufacturing the ink jetting nozzle falls within a certain range is poor. Therefore, in order to improve the accuracy of the ink droplet landing position and to improve the yield at the time of manufacturing the ink jet nozzle, it is required that the drive voltage value applied to each piezoelectric element can be varied.

As a method of controlling a charging current and a discharging current to a plurality of piezoelectric elements, for example, Japanese Patent Laid-Open No. 4-310747
And JP-A-9-39231. The former has a configuration in which the charge current value and the discharge current value are changed in common for a plurality of nozzles, and the latter repeatedly supplies a piezoelectric element circuit having a charge resistance and a discharge resistance with fine charge pulses of a constant voltage every time ink is ejected. Is formed for each injection, and a drive waveform is commonly given to a plurality of nozzles by a pattern described in a ROM. Both the former and the latter describe a method of digitally forming a drive waveform having a voltage and a pulse width common to a plurality of nozzles, but do not control the drive waveform of each of the plurality of nozzles.

Accordingly, an object of the present invention is to control the drive waveform of each of a plurality of nozzles in an ink jet head, that is, an ink jetting system including a piezoelectric element, to correct variations in the liquid velocities of each of the plurality of nozzles, and The object of the present invention is to improve the landing accuracy of ink droplets on a recording medium by making the liquid velocities the same. At the same time, it is another object of the present invention to enable trimming of the ink jet nozzles of the multi-nozzle ink jet recording apparatus to improve the yield at the time of manufacturing the ink jet nozzles.

[0009]

According to the present invention, there is provided a multi-function apparatus for ejecting ink from a nozzle by changing the volume of an ink chamber at room temperature by using a piezoelectric element at normal temperature. In a nozzle type ink jet recording apparatus, a current flowing from a positive current source connected to the piezoelectric element is charged in the piezoelectric element, and the volume of the ink chamber is increased by deforming the piezoelectric element, thereby forming an ink flow path. Controlling the supply of ink via the manifold, and then discharging the piezoelectric element so that current flows into the minus current source, restoring the piezoelectric element, compressing the ink in the ink chamber, and ejecting ink droplets from the nozzles And a drive signal generating circuit for performing the above.

In an ink jet recording apparatus configured to expand the volume of an ink chamber and discharge ink when electric charges are discharged from a piezoelectric element, the piezoelectric element is so arranged that a current flows to a minus current source connected to the piezoelectric element. Discharge
By deforming the piezoelectric element, the volume of the ink chamber is increased to supply ink via an ink flow path and a manifold, and thereafter, the piezoelectric element is charged with a current flowing from a positive current source, thereby charging the piezoelectric element. And a drive signal generating circuit for controlling the compression of the ink in the ink chamber and the ejection of ink droplets from the nozzles.

In this drive signal generating circuit, the amount of electric charge charged and discharged to each piezoelectric element is increased or decreased by adjusting the time during which the current flows or the time during which the current flows, for each current source connected to each piezoelectric element. By varying the drive voltage value applied to each piezoelectric element and changing the amount of expansion and contraction of the piezoelectric element for each nozzle, variations in the ink droplet ejection speed are corrected. As another method, the amount of electric charge charged / discharged to each piezoelectric element is increased / decreased by changing the current value of each current source connected to each piezoelectric element, and the amount of expansion / contraction of the piezoelectric element is changed for each nozzle. By doing so, variations in the ink droplet ejection speed are corrected.

In the above configuration, the voltage applied to the piezoelectric element is changed linearly by adjusting the amount of charge to be charged / discharged to the piezoelectric element, and the rising time constant and the falling time constant of the applied voltage are set to It is preferable that the reciprocal of the natural frequency of the vibration system constituted by the piezoelectric element is set to 0.8 to 1.2 times an integral multiple of the reciprocal, and the rise time constant is set to be equal to or larger than the fall time constant. If the value of the integer multiple is large, the time constant will be long,
The lowering of the nozzle driving frequency leads to a decrease in printing speed, and the voltage fluctuation rate is so small that a sufficient pressure to eject ink cannot be obtained. Is a small integer value of.

The time from charge to discharge or the time from discharge to charge of the piezoelectric element may be set so as to depend on the pulse width interval of the drive signal of the control signal generation circuit.

Further, in the ink jet recording apparatus having the above structure, the piezoelectric element corresponding to the nozzle for ejecting ink is charged / discharged with a predetermined amount of electric charge by the current source, thereby deforming the volume of the ink chamber to change the ink volume. It is desirable that the control signal generation circuit is controlled so as not to charge and discharge the piezoelectric element with respect to the piezoelectric element corresponding to the nozzle that does not eject ink and that does not eject ink.

A similar effect can be obtained even when the ink is a hot melt ink and a heater for heating is provided near the ink chamber and heated at a temperature in the range of 80 to 140 degrees Celsius. Can be.

As described above, the rise or fall time constant at the time of ink suction is set to 0.8 to 1.2 times an integral multiple of the reciprocal of the natural frequency of the ink ejection system of the ink jet recording apparatus, and the piezoelectricity at the time of ink suction is set. Suppressing the generation of harmonic vibrations of the elements, and further varying the voltage applied to each piezoelectric element or varying the time from charging to discharging of the piezoelectric element and trimming the variation of each piezoelectric element to reduce the variation of each piezoelectric element Can be precisely controlled.

An advantage of driving by a current source is that it is more resistant to electric interference and disturbance noise in a substrate wiring pattern and the like than voltage driving. On the other hand, there is a disadvantage that the circuit scale becomes large, but this can be solved by integration using an LSI or the like.

As in the configuration of the present invention, the voltage applied to the piezoelectric element and the time from charge to discharge or the time from discharge to charge of the piezoelectric element are individually controlled for each of the plurality of nozzles to reduce the liquid velocity of each ink droplet. It is possible to improve the landing accuracy of the ink droplets on the ink-jet recording material by making the ink jet system including the piezoelectric element constant and eliminating the variation in the liquid velocity of the ink jet system including the piezoelectric element. At the same time, it is possible to trim the ink jet nozzles of the multi-nozzle ink jet recording apparatus, thereby improving the yield when manufacturing the ink jet nozzles.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In an ink jet recording apparatus having the above-described structure, variations in the ink droplet ejection speed are suppressed by correcting variations due to the electro-mechanical conversion characteristics of the piezoelectric elements. Can be raised. At the same time, it is possible to trim the ink jet nozzles of the multi-nozzle ink jet recording apparatus, thereby improving the yield when manufacturing the ink jet nozzles.

An embodiment of the present invention will be described below. In the following embodiments, the same parts as those in the conventional example of FIG. 9 are denoted by the same reference numerals, and description thereof will be omitted.

In the present invention, the driving circuit 9 of FIG.
The applied voltage 22 to each piezoelectric element 1 is controlled by the waveform shown in FIG. FIG. 2 shows an example of a circuit having the configuration shown in FIG. Although only two drive circuits 9 are shown in FIG. 2, a plurality of drive circuits 9 are provided so as to correspond to the number of piezoelectric elements 1 on a one-to-one basis.

In FIG. 2, one terminal of each of the plurality of piezoelectric elements 1 is connected to the output of a drive circuit 9 provided separately, and the other terminal of the piezoelectric element 1 is connected to the ground potential. The potential of the piezoelectric element on the side connected to the ground potential may be the same as the lowest potential of the drive circuit 9 when the lowest potential of the drive circuit 9 is lower than the ground potential. The drive circuit 9 receives a charge / discharge control signal 6 and a drive signal 7 from a control signal generation circuit 8.

In the above-described configuration, the control signal generation circuit 8 and the drive circuit 9 synchronize with the high level of the charge / discharge control signal 6 and the high level of the drive signal 7 as shown in FIG. As a result, the charging transistor 4 in the driving circuit 9 shown in FIG. 2 is turned off, and the electric charge is charged from the charging positive current source 2 to the piezoelectric element 1. FIG. 3B shows an example of a positive variable current source for charging. The current value is varied by changing the variable resistance value in FIG.

This charging is performed during a pulse width time Tr in which the charge / discharge control signal 6 is at a high level and the drive signal 7 is at a high level. This pulse width time Tr is determined for each piezoelectric element 1
A predetermined pulse width is given to each element in accordance with the driving characteristics of the above. The pulse width time Tr is t, the piezoelectric element 1
Where c is the capacitance, i is the current value of the positive current source for charging, and v is the potential difference between both ends of the piezoelectric element.

[0025]

(Equation 1)

From equation 1, control is performed such that the potential difference between both ends of the piezoelectric element rises linearly in proportion to the pulse width time Tr. Similarly, during the time Tf when the charge / discharge control signal 6 is at a low level and the drive signal 7 is at a high level,
The discharge transistor 5 in the drive circuit 9 shown in FIG. 2 is turned off, and the electric charge charged in the piezoelectric element 1 is discharged to the negative current source 3 for discharge. FIG. 3B shows an example of the minus variable current source for discharging. The current value is varied by changing the variable resistance value in FIG. Equation 1
Similarly to the above, control is performed such that the potential difference between both ends of the piezoelectric element falls linearly in proportion to the pulse width time Tf to the discharge transistor. When the drive signal 7 is at a low level, the charge transistor 4 and the discharge transistor 5 are both turned on, so that the electric charge in the piezoelectric element 1 stays and the potential difference between both ends of the piezoelectric element is held. . By repeating the above-mentioned pulse signals of the charge / discharge control signal 6 and the drive signal 7, the control waveform 22 shown in FIG.
Is output from the drive circuit 9 and applied to the piezoelectric element 1. As shown in FIG. 4A, the control waveform 2 applied to the piezoelectric element 1 is changed by changing the pulse width of the drive signal 7.
2, the rise time Tr and the fall time Tf can be changed, and at the same time, the voltage Vm applied to the piezoelectric element 1 can be controlled.

The ink is sucked into the ink chamber 11 by the deformation of the piezoelectric element 1 and the contraction of the diaphragm 13 in synchronization with the rise of the control waveform 22. And
The ink in the ink chamber 11 is compressed by the restoration of the piezoelectric element 1 in synchronization with the fall of the control waveform 22, and the ink droplet 16 is ejected from the nozzle 12. In this example,
Although the trapezoidal control waveform 22 shown in FIG. 4A is used, the same applies to the triangular waveform control waveform 23 shown in FIG. 5A. What is required in the configuration of the present invention is that the control waveform rises linearly. Here, the rise time constant and the fall time constant of the control waveform 22 applied to the piezoelectric element with respect to the vibration system formed by the piezoelectric element are set to 0.8 to 1.2 times the reciprocal of the natural frequency of the vibration system. When the rise time constant is set to be equal to or larger than the fall time constant, harmonic vibration of the piezoelectric element can be suppressed. If the value of the integral multiple is large, the time constant becomes longer, leading to a decrease in the printing speed due to a decrease in the nozzle drive frequency, and the voltage fluctuation rate is so small that a pressure sufficient to eject ink cannot be obtained. The double value is generally 1,
It is assumed to be a small integer value of about two or three. By suppressing the harmonic vibration in this way, it is possible to suppress the turbulent flow of the ink fluid at the time of sucking the ink, stabilize the ejection of the ink droplet, and make the most effective variation correction for each piezoelectric element described later.

In the present embodiment, the pulse width time Tr during which the charging transistor is in the ON state is (1/100 kHz) when the natural frequency of the vibration system is 100 kHz, for example.
× 1 = 0.8 to 1.2 times 10 microseconds, that is, 8
The maximum value of Tr is set to 12 microseconds for ~ 12 microseconds. The minimum pulse width of Tr is 8 microseconds. The voltage of FIG. 4A corresponding to this pulse width,
That is, Vm is set as a control waveform for the piezoelectric elements, and a voltage is set for each piezoelectric element. Alternatively, the maximum value of Tr may be set to 24 microseconds and the minimum pulse width of Tr may be set to 16 microseconds by setting the integral multiple to 2.

The pulse width Tw from rise to fall of the voltage 22 applied to the piezoelectric element 1 shown in FIG. 4A is determined by the charge pulse of the drive signal 7 (the charge / discharge control signal 6 is at a high level and the drive signal 7 is at a high level). It is determined by an interval between a high level) and a discharge pulse (when the charge / discharge control signal 6 is at a low level and the drive signal 7 is at a high level). FIG. 4A shows an example of the operation.

Next, a description will be given of an ink jet recording apparatus having a configuration in which the volume of the ink chamber 11 is expanded and the ink is sucked when the electric charge is discharged from the piezoelectric element. In the drive circuit 9 constituting the circuit shown in FIG. 2, the timing of the charge / discharge control signal 6 with respect to the drive signal 7 is changed as shown in FIG.
a is output. By controlling the pulse width of the charge / discharge control signal 6 and the pulse width of the drive signal 7, it becomes possible to control the voltage Vm applied to the piezoelectric element 1 as in the above-described example. The piezoelectric element 1 is deformed in synchronization with the fall of the control waveform 22a, and the diaphragm 13 contracts, whereby ink is sucked into the ink chamber 11. Then, the ink in the ink chamber 11 is compressed by the restoration of the piezoelectric element 1 in synchronization with the rise of the control waveform 22a, and the ink droplet 16 is ejected from the nozzle 12. Here, the falling time constant and the rising time constant of the control waveform 22a applied to the piezoelectric element with respect to the vibration system constituted by the piezoelectric element are represented by:
0.8 to 1.2 times the reciprocal of the natural frequency of the vibration system,
When the fall time constant is set to be equal to or larger than the rise time constant, harmonic vibration of the piezoelectric element can be suppressed. If the value of the integral multiple is large, the time constant will be long,
In general, the value of the integral multiple is about 1, 2, or 3 because the lowering of the nozzle driving frequency leads to a decrease in the printing speed, and the voltage fluctuation rate is so small that a sufficient pressure for ejecting ink cannot be obtained. Use a small integer value. The pulse width Tw from the fall to the rise of the voltage 22a applied to the piezoelectric element 1 shown in FIG. ) And a charge pulse (when the charge / discharge control signal 6 is at a high level and the drive signal 7 is at a high level). FIG. 4B shows an example of the operation. In this example, FIG.
Although the trapezoidal control waveform 22a shown in FIG. 5B is used, the same applies to the triangular waveform control waveform 23a shown in FIG. 5B. What is necessary in the configuration of the present invention is
The control waveform may fall linearly.

As another example, the same control can be performed by using the positive current source 2 for charging and the negative current source 3 for discharging as variable current sources. As shown in Equation 1, the voltage applied to the piezoelectric element 1 rises linearly in proportion to the current value of the positive current source 2 for charging, and rises linearly in proportion to the current value of the negative current source 3 for discharging. Fall down. By repeating the charge / discharge control signal 6 and the pulse signal of the drive signal 7 as in the above example, a control waveform 24 shown in FIG. 6A is output from the drive circuit 9 and applied to the piezoelectric element 1. Is done. At this time, FIG.
As shown in (a), by changing the current value of the positive current source 2 for charging and the current value of the negative current source 3 for discharging, it is possible to change the step-up amount and the step-down amount of the control waveform 24 within a certain time. Thus, the voltage Vm applied to the piezoelectric element 1 can be controlled.

The ink is sucked into the ink chamber 11 by the deformation of the piezoelectric element 1 and the contraction of the diaphragm 13 in synchronization with the rise of the control waveform 24. And
When the piezoelectric element 1 is restored in synchronization with the fall of the control waveform 24, the ink in the ink chamber 11 is compressed, and the ink droplet 16 is ejected from the nozzle 12. In this example, a trapezoidal control waveform 24 as shown in FIG.
However, the same applies to the control waveform 23 having a triangular waveform shown in FIG. What is necessary in the configuration of the present invention is that the control waveform falls linearly. Here, the rise time constant and the fall time constant of the control waveform 24a applied to the piezoelectric element with respect to the vibration system constituted by the piezoelectric element are represented by:
0.8 to 1.2 times the reciprocal of the natural frequency of the vibration system,
When the rise time constant is set to be equal to or larger than the fall time constant, harmonic vibration of the piezoelectric element can be suppressed. If the value of the integer multiple is large, the time constant will be long,
In general, the value of the integral multiple is about 1, 2, or 3 because the lowering of the nozzle driving frequency leads to a decrease in the printing speed, and the voltage fluctuation rate is so small that a sufficient pressure for ejecting ink cannot be obtained. Use a small integer value.

The pulse width Tw from rise to fall of the applied voltage 24 applied to the piezoelectric element 1 shown in FIG. 6A is determined by the charge pulse of the drive signal 7 (the charge / discharge control signal 6 is at a high level and the drive signal 7 Is high level) and the discharge pulse (when the charge / discharge control signal 6 is low level and the drive signal 7 is high level). FIG. 6A shows an example of the operation.

Next, a description will be given of an ink jet recording apparatus having a configuration in which the volume of the ink chamber 11 is expanded and the ink is sucked when the electric charge is discharged from the piezoelectric element. In the drive circuit 9 constituting the circuit shown in FIG. 2, the timing of the charge / discharge control signal 6 with respect to the drive signal 7 is changed as shown in FIG.
a is output. By controlling the current values of the positive current source 2 for charging and the negative current source 3 for discharging, it is possible to control the voltage Vm applied to the piezoelectric element 1 as in the above-described example. The piezoelectric element 1 is deformed in synchronization with the fall of the control waveform 24a, and the diaphragm 13 contracts, whereby ink is sucked into the ink chamber 11. Then, the ink in the ink chamber 11 is compressed by the restoration of the piezoelectric element 1 in synchronization with the rise of the control waveform 24a, and the ink droplet 16 is ejected from the nozzle 12. Here, the fall time constant and the rise time constant of the control waveform 24a applied to the piezoelectric element with respect to the vibration system formed by the piezoelectric element are set to 0.8 to the reciprocal of the natural frequency of the vibration system.
When it is set to 1.2 times and the rising time constant is set to be equal to or larger than the falling time constant, harmonic vibration of the piezoelectric element can be suppressed. If the value of the integral multiple is large, the time constant becomes longer, leading to a decrease in the printing speed due to a decrease in the nozzle drive frequency, and the voltage fluctuation rate is so small that a pressure sufficient to eject ink cannot be obtained. The double value is generally a small integer value of about 1, 2, or 3.

The pulse width Tw from the fall to the rise of the voltage 24a applied to the piezoelectric element 1 shown in FIG. 6B is determined by the discharge pulse of the drive signal 7 (the charge / discharge control signal 6 is low level,
In addition, it is determined by the interval between the drive signal 7 is at a high level) and the charge pulse (when the charge / discharge control signal 6 is at a high level and the drive signal 7 is at a high level). FIG. 6B shows an example of the operation. In this example, the control waveform 24a has a trapezoidal waveform as shown in FIG. 6B, but the same applies to the control waveform 23a having a triangular waveform shown in FIG. 5B. What is necessary in the configuration of the present invention is that the control waveform falls linearly.

By these means, the amount of displacement of the piezoelectric element can be controlled for each piezoelectric element, the variation in the ink droplet ejection speed for each nozzle can be suppressed, and the accuracy of the ink droplet landing position can be improved. . At the same time, multi-nozzle
Trimming of the ink jet nozzle of the ink jet recording apparatus can be performed, and the yield at the time of manufacturing the ink jet nozzle can be improved.

The advantage of driving by a current source is that it is more resistant to electrical interference and disturbance noise in a substrate wiring pattern and the like than voltage driving. On the other hand, there is a disadvantage that the circuit scale becomes large, but this can be solved by integration using an LSI or the like.

In this embodiment, an example of an ink jet recording apparatus for ejecting liquid ink droplets at room temperature without using the heater 17 shown in FIG. 8A is described. In an ink path including an ink chamber heated at a temperature in a range of degrees, a hot-melt ink jet recording apparatus that converts a hot-melt ink that is solid at room temperature into a liquid by heating and ejects ink droplets also has the same configuration as described above. By means of this means, it is possible to correct the variation of the electro-mechanical conversion characteristics of the ink ejection system including the piezoelectric element and make the same ink droplet ejection speed, thereby improving the accuracy of the ink droplet landing position on the inkjet recording material. Become.

FIG. 12 shows an example of the variation of the ink droplet ejection speed of each nozzle by the conventional ink jet recording apparatus, and FIG. 7 shows an example of the variation of the ink droplet ejection speed of each nozzle by the ink jet recording apparatus of the present invention. The horizontal axis indicates each nozzle number, and the vertical axis indicates the ink droplet ejection speed. When the print head ejects ink droplets while sliding at a constant speed, not changing the ink droplet ejection speed means improving the landing position accuracy when the ink droplets fly and land on the recording medium. A prerequisite for evaluating image quality,
It can be seen that the variation of the injection speed of the present invention is smaller than the variation of the conventional injection speed. As a result, it is possible to prevent a decrease in print quality. The pulse width of the drive signal 7 is measured in advance by measuring the liquid velocity of the ink ejecting system including the piezoelectric element, or by measuring the variation of the landing position with respect to the model print pattern, and using a ROM (not shown) as the voltage trimming value of each piezoelectric element. And the control signal generation circuit 8 can easily control the pulse width.

For a piezoelectric element that does not eject ink droplets in response to a recording signal, the drive signal 7 is not generated so that the piezoelectric element is not charged or discharged, and the ink suction operation is not performed. Is controlled not to be injected.

[0041]

By using the ink jet recording apparatus of the present invention, the variation in the electromechanical conversion characteristics of the ink ejection system including the piezoelectric element is corrected to make the ink droplet ejection speeds from a plurality of ejection nozzles the same. High-precision recording on an inkjet recording material is possible. Trimming of the ink jet nozzles of the multi-nozzle ink jet recording apparatus can be performed by controlling individual pulse waveforms at the time of jetting to each piezoelectric element, which is also effective in improving the yield when manufacturing the ink jet nozzles.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a control circuit illustrating an example of a drive circuit of the present invention.

FIG. 2 is a circuit diagram showing an example of a plus variable current source for charging according to the present invention.

FIG. 3 is a circuit diagram showing an example of a minus variable current source for discharge of the present invention.

FIG. 4 is a voltage waveform diagram according to the drive circuit of the present invention.

FIG. 5 is a voltage waveform diagram showing another example of the drive circuit of the present invention.

FIG. 6 is a voltage waveform diagram showing another example of the drive circuit of the present invention.

FIG. 7 is a graph showing the ink droplet ejection speed for each nozzle in the ink jet recording apparatus of the present invention.

FIG. 8 is a schematic cross-sectional view illustrating a steady state of the inkjet recording apparatus.

FIG. 9 is a control circuit diagram showing an example of a conventional pulse drive circuit.

FIG. 10 is a waveform diagram of a voltage applied to a piezoelectric element in a conventional pulse drive circuit.

FIG. 11 is a conceptual diagram of a laminated piezoelectric element.

FIG. 12 is a graph showing the ink droplet ejection speed for each nozzle in a conventional ink jet recording apparatus.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Piezoelectric element, 2 ... Positive current source for charge, 3 ... Negative current source for discharge, 6 ... Charge / discharge control signal, 7 ... Drive signal, 9
... Drive circuit.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Keiji Kunimi 1060 Takeda, Hitachinaka-shi, Ibaraki F-term in Hitachi Koki Co., Ltd. (reference) 2C057 AF29 AG47 AH15 AM21 AM22 AR16 BA03 BA14

Claims (13)

[Claims] 1. A multi-nozzle type ink jet recording apparatus for ejecting ink from a nozzle by changing the volume of an ink chamber at room temperature by using a piezoelectric element at a normal temperature. Charging the piezoelectric element with a current flowing from a current source,
By deforming the piezoelectric element, the volume of the ink chamber is expanded to suck ink, and then, the piezoelectric element is discharged by discharging the piezoelectric element so that current flows into a minus current source connected to the piezoelectric element. And a drive circuit for controlling the ejection of the ink sucked into the ink chamber, and the voltage applied to the piezoelectric element by adjusting the amount of electric charge charged to the piezoelectric element from the positive current source. Is transiently changed, the rising time constant and the falling time constant of the applied voltage are set to integral multiples of the reciprocal of the natural frequency of the vibration system formed by the piezoelectric element, and An ink jet recording apparatus, wherein the constant is set to the same or a larger value. 2. The ink jet recording apparatus according to claim 1, wherein when the value of the rising time constant and the value of the integral time for setting the falling time constant are large, the time constant becomes long and the nozzle drive frequency becomes low. Since the printing speed is reduced and the fluctuation rate of the voltage is small and a pressure sufficient to eject ink cannot be obtained, an integer multiple of 1, 2,
An ink jet recording apparatus characterized in that it has a small integer value of about 3. 3. The ink jet recording apparatus according to claim 1, wherein, when setting the rising time constant and the falling time constant, the time constant is set to an integer multiple of a reciprocal of a natural frequency of a vibration system formed by the piezoelectric element. An ink jet recording apparatus, wherein a range of 8 to 1.2 times is set as an applied voltage correction range when controlling an applied voltage waveform for each nozzle. 4. A multi-nozzle type ink jet recording apparatus in which a volume of an ink chamber is changed by using a piezoelectric element at a normal temperature to eject ink in the ink chamber from a nozzle. Discharging the piezoelectric element so that current flows into the current source, deforming the piezoelectric element to expand the volume of the ink chamber, sucking ink, and then flowing out of the plus current source connected to the piezoelectric element A drive circuit that controls the piezoelectric element to be restored by charging the piezoelectric element with current and ejecting the ink that has been sucked into the ink chamber, and the amount of electric charge discharged from the piezoelectric element to a negative current source , The voltage applied to the piezoelectric element is changed transiently, and the falling time constant and the rising time constant of the applied voltage are changed. Wherein an integral multiple of a reciprocal of a natural frequency of a vibration system formed by the piezoelectric element and the falling time constant is set to be equal to or larger than the rising time constant. apparatus. 5. The ink jet recording apparatus according to claim 4, wherein when the rising time constant and the falling time constant are set to integral multiples that are large, the time constant becomes longer and the nozzle driving frequency becomes lower. This leads to a decrease in printing speed, and a voltage fluctuation rate is small, so that a pressure sufficient to eject ink cannot be obtained.
An ink jet recording apparatus characterized by a small integer value of about two or three. 6. The ink jet recording apparatus according to claim 4, wherein, when setting the rise time constant and the fall time constant, 0.times. An integral multiple of a reciprocal of a natural frequency of a vibration system formed by the piezoelectric element. An ink jet recording apparatus, wherein a range of 8 to 1.2 times is set as an applied voltage correction range when controlling an applied voltage waveform for each nozzle. 7. An ink jet recording apparatus according to claim 1, wherein a current is supplied to each current source in a drive circuit connected to each of said piezoelectric elements, or an adjustment of a time during which the current flows is performed. An ink jet recording apparatus, wherein the amount of charge charged and discharged to each piezoelectric element is increased / decreased, the amount of expansion / contraction of each piezoelectric element is changed for each nozzle, and the speed of ejecting ink droplets is controlled. 8. An ink jet recording apparatus according to claim 1, wherein electric charges charged and discharged to each piezoelectric element by changing a current value of each current source in a drive circuit connected to each piezoelectric element. An ink jet recording apparatus that controls the ejection speed of ink droplets to be ejected by increasing or decreasing the amount of ink droplets and changing the amount of expansion or contraction of the piezoelectric element for each nozzle. 9. The ink jet recording apparatus according to claim 1, wherein a time from charging to discharging of the piezoelectric element depends on a pulse interval of a driving signal of a control signal generating circuit. Inkjet recording apparatus. 10. An ink jet recording apparatus according to claim 4, wherein a time period from discharge to charging of said piezoelectric element depends on a pulse interval of a drive signal of a control signal generation circuit. apparatus. 11. The ink jet recording apparatus according to claim 7, wherein by controlling the current source for each of the piezoelectric elements, the amount of expansion and contraction of the plurality of piezoelectric elements having non-uniform electro-mechanical conversion characteristics is determined for each of the piezoelectric elements. An ink jet recording apparatus, comprising: correcting a variation in ink droplet ejection speed for each nozzle; 12. The ink-jet recording apparatus according to claim 1, wherein the volume of the ink chamber heated at a temperature in a range of 80 degrees Celsius to 140 degrees Celsius is changed by using a piezoelectric element, whereby the ink is discharged. A hot-melt ink jet recording apparatus characterized by ejecting from a nozzle. 13. An ink jet recording apparatus according to claim 1, wherein said piezoelectric element corresponding to a nozzle for ejecting ink is charged and discharged with a predetermined amount of electric charge by said current source. Ink jet recording device.