JP2003053969A - Control method for driving inkjet head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent delay or deformation of a driving waveform and occurrence of vibration which may occur when a driving waveform is changed due to a number of piezoelectric elements and self-heating thereof in terms of a method for controlling a piezoelectric element of an inkjet printer. SOLUTION: In this method of controlling the piezoelectric elements 7 of the inkjet printer, the number of piezoelectric elements 7 to be driven and the self-heating of the piezoelectric elements are managed to correct an input waveform 9 to an amplifier section 3 so that a predetermined driving waveform is applied to the piezoelectric elements 7 insusceptible of the number of piezoelectric elements 7 to be driven.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inkjet printing apparatus, and more particularly to a method of controlling a drive waveform applied to a piezoelectric element.

[0002]

2. Description of the Related Art Conventionally, since the number of piezoelectric elements that are simultaneously driven is relatively small and the inductance of the cable connecting the amplifying section and the head section is not taken into consideration, the piezoelectric elements are not affected by the number of driving elements. The input waveform to the amplifier is corrected by assuming that the drive waveform of (3) is applied.

In Japanese Patent Laid-Open No. 2000-203014, when a capacitive load is connected to a push-pull circuit (amplifier circuit), oscillation easily occurs, and stable operation is achieved for all combinations of simultaneously driven piezoelectric elements. Since it is difficult to design a push-pull circuit like this, by providing push-pull circuits for the number of piezoelectric elements inside the carriage and operating only the push-pull circuits of the piezoelectric elements to be driven, the drive waveform can be applied to the piezoelectric elements. It is described that the voltage is applied.

[0004]

The drive waveform applied to the piezoelectric element causes a potential difference between the cable and the analog switch arranged in the preceding stage of the piezoelectric element.
The drive waveform has a time delay with respect to the output waveform of the amplifier.

The number of piezoelectric elements to be driven is smaller than the reference number of lines which is the boundary between overdamping and vibration damping, due to the values of the inductance component of the cable, the resistance component of the analog switch and the capacitance component of the piezoelectric element. At the time of decay, the drive waveform applied to the piezoelectric element does not exceed a predetermined potential, but converges to a predetermined potential in a dull manner.

On the other hand, when the number of piezoelectric elements to be driven is greater than the reference number, which is the boundary between over-damping and vibration damping, the driving waveform applied to the piezoelectric elements vibrates up and down at a predetermined potential. To converge.

Further, in order to achieve high-density mounting of piezoelectric elements and securing of displacement at the same time, a laminated type piezoelectric element is generally used. Although it is important to increase the driving frequency of the piezoelectric element in order to increase the printing speed, the capacitance of the piezoelectric element increases due to self-heating, which causes the above-described over-damping and vibration damping.

In order to perform high-definition printing, it is necessary to ensure the precision of the mechanical parts and the assembly of the print head, such as the ink chambers and piezoelectric elements. However, if the target drive waveform cannot be provided to the print head with high accuracy, the performance of the print head will be degraded as a result.

As described above, the driving waveform applied to the piezoelectric element causes a problem that the driving waveform changes due to the number of piezoelectric elements to be driven or self-heating, and as a result, ink ejection is performed in an ink jet printer. It affects the speed of ink and the weight of ink, and has been an important issue in obtaining high-definition printing.

In order to solve such a problem, the present invention corrects the input waveform to the amplifying section and, even if the number of piezoelectric elements to be driven and the capacitance of the piezoelectric elements are changed, the piezoelectric elements are driven in a predetermined manner. An object is to provide a control method for applying a waveform.

[0011]

The output waveform of the amplifier is not affected by the number of piezoelectric elements to be driven, but since the cable has an inductance component and the analog switch has a resistance component, the potential difference between the cable and the analog switch is different. Occurs. As a result, the drive waveform applied to the piezoelectric element according to the number of piezoelectric elements to be driven causes a time delay, dullness, and vibration with respect to the output waveform of the amplification section. The input waveform to the amplifier was corrected so that

The method of correcting the input waveform to the amplifying section may derive the correction element by comparing the drive waveform applied to the piezoelectric element with the output waveform of the amplifying section.

When the input waveform to the amplifying section changes from a constant potential, a potential difference occurs between the cable and the analog switch, so that the drive waveform applied to the piezoelectric element is delayed in time with respect to the output waveform of the amplifying section. Drive waveform. Therefore, the driving waveform applied to the piezoelectric element is set in advance so that the time at which the input waveform to the amplifying unit starts changing from a constant potential is set early so that there is no time delay with respect to the output waveform of the amplifying unit. It is possible to obtain a predetermined drive waveform with.

When the number of piezoelectric elements to be driven is overdamped (the drive waveform converges so as to become dull with respect to a predetermined potential), which is smaller than the reference number of boundaries which is a boundary between overdamping and vibration damping,
At the end of the rising edge of the input waveform to the amplifier, the drive waveform applied to the piezoelectric element is set to the predetermined end of the rising edge by the correction method that sets the start time of the input waveform to the amplifier early. Since the output waveform of the amplifier, which is a waveform, converges in a dull manner, a predetermined drive waveform is obtained by a correction method that temporarily sets a potential higher than the original potential at the rising end portion of the input waveform to the amplifier. It was

Similarly, the drive waveform applied to the piezoelectric element at the trailing end of the input waveform to the amplifier is also:
With only the correction method that sets the start time of the input waveform to the amplification section earlier, the fall end section converges so as to become dull with respect to the output waveform of the amplification section. A predetermined drive waveform was obtained by a correction method in which a potential lower than the original potential was temporarily set in the falling end portion.

When the number of piezoelectric elements to be driven is vibration damping (converging so that the driving waveform vibrates with respect to a predetermined potential) larger than the reference number which is the boundary between over-damping and vibration damping, the amplifier unit is driven. Only with the correction method that sets the start time of the input waveform to start rising earlier, the rising end part converges so as to oscillate a predetermined potential up and down with respect to the output waveform of the amplification part that is the predetermined drive waveform. , The input waveform to the amplification section has a rising slope that is higher than the input waveform to the amplification section before correction from the time of the potential lower than the original potential before the time of reaching the original potential. A predetermined drive waveform was obtained by a correction method that loosens the time to reach the original potential.

Similarly, the drive waveform applied to the piezoelectric element at the trailing end of the input waveform to the amplifier is also:
With only the correction method that sets the time to start the fall of the input waveform to the amplification section earlier, the fall end section converges so that the output potential of the amplification section oscillates a predetermined potential up and down. The input waveform to the amplifying part is the falling slope of the end waveform from the time of the potential higher than the original potential before the time when the original potential is reached to the original waveform. Was obtained, and a predetermined drive waveform was obtained by a correction method in which the time to reach the original potential was delayed.

Further, a predetermined drive waveform was obtained by detecting an increase in capacitance due to self-heating of the piezoelectric element and performing the correction method described above together.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a drive circuit diagram of an ink jet printing apparatus as an example of the present invention. In FIG.
1 is a CPU, 2 is a D / A converter, 3 is an amplification section, 4 is a head section, 5 is a cable connecting the amplification section 3 and the head section 4, 6 is an analog switch, 7 is a piezoelectric element, 8 is a counter, 30 Shows a thermistor for temperature detection of the piezoelectric element.

In the configuration of this example, the number of the piezoelectric elements 7 to be driven is counted by the counter 8, and the input data to the D / A converter 2 corresponding thereto is set by the CPU 1 and the output of the D / A converter 2 is set. The output waveform amplified by the amplification unit 3 is applied to the analog switch 6 arranged in the subsequent stage of the cable 5, and the piezoelectric element 7 is driven only when the analog switch 6 is in the ON state.

FIG. 2 is an equivalent circuit diagram of the cable 5, the analog switch 6 and the piezoelectric element 7. Here, there is an RLC circuit in which the equivalent component of the analog switch 6 is used as the resistance component 6a of the analog switch, and the equivalent component of the piezoelectric element 7 is used as the capacitance component 7a of the piezoelectric element 7.

First, the driven piezoelectric element according to the present invention
An example of control when the number of 7 is less than the reference number which is the boundary between overdamping and vibration damping will be described.

FIG. 3 shows that when the number of driven piezoelectric elements 7 is less than the reference number which is the boundary between overdamping and vibration damping, the input waveform 9 (dotted line) to the amplifying section 3 before correction and the correction FIG. 11 is a diagram comparing the input waveform 10 (solid line) to the amplification unit 3 after the above. When the input waveform 9 to the amplifier 3 before this correction is amplified, the output waveform of the amplifier 3 is 13 in FIG. However, since the cable 5 has an inductance component, a potential difference (hereinafter referred to as V _L ) occurs. Further, since the analog switch 6 also has a resistance component, a potential difference (hereinafter referred to as V _R )
Is generated, and the sum thereof is expressed by Equation 1, and when the input waveform 9 to the amplifying section 3 rises, Equation 2 is changed with respect to a predetermined potential E ₀ .
It converges to be dull in the form of.

[0024]

[Equation 1]

[0025]

[Equation 2]

On the contrary, when the input waveform 9 to the amplifying section 3 falls, it converges to a predetermined potential E ₁ so as to become dull in the form of Expression 3.

[0027]

[Equation 3]

As a result, since the drive waveform shown by 14 in FIG. 4 is applied to the piezoelectric element 7, the input waveform 9 to the amplifying section 3 is set as follows in order to apply a predetermined drive waveform to the piezoelectric element 7. It was corrected by various methods.

In FIG. 4, the drive waveform 14 applied to the piezoelectric element 7 is compared with the output waveform 13 of the amplification section 3, and when the input waveform 9 to the amplification section 3 changes from a constant potential, the drive waveform 14 becomes The output waveform 13 of the amplification section 3 has a waveform that is delayed in time. When the drive waveform 14 approaches the predetermined potential, it converges to the predetermined potential in a dull form. The means for correcting the time delay performs control to set the time at which the input waveform 9 to the amplifying section 3 starts to change as fast as 11a shown in FIG. 3 at the time of rising and 11b at the time of falling. .

The means for correcting the dullness temporarily sets a potential higher than the original potential as shown at 12a in FIG. 3 at the time of rising of the input waveform 9 to the amplifying section 3, and the conventional rising ends. Control is performed to return to the original potential at time.

When the input waveform 9 to the amplifier 3 falls,
As indicated by 12b shown in FIG. 3, a potential lower than the original potential is temporarily set, and control is performed to return to the original potential at the time when the conventional fall ends.

When the input waveform 9 to the amplifying unit 3 before being corrected as described above is corrected and amplified like the input waveform 10 to the amplifying unit 3, the output waveform of the amplifying unit 3 is the waveform 15 shown in FIG. However, a driving waveform 16 such as the waveform 13 (predetermined driving waveform) is applied to the piezoelectric element 7.

Next, in the present invention, a piezoelectric element to be driven
An example will be described in which the number of 7 is greater than the reference number of boundaries that is the boundary between overdamping and vibration damping.

FIG. 6 shows that when the number of piezoelectric elements 7 to be driven is greater than the reference number, which is the boundary between overdamping and vibration damping, the input waveform 9 (dotted line) to the amplifying section 3 before correction and the correction FIG. 11 is a diagram comparing input waveforms 17 to the amplification unit 3 after performing.
When the input waveform 9 to the amplifier 3 before this correction is amplified,
The output waveform of the amplification section 3 is as shown by 13 in FIG. But,
The number of piezoelectric elements 7 to be driven is less than the standard number, which is the boundary between overdamping and vibration damping.
Since 5 has an inductance component, the potential difference (hereinafter V _L '
Is described) occurs. Further, since the analog switch 6 also has a resistance component, a potential difference (hereinafter referred to as V _R ') occurs,
The sum is expressed in the form of Equation 4, the rising time of the input waveform 9 to the amplifying unit 3 'to the predetermined potential E ₀ in the form of Equation 5' predetermined potential E ₀ to vibrate up and down Converge to.

[0035]

[Equation 4]

[0036]

[Equation 5]

On the contrary, when the input waveform 9 to the amplifying section 3 falls, the predetermined potential E ₁ ′ is converged so as to oscillate up and down with respect to the predetermined potential E ₁ ′ in the form of Formula 6. .

[0038]

[Equation 6]

As a result, since the drive waveform shown by 20 in FIG. 7 is applied to the piezoelectric element 7, the input waveform 9 to the amplifying section 3 was corrected by the following method in order to apply a predetermined drive waveform. .

In FIG. 7, when the drive waveform 20 applied to the piezoelectric element 7 is compared with the output waveform 13 of the amplification section 3, the amplification section 3
Drive waveform 2 when input waveform 9 to
0 is a waveform that is delayed with respect to the output waveform 13 of the amplification unit 3. When the drive waveform 20 approaches the predetermined potential, the predetermined potential converges so as to oscillate up and down. The means for correcting the time delay is the same as when the number of the piezoelectric elements 7 to be driven is less than the reference number which is the boundary between the overdamping and the vibration damping, as in the case of the input waveform 9 to the amplifying section 3. The control is performed so that the time when the change starts is set to 18a at the time of rising, while it is set to 18b at the time of falling, at the beginning.

The means for compensating for the vibration is such that the rising edge of the input waveform 9 to the amplifying section 3 is earlier than the time when the original potential is reached as shown by 19a shown in FIG. The slope of the input waveform 9 to the input waveform 9 is relaxed from the time of the lower potential before the time of reaching the original potential of the rising end portion, and control is performed to reach the original potential at a later time than before correction.

On the other hand, when the input waveform 9 to the amplifying section 3 falls, the input waveform to the amplifying section 3 before correction is earlier than the time when the original potential is reached as shown in 19b in FIG. 9
The control is performed such that the gradient is relaxed from the time of the high potential before the time of reaching the original potential of the falling end portion, and the original potential is reached at a later time than before correction.

When the input waveform 9 to the amplifying section 3 is corrected and amplified like the input waveform 17 to the amplifying section 3 as described above, the output waveform of the amplifying section 3 is the waveform 21 shown in FIG. , The piezoelectric element 7 has a drive waveform 22 such as waveform 13 (predetermined drive waveform).
Is applied.

The number of piezoelectric elements 7 to be driven is counted by the counter 8, and it is determined whether the number of piezoelectric elements 7 to be driven is less than or greater than the reference number of boundaries between over-damping and vibration damping. If the input waveform 9 is corrected and amplified as 10 or 17, the number of piezoelectric elements 5 to be driven changes when the input waveform 9 to the amplifying unit 3 is not corrected and the drive waveform is compared. It can be said that, by correcting the input waveform 9 to the amplifying unit 3 as 10 or 17, it is possible to apply a predetermined drive waveform even if the number of piezoelectric elements 7 driven changes.

Further, not only is the counter 8 counting the number of piezoelectric elements 7 to be driven to determine whether or not the number of piezoelectric elements 7 to be driven is smaller or larger than the reference number of boundaries which is the boundary between over-damping and vibration damping, Amplification unit that is optimally corrected according to the number of drives
If the input waveform 9 to 3 is amplified, a predetermined drive waveform is applied to the piezoelectric element 7 even if the number of piezoelectric elements 7 to be driven changes.

FIG. 9 shows the temperature-capacitance characteristic of the piezoelectric element, which shows a large capacitance variation with temperature rise due to self-heating. Therefore, by applying the series of correction methods described above in consideration of the increase in capacitance due to self-heating of the piezoelectric element, it is possible to similarly apply a predetermined drive waveform to the piezoelectric element 7.

[0047]

EFFECTS OF THE INVENTION The potential difference between the cable and the analog switch causes the delay, dullness and vibration of the drive waveform applied to the piezoelectric element to be improved, and the number of piezoelectric elements to be driven and the capacitance due to self-heating. By applying a predetermined drive waveform to the piezoelectric element without being affected by the change in the ink, it is possible to make the ink ejection speed and the ink weight uniform.

[Brief description of drawings]

FIG. 1 Drive circuit of inkjet printing apparatus

[Fig. 2] Equivalent circuit of cable, analog switch, and piezoelectric element

FIG. 3 is an input waveform to the amplifying unit when the number of driven piezoelectric elements is less than the reference number which is the boundary between overdamping and vibration damping

FIG. 4 shows an output waveform of the amplifying section and a piezoelectric element before correcting the input waveform to the amplifying section when the number of driven piezoelectric elements is less than the reference number which is the boundary between overdamping and vibration damping. Drive waveform applied

FIG. 5: When the number of driven piezoelectric elements is less than the reference number which is the boundary between over-damping and vibration damping, when there is over-damping, the output waveform of the amplifier after correction of the input waveform to the amplifier and the piezoelectric element Drive waveform applied

FIG. 6 is a diagram illustrating an input waveform to the amplifying unit before correction and an input to the amplifying unit after correction when the number of driven piezoelectric elements is greater than the reference number that serves as a boundary between over-damping and vibration damping. Waveform

FIG. 7 shows a case where the number of driven piezoelectric elements is greater than the reference number, which is the boundary between over-damping and vibration damping, when the output waveform of the amplification section and the piezoelectric element before correction of the input waveform to the amplification section Drive waveform applied

FIG. 8 shows a case where the number of driven piezoelectric elements is greater than the reference number which is the boundary between over-damping and vibration damping, and when the vibration is attenuated, the output waveform of the amplifier and the piezoelectric element after the input waveform to the amplifier is corrected Drive waveform applied

FIG. 9 is a graph showing temperature-capacitance characteristics of a piezoelectric element.

[Explanation of symbols] 1 ... CPU, 2 ... D / A converter, 3 ... Amplifying unit, 4 ... Head unit, 5 ...
A cable having an inductance component connecting the amplification unit and the head unit, 6 ... Analog switch, 6a ... Resistance component of analog switch, 7 ... Piezoelectric element, 7a ... Capacitance component of piezoelectric element, 8 ... Counter, 30 ... Thermistor.

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Claims (7)

[Claims] 1. A plurality of nozzles and an ink chamber communicating with each nozzle are provided, and by applying a drive signal to a piezoelectric element, a pressure change to ink in the ink chamber is caused to cause an ink droplet to be ejected from the nozzle. In the inkjet head, the drive control means of the piezoelectric element is a D / A converter, a CPU that sets input data to the D / A converter, and the number of piezoelectric elements to be driven is counted, and the CPU selects data. Counter, an amplifier that amplifies the output of the D / A converter, a cable that connects the amplifier and the piezoelectric element to apply an amplified drive signal to the piezoelectric element, and a cable that is placed after the cable. A series resonance circuit composed of the capacitance of the piezoelectric element, the inductance of the cable, and the resistance of the analog switch. Of the ink jet head, wherein it is determined whether the drive waveform is overdamped or vibration dampened, the input waveform to the amplifier is corrected, and a predetermined drive waveform is applied to the piezoelectric element. Drive control method. 2. A plurality of nozzles and an ink chamber communicating with each nozzle are provided, and by applying a drive signal to a piezoelectric element, a pressure variation to the ink in the ink chamber is generated and an ink droplet is ejected from the nozzle. In the inkjet head, the drive control means of the piezoelectric element is a D / A converter, a CPU that sets input data to the D / A converter, and the number of piezoelectric elements to be driven is counted, and the CPU selects data. Counter, an amplifier that amplifies the output of the D / A converter, a cable that connects the amplifier and the piezoelectric element to apply an amplified drive signal to the piezoelectric element, and a cable that is placed after the cable. Number of the piezoelectric elements driven by forming a series resonance circuit composed of the capacitance of the piezoelectric element, the inductance of the cable, and the resistance of the analog switch. And whether it is overdamped or vibration dampened by the heat generation temperature of the piezoelectric element, correct the input waveform to the amplification section, and apply a predetermined drive waveform to the piezoelectric element. Inkjet head drive control method. 3. The drive control method for an ink jet head according to claim 1, wherein the time at which the drive waveform starts to change from a constant potential is corrected so as to be set earlier with the input waveform. . 4. The ink jet head according to claim 1, wherein when the drive waveform is overdamped, a potential higher than the original potential is temporarily set near the end of rising of the input waveform. Drive control method. 5. The ink jet head according to claim 1, wherein when the drive waveform is overdamped, a potential lower than the original potential is temporarily set near the end of the fall of the input waveform. Drive control method. 6. When the drive waveform is vibrationally attenuated, the potential is adjusted so as to delay the rise end time by grading the input waveform from the time of a lower potential before the time of reaching the original potential near the rise end. The drive control method for an inkjet head according to claim 1 or 2, wherein: 7. When the drive waveform vibrates and attenuates, the slope of the input waveform is relaxed from the time of a high potential before the time of reaching the original potential near the end of the fall to delay the fall end time. 3. The drive control method for an ink jet head according to claim 1, wherein the potential is set to.