JP3387243B2 - Driving device for inkjet recording head - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving device for an ink jet recording head using a piezoelectric material, and more particularly to a driving device for an ink jet recording head which can make ink ejection characteristics uniform regardless of aging and temperature changes.

[0002]

2. Description of the Related Art FIG. 1 illustrates an on-demand type ink jet head which has been conventionally used in an ink jet printer. FIG. 1 (a) is a sectional view thereof and FIG. An equivalent circuit is shown.

Reference numeral 2 is an ink chamber formed by a chamber frame 1 and a vibrating plate 4. A piezoelectric body 5 which expands and contracts due to an electric field is fixed to the vibrating plate 4, and the vibrating force of the piezoelectric body 5 causes vibration. The plate 4 is displaced and the volume of the ink chamber 2 is expanded and contracted. When a voltage is suddenly applied from the drive line 7 to the electrode 6 provided on the surface of the piezoelectric body 5, the piezoelectric body 5 contracts above and below the paper surface, and the vibrating plate 4 warps in the direction of rapidly contracting the ink chamber, so that the ink is pressed. The ink droplet 3 is ejected from the nozzle 8 which is a fine hole provided in the chamber frame 1. When the electric field is removed, it is gently performed to prevent the intake of air bubbles from the nozzle 8 and to quickly settle the vibration of the meniscus. Inkjet heads are provided with a plurality of such actuators.

In FIG. 1, the relationship between the vibrating plate 4 and the piezoelectric body 5 is shown as a bimorph, but there is also a method of directly transmitting the displacement of the piezoelectric body to the vibrating plate 4 to enlarge or reduce the ink chamber 2. In any case, since the piezoelectric body 5 is electrically capacitive as shown in FIG. 1B, a current proportional to the time derivative of the waveform of the applied voltage flows as a charge / discharge current at the time of applying and removing the electric field. It will be. That is, this charging / discharging current becomes larger as the voltage is rapidly applied to and removed from the piezoelectric body 5, so that the number of elements of the piezoelectric body 5 is large. Values can be tens of amps.
Therefore, a large voltage drop occurs in the drive line 7, and the ejection characteristics are affected by the number of drive elements of the piezoelectric body 5, and the electronic components are broken. Here, if the equivalent capacitance of the piezoelectric body is c, the maximum applied voltage is v, the drive frequency is f, and the number of elements of the piezoelectric body is n, the power consumption is f · c · v ^ 2 · n.

Therefore, in the conventional driving method, as shown in US Pat. Nos. 4,459,599, 4,126,867, 4,282,535, etc., a current is serially connected to a piezoelectric body. A limiting resistor was inserted to suppress the peak value of charge / discharge current.

However, according to this method, the charging / discharging time of each piezoelectric body is changed due to the variation of the resistance value for current limiting, which greatly affects the ink ejection characteristics. For that reason,
There is a problem in forming an IC including the current limiting resistor. Even if the current limiting resistor can be made into an IC with high accuracy, the capacity variation of the piezoelectric body 5 results in a change in the charging / discharging time of the piezoelectric body, which causes a problem in the ink ejection characteristics. .

There is also a method of driving one piezoelectric body by a flow type constant current source and a sink type constant current source as seen in US Pat. No. 4,284,996. There is a problem that it is difficult to make the driving characteristics uniform when driving a plurality of piezoelectric bodies because of the variation in the current value.

Therefore, the applicant of the present invention has filed Japanese Patent Application Laid-Open No. 2-16454.
4, JP-A-2-274554, JP-A-3-
In Japanese Patent No. 36036 and Japanese Patent Laid-Open No. 3-133647,
By connecting a plurality of piezoelectric bodies directly to one drive source and varying the output voltage of the drive source with a predetermined gradient within one drive cycle of the piezoelectric body, the charge / discharge current value peak value can be adjusted without using a current limiting resistor. -A driving device that suppresses the peak value and is not affected by the variation in the capacity of the piezoelectric body has been released.

FIG. 2 is a diagram for explaining a conventional driving device by summing up these components, in which Vp is a high-voltage power source of about 20 V, GND is a ground, and Vs is a common drive to a piezoelectric body having a predetermined waveform. It represents the voltage. Hereinafter, the same numbers or reference numerals have the same meaning.

Reference numeral 10 is a drive voltage generator, which charges and discharges the capacitor C with a constant current If and a constant current Is generated by a flow-type constant current source 11 and a sink-type constant current source 12 to form a straight line. A trapezoidal charge / discharge voltage that changes dynamically is obtained.
This charging / discharging voltage is power-amplified by the power amplifier 13 including an emitter follower (source follower) and becomes the driving voltage Vs. ON / O of constant current source 11 and constant current source 12
In the FF, the system control means 14 has the signal line 14a and the signal line 1
4b. Although not shown, the system control means 14 also executes head carriage control, paper feed control, and the like.

Then, the drive voltage Vs is given to the piezoelectric body by selectively conducting the selection switch 16 composed of a bidirectional transfer gate by the print data signal from the system control means 14, and a predetermined printing is performed. Ink drops are ejected to record a pattern. The switch control means 15 converts the level of the signal from the system control means 14 into a voltage value suitable for driving the selection switch 16.

FIG. 3 (a) shows the waveform of the drive voltage Vs, and FIG. 3 (b) shows the charge / discharge current flowing through the selected piezoelectric element. As shown, the drive voltage Vs is repeatedly and selectively applied to the piezoelectric body in the cycle T.

More specifically, in the waiting period of τ2 hours, in order to keep all the ink chambers in a contracted state, the all selection switch 1
6 is turned on and all the piezoelectric bodies are charged. Then, from the fall of the drive voltage Vs, the selection switch is selectively turned on by the print data signal to discharge the corresponding piezoelectric body to gently expand the ink chamber and suck the ink (τ3).
time). Thereafter, when the meniscus is in the restoring direction after τ4 hours, a driving voltage Vs having a sharp voltage gradient is applied for τ1 hour to rapidly press the ink chamber, eject ink droplets, and set the standby state. It is a return.

There is also a structure in which the ink chamber is contracted by applying an electric field to the piezoelectric body, but in this case, it is the reverse of FIG.
The drive voltage Vs rises slowly and falls quickly.

By the way, in reality, there is a change in the ink characteristics such as viscosity depending on the ambient temperature, which changes the ink ejection characteristics and affects the print quality.
As shown in A and B of (a), it is necessary to adjust the peak value according to the ambient temperature. Therefore, in the conventional example shown in FIG. 2, the peak value of the drive voltage Vs is adjusted by adjusting the charging time of the capacitor-C. If you do this,
As can be seen from (a), the time width of τ1 time for ejecting ink droplets and τ3 time for expanding the ink chamber may change, and the effect of suppressing ink vibration may be lost.

Further, the accuracy of the constant current source 11 and the constant current source 12 is not always good, the slope of the waveform of the drive voltage Vs varies, the timing relationship becomes inaccurate, and good ink ejection characteristics are obtained. There is a problem that cannot be solved.

For example, in the constant current source shown in FIG. 2 of Japanese Patent Application Laid-Open No. 2-164544, the reference voltage is the sum of the Zener voltage of the Zener diode and the base-emitter saturation voltage of the transistor. Although a constant current source is constructed by applying a voltage to the emitter resistance, the Zener voltage is not set to a high voltage of 6 volts or more because the base-emitter saturation voltage of the transistor fluctuates due to temperature changes. And an accurate reference voltage cannot be obtained. However, when the Zener voltage is increased, the potential of the drive voltage Vs is greatly separated from GND or Vp, and not only the utilization efficiency of the supply voltage Vp is deteriorated, but also the high potential from GND gives distortion to the piezoelectric body from the beginning. Deteriorate the ejection characteristics.

On the contrary, when the Zener voltage is set to, for example, about 1 volt, the supply voltage efficiency is improved, but the Zener diode
There is a problem in that the temperature characteristic of the battery itself becomes stronger and the temperature characteristic of the sum voltage with the transistor is added, and an accurate constant current source cannot be obtained.

[0019]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to accurately raise and raise a drive voltage waveform of a piezoelectric body at a desired time. (EN) A drive device for an ink jet head, which can be lowered and at which the crest value of a drive voltage waveform can be set accurately and freely to control ink ejection characteristics to be constant. Further, the present invention provides a drive device for an ink jet head that does not depend on temperature and does not change over time.

[0020]

In order to achieve the above object, the present invention enlarges and contracts a pressure generating chamber by the expansion and contraction force of a piezoelectric body, and ejects an ink droplet from a nozzle hole corresponding to the pressure generating chamber for recording. In the inkjet recording head drive device for performing, based on a correction signal, from a variable constant voltage source whose output value is variable, and an output voltage of the variable constant voltage source,
Divided voltage generation means for generating a plurality of divided voltages, voltage waveform generation means for generating a stepwise voltage waveform voltage using the divided voltage generated by the divided voltage generation means, and the voltage waveform generation means And a power amplifying means for linearly amplifying the power, and applying a voltage generated by the power amplifying means to the piezoelectric body. In a method of driving an inkjet recording head that expands and contracts a pressure generating chamber by expansion and contraction and ejects ink droplets from nozzle holes corresponding to the pressure generating chamber to perform recording, the output value can be varied based on a correction signal. Generating a plurality of divided voltages from the output voltage of the constant voltage source, generating a stepwise voltage waveform voltage using the divided voltage, and linearly amplifying the voltage waveform voltage. Has a degree, a, and applying the linear power amplified voltage to the piezoelectric element.

Further , the voltage waveform generating means is configured to divide the voltage.
The divided voltage output by the voltage generation means is sequentially
Next or jump switching, stepwise voltage waveform voltage
Which is a multiplexer for generating
Further comprising a filter for smoothing the output of the chipplexer,
The output of the multiplexer is fed through the filter to
It is characterized in that it is inputted to a force amplifier.

Furthermore, a filter for smoothing the output of the multiplexer is further provided, and the output of the multiplexer is input to the power amplifier via the filter.

[0023]

According to the above construction, the peak value of the driving voltage matched with the temperature and the head characteristics can be independently set by the variable constant voltage source, and the rising and falling times of the driving voltage are set by the switching time interval of the multiplexer. It can be set independently, and there will be no factors affected by aging.

[0024]

FIG. 4 is a diagram showing a concrete block configuration of the present invention. Reference numeral 20 is a drive voltage generator, which is internally composed of a variable constant voltage source 21, a dividing means 22, a multiplexer 23, a filter 24, a power amplifier 13, a decoder 25, and a level converter 26.

The variable constant-voltage power supply 21 outputs the input voltage Vp as a voltage Vk controlled by a signal from a system control means 27, which will be described later. Based on the output voltage Vk, the dividing means 22 divides the input voltage Vp into a plurality of divisions. A voltage is generated and the divided voltage is guided to the multiplexer 23. The multiplexer 23 is
A control signal from the system control means 27 cyclically switches from the lower voltage to the highest voltage of the divided voltage and from the highest voltage to the lowest voltage in unit steps or every plural steps to generate a staircase waveform voltage. .
The voltage having the step waveform is smoothed by the filter 24 and selectively supplied to the piezoelectric body as the drive voltage Vs via the power amplifier 13.

In this embodiment, since the control signal of the multiplexer output by the system control means 27 is binary data corresponding to a predetermined driving voltage waveform, the decoder 25 decodes the binary data according to a predetermined rule. Further, although the level converter 26 converts the voltage to a predetermined voltage level and inputs the voltage to the multiplexer 23, it is obvious that there are various supply methods.

The above is the basic structure of the drive voltage generator 20. Of course, since there is no element that loses its capacity due to aging like a capacitor, it is possible to generate a drive voltage corresponding to the characteristics of the print head and temperature changes. There is.

Next, the system control means 27 will be described. The system control means 27 comprises a first data processing means and a second data processing means. The first data processing means includes temperature data from a temperature sensitive element 31 provided in the print head 30 and the head. Each characteristic data is taken in and a control signal for generating the reference output voltage Vk is output to the variable constant voltage source 21. This processing can be performed by referring to a table stored in the ROM in advance. The second data processing means cyclically fetches the timing data corresponding to the drive voltage waveform from the ROM and outputs it to the decoder 25.

The printer head 30 has a driving voltage Vs.
Also, a selection switch for selectively supplying the electric field to the piezoelectric body and a selection switch control means based on the print data from the system control means 27 are mounted.

FIG. 5 shows the output waveform of the multiplexer 23, and the A and B waveforms show the case where the output voltage Vk of the variable constant voltage source 21 is Vk1 and Vk2 (Vk1> Vk2).

FIG. 5 shows the division of the output Vk at eight levels. The number of switches of the multiplexer 23 is required to be at least eight, but it is necessary to rapidly raise the drive voltage in the section where ink droplets are ejected. Therefore, there are five levels of interlaced switching in view of the response speed of the switch. Because the switching element O
The N / OFF speed is limited to 50 nS at best, and a slow switching cycle of 250 nS or more, which is 5 times, is desirable for accurate switching. If a rise or fall of several μS is required, interlaced switching is performed in this way. Required. Therefore, since the staircase voltage waveform is rough, it is necessary to smooth it with a filter. If not smoothed, the charging / discharging current of the piezoelectric body does not become a constant current as shown in FIG. 3B, but becomes a pulsating current and the peak current increases, which may cause a problem.

The dotted line along the stepped B waveform in FIG. 5 shows the waveform smoothed by the filter 24, and τ
The relationship between 1 ′ and τ1 and between τ3 ′ and τ3 is the filter 24
The delay of the waveform is shown by passing through.

The procedure for generating the drive voltage shown in FIG. 5 will be described with reference to FIG. FIG. 6 shows the binary data supplied to the decoder 25.
Data is generated by a 3-bit binary counter, the count value is 8 ways from 0 to 7, and at the time of rising of the waveform, it is counted to 3 to 7 in decimal as shown on the left end of FIG. , And at the time of falling, count down to 7-0. By repeating this, predetermined binary data is created.

The second value from the left in FIG.
The third is a converted binary value code-converted by the second data processing means 29, and the right end represents this in decimal. The second data processing means also sets the count value 3 at startup. In this way, the switch position of the multiplexer is selected by skipping and the waveform of FIG. 5 is generated.

In this case, the operating clock of the counter is around 25 MHz due to the element response, and the voltage change time is set to several μS during the ink ejection process, and the voltage change time is set to several tens μS during the ink suction process. It is economically appropriate to set the counter capacity to about 4 or 5 bits.

In the above description, the operation clock frequency of the counter is fixed, but the clock frequency is changed at the time of rising and the time of falling in order to set the rising time and the falling time more accurately. In some cases.

Next, each block configuration shown in FIG. 4 will be described in detail.

FIG. 7 shows the dividing means 22 and the multiplexer 2.
3 is a diagram showing specific circuit configurations of the filter 3, the filter 24, and the power amplifier 13. FIG.

In the constitution of the dividing means 22, the gate electrode and the drain electrode are directly connected to each other, and the P channel transistor 40a is arranged on the output Vk side of the variable constant voltage source 21 and the N channel transistor 40b is arranged on the GND side. In the meantime, n-
One resistor Rd is connected in series to obtain n divided voltages V1, V2, ..., Vn-1, Vn from each node. n is 32 in the case of 5 bits. The provision of the transistors 40a and 40b is related to the dynamic range of the power amplifier described later, and eliminates the dead voltage, and need not always be provided.

The n divided voltages are connected to a P-channel transistor TP and an N-channel transistor TN which form a multiplexer, and these n transistors are collected from the left to the right end or the right to the left end in the figure. It is controlled by the control signal from the level converter 26 so as to sequentially turn on one by one.

The reason why the P-channel transistor is used on the higher voltage side and the N-channel transistor is used on the lower voltage side is to ensure that a sufficient gate voltage is applied in the ON state. Approximately half each.
Therefore, the level converter 26 is designed to output a bipolar control signal, so that a voltage near GND is applied to the P-channel transistor and V is applied to the N-channel transistor.
Voltages in the vicinity of k are given respectively. Conversely, in order to turn off each transistor, the reverse voltage is applied.

The structure of the filter 24 is a simple combination of a capacitor and a resistor, or only a capacitor is used to approximate a step waveform to an exponential function to form a smooth waveform. In addition, when the drive voltage generator 20 is integrated into an IC including other components, the drive voltage generator 20 can be smoothed by the parasitic capacitance and can be configured to have no filter apparently.

Next, a configuration example of the power amplifier 13 will be described. The P-channel transistor 41a and the N-channel transistor 41b use the output of the multiplexer 23 as a common input, and perform a source follower operation using the constant current sources 42a and 42b as loads. The potential on the source side rises and falls by the threshold value between the gate and the source at which the transistor turns on, and follows the input voltage.

The sources of the transistors 41a and 41b are NPN transistors 43 which are connected in a dillington.
a and the PNP transistor 43b.
The transistors 43a and 43b operate as emitter followers, and while one is energized, the other is reverse biased and is not energized. That is, when the drive voltage rises, the transistor 43a turns on and the transistor 43b turns off.
F, and when descending, the opposite relationship will occur. With this configuration, the load can be charged or discharged with a current of several amperes. The power may be supplied to the power amplifier 13 not by the output Vk of the variable constant voltage source illustrated but by the input power supply Vp.

Next, a block of a concrete embodiment of the second data processing means 29 will be described with reference to FIG. In FIG. 8A, the clock generator 50 outputs a clock of about 25 MHz as described above, and includes a start counter 51, an a-state counter 52, and a b slate counter 5.
3, c-state counter 54, d-state counter 55
Is supplying a clock signal to.

Each of the counters 51 to 55 is configured to be reset by a control unit (not shown). When the print head reaches the print area, the reset is released and the counting operation can be started. It will be. Here, the start counter 51 repeatedly counts the drive voltage repetition period T after reset release, and outputs a count start signal to the a-state counter 51 every time the count value of the start count 51 reaches the initial value. . The a-state counter 52 has the a-state shown in FIG.
When the count in the state section is completed, the count operation is stopped and the count start signal is output to the next b-state counter 53. Similarly to the a-state counter 52, the b-state counter 53 stops counting when it finishes counting in the b-state section, and outputs a count start signal to the next c-state counter 54. Hereinafter, the c-state counter 54 and the d-state counter 55 perform the same operation. The operation status of each state count is the condition setting means 60.
And is used to control the gate 56. still,
The count end value of each state counter can be varied by storing the timing data taken in by the condition setting means 60 from the outside and applying it to the state means.

The gate 56 controls the passage of the clock as described above, and the clock passing through the gate 56 is counted by the pre-counter 57 and the pre-counter 57.
Carry signal is output as a count signal of the main counter 58. The count value of the main counter 58 is set by the code converter 5 in order to obtain the above-mentioned interlaced waveform.
It is output to the decoder via 9.

The count capacity of the pre-counter 57 is
The condition setting means 60 can adjust the driving waveform Vs according to the required characteristics of rising and falling, and the conversion format of the code converter 59 can be changed by the condition setting means 6.

Next, another embodiment of the second data processing means 28 will be described with reference to FIG. The ROM 72 stores drive waveform data in a table in the order of addresses, and the data length is set to match the number of switches of the multiplexer 23. The address counter 71 sequentially calls the ROM 72 at a predetermined timing and gives it to the decoder 25. The condition setting means 70 receives and stores timing data from the outside, and sets and stops the cycle of the clock given to the address counter 71. This has a feature that it is simpler than the configuration of FIG. To obtain an arbitrary drive waveform, the ROM 72 may be made a flash memory so that data can be rewritten from the outside.

Next, the first data processing means 29 will be briefly described with reference to FIG. Since the temperature data from the temperature sensitive element 31 is analog, it is converted into a digital quantity by the A / D means 80 for analog / digital conversion and is led to the arithmetic means 81. The calculation means 81 calculates with a predetermined calculation algorithm including the correction data according to the head characteristics, and the result is digitally calculated.
The D / A means 82 for analog conversion restores the analog amount.
This analog amount serves as correction data for the reference voltage of the variable constant voltage power supply 21 that releases the required Vk.

Next, an example of the configuration of the variable constant voltage power source 21 is shown in FIG.
It will be explained in 1. In FIG. 11A, reference numeral 90 is a transistor controlled to output a predetermined voltage Vk from the input voltage Vp. Zener diode ZD has resistance R
A fixed reference voltage Vz is generated by receiving a bias current at b. The analog multiplier 92 multiplies the correction data Vc from the first data processing means 29 by the coefficient α, and the variable reference Vx =
Output αVc. The multiplier 92 is not always necessary, but it is convenient for determining the ratio of the fixed reference and the variable reference in the reference voltage Vr.

The adder 93 has a final reference voltage Vr = Vz +.
Output Vx. The operational amplifier 91 controls the transistor 90 so that the feedback voltage Vf obtained by dividing Vr and Vk by the resistors Rf1 and Rf2 matches. as a result,
Vk = Vr · (1 + Rf1 / Rf2) is obtained. FIG. 11B shows the relationship depending on these temperatures.

Although most of FET (field effect type) transistors are shown in the circuit configuration, these are bipolar transistors.
It may be composed of a transistor. Further, it goes without saying that various modifications can be considered in detail.

[0054]

As described above, according to the configuration of the present invention, the output of the variable constant voltage power supply for generating a desired output voltage is divided into a plurality of outputs by the correction data, and the divided voltage is multiplexed. In order to generate a drive waveform by sequentially selecting so as to obtain a desired voltage waveform, a drive voltage matched to the printer environment can be obtained.

The control signal generated by this multiplexer is generated by a counter or a ROM which operates based on a clock from a highly accurate oscillator, so that an arbitrary drive voltage waveform can be obtained without any secular change, and an analog element is unnecessary and IC It becomes easy to make it.

[Brief description of drawings]

FIG. 1 is a diagram illustrating an inkjet head using a piezoelectric body.

FIG. 2 is a drive circuit diagram of a conventional inkjet head.

3A is a voltage waveform diagram of a drive voltage Vs output from a conventional drive voltage generator 10, and FIG. 3B is a drive voltage Vs.
It is a figure which shows the charging / discharging current of a piezoelectric material by s, and a drive current waveform.

FIG. 4 is a diagram showing specific configuration blocks of the present invention.

FIG. 5 is a diagram showing an example of drive voltage waveforms of the present invention.

6 is a diagram showing a stepwise state of a counter that generates the drive voltage waveform of FIG.

FIG. 7 is a diagram showing a specific circuit of a basic configuration unit of the present invention.

FIG. 8 is a diagram showing blocks constituting a second data processing means.

FIG. 9 is a diagram showing a block configuration of another second data processing means.

FIG. 10 is a diagram showing blocks constituting a first data processing means.

FIG. 11A shows a circuit of a variable constant voltage source, and FIG.
FIG. 6 is a diagram showing the characteristics of (a).

[Explanation of symbols]

21 ... Variable constant voltage source 22 ... Dividing means 23 ... Multiplexer 24 ... Filter 13 ... Power amplifier 25 ... Decoder 28 ... First data processing means 29 ... Second data processing means 30 ... Printer head

Claims (5)

(57) [Claims] 1. A drive device of an ink jet recording head, which expands and contracts a pressure generating chamber by expansion and contraction force of a piezoelectric body, and ejects ink droplets from nozzle holes corresponding to the pressure generating chamber to perform recording, based on a correction signal. A variable constant voltage source whose output value is variable; a divided voltage generation unit that generates a plurality of divided voltages from the output voltage of the variable constant voltage source; and a divided voltage generated by the divided voltage generation unit. A voltage waveform generation unit that generates a stepwise voltage waveform voltage using a power amplification unit that linearly power-amplifies the voltage waveform generation unit. The voltage generated by the power amplification unit is applied to the piezoelectric body. A drive device for an inkjet recording head, characterized in that it is applied to. 2. The voltage waveform generating means is a multiplexer for generating a stepwise voltage waveform voltage by switching the divided voltage output from the divided voltage generating means sequentially or in an interlaced manner in the order of voltage levels. Claim 1
The drive device for the ink jet recording head according to 1. 3. The drive device for an ink jet recording head according to claim 1, wherein the correction signal is for correcting the ink ejection characteristic according to the ambient temperature. 4. A drive device for an ink jet recording head according to claim 2, further comprising a filter for smoothing an output of the multiplexer, and the output of the multiplexer is input to the power amplifier via the filter. . 5. A method of driving an ink jet recording head, wherein a pressure generating chamber is expanded or contracted by expansion and contraction force of a piezoelectric body, and ink droplets are ejected from nozzle holes corresponding to the pressure generating chamber to perform recording, based on a correction signal. A step of generating a plurality of divided voltages from an output voltage of a variable constant voltage source whose output value is variable, a step of generating a stepwise voltage waveform voltage using the divided voltage, the voltage waveform voltage And linearly amplifying the power, and applying the linearly power amplified voltage to the piezoelectric body.