JP2002079181A - Piezoelectric element driver and its driving method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a piezoelectric element impression voltage of positive/negative signal pulse and to form a waveform suitable for the measurement of the exact propagation time particularly by using the same. SOLUTION: In Figure 3 (c), the piezoelectric element impression voltage V2 is matched in the phases at the timing of (A) to the piezoelectric element resonance waveform of Figure (a), by which resonance vibration is intensified (accelerated). The voltage described above is reversed in the phases at the timing of (c), by which the resonance vibration is attenuated (decelerated).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a piezoelectric element driver and a driving method thereof.

[0002]

2. Description of the Related Art FIG. 8 is a diagram showing an example of a circuit configuration of a conventional piezoelectric element driver. The piezoelectric element driver is a drive circuit for driving (applying a voltage to vibrate) a piezoelectric element that generates an ultrasonic pulse in an ultrasonic flow meter / level meter, for example. Although a method of applying a voltage having the same frequency as the resonance frequency of the element is known, the inventors of the present invention have found a method of driving with a rising impulse voltage, and this driving circuit is shown in FIG. Show.

In FIG. 1, a piezoelectric element 11 is connected to a secondary winding 12b of a transformer 12, and is driven by a voltage boosted by the transformer 12. The primary winding 12a of the transformer 12 is connected to a power supply 1 via a capacitor 13 and a resistor 15.
6 is connected. The connection point between the capacitor 13 and the resistor 15 can be grounded by the switch 14. The inductance of the primary winding 12a of the transformer 12 is L1, the capacitance of the capacitor 13 is C1, the resistance of the resistor 15 is R1, and the voltage of the power supply 16 is V1.

The operation of the piezoelectric element driver will be described with reference to FIG. Normally, switch 14 is OFF
State. At this time, the resistor 15 is connected to the resistor 15.
, The voltage V1 of the power supply 16 is charged.
Since the DC current is cut by the capacitor 13, no current flows through the primary winding 12 a of the transformer 12. Therefore, no voltage is generated in the secondary winding 12b, and no voltage is applied to the piezoelectric element 11.

When the piezoelectric element 11 is driven, a switch 14 is driven by a drive control signal from a control unit (not shown).
Is turned on for the ton time (FIG. 9A). Switch 1
At the moment when 4 is turned on, the voltage of the capacitor 13 on the switch 14 side becomes 0 (V) (ground fault).

As a result, the primary winding 12a of the transformer 12
Is applied with a voltage V1. Assuming that the turns ratio of the primary winding and the secondary winding of the transformer 12 (1: N), the moment the switch 14 is turned on, the secondary winding 12b is impulse-like as shown in FIG.
A voltage of V2 = -N.times.V1 as shown in (b) is generated to drive the piezoelectric element. After that, as shown in the drawing, the vibration is attenuated while oscillating at a resonance frequency f (the following equation) determined by the inductance L1 of the primary winding 12a of the transformer and the capacitance C1 of the capacitor 13.

[0007]

(Equation 1)

[0008] As shown in FIG.
Is controlled to be OFF after ton time after being controlled to be ON.
When the switch 14 is turned off, the capacitor 13 starts to be charged by the voltage V1 of the power supply 16 via the resistor 15, but in general, the capacitor 13 and the resistance R1 of the resistor 15 are used to gradually store energy. Since the constant C1.times.R1 is set much higher than the resonance frequency f, it hardly affects the waveform shown in FIG. 9B.

In the above-described circuit configuration, since switching control is not directly performed on the secondary winding 12b which is high in voltage, a voltage of several thousand volts can be applied to the piezoelectric element with a simple configuration. The piezoelectric element driver is used for generating an ultrasonic pulse, for example, an ultrasonic flow meter / level meter, and the above-mentioned circuit is used for, for example, thousands of volts such as a flow meter for measuring the flow rate of a gas such as a gas pipe. Suitable for high-grade applications. However, the scope of the present invention is not limited to such applications.

[0010]

In the above conventional circuit,
Since the impulse voltage generated at the moment when the switch 14 is turned on includes all frequencies, it is possible to drive piezoelectric elements having various resonance frequencies.
As a result, a voltage that vibrates (damps) is also applied to the piezoelectric element. As a result, when the frequency f does not coincide with the resonance frequency of the piezoelectric element, distortion occurs in the vibration waveform of the piezoelectric element.

For this reason, usually, the resonance frequency of f is made to coincide with the resonance frequency of the piezoelectric element. However, in this case, only the piezoelectric element having the resonance frequency of f can be driven. In order to drive a plurality of types of piezoelectric elements (that is, having different resonance frequencies), L / C circuits having values corresponding to the resonance frequencies of the respective piezoelectric elements are prepared, and the corresponding piezoelectric elements are driven at different times. It is necessary to adopt a circuit configuration for switching to an L / C circuit to perform the circuit, and the circuit becomes redundant.

In a conventional circuit, a waveform (for example, an ultrasonic pulse waveform) transmitted and received between piezoelectric elements is also similar to the above-described generally known technique.
This is a waveform having a large wave number and a gradual increase and decrease in amplitude as shown in (b) (theoretically, although it is not clear yet, such a waveform can be obtained by one rising impulse voltage). The inventor of the invention has actually confirmed). For such a waveform, generally,
It is known that the timing of triggering may be shifted, and in order to avoid this, it is desired to reduce the number of waves or to increase the amplitude difference between the wave to be triggered and the waves before and after it. ing.

An object of the present invention is to drive a piezoelectric element with a single pulse independently of the resonance frequency of the piezoelectric element and to freely set the pulse width of this single pulse.
For example, it is an object of the present invention to provide a piezoelectric element driver capable of generating a waveform suitable for triggering at a normal timing on a receiving side, and a driving method thereof.

[0014]

A piezoelectric element driver according to the present invention is a driver circuit for driving a piezoelectric element,
At least one end is connected to a power supply and the other end is grounded via a switch. A transformer including a primary side winding and a secondary side winding, and a piezoelectric connected to a secondary side of the transformer. An element, a diode and a Zener diode connected in series are connected in parallel to the primary winding, the anode of the diode being on the switch side, and the anode of the Zener diode being connected to the power supply. Or the cathode of the diode is connected to the power supply side, and the cathode of the Zener diode is connected to the switch side.
A zener voltage of the zener diode and a forward voltage of the diode are set according to a resonance waveform of the piezoelectric element.

With the above configuration, the piezoelectric element can be driven by a single pulse without depending on the resonance waveform of the piezoelectric element. Further, as described above, various effects can be obtained by setting the ON time of the switch, the Zener voltage of the Zener diode, and the forward voltage of the diode according to the resonance waveform of the piezoelectric element.

For example, the ON time of the switch is set to half the period of the resonance waveform of the piezoelectric element, and the sum of the Zener voltage of the Zener diode and the forward voltage of the diode is made to match the voltage of the power supply. By setting, the resonance waveform of the piezoelectric element can be strengthened (accelerated) over several degrees, and the piezoelectric element can be driven more strongly than before.

Further, for example, the ON time of the switch is set to half of the period of the resonance waveform of the piezoelectric element, and the sum of the Zener voltage of the Zener diode and the forward voltage of the diode is set to half of the voltage of the power supply. By performing the setting, the drive waveform can be controlled so that the resonance waveform of the piezoelectric element is accelerated and then decelerated. This way,
A wave having a small number of waves and a large difference in amplitude from the waves before and after the wave can be generated. If this wave is triggered, for example, the propagation time can be accurately measured. .

Next, another piezoelectric element driver according to the present invention is the above-mentioned piezoelectric element driver, further comprising a second switch connected in parallel to the Zener diode, wherein the second switch is , Switch the switch to O
It is turned on before N, and is turned off with a predetermined time delay after the switch is turned off.

Then, for example, the ON time of the switch is set to の of the period of the resonance waveform of the piezoelectric element, and the sum of the Zener voltage of the Zener diode and the forward voltage of the diode is calculated as the voltage of the power supply. The resonance waveform of the piezoelectric element is accelerated by setting / control so that the second switch is turned off after a lapse of a half of the cycle since the switch is turned off. Can slow down strongly.

In the method of driving a piezoelectric element according to the present invention, a positive applied voltage and a negative applied voltage following the positive applied voltage are adjusted to the resonance waveform of the piezoelectric element to be driven, and the resonance waveform is accelerated. It is applied at the timing of deceleration afterwards.

Alternatively, a positive applied voltage and a negative applied voltage delayed by a predetermined time from the positive applied voltage are adjusted to the resonance waveform of the piezoelectric element to be driven, and the resonance waveform is accelerated and then decelerated twice. Apply at the timing.

[0022]

An embodiment of the present invention will be described below with reference to the drawings. FIGS. 1A and 1B are diagrams illustrating an example of a circuit configuration of a piezoelectric element driver according to the present embodiment.

In the circuit shown in FIG.
Is connected to the transformer secondary winding 2b and is driven by the voltage (piezoelectric element applied voltage V2) boosted by the transformer 2. One end of the transformer primary winding 2a is connected to the power supply 4 and the other end can be grounded by the switch 3.

The diode 5 and the Zener diode 6 are connected in series to form the transformer primary winding 2a.
The anode of the Zener diode 6 is connected to the power supply 4 side, and the anode of the diode 5 is connected to the switch 3 side.

FIG. 1B is a diagram showing another example of the circuit configuration, and its operation is the same as that of the circuit of FIG. 1A. FIG.
In the circuit shown in (b), the piezoelectric element 1 is connected to the transformer secondary winding 2b and is driven by the voltage boosted by the transformer 2. One end of the transformer primary winding 2a is
And the other end can be grounded by the switch 3.

In the circuit shown in FIG.
1 and FIG. 2A is different from FIG. That is, the diode 5 and the Zener diode 6 connected in series are connected to the transformer primary winding 2.
a, the cathode of the diode 5 is connected to the power supply 4 side, and the cathode of the Zener diode 6 is connected to the switch 3 side.

1 (a) and 1 (b), the transformer 2
The inductance of the primary winding 2a is L1, the voltage of the power supply 4 is V1, the forward voltage VF of the diode 5, and the zener voltage of the zener diode 6 is Vz. The ratio of the number of turns between the primary winding and the secondary winding of the transformer 2 is 1: N.
(A)-(c) is a figure for demonstrating an example of operation | movement of the circuit of FIG.

As described above, FIGS. 1 (a) and 1 (b)
Is the same. First, normally, switch 3 is OFF
State. In this state, since no current flows through the transformer primary winding 2a, no voltage is generated on the transformer secondary winding 2b. Therefore, the piezoelectric element 1 is not driven.

When driving the piezoelectric element 1, the control unit (not shown) turns on the switch 3 for ton time (FIG. 2 (a)). From the moment when the switch 3 is turned on, a current I1, which increases with a gradient V1 / L1 with time, starts flowing in the transformer primary winding 2a as shown in FIG. 2 (b).
At this time, a constant voltage N · V1 is generated in the transformer secondary winding 2b as the piezoelectric element applied voltage V2 and applied to the piezoelectric element 1.

When the switch 3 is turned off after the ton time, a counter electromotive force is generated in the primary winding 2a of the transformer, and a commutation current flows through the diode 5. At this time, the current I1 flowing through the transformer primary winding 2a is almost negligible since the load on the transformer secondary winding 2b is only the piezoelectric element 1, and therefore, the slope I-I continuously changes from the moment when the switch is turned off.
(Vz + VF) / L1 (Vz: Zener voltage of Zener diode 6, VF: Forward voltage of diode 5).

The current I1 is set to 0 in the transformer secondary winding 2b.
Until (zero), back electromotive force -N. (Vz + VF) is generated. The time tb is ton · V1 / (Vz + VF)
Becomes

As a result, as shown in FIG. 2C, the piezoelectric element 1 has a pulse voltage of width ton, voltage N.V1, a width tb = ton.V1 / (Vz + VF), and voltage = -N.・ (V
z + VF). Since the resonance waveform determined by L and C does not occur in this pulse voltage, the piezoelectric element 1 can be driven purely by the pulse voltage.
As a result, unnecessary distortion does not occur in the vibration waveform of the piezoelectric element 1.

Next, an application of the above circuit will be described.
If the above driver circuit is used, the width ton and the pulse width ton of the pulse voltage N · V1 can be freely changed according to the resonance frequency of the piezoelectric element 1 by a control signal from the above-mentioned control unit (not shown). Can be. Further, the width tb =
ton · V1 / (Vz + VF), voltage = −N · (Vz + V
The pulse width of the pulse voltage F) can also be freely changed according to the resonance frequency of the piezoelectric element 1 by setting the values of Vz and VF.

As a result, the waveform of a pulse (ultrasonic pulse or the like) transmitted from the piezoelectric element 1 can be formed into a form suitable for measurement, particularly in applications such as an ultrasonic flowmeter. Details will be described below.

FIGS. 3A to 3C show the pulse width ton and the pulse width tb (= ton · V) according to the resonance frequency of the piezoelectric element.
It is a diagram for explaining how to change 1 / (Vz + VF)).

FIG. 3A shows the resonance waveform (period T) of the piezoelectric element, and FIGS. 3B and 3C show examples of the pulse voltage applied to the piezoelectric element. Although FIG. 3A shows a waveform having a constant amplitude, the amplitude of an actual waveform changes as described later.

First, the resonance waveform of the piezoelectric element shown in FIG. 3A starts its resonance oscillation at the rise of the pulse voltage shown in FIG. 3B or 3C. That is, FIG.
Since the step-like waveform such as the rise of the pulse voltage in (c) includes all frequency components, a resonance waveform as shown in FIG. 3A starts in synchronization with the rise.

In FIG. 3B, in the piezoelectric element driver circuit of FIG. 1, the pulse width ton and the pulse width tb
Both (= ton · V1 / (Vz + VF)) are set so as to be の of the resonance period T of the piezoelectric element 1 (set ton = T / 2, and set Vz + VF = V1). ). That is, the resonance waveform of the piezoelectric element shown in FIG.

When the pulse width is set as described above, FIG.
FIG. 3A shows the fall of the resonance waveform of the piezoelectric element 1 and FIG.
Since the falling of the pulse voltage in (b) coincides (timing in (a)), it works to strengthen (accelerate) the resonance vibration of the piezoelectric element 1. Furthermore, since the rise of the resonance waveform of the piezoelectric element 1 in FIG. 3A coincides with the rise of the pulse voltage in FIG. 3B (timing (b)),
It works to further strengthen (accelerate) the resonance vibration of the piezoelectric element 1.

In this way, not only does the piezoelectric element 1 be driven at the first rise of the pulse voltage, but it also acts to accelerate the resonance vibration once at each of the subsequent fall and rise of the pulse voltage. The piezoelectric element can be driven more strongly than the method of driving only with the impulse voltage.

On the other hand, in FIG. 3C, the pulse width ton is
As in FIG. 3B, the resonance period T of the piezoelectric element 1 is set to １ ／ (ton = T / 2), but the pulse width tb (= ton · V1).
/ (Vz + VF)) is set to be the same as the resonance period T of the piezoelectric element 1 (set to Vz + VF = V1 / 2).

When the pulse width is set as described above, FIG.
FIG. 3A shows the fall of the resonance waveform of the piezoelectric element 1 and FIG.
Since the falling of the pulse voltage in (b) coincides (timing in (a)), it works to strengthen (accelerate) the resonance vibration of the piezoelectric element 1.

On the other hand, since the pulse width of the negative voltage is set to T as described above, the falling of the resonance waveform of the piezoelectric element 1 in FIG. 3A and the pulse in FIG. Since the rises of the voltages are synchronized (timing (c)), it works to cancel (decelerate) the resonance vibration of the piezoelectric element 1 here.

Thus, in FIG. 3C, both acceleration and deceleration are performed. The reason why the driving method of accelerating and decelerating as shown in FIG. 3 (c) is effective will be described below with reference to FIGS. 4 (a) to 4 (c).

FIG. 4A is a diagram showing an example of an apparatus using a piezoelectric element, in which a piezoelectric element 1A on the transmitting side and a piezoelectric element 1B on the receiving side are arranged to face each other, and the piezoelectric element 1A is connected to a transmitting circuit. (Piezoelectric element driver) to generate vibrations such as ultrasonic waves, and a medium (for example, liquid such as tap water or oil, or city) existing between the piezoelectric elements 1A and 1B in the receiving piezoelectric element 1B. FIG. 2 shows a configuration for detecting a vibration that has propagated through a gas such as a gas.

Such a configuration is used, for example, in an ultrasonic flow meter or the like. Generally, in an ultrasonic flowmeter, the difference between the propagation time when the ultrasonic wave is propagated from the upstream side to the downstream side of the fluid to be measured and the propagation time when the ultrasonic wave is propagated from the downstream side to the upstream side. Calculate the flow velocity / flow rate from the above.
Therefore, the measurement is performed by alternately switching the opposing piezoelectric elements between the transmitting side and the receiving side, so that the resonance frequency of the transmitting side piezoelectric element 1A and the receiving side piezoelectric element 1B are generally the same. .

Although not shown, in the configuration using the piezoelectric element 1 as a level meter, the vibration generated by the piezoelectric element is reflected on the liquid surface or the like, and the returned vibration is detected by the piezoelectric element itself used for transmission. It is common to do.

In any case, in the above-mentioned application, the transmission / reception-side piezoelectric elements are configured to have the same resonance frequency, and by measuring the propagation time of vibration such as ultrasonic waves, the flow velocity is reduced. , The flow rate, the liquid level (water level) and the like are calculated.

FIG. 4 (b) shows an example of a reception waveform detected when a conventional piezoelectric element driver is used in the above configuration (the transmission waveform itself (the amplitude may be different). Can be considered almost the same). When the piezoelectric element is driven by the conventional driver, the waveform of the generated ultrasonic wave or the like becomes a waveform whose amplitude gradually increases and the amplitude gradually attenuates as shown in FIG. Although not shown, the inventor of the present invention has actually confirmed that such a waveform is generated by one rising impulse voltage, and this waveform is obtained by a generally known driving method. It is almost the same as the generated waveform).

Here, the propagation time is generally measured from the rise of the pulse voltage on the transmission side to the time when it is detected that the reception waveform on the reception side has exceeded a certain trigger level. The trigger level is determined in advance as to what number of waveform is to be detected, and is set in accordance with this.
For example, as shown in the figure, when the trigger level is set so that a trigger is activated at the third wave in a waveform that reaches the maximum amplitude at the fourth and fifth waves (although the fourth wave may be set separately). In the case of a waveform whose amplitude gradually increases as shown in the figure, there is a great risk that a slight waveform change will trigger a trigger other than the third wave (usually the second or fourth wave). Then, an error occurs in the propagation time measurement result by the period of the resonance frequency, and accurate measurement cannot be performed.

On the other hand, using the piezoelectric element driver of FIG.
When the pulse voltage shown in FIG. 3C is applied to the piezoelectric element, an ultrasonic waveform as shown in the upper part of FIG. 4C can be obtained. That is, first, the acceleration of the above (a) is performed so that the amplitude of the second wave of the ultrasonic waveform becomes
It increases rapidly from the first wave. Next, by performing the deceleration described in (c), the amplitude of the third wave sharply decreases.

For example, if a trigger level as shown in the drawing is set for the second wave of such a waveform, even if the waveform slightly fluctuates due to any influence, the amplitude difference between the adjacent wave and the adjacent wave will be small. Since it is large, the possibility that a trigger is erroneously applied to a wave other than the second wave (the first wave or the third wave) is extremely low, and the trigger can be stably applied.

When the piezoelectric element is used for measuring the propagation time as described above, as shown in FIG.
A drive control method having a phase relationship in which acceleration is followed by deceleration as in (c) is effective.

Next, another embodiment will be described. FIG. 5 is a diagram illustrating an example of a circuit configuration of a piezoelectric element driver according to another embodiment.

In the figure, the same components as those in FIG. 1A are denoted by the same reference numerals, and the description thereof will be omitted. FIG.
The difference from the circuit of (a) is that the switch 7 is connected to the Zener diode 6 in parallel.

FIG. 6 is a diagram for explaining the operation of the circuit of FIG. First, normally, the switch 3 is in an OFF state. In this state, since no current flows through the transformer primary winding 2a, no voltage is generated on the transformer secondary winding 2b. Therefore, the piezoelectric element 1 is not driven. The switch 7 is turned on before driving the piezoelectric element as shown in FIG.

When driving the piezoelectric element 1, the control unit (not shown) turns on the switch 3 for a time ton (FIG. 6A). From the moment when the switch 3 is turned on, a current I1, which increases with a gradient V1 / L1 with time, starts flowing in the transformer primary winding 2a as shown in FIG. 6 (c). At this time, a constant voltage N is applied to the transformer secondary winding 2b.
V1 is output and applied to the piezoelectric element 1.

When the switch 3 is turned off after the ton time, a back electromotive force is generated in the primary winding 2a of the transformer, and a commutation current flows through the diode 5 and the switch 7. At this time, the current I1 flowing through the transformer primary winding 2a is almost negligible since the load on the transformer secondary winding 2b is only the piezoelectric element 1, so that the gradient -VF / L1 is continuously obtained from the moment when the switch is turned off. It decreases with. At this time, a constant voltage −N · VF is output to the transformer secondary winding 2 b and applied to the piezoelectric element 1.

At time td after the switch 3 is turned off,
The switch 7 is turned off this time by a control unit (not shown) (FIG. 6B). As a result, the commutation current flowing in the transformer primary winding 2a changes so as to flow through the diode 5 and the Zener diode 6. At this time, the current I1 flowing through the transformer primary winding 2a continuously changes so as to decrease at a slope of-(Vz + VF) / L1 (Vz; the Zener voltage of the Zener diode 6, V
F: forward voltage of the diode 5).

Further, a constant voltage −N · (Vz + VF) is generated in the transformer secondary winding 2 b and is applied to the piezoelectric element 1. At that time tc, td becomes ton
If V1 and Vz≫VF, the value is about (tcon) ton · V1 (Vz + VF).

As a result, as shown in FIG. 6D, the piezoelectric element 1 has a pulse voltage having a width ton and a voltage N.V1 and a time delay td from the pulse voltage, and the width tc ≒ ton.V1 / (Vz + VF) A negative pulse voltage of voltage = -N ・ (Vz + VF) is applied. Since the resonance waveform determined by L and C does not occur in this pulse voltage, the piezoelectric element 1 can be driven purely by the pulse voltage.
As a result, unnecessary distortion does not occur in the vibration waveform of the piezoelectric element 1.

During the time td after the switch 3 is turned off, the current I1 is supplied to the transformer secondary winding 2b as 0 (zero).
Back electromotive force -N.VF occurs until
Since it is ≫VF, it can be almost ignored.

Next, application of the above circuit will be described.
When the driver circuit is used, the pulse width ton and the pulse width tc can be arbitrarily changed by a control signal from the control unit (not shown) (further, by setting the values of Vz and VF). Since the generation timing of the negative pulse voltage having the pulse width tc can be delayed by the time td, the above-mentioned effect obtained by the circuit of FIG. 1 can be further enhanced. Details will be described below.

FIGS. 7A and 7B are diagrams for explaining how to change the pulse widths ton and tc and the delay time td according to the resonance frequency of the piezoelectric element. . FIG. 7A shows a resonance waveform of the piezoelectric element.
(B) shows an example of a pulse voltage applied to the piezoelectric element.

First, at the rise of the pulse voltage applied to the piezoelectric element shown in FIG. 7B, the piezoelectric element 1 starts resonance oscillation as shown in FIG. 7A. The control unit (not shown) turns on and off the switch 3 and the switch 7 so that the pulse voltage shown in FIG. This is the result of the control (note that the value of the resonance period T of the piezoelectric element to be controlled is set / input to the control unit (not shown) in advance).

Further, it is set so that (Vz + VF) = V1, whereby the width tc ≒ ton · V1 / (Vz
+ VF) = ton. That is, the width tc is also set to be T / 2.

When the piezoelectric element 1 is driven by such a pulse voltage, first, as shown in FIGS. 7A and 7B, the first falling of the resonance waveform of the piezoelectric element and the rising of the pulse voltage having the width ton. Since the falling coincides with the timing (timing (d)), it works to accelerate the vibration of the piezoelectric element. next,
Since the second rise of the resonance waveform of the piezoelectric element and the fall of the negative pulse voltage having the width tc are synchronized (timing (e)), the resonance vibration of the piezoelectric element is canceled (deceleration).
Work like that. This deceleration is also performed at the second fall of the resonance waveform of the piezoelectric element and at the rise (timing (f)) of the negative pulse voltage having the width tc, so that the deceleration is further enhanced.

As described above, the driving method of accelerating and then decelerating is effective for measuring the propagation time.

[0069]

As described above in detail, according to the piezoelectric element driver and the driving method of the present invention, it is possible to apply a pair of positive / negative voltage pulses having an arbitrary pulse width to the piezoelectric element. Thus, a piezoelectric element having an arbitrary resonance frequency can be handled.

At this time, when the pulse width of both the positive and negative voltage pulses is set to １ ／ of the period of the resonance frequency (resonance period) of the piezoelectric element, the piezoelectric element is much stronger than the conventional circuit. Can be driven.

When the pulse width of the positive voltage pulse is set to の of the resonance period of the piezoelectric element and the pulse width of the negative voltage pulse is set to be equal to the resonance period of the piezoelectric element, the propagation time is measured. This makes it possible to obtain a waveform that is particularly suitable for use in performing measurement.

Further, according to another piezoelectric element driver according to the present invention, a set of positive / negative voltage pulses having an arbitrary pulse width is arbitrarily delayed by arbitrarily delaying the generation timing of the negative voltage pulse (an arbitrary delay time is set). ), It is possible to apply to the piezoelectric element, and it is possible to cope with the piezoelectric element having an arbitrary resonance frequency, and to set all of the positive pulse width, the negative pulse width, and the delay time to the resonance cycle of the piezoelectric element In the case of １ ／, the effect of obtaining a waveform particularly suitable for the purpose of performing measurement by measuring the above-mentioned propagation time becomes more remarkable.

[Brief description of the drawings]

FIGS. 1A and 1B are diagrams illustrating an example of a circuit configuration of a piezoelectric element driver according to the present embodiment.

FIGS. 2A to 2C are diagrams for explaining an example of the operation of the circuit in FIG. 1;

FIGS. 3A to 3C are diagrams for explaining how to set a pulse width according to a resonance frequency of a piezoelectric element.

FIGS. 4A to 4C are diagrams for explaining the reason why the driving method shown in FIG. 3C is effective.

FIG. 5 is a diagram illustrating an example of a circuit configuration of a piezoelectric element driver according to another embodiment.

FIGS. 6A to 6D are diagrams for explaining the operation of the circuit in FIG. 5;

FIGS. 7A and 7B are diagrams for explaining how to set a pulse width and a delay time according to a resonance frequency of a piezoelectric element.

FIG. 8 is a diagram illustrating an example of a circuit configuration of a conventional piezoelectric element driver.

FIGS. 9A and 9B are diagrams for explaining an example of the operation of the circuit in FIG. 8;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Piezoelectric element 2 Transformer 2a Transformer primary winding 2b Transformer secondary winding 3 Switch 4 Power supply 5 Diode 6 Zener diode 7 Switch

Claims (7)

[Claims] 1. A driver circuit for driving a piezoelectric element, comprising: a primary winding having at least one end connected to a power supply and the other end grounded via a switch; And a piezoelectric element connected to the secondary side of the transformer, a diode and a Zener diode connected in series, connected in parallel to the primary winding,
Whether the anode of the diode is connected to the switch and the anode of the Zener diode is connected to the power supply,
Alternatively, the cathode of the diode is connected to the power supply side, and the cathode of the zener diode is connected to the switch side. The ON time of the switch, the zener voltage of the zener diode, and the forward voltage of the diode are A piezoelectric element driver which is set according to a resonance waveform of a piezoelectric element. 2. The method according to claim 1, wherein an ON time of the switch is set to a half of a cycle of a resonance waveform of the piezoelectric element, and a sum of a Zener voltage of the Zener diode and a forward voltage of the diode is made equal to a voltage of the power supply. The piezoelectric element driver according to claim 1, wherein: 3. An on-time of the switch is set to a half of a cycle of a resonance waveform of the piezoelectric element, and a sum of a Zener voltage of the Zener diode and a forward voltage of the diode is set to a half of a voltage of the power supply. The piezoelectric element driver according to claim 1, wherein: A second switch connected in parallel to said Zener diode, wherein said second switch is turned on before said switch is turned on.
2. The piezoelectric element driver according to claim 1, wherein the switch is turned off with a delay of a predetermined time after the switch is turned off. 5. An on-time of the switch is set to a half of a cycle of a resonance waveform of the piezoelectric element, and a sum of a Zener voltage of the Zener diode and a forward voltage of the diode is made equal to a voltage of the power supply. 5. The piezoelectric element driver according to claim 4, wherein the second switch is turned off after a lapse of a half of the period from when the switch is turned off. 6. A method for driving a piezoelectric element, comprising: applying a positive applied voltage and a negative applied voltage subsequent to the positive applied voltage,
A driving method characterized in that the resonance waveform is applied at a timing of accelerating and then decelerating the resonance waveform in accordance with the resonance waveform of the piezoelectric element to be driven. 7. A method for driving a piezoelectric element, comprising: applying a positive applied voltage and a negative applied voltage delayed by a predetermined time from the positive applied voltage to a resonance waveform of a piezoelectric element to be driven. A driving method characterized in that the voltage is applied at a timing of decelerating twice after accelerating.