JPH04351200A - Piezoelectric ceramic actuator drive circuit - Google Patents

Abstract

PURPOSE:To realize the piezoelectric actuator drive circuit for repetitive operation with high efficiency. CONSTITUTION:A reactor 7 is connected in series with a ceramic actuator 9 and its inductance is set so that the resonance frequency of a series resonance circuit is higher than the drive frequency. Moreover, charge/discharge switching elements 5, 6 are interrupted when a current flowing to the ceramic actuator 9 is zero and a diode 8 is connected in parallel with the ceramic actuator 9 to clamp a negative voltage to zero. The energy consumption at charge/ discharge is halved by connecting a reactor 7 to the elements and the allowable current of the switching elements is reduced and the positive voltage is applied to the ceramic actuator 9 by connecting a diode to the elements, the efficient drive circuit is realized.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit for driving a capacitive load such as a piezoelectric ceramic actuator, and particularly to a driving circuit for repeatedly driving the piezoelectric ceramic actuator.

0002

[Prior art] Piezoelectric ceramic actuator (hereinafter referred to as
A piezoelectric actuator (abbreviated as a piezoelectric actuator) is an actuator that utilizes the piezoelectric inverse effect in which the thickness of ceramic changes when voltage is applied, and the amount of elongation can be controlled at high speed and with high precision according to the applied voltage. It is used for opening and closing gas flow valves, controlling the position of X-Y tables, adjusting the resin thickness of injection molding machines, piezoelectric dot printer heads, etc.

[0003] The operation of the actuator can be roughly divided into two types: one in which a constant amount of expansion is maintained for a long time, and one in which the actuator is repeatedly expanded and contracted. In the former case, if charge is supplied at the beginning of operation, there is almost no need to supply charge thereafter, and a DC power supply circuit can be used. On the other hand, the latter requires a charging/discharging circuit for the actuator during repeated operations.

As a drive circuit for an actuator, a drive circuit using a switching element shown in FIGS. 5(a) and 5(b) disclosed in Utility Model Application No. 64619/1983 previously filed by the present applicant is generally used. It is true. In these examples, the actuator 9 is charged by applying a control signal to the switching elements 5, 11 for charging the actuator.
A current I1 flows through and charges the actuator 9, and the actuator 9 generates strain in the thickness direction according to the amount of charge.

On the other hand, in order to discharge the charge of the actuator and reduce the amount of distortion, the charging switching element 5
, 11 and replace them with discharge switching elements 6, 1.
This is achieved by adding a control signal to 2 to cause current I2 to flow.

If the actuator 9 is to be operated repeatedly, this can be achieved by alternately and repeatedly applying control signals to the charging/discharging switching elements 5, 11, 6, and 12.

[0007]

[Problem to be solved by the invention] By the way, Fig. 5(b)
The drive circuit shown in Fig. 1 is suitable for continuously varying mechanical displacement by changing the voltage applied to the actuator, but because the power consumed inside the switching elements 5 and 6 is large, the drive power is low. efficiency is low.

On the other hand, in the drive circuit shown in FIG. 5A, the current drive is a low input impedance operation and the applied voltage is constant, but the energy loss due to discharge is large.

Furthermore, in both drive circuits, a large amount of charging and discharging current flows during charging and discharging, so it is necessary to use a switching element with a large allowable current. Furthermore, a discharge resistor 10 was connected to limit the current during discharge and protect the switching element.

0010

[Means for Solving the Problems] The present invention is proposed to solve the above problems. The present invention is characterized in that a piezoelectric actuator and a reactor are connected in series, and the inductance of the reactor is set so that the resonant frequency of the series resonant circuit made up of the piezoelectric actuator is higher than the drive frequency, and the timing of cutting off the charging/discharging switching element of the piezoelectric actuator. Let be the point at which the current flowing through the piezoelectric actuator becomes zero, and furthermore, connect a diode in parallel to the piezoelectric actuator and clamp the applied voltage to approximately zero volts so that negative polarity voltage is not applied to the piezoelectric actuator during discharge. It is characterized by

[0011]

[Operation] According to the above configuration, if the capacitance of the piezoelectric actuator is C and the charging voltage is Vc, the energy supplied from the power source when charging the piezoelectric actuator is P1 = CVc2 when a reactor is not used. On the other hand, when using a reactor, P2 = 1/2CVc2
Calculated, it is only necessary to supply half the energy. Furthermore, the maximum current Ipc,I flowing through the charging and discharging circuit during charging and discharging
If the impedance of the switching element is Zsw, pd is Ip=Vc/Zs when a reactor is not used.
w, whereas when using a reactor,

It becomes [Formula 1]. Since Zsw is generally small, the current flowing through the switching element will be very large if a reactor is not used. However, by using a reactor, the maximum current value flowing through the switching element can be lowered, so the allowable current can be reduced. Small switching elements can be used.

On the other hand, in the above configuration, a voltage of negative polarity is applied. Figure 3 shows the applied voltage-displacement characteristics of the piezoelectric actuator.

FIG. 3 shows that between the terminals of the piezoelectric actuator,
It shows applied voltage-displacement characteristics when voltages are applied in the order of 0 volts → positive polarity voltage → 0 volts → negative polarity voltage → 0 volts → positive polarity voltage.

[0014] When the applied voltage is increased from 0 volts to an unpolarized piezoelectric actuator, the displacement does not reach the coercive electric field (
Figure 3 ■). When a voltage higher than the coercive electric field is applied, voltage-displacement characteristics as shown in (■) are exhibited. Next, when the voltage is lowered from the maximum value, a characteristic like ■ appears, and when a negative polarity voltage is further applied, a characteristic like ■→■ appears. In this way, when a piezoelectric actuator is operated by applying a voltage with both positive and negative polarities,
An inflection point occurs in the voltage-displacement characteristics, which is inconvenient in controlling the operation. Most of the general voltage application methods for piezoelectric actuators apply a unipolar voltage, and the voltage-displacement characteristic in that case is as shown in Figure 3 as ■→■→■, and the amount of displacement changes depending on the applied voltage. Easy to control.

Therefore, in the present invention, the above problem is solved by connecting a diode in parallel to the piezoelectric actuator in the above configuration and clamping the negative polarity voltage applied to the piezoelectric actuator at 0 volts during discharge. Furthermore, even when a diode is connected, the voltage-displacement characteristics during charging operate normally, exactly the same as when no diode is used.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained below with reference to the drawings. FIG. 1 is a block diagram of a drive circuit according to an embodiment of the present invention, and FIG. 2 is a timing chart of output voltage and output current. FIG. 1 shows a power supply terminal 1, a DC-DC converter 2 that converts the input voltage of the power supply terminal 1 into the operating voltage required by the piezoelectric actuator 9, an oscillation circuit 3 that determines the repetition frequency of the piezoelectric actuator 9, and a Timing control circuit 4 that controls charging and discharging time, turned on by a control signal from timing control circuit 4
, a reactor 7 connected in series to a discharge switching element 6 and a piezoelectric actuator 9, and a diode 8 connected in parallel. 16 and 17 are backflow prevention diodes.

Next, the operating principle of this circuit will be explained as shown in FIGS. 1 and 2.
This will be explained in detail with reference to the timing chart. In addition, in FIG. 2, 4a and 4b are charge switching elements 5.
, is a signal that controls the discharge switching element 6, and the upper level is ON and the lower level is OFF, as shown in FIGS.
) are the timings of T1 and T2 shown in FIG.

Now, if the timing is time T0 shown in FIG. 2, the charging switching element 5 is turned on in FIG.
A GND circuit is constructed, and the terminal voltage 9t of the piezoelectric actuator 9 is charged to the voltage value shown in FIG. 2(c). At this time, the current flowing through the piezoelectric actuator 9 is as shown in FIG.
The Ipc shown in e) is obtained. Next, when the current of the piezoelectric actuator 9 tries to become negative, it is blocked by the diode 16, and as a result, the charging switching element 5 is turned off at time T1, and the piezoelectric actuator 9 and the DC-DC converter 2 are disconnected. Therefore, the terminal voltage of the piezoelectric actuator 9 maintains the highest voltage as shown in FIG. 2(c).

Next, when the discharge switching element 6 is turned on at time T2, the piezoelectric actuator 9-
A circuit of reactor 7-discharge switching element 6-GND is configured, and the electric charge stored in piezoelectric actuator 9 is discharged. At this time, the current flowing through the piezoelectric actuator 9 becomes Ipd shown in FIG. 2(e). Furthermore, if the diode 8 is not connected, a negative polarity voltage will be generated during discharge. The situation is shown in FIG. 2(d). By connecting the diode 8 in parallel to the piezoelectric actuator 9 as shown in FIG. 1, the negative voltage is clamped to approximately 0 volts, and no negative voltage is applied to the piezoelectric actuator 9. Therefore, the displacement of piezoelectric actuator 9 -
The voltage characteristics show the applied voltage characteristics of 0 volts or more as shown in FIG. 3, and the characteristics are stable.

[0020]

Embodiment 2 FIG. 4 is a block diagram of a drive circuit according to a second embodiment of the present invention. This embodiment is similar to the first embodiment except that a thyristor 13 is used in place of the charging switching element 5 of the first embodiment shown in FIG. In this embodiment, the basic operation of the thyristor 13 is realized by a combination of a PNP transistor 14 and an NPN transistor 15. Next, the operation of this drive circuit will be explained. When the turn-on signal 4t0 is applied from the timing control circuit 4 to the thyristor 13, the thyristor 13 is turned on, and a circuit of the DC-DC converter 2, the thyristor 13, the reactor 7, the piezoelectric actuator 9, and the GND is configured.

At this time, the current flowing through the piezoelectric actuator 9 becomes Ipc as shown in FIG. Therefore, the piezoelectric actuator 9 and the DC-DC converter 2 are separated. Therefore, it is not necessary to turn off the thyristor 13 by the timing control circuit 4 when charging of the piezoelectric actuator 9 is completed. Therefore, the configuration of the second embodiment simplifies the design of the timing control circuit, and even if the capacitance of the piezoelectric actuator 9 fluctuates and the charging time fluctuates, the time constant of the timing control circuit can be adjusted. There's no need to.

[0022]

Effects of the Invention According to the present invention, a reactor is connected in series with a piezoelectric actuator, the inductance of the reactor is set so that the resonance frequency of the series resonant circuit is higher than the drive frequency, and the piezoelectric actuator is charged. By opening the charge/discharge switch when the discharge current reaches zero and further connecting a diode in parallel to the piezoelectric actuator, the energy supplied from the power supply when charging the piezoelectric actuator is halved, reducing the tolerance of the charge/discharge switching element. The current value can be reduced, and the piezoelectric actuator can operate stably with positive polarity. Furthermore, even a piezoelectric actuator with a large capacitance can be operated efficiently and easily.

[Brief explanation of drawings]

[Fig. 1] Block diagram of a drive circuit showing a first embodiment of the present invention

[Figure 2] Waveform diagram showing the time course of the output voltage of the drive circuit and the current flowing through the piezoelectric ceramic actuator

[Figure 3] Applied voltage-displacement characteristic diagram of piezoelectric ceramic actuator

[Fig. 4] Block diagram of a drive circuit showing a second embodiment of the present invention

[Figure 5] Conventional general drive circuit diagram

[Explanation of symbols]

1 Power terminal 2 DC-DC converter 3 Oscillation circuit 4 Timing control circuit 5 Charging switch 6 Discharge switch 7 Reactor 8 Diode 9 Piezoelectric ceramic actuator 10 Discharge resistance 11 Charging amplifier element 12 Discharge amplification element 13 Thyristor 14 PNP transistor 15 NPN transistor

Claims (4)

[Claims] 1. In a circuit that converts a DC power output into a drive pulse using a switching element to drive a piezoelectric ceramic actuator, a reactor is connected in series with the piezoelectric ceramic actuator, and the inductance of the reactor is determined by the capacitance of the piezoelectric ceramic actuator. A piezoelectric ceramic actuator drive circuit characterized in that the series resonance frequency due to the inductance of the reactor is set to be higher than the drive frequency. 2. The piezoelectric ceramic actuator according to claim 1, wherein the charging/discharging switching element of the piezoelectric ceramic actuator is cut off at a point in time when the current flowing through the piezoelectric ceramic actuator becomes zero. drive circuit. 3. In the drive circuit according to claim 1, a diode is connected in parallel to the piezoelectric ceramic actuator,
A piezoelectric ceramic actuator drive circuit characterized by clamping a voltage so that a negative polarity voltage is not applied to the piezoelectric ceramic actuator during discharge. 4. The piezoelectric ceramic actuator drive circuit according to claim 1, wherein the charging switching element of the piezoelectric ceramic actuator is comprised of a thyristor.