JPH04208080A - Driver for monolithic piezoelectric element - Google Patents

Abstract

PURPOSE:To improve reliability and to provide excellent durability by forming a circuit for reducing a time constant at the time of falling an applied voltage smaller than a mechanical resonance time constant of a piezoelectric element. CONSTITUTION:At the time of Vi2=0 at Vi1=5V, a transistor 3 is turned ON, and a transistor 4 is turned OFF. Accordingly, since a current flows to a laminated piezoelectric element 1 through resistors Ru, Rc, the applied voltage V of the element exhibits a value substantially equal to VD. Then, at the time of Vi2=5V at Vi1=0, the transistor 3 is turned OFF, and the transistor 4 is turned OFF. Accordingly, charge stored in the element 1 is discharged through the resistors Rc, Rd. In this case, in order to prevent an erroneous operation by switching, a pause time Tc is provided at the time of switching input voltages Vi1 and Vi2. Thus, simultaneous ON of the transistors is prevented. Further, VP rises when the Vi1 rises, and VP starts, on the contrary, to fall when the Vi2 rises.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a drive circuit for a laminated piezoelectric element used in a minute positioning mechanism, a mass flow controller, and the like.

[Conventional technology]

Conventionally, as shown in FIG. 2, a drive circuit for a laminated piezoelectric element has been constructed of, for example, a transistor, and the applied voltage has been controlled.

The conventional technology will be described below with reference to FIG.

A multilayer piezoelectric element 1 is connected to the collector terminal of the transistor 2.
is connected to the collector, and a voltage VD for directly driving the multilayer piezoelectric element 2 is applied to the collector via a resistor Ru. -This VD for boat fishing is about 100-1
50V is normal, but depending on the specifications of laminate 1, 400V
A high voltage on the order of V may be applied. Now, when the control voltage v1 is zero, the collector-emitter of the transistor 2 is in an open state, so the stacked piezoelectric element 2 has
A voltage approximately equal to VD is applied. Next, when vl is increased, the emitter current ie flows accordingly, so that the voltage applied to the piezoelectric element 2 decreases.

With the above configuration, the voltage applied to the piezoelectric element 2 is configured to change depending on the input voltage Vi.

[Problem to be solved by the invention]

However, with the method described above, there is no problem when driving a stacked piezoelectric element in a static state, but when driving with a stepping waveform, etc., the time constant increases (impacts) the life of the element. give.

Originally, a laminated piezoelectric element has a mechanical resonance frequency, and when driven at a higher frequency than that, a large compressive load and a large tensile load are applied to the laminated piezoelectric element. In particular, because of its laminated structure, laminated piezoelectric elements are extremely stable under compressive loads, but extremely weak under tensile loads, and over long-term use, this can lead to delamination between the laminated bodies or dielectric breakdown. .

[Means to solve the problem]

In order to solve the above-mentioned problems, the present invention has a drive circuit for a multilayer piezoelectric element configured such that the time constant when the applied voltage falls is approximately smaller than the mechanical resonance time constant of the piezoelectric element. This is a drive circuit characterized by the following.

C Example] One embodiment of the invention is shown in FIG.

In FIG. 1, in order to apply a stepping waveform to the piezoelectric element, two transistors are used so that the voltage can be switched independently when the voltage rises or falls. The explanation will be given below according to the figures.

Base resistors of Ω to RI+−10 and Ω to R1□;10 were connected to the base terminals of the transistors 3 and 4, respectively, and the emitter of the 1 helang transistor 3 and the collector of the transistor 4 were made common. Further, the multilayer pressure element 1 was connected to the connection point via the protective resistor Rc. The operating principle of this circuit will be described.

When Vi = 5V and V1□ = zero, 1 to transistor 3
Since 4 is in the ON state and 4 is in the OFF state, the current is Ru
, Rc into the multilayer piezoelectric element 1, the voltage Vp applied to the piezoelectric element has a value approximately equal to VD. Next, when ViH=zero and (2)+2=5V, transistor 3 is turned off and transistor 4 is turned on, so that the charge stored in piezoelectric element 1 is discharged via Re and Rd. At this time, in order to prevent malfunctions due to switching, a pause time TC is provided when switching between input voltages Vi1 and Vi2 as shown in FIG. This prevents the transistors from turning on at the same time.

Furthermore, the voltage operation waveforms of this circuit are shown in FIG.
When l rises, Vp also rises, and when Vi2 rises, Vp begins to fall. The time constant at the rise and fall of this Vp is as follows: Tu=Ru-R
c-C.

When descending Td=Rd-Rc-G.

becomes. In this embodiment, the piezoelectric element 2 is a PZT-based element 5m.
The capacitance was 1 μF. Furthermore, when the mechanical resonance frequency was investigated, it was approximately 20 kHz. Therefore, the mechanical resonance time constant of this element is TM=1/20xlO'=50 μsec.

In this circuit, in order to intentionally make the falling time constant smaller than this time constant, Rc=Rd=short circuit in the circuit. Further, Ru was set to be constant at 2Ω.

As a result, the time constants for rising and falling are respectively Tu=Ru-Rc-G.

=2xlO''xlXIO' =0.002=2msec Td is determined by the discharge constant of only the capacitance since it is in a short circuit state, but it was approximated as Td=txto'=lμsec.

The device was driven under the above conditions with a repetition period of applied voltage of 3 seconds and a duty cycle of 3 seconds. As a result, results as shown in FIG. 5(a) were obtained. When the above circuit was subjected to a drive test 106 times, 25 out of 30 samples had defects such as cracks and spark discharge. This result shows that if the falling time constant is smaller than the mechanical time constant, defects are likely to occur.

Next, in order to prove the validity of the present invention, a driving test was conducted under the following conditions.

(1) Common items Maximum applied voltage: 150 ■ Repeat duty: 3 sec: 3 sec Ru = 2 to Ω (2) Parameter (i) Rc - short circuit Rd = 50 Ω (ii) Rc = short circuit Rd = IKΩ In case of i), the time constant of the fall is Td=50X IX 10'=50μsec,
It is equal to the mechanical resonance time constant of the laminated piezoelectric element. Also(
11), Td=l x 103X I x 10'=I
10-" = 1 msec, which is clearly larger than that of the laminated piezoelectric element. Under these conditions, an experiment similar to that described above was conducted, and the results shown in Figure 5 (b) were obtained. It can be seen that the value of , as well as the defect rate, has been greatly improved.

Therefore, in order to improve the reliability of the multilayer piezoelectric element, the time constant of the applied voltage, especially the rise, may be made thicker than the mechanical resonance time constant of the element.

〔Effect of the invention〕

According to the present invention, the reliability of the laminated piezoelectric element, which has been insufficient in the past, is further improved, and a piezoelectric actuator with excellent durability can be provided.

[Brief explanation of the drawing]

FIG. 1 is an electric circuit diagram showing an embodiment of the drive circuit according to the present invention, FIG. 2 is a conventional circuit diagram, and FIG. 3 is a time chart diagram of the control voltage manually applied to the drive circuit according to the present invention. FIG. 4 is a time chart showing the operation within the drive circuit according to the present invention, and FIG. 5 is a diagram showing the occurrence of defects when the drive circuit according to the present invention is used. 1 stacked piezoelectric element, 2 transistors, 3 transistors,
4. transistor. Figure 1 n Figure 2 Figure 3 Figure 4 1yo VP Figure 5 (G) (b) Number of flight movements (times) (ii)

Claims (1)

[Claims] By layering piezoelectric ceramic plates and applying voltage,
This is a circuit for driving a laminated piezoelectric element configured to obtain displacement, and the time constant when the applied voltage falls is
A drive circuit for a laminated piezoelectric element, characterized in that it is configured to be smaller than the mechanical resonance time constant of the piezoelectric element.