JPS6024415A - Electro-pneumatic converter - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application This invention relates to an electric-to-rush transducer used for process control, etc., and particularly to an electric-to-rush transducer using a piezoelectric element in a nozzle flapper.

(b) Background Some electric-to-radial transducers use a piezoelectric element in the nozzle flapper. Conventionally, this type of electric-to-rush transducer applies a unidirectional (positive polarity) DC voltage to the piezoelectric element flapper in accordance with the input signal to displace the piezoelectric element flapper. However, when a direct current voltage is applied to the piezoelectric element, the piezoelectric element undergoes retrograde deformation in the direction of the generated strain, resulting in a shift in the operating point. Therefore, in order to eliminate this drawback, the inventors of this application set the control voltage applied to the piezoelectric element flapper to be around 0■ at the middle level of the input signal, so that it can respond to the input signal becoming large or small. He has created an electric-to-rush converter that has both positive and negative polarities, and has already filed an application.

The electric to sudden converter according to this prior application includes a piezoelectric element that is displaced according to an applied voltage, a first DC voltage source that outputs a constant DC voltage and applies this DC voltage to the piezoelectric element, and an input electric signal. and when the input electrical signal is at the middle level of the expected change range, outputs a DC voltage that has approximately the same value as the output DC voltage of the first DC voltage source, and converts this output DC voltage into the first DC voltage source. a second DC voltage source applied to the piezoelectric element in a manner that cancels out the DC voltage from the DC voltage source; a nozzle that uses the displacement part of the piezoelectric element as a flapper to receive supply pressure and derive back pressure; a pilot valve that converts back pressure into output pressure; a circuit that converts the output pressure into an electrical signal; and the electrical signal converted by this conversion circuit is applied to the input side of the second DC voltage source, and the input electricity is It consists of a feedback circuit that balances the signal.

However, in this electric-to-rush transducer, when the input electric signal is at a medium level (50%), the displacement of the piezoelectric element flapper is O.
Therefore, it is impossible to distinguish between when there is no input electrical signal and when the input electrical signal is about 50%. That is, there is a problem in that when the input electric signal is cut off, the output air pressure does not become Okg/cJ and deviates.

(C) Purpose The purpose of the present invention is to solve the above-mentioned problems and provide an electric-to-rush converter that can reliably maintain the output air pressure at Okg/ca even if the power electric signal is cut off. It is to be.

(D) Structure In order to achieve the above object, the electric-to-rush converter of the present invention has the following features:
In addition to the above-mentioned components of the electric-to-seismic converter of the earlier application, there is also a nozzle holding means such as a diaphragm that elastically supports the nozzle on a fixed part and is displaced in response to nozzle back pressure, and a nozzle holding means such as a diaphragm that is displaced in response to nozzle back pressure. The nozzle is heated at a nozzle back pressure that is slightly lower than the nozzle back pressure, and the voltage of the first DC voltage source is maintained for a predetermined time even after the power is turned off, and the voltage of the first DC voltage source is maintained for a predetermined time even after the power is turned off. voltage holding means for applying a voltage in the same manner as the source to the piezoelectric element, and when an input signal is input within a predetermined range, the nozzle holding means is brought into contact with the stopper by the nozzle back pressure. Control operation is not performed, and when the power supply is cut off,
By applying a voltage from the voltage holding means, the flapper is moved away from the nozzle, the nozzle holding means is separated from the strike collar, and the output pressure is controlled to move in the O direction.

(e) Examples The present invention will now be described in more detail with reference to examples shown in the drawings.

FIG. 1 is a circuit diagram of an electric-to-rush converter showing one embodiment of the present invention. In the same figure, an input current 1i flows through the Zener diode z1 and the volume VR, and a voltage ei proportional to the input current iG is obtained at the input resistance Ri of the volume VR, and this voltage ei and the voltage of the Zener diode Z2 are connected to the resistor R2. and R3, and the micropower operational amplifier 1
It is designed to be applied to the 0 inversion input terminal. The output voltage EO of the operational amplifier 1 is applied to the oscillation circuit 9, and the oscillation circuit 9 oscillates by rejecting the amplitude modulation by the output voltage EO. That is, the oscillation circuit 9 outputs an oscillation signal with an amplitude corresponding to the output voltage EO2 and therefore the input current It. The oscillation output signal of the oscillation circuit 9 is rectified by a full-wave rectifier circuit 11,
A DC voltage of +E2 is now derived across the discharge resistor Rb.

The output DC voltage E2 of this rectifier circuit 11 is applied to the metal plate 2a of the piezoelectric element flapper 2.

In addition, the input current Ti is connected to the Zener diode Z1 and the volume V
Under the condition where the voltage is applied to R, a voltage of +■ is supplied to the oscillation circuit 8, and the oscillation circuit 8 outputs an oscillation signal with a constant amplitude. The oscillation output signal of the oscillation circuit 8 is rectified by the full-wave rectifier circuit IO, and the output voltage E1 is used to charge the capacitor Ca through the discharge resistor Ra. This rectifier circuit 1
The output DC voltage E1 of 0 is applied to the piezoelectric elements 2b and 2C of the piezoelectric element flapper 2. The DC voltages E1 and E2 are both positive polarity voltages, but they are applied to the piezoelectric element flapper 2 with opposite polarities, so that the two voltages cancel each other out, that is, the voltage EO' of E2-El is applied. It is now possible to do so. The DC voltage E2 is configured to vary from O to 2E1 depending on the input current, and in the case of an input current corresponding to 50%, E2=E1, and in this case, EO' becomes O. The piezoelectric element flapper 2 is displaced according to the applied voltage E O'. E O' is negative polarity (E2
In the case of <El), it is displaced away from the nozzle 3, which will be described later, and conversely, in the case of positive polarity (E2>El), it is displaced in the direction closer to the nozzle 3. However, EO'-0(E2
=81), there is no displacement.

On the other hand, in the pneumatic system, the jet nozzle 3 faces the piezoelectric flapper 2 and receives supply pressure, and the back pressure is amplified by the pilot valve 4 and derived as output pressure. In addition to an electro-pneumatic conversion circuit consisting of a source 5 and a pressure sensor 6, the output pressure is converted into a voltage signal.

As shown in FIG. 2, the piezoelectric element flapper 2 is made by bonding bare plate type semi-conductor ultrasonic transducers 2b and 2C to both sides of a thin metal plate 2a. The direction of polarization is the thickness direction of the plate (arrow A), the direction of expansion and contraction due to voltage application is the longitudinal direction of the plate (arrow B), and the direction of displacement is the thickness direction (arrow C). The relationship between applied voltage and flapper tip displacement is 20μm/IOV
are used.

Note that the nozzle 3 is connected to the fixed portion 13 via the diaphragm 12.
is supported by The diaphragm 12 is displaced towards the piezoelectric flapper 2 by the nozzle back pressure. However, a stopper 14 is provided between the diaphragm 12 and the piezoelectric flapper 2, and the output air pressure is reduced to 0.2
~1.0 kg/cIII nozzle back pressure (approximately 0.4
At a pressure slightly lower than 0.5 kg/cJ), the diaphragm 12 hits the stopper 14 and is no longer displaced in the direction approaching the piezoelectric element flap 2. The distance between the diaphragm 12 and the stopper 11 when there is no displacement is about 80 μm.

Further, the voltage signal from the pressure sensor 6 is fed back to the non-inverting input terminal of the operational amplifier 1 via the differential amplifier 7. Then, the output voltage EO of the operational amplifier 1 changes so that the input signal voltage and the voltage fed back from the differential amplifier 7 become equal, and this output voltage EO controls the displacement of the piezoelectric element flapper 2, and the input current II Proportional output air pressure is obtained.

In the electro-transformer configured as described above, when the input current It flows, the voltage applied to the piezoelectric element flapper 2 rises to the maximum value, and the piezoelectric element flapper 2 is connected to the nozzle 3.
, and the nozzle back pressure increases. When the nozzle back pressure increases, the output pressure also increases, and the diaphragm 12 is also displaced in the direction closer to the piezoelectric element flapper 2.

The nozzle back pressure and output air pressure are 0.2 to 1.0 kg.
/ cnT, the diaphragm 12
hits the stopper 14 and is no longer displaced thereafter. After that, the output voltage EO of the operational amplifier 1 is changed so that the input signal voltage ei and the output pressure fed back through the pressure sensor 6 and the differential amplifier 7 are equal to each other, and the piezoelectric element flapper 2
and the air gap of the nozzle 3 is adjusted. That is, an output air pressure signal is derived according to the input signal.

If the power supply is cut off and the input current 1i becomes O, the output EO of the operational amplifier 1 becomes O, and therefore the full-wave rectifier circuit 1
1's output voltage E2 also becomes O, and the negative polarity voltage El charged in the capacitor Ca is applied to the piezoelectric element flapper 2, and the piezoelectric element flapper 2 is displaced in the direction away from the nozzle 3. This displacement reduces nozzle back pressure. When the nozzle back pressure decreases, the diaphragm 12 that has been in contact with the stopper 14 also moves to the stopper 14.
Therefore, the piezoelectric element flapper 2 and the nozzle 3 are further separated from each other, and the nozzle back pressure is also reduced. Therefore, the output pressure is forced to Okg/cJ at a relatively early time after the input current is cut off.

Even if the charge in the capacitor Ca is completely discharged (e.g. 30 minutes after disconnection), the output air pressure will remain at Okg/c+A until the electric current It is reapplied. Therefore, the output air pressure will wander while the signal input is interrupted. There's nothing to do.

Further, in the above embodiments, the nozzle is supported by the fixed portion by a diaphragm, but a bellows may be used instead of the diaphragm.

(f) Effects According to the electric to sudden transducer of the present invention, when the input signal is cut off, the piezoelectric element flapper is displaced away from the nozzle,
This lowers the nozzle back pressure, which causes the displacement of the diaphragm, etc., to move the nozzle further away from the piezoelectric flapper, thereby lowering the nozzle back pressure, ensuring that the output air pressure is Okg/Ca. can.

Furthermore, since circuit means for maintaining the voltage of the first DC voltage source is provided when the power is turned off, a battery for the bank amplifier is not required.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of an electric-to-pneumatic transducer showing one embodiment of the present invention, and Fig. 2 is a diagram showing a piezoelectric element flapper of the same type of pneumatic transducer. Plan view, Figure 2 (b
) is its cross-sectional view: 1: arithmetic operation unit, 2: piezoelectric flapper, 3: nozzle, 4: birosoto valve, 5: constant current source, 6: pressure sensor, 7: differential amplifier, 8 and 9: Oscillation circuit, 10/11: Rectifier circuit, 12: Diaphragm, 13: Fixed part, 14:
Stosova, Ca: Capacitor patent applicant Shimadzu Corporation Representative Patent attorney Shigenobu Nakamura

Claims (1)

[Claims] (1) a piezoelectric element that is displaced according to an applied voltage; a first DC voltage source that outputs a constant DC voltage and applies this DC voltage to the piezoelectric element; and a first DC voltage source that changes according to an input electrical signal;
And when the input electric signal is at the middle level of the planned change range, outputs a DC voltage that is approximately the same value as the output DC voltage of the first DC voltage source, and converts this output DC voltage into a voltage that is approximately the same as the output DC voltage of the first DC voltage source. a second DC voltage source that applies to the piezoelectric element in a manner that offsets the DC voltage; a nozzle that uses the displacement part of the piezoelectric element as a flapper to receive supply pressure and derive back pressure; and a nozzle that receives supply pressure and derives back pressure; a pilot valve for conversion, a circuit for converting the output pressure into an electric signal, and a feedback circuit for applying the electric signal converted by the conversion circuit to the input side of the second DC voltage source to balance it with the input electric signal. An electric-to-seismic converter comprising: a nozzle holding means that elastically supports the nozzle on a fixed part and is displaced in response to nozzle back pressure; and a nozzle whose output pressure is slightly lower than the nozzle back pressure within a predetermined range. A stopper, which the diaphragm comes into contact with due to back pressure, maintains the voltage of the first DC voltage source for a predetermined time even after the power is turned off, and
voltage holding means for applying a voltage in the same manner as a DC voltage source to the piezoelectric element, and when the input signal is input within a predetermined range, the nozzle holding means is brought into contact with the stopper by the nozzle back pressure. A control operation is carried out in the state in which they are in contact with each other, and when the power source is manually cut off, the flapper is moved away from the nozzle by applying a voltage to the voltage holding means, the nozzle holding means is separated from the stopper, and the output pressure is set in the zero direction. An electric to thrust converter whose movement is controlled.