JPH0321050B2 - - Google Patents

Description

[Detailed description of the invention] (a) Industrial application field This invention is applicable to electric power used for process control, etc.
The present invention relates to pneumatic transducers, particularly electro-pneumatic transducers using piezoelectric elements in nozzle flappers.

(b) Background Some electro-pneumatic converters use piezoelectric elements in the nozzle flapper. Conventionally, this type of electro-pneumatic converter applies a unidirectional (positive polarity) DC voltage according to an input signal to a piezoelectric element flapper to displace the piezoelectric element flapper. When a directional DC voltage is applied, the piezoelectric element undergoes retrograde deformation in the direction of the generated strain, resulting in a disadvantage that the operating point shifts. 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 0V at the middle level of the input signal, and set it to have both positive and negative polarities in response to the increase or decrease of the input signal. We have created an electro-pneumatic converter using the same technology and have already filed an application. The electro-pneumatic 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 electrical 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 applies this output DC voltage to the first DC voltage source. a second DC voltage source that applies to the piezoelectric element in a manner that cancels out the DC voltage from the first DC voltage source; a nozzle that uses a displaced portion of the piezoelectric element as a flapper to receive supply pressure and derive back pressure; a pilot valve that converts this back pressure into an output pressure; a conversion 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; It consists of a feedback circuit that balances the input electrical signal.

However, this electro-pneumatic converter is configured so that the displacement of the piezoelectric element flapper is 0 when the input electrical signal is at a medium level (50%). 50 electrical signals
It is not possible to distinguish between % and %. In other words, there is a problem in that 50% of the air pressure is output even when the input electrical signal is cut off.

(C) Purpose Therefore, the purpose of the present invention is to reduce the change in the operating point due to changes in the initial value of mechanical strain of the piezoelectric element material, and to reduce the output pressure to 0% or The object of the present invention is to provide an electro-pneumatic converter that can achieve 0 kg/cm ² .

(d) Configuration In order to achieve the above object, the electro-pneumatic converter of the present invention has, in addition to the components of the electro-pneumatic converter of the prior application mentioned above, The pneumatic system is provided with a pneumatic opening means for swinging the output pressure to 0%. That is, the electro-pneumatic converter of the present invention includes a piezoelectric element that is displaced according to an applied voltage, and a first DC voltage that outputs a constant DC voltage when an input electric signal is applied and applies this DC voltage to the piezoelectric element. outputting a DC voltage that changes in accordance with a voltage source and an input electrical signal and has approximately the same value as the output DC voltage of the first DC voltage source when the input electrical signal is at an intermediate level in a predetermined change range; A second DC voltage source is applied to the piezoelectric element in such a manner that this output DC voltage is offset with the DC voltage from the first DC voltage source, and a displacement part of the piezoelectric element is used as a flapper to receive supply pressure and back. A pneumatic system comprising a nozzle for deriving pressure and a pilot valve for converting the back pressure into output pressure, a circuit for converting the output pressure into an electrical signal, and a circuit for converting the electrical signal converted by this conversion circuit into the second In addition to the input side of the DC voltage source, a feedback circuit that balances the input electrical signal;
The pneumatic opening means is provided in the pneumatic system and releases the air pressure of the pneumatic system when the input electrical signal is below a predetermined value.

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

FIG. 1 is a circuit diagram of an electro-pneumatic converter which is the premise of this invention. In the figure, an input current Ii flows through a Zener diode Z1 and a volume VR, and a voltage ei proportional to the input current Ii is obtained at the input resistance Ri of the volume VR, and this voltage ei and a Zener diode Z
2 voltages are added by resistors R2 and R3 and applied to the inverting input terminal of the micropower operational amplifier 1. The output voltage E0 of the operational amplifier 1 is applied to the oscillation circuit 9, and the oscillation circuit 9 undergoes amplitude modulation by the output voltage E0 and oscillates. That is, the oscillation circuit 9 outputs an oscillation signal with an amplitude corresponding to the output voltage E0 and therefore the input current Ii. The oscillation output signal of the oscillation circuit 9 is rectified by a full-wave rectifier circuit 11, so that a DC voltage of +E2 is 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.

Further, under a condition in which the input current Ii is passed through the Zener diode Z1 and the volume VR, a voltage of +V 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 a full-wave rectifier circuit 10, so that a DC voltage of +E1 is derived across the discharge resistor Ra. The output DC voltage E1 of the rectifier circuit 10 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 E2-E1 voltage E0'It's starting to be applied. Then, the DC voltage E2 is configured to vary from 0 to 2E1 according to the input current, and in the case of an input current corresponding to 50%, E
2=E1, and in this case E0' becomes 0.
The piezoelectric element flapper 2 is displaced according to the applied voltage E0'. When E0' is of negative polarity (E2<E1), it is displaced equally from the nozzle 3, which will be described later, and conversely, when it is positive and reversed (E2>E1), it is displaced in the direction approaching the nozzle 3. However, E0'=0(E2
=E1), there is no displacement.

On the other hand, in the pneumatic system, the blowhole of the nozzle 3 faces the piezoelectric element 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 a pneumatic conversion circuit consisting of a power source 5 and a pressure sensor 6,
The output pressure is converted into a piezoelectric signal.
Also, the voltage signal from the pressure sensor 6 is sent to a differential amplifier 7.
The signal is fed back to the non-inverting input terminal of the operational amplifier 1 through the . Here, the input signal voltage to the operational amplifier 1 and
When there is a difference between the voltage fed back from the differential amplifier circuit 7 and the input signal voltage is larger, the output voltage E ₀ of the operational amplifier 1 changes to a larger value,
Accordingly, the voltage E ₂ obtained from the oscillation circuit 9, via the rectifier circuit 11, across the resistor Rb also increases,
The voltage E ₀ ' applied to the piezoelectric element flapper 2 increases, and the piezoelectric element flapper 2 is displaced in the direction closer to the nozzle 3. Correspondingly, the back pressure of the nozzle 3 increases, the output pressure also increases, and the voltage fed back to the operational amplifier 1 via the differential amplifier 7 increases and approaches the input signal voltage. to the input signal voltage,
As the voltage fed back from the differential amplifier 7 approaches, the change in the output voltage _E0 of the operational amplifier 1 in the larger direction becomes smaller, and eventually the input signal voltage and the differential amplifier 7
When the voltages fed back from the operational amplifier 1 become equal, the output voltage E ₀ of the operational amplifier 1 stops changing and is maintained as it is. Therefore, the back pressure of the nozzle 3 is also constant, and the output pressure is also constant. When the signal input voltage becomes larger, it becomes larger than the voltage fed back from the differential amplifier 7, so the output voltage E ₀ changes again in the direction of increasing by inputting this difference voltage to the operational amplifier 1. Accordingly, the voltage E ₂ also increases in the same way as above, so the voltage E ₀ ' applied to the piezoelectric element flapper 2 increases, and the piezoelectric element flapper 2 is displaced in the direction closer to the nozzle 3. Correspondingly, the back pressure of the nozzle 3 further increases, and the output pressure also increases. When the input signal voltage and the voltage fed back from the differential amplifier 7 match, the operational amplifier 1 maintains its output voltage E ₀ at the value at that time, and responds to the back pressure of the nozzle 3 and output pressure leakage. It remains constant. That is, this electro-pneumatic converter is
The output voltage E ₀ of the operational amplifier 1 is changed so that the voltage fed back from the differential amplifier 7 approaches the input signal voltage, and so that both become equal. When the two become equal, the output voltage E ₀ is maintained. , we obtain an output air pressure proportional to the input signal voltage Ei and therefore to the input current Ii.

As long as the input current Ii is flowing in the electro-pneumatic converter shown in FIG. It is possible to maintain operation in a small state, and to suppress fluctuations in the operating point due to fluctuations in the initial value of mechanical strain of the piezoelectric element. However, when the input current Ii is cut off and becomes 0, the oscillation of the oscillation circuits 8 and 9 decreases, and the output DC voltages E1 and E2 of the rectifier circuits 10 and 11 become 0. In this case, the applied voltage E0' of the piezoelectric element 2 is also 0. Since the piezoelectric element flapper 2 is not displaced, an air pressure of around 50% is output.

Therefore, in the first embodiment of the present invention, as shown in FIG. 2, a pneumatic opening means 12 is provided in the pneumatic path between the nozzle 3 and the pilot valve 4 to turn on and off the nozzle back pressure. This example
In the pneumatic transducer, when the input voltage Ii shown in FIG. voltage E applied to
The output air pressure corresponding to 0' is derived. On the other hand, when the input current Ii becomes less than a predetermined value (rated value), the pneumatic opening means 12 is turned on, the back pressure of the nozzle 3 is released, and the output pressure from the pilot valve 4 is thereby swung in the zero direction. , the output pressure is forced to 0%. Specific examples of the pneumatic circuit means 12 used here are shown in FIGS. 3 and 4.

FIG. 3 shows a pneumatic opening means using a solenoid valve. In the figure, the core 20 includes an electromagnetic coil 21.
is wound around the nozzle, and a communication hole 22 is provided in the center to receive nozzle back pressure, and a valve 23 is provided at the back pressure outlet of this communication hole 22 to block the outlet using the suction force of the electromagnetic coil 21. It is being When the current of the electromagnetic coil 21 becomes less than a predetermined value, the valve 2 is closed by nozzle back pressure against the attraction force of the electromagnetic coil 21.
3 is separated from the outlet of the communication hole 22 and moved to the right. 24 is a valve stopper, and 25 is a stopper presser. In addition, the valve stopper 24 has
A hole 26 is provided to release nozzle back pressure. Of course, the valve 23 is made of a magnetic material such as permalloy.

In this electromagnetic valve type pneumatic circuit opener, when the input current flowing through the electromagnetic coil 21 exceeds the rated value, the valve 23 is attracted by the electromagnetic force, so the communication hole 2
The outlet of No. 2 is blocked and is in the off state, and the nozzle back pressure is not released. However, when the input current flowing through the electromagnetic coil 21 becomes less than the rated value, the attraction force of the electromagnetic coil 21 becomes weaker, and the valve 23 is pushed to the right by the nozzle back pressure, creating a gap between the communication hole 22 and the valve 23. , the nozzle back pressure is released to the outside through the hole 26 from this gap.

FIG. 4 shows a pneumatic circuit using a piezoelectric diaphragm. In the same figure, 30 is the base 31
The nozzle 32 is a piezoelectric diaphragm whose end is supported by the base 31, and the piezoelectric element of the piezoelectric diaphragm 32 generates a voltage corresponding to the input current. is applied, and the applied voltage causes deflection. When the applied voltage is higher than the rated value, the deflection is large, and the piezoelectric element diaphragm 32 closes the jet port of the nozzle 30. In order to improve the contact between the nozzle 30 and the piezoelectric element diaphragm 32, a small hole is provided in the center of the piezoelectric element. Note that 33 is base 31
This is a back pressure relief hole provided in the

In this diaphragm type pneumatic circuit opener, when the voltage applied to the piezoelectric element diaphragm 32 is equal to or higher than the rated value, the piezoelectric element diaphragm 32
Since the nozzle 30 is blocked by the deflection, it is in the off state and no back pressure is released. However, when the voltage applied to the piezoelectric element diaphragm 32 becomes lower than the rated value, the deflection of the piezoelectric element diaphragm 32 becomes weaker.
Since a gap occurs between the tip of the nozzle 30 and the piezoelectric diaphragm 31, the nozzle back pressure from the nozzle 3 is transferred to the base 3 through the nozzle 30 and the gap.
1 and escapes to the outside through the small hole 33 of the base 31.

In another embodiment of the invention, the pneumatic circuit of FIG. 5 is applied to the electro-pneumatic converter shown in FIG.

This embodiment differs from the embodiment shown in FIG. 2 in that the supply pressure is released through a pneumatic opening means 13. A swing-off nozzle 14 is provided on the output side of the pneumatic circuit opening means 13 so as to face the piezoelectric element flapper 2. In addition, the pneumatic opening means 13
As shown in FIG. 3 or 4, the one shown in FIG. 3 or 4 is used.

In FIG. 5, when the input electrical signal is equal to or higher than the rated value, the pneumatic opening means 13 is turned off and supply pressure is not released, so that the electro-pneumatic converter performs normal control operations. However, when the input electrical signal becomes less than the rated value, the pneumatic circuit means 13 is turned on, and the air is ejected from the blow-off nozzle 14 via the supply pressure opening means 13, blowing up the piezoelectric element flapper 2. As a result, the gap between the piezoelectric element flapper 2 and the nozzle 3 increases, and the output of the pilot valve 4 decreases together with the above-mentioned release of the air supply pressure, and swings completely in the zero direction.

(F) Effects According to this invention, when the input electrical signal falls below the lowering value, the pneumatic opening means is turned on to release the pneumatic pressure and forcefully swing the output in the zero direction. The control system can be operated safely even if the input electrical signal is interrupted.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of an electro-pneumatic converter which is the premise of this invention, Fig. 2 is a pneumatic circuit diagram showing the main parts of an electro-pneumatic converter according to an embodiment of the invention, and Fig. 3 is a circuit diagram of the above-mentioned embodiment. FIG. 4 is a diagram showing a solenoid valve type pneumatic opener used in the electro-pneumatic converter, and FIG. FIG. 2 is a pneumatic circuit diagram showing essential parts of an electro-pneumatic converter according to another embodiment of the present invention. 1: Operational amplifier, 2: Piezoelectric flapper, 3:
Nozzle, 4: Pilot valve, 5: Constant current source, 6:
Pressure sensor, 7: differential amplifier, 8, 9: oscillation circuit, 10, 11: rectifier circuit, 12, 13: pneumatic opening means.

Claims (1)

[Claims] 1. A piezoelectric element that is displaced according to an applied voltage, and a first piezoelectric element that outputs a constant DC voltage when an input electrical signal is applied and applies this DC voltage to the piezoelectric element.
DC voltage source and varies depending on the input electrical signal,
And when the input electrical signal is at the middle level of the planned change range, a DC voltage having approximately the same value as the output DC voltage of the first DC voltage source is outputted, and this output DC voltage is output from the first DC voltage source. a second DC voltage source applied to the piezoelectric element in a manner that offsets the DC voltage of the piezoelectric element; a nozzle that receives supply pressure and derives back pressure by using the displacement part of the piezoelectric element as a flap; and a nozzle that receives supply pressure and derives back pressure, and converts the back pressure into output pressure. A pneumatic system consisting of a pilot valve to convert, a conversion circuit to convert the output pressure into an electric signal, and an electric signal converted by this conversion circuit to the input side of the second DC voltage source, An electro-pneumatic converter comprising: a feedback circuit for balancing the signal; and pneumatic opening means provided in the pneumatic system to release the air pressure in the pneumatic system when the input electrical signal is below a predetermined value. 2. The electro-pneumatic converter according to claim 1, wherein the pneumatic opening means is configured to release back pressure of the nozzle. 3. The electro-pneumatic converter according to claim 1, wherein the pneumatic opening means is configured to release the supply pressure. 4. The pneumatic opening means is a solenoid valve, and the solenoid coil of the solenoid valve is supplied with a current according to the input electric signal to attract the valve, and when the input electric signal becomes less than a predetermined value, the valve is closed. 4. The electro-pneumatic converter according to claim 2, wherein the air pressure is released by releasing suction. 5. The pneumatic opening means includes a nozzle that receives air pressure from the pneumatic system and a piezoelectric element diaphragm to which a voltage according to the input electric signal is applied, and when the applied voltage is equal to or higher than a predetermined value, the piezoelectric element diaphragm closes the nozzle. Claim 2 or 3, characterized in that the jet nozzle is closed, and when the applied voltage falls below a predetermined value, the piezoelectric element diaphragm is separated from the nozzle to release the air pressure. The electro-pneumatic converter described.