JPH0321051B2 - - 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 to the piezoelectric element flapper in response to an input signal to displace the piezoelectric element flapper. When a high DC 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 0V at the middle level of the input signal, so that it corresponds to the increase or decrease of the input signal. He has created an electro-pneumatic converter that has both positive and negative polarities, and has already filed an application. E-mail related to this earlier application
The air transducer 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 a first DC voltage source that changes according to an 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 output, and this output DC voltage is applied to the DC voltage from the first DC voltage source. a second DC voltage source that applies to the piezoelectric element in a manner that offsets the 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 converts this back pressure into output pressure. a conversion circuit that converts the output pressure into an electrical signal; and a feedback circuit that applies the electrical signal converted by the conversion circuit to the input side of the second DC voltage source to balance it with the input electrical signal. It is made up of.

However, this electro-pneumatic converter is configured so that the potential 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 %. That is, there is a problem in that burnout in which the output air pressure is 0 kg/cm ² when the input electric signal is cut off cannot be realized.

(c) Purpose Therefore, the purpose of the present invention is to provide an electro-pneumatic converter that has little change in the operating point due to changes in the initial value of mechanical strain of the piezoelectric element material, and can realize burnout when the input electric signal is cut off. There is something to do.

(d) Configuration In order to achieve the above object, the electro-pneumatic converter of the present invention includes, in addition to the components of the electro-pneumatic converter of the prior application described above, a DC voltage source for realizing burnout, When the input electrical signal is interrupted, a DC voltage from this DC voltage source is applied to the voltage element. 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 piezoelectric element that outputs a constant DC voltage when an input electric signal is applied and applies this DC voltage to the piezoelectric element. outputs a DC voltage that changes in accordance with the DC 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 a middle level of a predetermined change range; , a second DC voltage source 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 as a flap, receiving supply pressure. A nozzle that derives back pressure, a pilot valve that converts this back pressure into output pressure, a conversion circuit that converts the output pressure into an electrical signal, and an electrical signal converted by the conversion circuit that converts the electrical signal into the second DC voltage. In addition to the input side of the source,
a feedback circuit that balances the input electric signal; and when the input electric signal is not applied, a DC voltage having the same value and the same polarity as the constant DC voltage is applied to the piezoelectric element in place of the first DC voltage source. and a third DC voltage source.

(e) Examples The present invention will be described 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 across resistors R2 and R3 and applied to the inverting input terminal of the micropower operational amplifier 1. The output voltage E ₀ of the operational amplifier 1 is applied to the oscillation circuit 9, and the oscillation circuit 9 undergoes amplitude modulation by the output voltage E ₀ and oscillates. That is, the oscillation circuit 9 outputs an oscillation signal with an amplitude corresponding to the output voltage E ₀ 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. This rectifier circuit 1
The output DC voltage E2 of 1 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. Output DC voltage E1 of this 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 is starting to be applied. Then, the DC voltage E2 is configured to vary from 0 to 2E1 depending on the input current, and in the case of an input current corresponding to 50%,
E2=E1, and in this case E0' becomes 0.
The piezoelectric element flapper 2 is displaced according to the applied voltage E0'. When E0' has negative polarity (E2<E1), it moves away from the nozzle 3, which will be described later, and conversely, when it has positive and reverse polarity (E2>E1), it moves toward 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.

In the electro-pneumatic converter of FIG. 1 described above, as long as the input current Ii is flowing, the voltage E0' applied to the piezoelectric element flapper 2 becomes 0 at an input current corresponding to 50%.
The operation can be maintained in a state where the displacement of the piezoelectric element flapper 2 is small, and fluctuations in the operating point due to fluctuations in the initial value of the mechanical strain of the piezoelectric element can be suppressed. However, when the input current Ii is cut off and becomes 0, the oscillation of the oscillation circuits 8 and 9 stops, and the output DC voltages E1 and E2 of the rectifier circuits 10 and 11 become 0, and in this case as well, the applied voltage E0' of the piezoelectric element 2 becomes 0, and the piezoelectric element flapper 2 is not displaced, so the output pressure does not change by more than 50% and burnout cannot be realized.

Therefore, in the first embodiment of the present invention, a series circuit consisting of a resistor RA and a capacitor CA as shown in FIG. 2 is connected in place of the discharge resistor Ra at the output end of the full-wave rectifier circuit 10 in FIG. I have to. The capacitance of the capacitor CA used here is selected to be much larger than the capacitance of the piezoelectric element flapper 2 and the diode capacitance of the rectifier circuit 10.

In this embodiment, if the input current Ii flows and the power supply is normally obtained, the voltage shown in FIG.
As explained in connection with the empty converter, a constant DC voltage E1 is applied to the output of the full-wave rectifier circuit 10.
The output of 1 is a DC voltage E2 corresponding to the input current Ii.
are obtained, and the piezoelectric element flapper 2 has E2.
A voltage of -E1 is applied, and by displacement according to this applied voltage, it is possible to ultimately obtain an output pressure corresponding to the input current Ii. In this operating state, a charging current flows through the resistor RA to the capacitor CA, and the capacitor CA is charged to a voltage approximately equal to the DC voltage E1. Therefore the input current
When Ii is disconnected, the charging voltage of this capacitor CA becomes
Instead of the full-wave rectifier circuit 10, a DC voltage E1 is supplied to the piezoelectric element flapper 2. On the other hand, when the input power Ii is cut off, the oscillation circuit 9 stops oscillating, and the output DC voltage E2 of the full-wave rectifier circuit 11 becomes 0, so a voltage of -E1 is applied to the piezoelectric element flapper 2. Therefore, the piezoelectric element flapper 2 is displaced away from the nozzle 3 by this applied voltage -E1, lowering the back pressure and lowering the output pressure to 0 kg/cm ² . Burnout is achieved in this way.

According to the electric-to-air converter of this embodiment, a charging current flows through the capacitor CA when the power is first turned on, but once charging is completed, no charging current flows, so almost no power is consumed. Also, when the power is turned off, the charging voltage of capacitor CA is applied to the piezoelectric element flapper and attempts to start discharging, but since the piezoelectric element is an insulator, the capacitor
The charge of CA is hardly discharged, and the DC voltage of approximately E1 is maintained for a long period of time.

In addition, as another example, the resistor shown in FIG.
In place of the series circuit of RA and capacitor CA, a series circuit of battery VB1 and diode d1 is connected as shown in Figure 3, and the DC voltage of this battery VB1 is
It may be applied to the piezoelectric element flapper 2 in parallel with the DC voltage E1 of the full-wave rectifier circuit 10 shown in the figure. While the power is on and there is electrical input, the full-wave rectifier circuit 11 outputs the DC voltage E1, so that the battery does not discharge charge. If the power is cut off, the battery
Due to the voltage EB1 (=E1) of VB1, a DC voltage of -E1 is applied to the piezoelectric element flapper, and burnout is realized.

As another example, as shown in FIG. 4, a series circuit consisting of a battery VB2 and a diode d3 is connected between the +V line and the common line of the electro-pneumatic converter shown in FIG. The +V power source and the voltage of the battery VB may be supplied to the oscillation circuit 8 in parallel. In this embodiment of the electro-pneumatic converter, when the input current Ii is cut off, +V
The DC voltage of battery VB2 becomes higher than that of the line,
The oscillation circuit is driven by the battery VB2, a DC voltage of +E1 is derived to the full-wave rectifier circuit 10, and a voltage of -E1 is applied to the piezoelectric element flapper 2, so that burnout is also achieved. When the input current Ii exists, the oscillation circuit 8 is operated by the +V power supply, so the charge in the battery VB2 is not discharged. According to this embodiment, since the voltage of the battery VB2 is boosted by the oscillation circuit 8, a lower battery voltage is required than when connecting the battery directly to the piezoelectric flapper 2, and conversely, batteries with the same electromotive force can be used. In this case, a wide span applied voltage E1 can be obtained.

(F) Effect According to the present invention, when no input electrical signal is applied, a DC voltage of negative polarity is forcibly applied to the piezoelectric element flapper from a separately provided DC voltage source. Burnout can be achieved.

[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 circuit diagram applied to an electro-pneumatic converter as an embodiment of this invention, and Figs. FIG. 6 is a circuit diagram applied to an electro-pneumatic converter according to another embodiment of the 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, RA: Resistor, CA:
Capacitor, VB1, VB2: battery.

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 that applies to the piezoelectric element in a manner that cancels out the DC voltage of the piezoelectric element; 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 converting the output pressure into an electric signal, a conversion circuit for converting the output pressure into an electric signal, and 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. a feedback circuit; and a third DC voltage source that applies a DC voltage having the same value and the same polarity as the constant DC voltage to the piezoelectric element in place of the first DC voltage source when the input electric signal is not applied. An electro-pneumatic converter consisting of 2. The third DC voltage source is composed of a resistor and a capacitor connected in series, and the capacitor is charged with the DC voltage applied from the first DC voltage source while the input electric signal is applied. 2. The electro-pneumatic converter according to claim 1, wherein the charging voltage is applied to the piezoelectric element when the input electric signal is not applied. 3. The electro-pneumatic converter according to claim 1, wherein the third DC voltage source is a battery. 4. The first DC voltage source includes a first oscillation circuit that oscillates with a constant amplitude, and a first rectifier circuit that rectifies the oscillation output of the first oscillation circuit, and
The third DC voltage source includes a second oscillation circuit whose amplitude changes according to the input electric signal, and a second rectifier circuit that rectifies the oscillation output of the second oscillation circuit. a battery, a diode that supplies a DC voltage from the battery to the first oscillation circuit when the input electrical signal is not applied; and the first oscillation circuit.
2. The electro-pneumatic converter according to claim 1, comprising: an oscillation circuit; and said first rectifier circuit.