JPH0341767B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electro-pneumatic converter using an electrostrictive element as a nozzle flapper.

Until now, we have constructed a nozzle flapper using an electrostrictive element, applied an input voltage (DC voltage) to this electrostrictive element, and caused strain in the electrostrictive element according to the applied voltage. An electric/pneumatic converter has been proposed in which a nozzle opening is opened and closed to obtain back pressure according to the input voltage. However, the previously proposed electro-pneumatic converters described above have the disadvantage that the displacement of the nozzle flapper is small because the voltage applied to the electrostrictive element is a DC voltage.

An object of the present invention is to provide an electro-pneumatic converter which eliminates the drawbacks of the previously proposed electro-pneumatic converters mentioned above, allows a large displacement of the nozzle flapper, and can drive the nozzle flapper in a stable position.

In order to achieve the above object, the electro-pneumatic converter of the present invention uses an AC voltage whose frequency changes depending on the input voltage and whose instantaneous value changes over time like a triangular wave, sawtooth wave, sine wave, etc. A circuit is provided to generate
The change range of the signal frequency of this AC voltage generation circuit is set to be near the mechanical resonance frequency of the electrostrictive element and either lower or higher than this resonance frequency, and the frequency due to changes in the input voltage is By changing the displacement amplitude value of the nozzle flapper in response to a change in the nozzle, the ratio of the nozzle fully closed time is changed to obtain a back pressure corresponding to the input voltage.

The present invention will be explained in detail below with reference to embodiments shown in the drawings.

FIG. 1 is a block diagram of an electric/pneumatic converter showing one embodiment of the present invention. In the figure, input terminal 1
The input voltage Vi is applied to a and 1b. 2 is a PI regulator with capacitor C1,
This circuit, which is composed of C2, a resistor R, and an operational amplifier 3, is already a well-known circuit. The output of PI regulator 2 is connected to voltage/frequency converter 4
It is now being added to This voltage/frequency converter 4 is adapted to output an alternating current signal of a frequency corresponding to the voltage value applied to the input side (see FIG. 2). In this embodiment, the AC signal output from the voltage/frequency converter 4 is a triangular wave. A triangular wave signal output from the voltage/frequency converter 4 is applied to a nozzle flapper 5. The nozzle flapper 5 includes an electrostrictive element 6a,
6b is constructed in such a manner that a thin metal plate 7 is sandwiched between the metal plates 7 in the shape of a sandwich. A triangular wave signal from the voltage/frequency converter 4 is applied to the electrostrictive elements 6a and 6b, and the thin metal plate 7 is grounded. Furthermore, one end of the nozzle flapper 5 is cantilevered on the support part 8, and the protrusion 7a of the thin metal plate 7 at the other end vibrates in response to the applied alternating current voltage.

On the other hand, the air supply pressure applied from the air supply port 9 is applied to a pilot valve 10 and is also supplied to a nozzle 12 via a throttle 11. The nozzle 12 is disposed opposite to the protrusion 7a so that the blowhole is opened and closed by the flapper 5. The back pressure from the nozzle 12 is converted into output pressure by the pilot valve 10 and is led out from the output port 13 and applied to the pressure sensor 14. The pressure sensor 14 outputs an electrical signal according to the applied output pressure, and feeds this back to the input of the operational amplifier 3.

Assuming that the mechanical resonance frequency of the electrostrictive element is fmr, the signal of frequency fmr is transmitted to the electrostrictive element 6 as shown in Fig. 3.
When the voltage is applied to ports a and 6b, the tip of the nozzle flapper 5 is displaced the most. In this embodiment, the highest value of the signal frequency output from the voltage/frequency converter 4
Both fmax and minimum value fmin are mechanical resonance frequencies.
It is configured to enter the low frequency side of FMR. With this configuration, it is possible to obtain a displacement of the flapper that is proportional to the frequency of the signal voltage applied to the nozzle flapper 5, that is, the input voltage. In addition, when the tip 7a of the nozzle flapper 5 is free (when no AC voltage is applied), the tip 7a and the nozzle 12
The air gap d between the two and the displacement at the signal frequency fmin is
I'm trying to make it even smaller.

Next, the operation of the electro-pneumatic converter of the embodiment configured as above will be explained.

Now, the lowest voltage that can be controlled is sent to the voltage/frequency converter 4 via the input terminals 1a and 1b and the PI regulator 2.
If Vmin is added, the signal frequency of the output triangular wave will be fmin (see Figure 2). The signal voltage waveform at this time is illustrated as a in FIG. 4.
Since the signal frequency fmin in this case is far from the resonance frequency fmr, the displacement of the nozzle flapper 5 is small, and if the nozzle 12 is not provided, the displacement is the distance between the free potential of the nozzle flapper 5 and the nozzle 12 position. The period greater than d is t1. However, since the nozzle 12 is provided, the nozzle flapper 5 remains in the position of the nozzle 12 during this period t1, as shown in FIG. 5A.
That is, the nozzle 12 is fully closed by the nozzle flapper 5 for a period t1 with respect to the period T1 of the triangular wave.

On the other hand, when the maximum controllable voltage Vmax is applied to the voltage/frequency converter 4, the signal frequency of the triangular wave becomes fmax (see FIG. 2) in proportion to the input voltage. The signal voltage waveform in this case becomes b shown in FIG.
Since the signal frequency fmax is close to the resonant frequency fmr, if a triangular wave of this frequency fmax is applied to the nozzle flapper 5, it would vibrate with a large amplitude if the nozzle 12 were not present. Since the nozzle 12 is provided, the nozzle flapper 5 is connected to the nozzle 12.
However, as shown in FIG. 5B, the period during which the nozzle 12 is fully closed with respect to the period T2 of the triangular wave is t2. Nozzle 12 for period T
Comparing the ratio of the period t during which the is fully closed, the frequency
At fmin and frequency fmax, t1/T1<t2/T2. In other words, the fully closed time ratio is greater when the signal of frequency fmax is applied. The voltage Vn applied to the voltage/frequency converter 4 is Vmin<Vn<
In the case of Vmax, the nozzle fully closed time ratio is also t1/
T1<tn/Tn<t1/T2.

As described above, as the input voltage increases, the signal frequency increases, and as the frequency increases, the fully closed time ratio of the nozzle 12 increases. When the fully closed time ratio of the nozzle 12 increases, the nozzle back pressure also increases integrally, and the output air pressure of the pilot valve 10 increases accordingly. The output air pressure of the pilot valve 10 is derived from the output port 13 as an output pressure, but the pressure sensor 1
4, it is converted into an electrical signal according to the output pressure, and is fed back to the operational amplifier 3 of the PI regulator 2 to balance the voltage corresponding to the input voltage fed back output pressure.

Note that the back pressure of the nozzle 12 pulsates because the electrostrictive elements 6a and 6b of the nozzle flapper 5 are driven by an alternating current signal, but because the pilot valve 10 has a large capacity and the throttle 10 is provided, the pulsations extend to the output pressure. No worries.

Further, in the above embodiments, a triangular wave was used as an example of the AC signal, but the AC signal may be any signal whose instantaneous value changes over time, and may be a sawtooth wave, a sine wave, etc. In the above embodiments, the nozzle flapper including the electrostrictive element has a cantilevered structure, but a double-sided structure or a fixed circumferential structure may also be used.

Furthermore, in the above embodiment, the frequency change range of the AC signal in response to a change in input voltage is set to be on the low range side near the mechanical resonance frequency of the electrostrictive element, but this is conversely set to be on the high range side. It's okay.

As described above, according to the electro-pneumatic converter of the present invention, the frequency of driving the electrostrictive element constituting the nozzle flapper changes according to the input voltage, and the frequency is close to the mechanical resonance frequency of the electrostrictive element. Since the operation is performed using an AC signal, it is possible to obtain a large displacement in the nozzle flapper with a small input voltage, and the back pressure is determined by the time ratio during which the nozzle is fully closed.
The concerns that the stability of the entire loop would be affected by changes in temperature, fluctuations in supply pressure, and tilt due to the flapper's own weight, which were problems caused by the small displacement of air converters, have been eliminated, and the stability of the entire loop has been eliminated. You can get an empty transducer.

[Brief explanation of drawings]

Fig. 1 is a block diagram of an electric/pneumatic converter showing one embodiment of the present invention, and Fig. 2 shows the input voltage/frequency of the voltage/frequency converter used in the electric/pneumatic converter of the embodiment shown in Fig. 1. Figure 3 is a diagram showing the frequency and displacement characteristics of a nozzle flapper using an electrostrictive element, and Figure 4 is a triangular wave signal applied to the electrostrictive element of the electro-pneumatic converter of the embodiment shown in Figure 1. A diagram showing an example waveform of
FIG. 5 is a diagram showing the displacement of the nozzle flapper when the triangular wave signal shown in FIG. 4 is applied.
FIG. 5A shows a case where the signal a shown in FIG. 4 is applied, and FIG. 5B shows a case where the signal b shown in FIG. 4 is applied. 1a, 1b: Input terminal, 2: PI controller, 3:
Operational amplifier, 4: Voltage/frequency converter, 5: Nozzle flapper, 6a, 6b: Electrostrictive element, 7: Thin metal plate, 7a: Projection of thin metal plate, 8: Support part, 9:
Air supply port, 10: Pilot valve, 11: Throttle, 1
2: Nozzle, 13: Output port, 14: Pressure sensor.

Claims (1)

[Claims] 1. A PI regulator that receives input voltage and feedback voltage and outputs a voltage according to the difference between the two voltages, and receives the output voltage of this PI regulator, and the instantaneous value changes over time at a frequency that corresponds to the voltage. An AC voltage generation circuit that generates an AC voltage, a nozzle flapper that includes an electrostrictive element and to which the AC voltage is applied, and a nozzle flapper that is disposed opposite to the vibrating part of the nozzle flapper and receives supply pressure and generates back pressure. a pilot valve that converts this back pressure into output pressure, and a pilot valve that receives the output pressure and converts it into a voltage signal and outputs the voltage as a feedback voltage.
a piezoelectric conversion circuit added to the PI regulator, the change range of the signal frequency of the AC voltage generating circuit is near the mechanical resonance frequency of the electrostrictive element, and is either lower or higher than the resonance frequency. By setting the displacement amplitude value of the nozzle flapper to change in response to a change in frequency due to a change in input voltage, the ratio of the fully closed time of the nozzle is changed to obtain back pressure in accordance with the input voltage. An electric/pneumatic converter characterized by: