JPS624902A - Electricity-air pressure converter - Google Patents

Abstract

PURPOSE:To increase electricity-air pressure gain by performing control of opening/closing of both a pressure leading nozzle which leads output air pressure and a pressure leading nozzle which communicated with the atmosphere by means of a plate-shaped piezoelectric element. CONSTITUTION:An atmosphere chamber 42 and a tightly closed chamber 43 are formed in the casing 41 of a selector valve 9, while bimorph type piezoelectric elements 44, 45 are fitted, in a cantilever condition of being supported, in respective chambers. An atmosphere hole 46 is drilled in the atmosphere chamber 42, and a fluid passage 48 leading to said chamber 42 is formed in the tightly closed chamber 43, while a pressure leading nozzle 47 is formed on the atmosphere chamber 42 side of the fluid passage 48 so as to contact the mobile end 44A of the piezoelectric element 44. On the other hand, a pressure leading nozzle 50, which is made so as to contact the mobile end 45A of the piezoelectric element 45 and to which the output air pressure is led, and a through hole 53 for outputting air pressure are formed in the tightly close chamber 43.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electric to pneumatic converter used for process control and the like.

[Conventional technology]

Conventional electro-pneumatic converters convert electrical signals to pneumatic signals by converting them to nozzle back pressure. For example, in the invention disclosed in Japanese Patent Publication No. 59-25962, a piezoelectric element is used in the nozzle flapper, and the nozzle flapper, which is arranged so as to come into contact with the nozzle opening, is displaced according to an input signal, thereby increasing the gap between the nozzle opening and the nozzle flapper. The opening degree of the nozzle is controlled to change the nozzle back pressure. In addition, in the device disclosed in Japanese Utility Model Application Publication No. 58-130105, instead of controlling the opening degree of the gap between the nozzle flapper and the nozzle opening, the nozzle flapper is vibrated near its resonance frequency, and the nozzle flapper is vibrated in one period according to the input signal. The nozzle back pressure is changed by controlling the ratio between the fully open time and the fully closed time.

[Problem that the invention seeks to solve]

However, in any of the above-mentioned methods, since the method converts an electrical signal into nozzle back pressure, there is a problem in that a sufficient gain cannot be obtained for the input signal.

[Means for solving problems]

The electric-pneumatic converter of the present invention has been made in view of the above problems, and is provided with a first nozzle communicating with the air pressure supply path, a second nozzle communicating with the atmosphere, and an output hole. When no voltage is applied, the tip of the sealed chamber is the first
A first plate-shaped piezoelectric element is cantilevered so that it closes a nozzle and opens the first nozzle when a voltage is applied, and its tip closes a second nozzle when no voltage is applied. The switching valve includes a second plate-shaped piezoelectric element that is cantilevered so that the tip part opens the second nozzle when a voltage is applied, and the switching valve has a first and second plate-shaped piezoelectric element. The electric signal is converted into a pneumatic signal by applying a signal obtained by pulse width modulating the deviation between the input signal and the feed hack signal and its inverted signal to the piezoelectric element.

[Effect]

In the switching valve, when the first nozzle to which the output air pressure PO is introduced and the second nozzle communicating with the atmosphere are opened and closed by a plate-shaped piezoelectric element, the air pressure in the sealed chamber changes and the output air pressure PO also changes significantly.

〔Example〕

Hereinafter, the present invention will be described in detail along with examples.

FIG. 1 is a block diagram showing one embodiment of the present invention. The input circuit 1 is a circuit that inputs a current signal of 4 to 20 mA from input terminals 2 and 3 and converts it into a voltage signal, and
It also functions as a power supply circuit for other circuits. FIG. 2 shows a specific circuit of the input circuit 1, and includes an operational amplifier 23.
．． Transistor Tr 1. A constant current circuit 21 is constituted by a resistor R3 and a constant voltage source E1, and an operational amplifier 24. Transistor T r 2 , resistors R1, R2, and constant voltage source E
2 constitutes a constant voltage circuit 22. 25 is an operational amplifier, R4-R8 are resistors, and 26 is an output terminal.

The operational amplifier 4 outputs the deviation between the input signal Va from the input circuit 1 and the feedback signal vb from the amplification means 5, which will be described later, as a voltage value, and its output signal line is connected to the negative terminal of the comparator 6 and the deviation signal, which will be described later. It extends to the determining means 13.

An output signal line of a reference waveform generation circuit 7 that generates a stable triangular wave signal is connected to the positive terminal of the comparator 6. The output signal line of the comparator 6 is extended to one input terminal of the AND gate circuit 16 via one input terminal of the AND gate circuit 15 and the NOT circuit 14, respectively. 14 constitutes the pulse width modulation means 8.

The reference waveform generating circuit 7 is a circuit that generates a stable triangular wave signal as described above, and a specific circuit thereof is shown in FIG. In the figure, 31 is an operational amplifier, which together with a capacitor 32 constitutes an integrator. 33 is an operational amplifier constituting a comparator, R1, R2 and R3, R4 are resistors constituting a voltage divider, and RO is a resistor. The switch 34 is activated by the output of the operational amplifier 33.
is controlled, and the reference voltage power supply 35 and the common terminal side 36 are switched and connected to the inverting input of the operational amplifier 31. With this configuration, a triangular wave signal with extremely stable period and amplitude can be obtained.

The output signal line of the deviation determination means 13 is connected to the AND gate circuit 15.
．． 16 to the other terminal of the operational amplifier 4, that is, the deviation (Va
-Vb) is near zero, a signal is output to close the AND gate circuits 15 and 16. Specifically, the voltage value ε is −δ. ≦ε≦δ. It outputs a signal to close the AND gate circuits 15 and 16 when (±δ0: required accuracy) is satisfied, and is composed of a known comparator. Note that the output signal lines of the controllers 15 and 16 are connected to input terminals 58 and 59 of the switching valve 9, respectively.

The switching valve 9 is a device that switches and controls the flow of air according to the output signal of the pulse width modulating means 8, and its specific configuration is shown in the sectional view of FIG.

The switching valve 9 has an atmospheric chamber 42 and a sealed chamber 43 in the housing 41.
A bimorph type piezoelectric element 4,4,45 is installed in a cantilevered state inside each chamber 42,43. An atmospheric hole 46 is bored in the atmospheric chamber 42, and the interior of the atmospheric chamber 42 is constantly in communication with the atmosphere through the atmospheric hole 46. Further, the atmospheric chamber 42 and the sealed chamber 43 are communicated with each other by a fluid passage 48.
A pressure guiding nozzle 47 is formed on the atmospheric chamber 42 side of 8. This pressure nozzle 47 is a bimorph type piezoelectric element 44.
When the movable end 4.4A swings as shown by arrow A, the pressure guiding nozzle 47 is opened and closed.

In the sealed chamber 43, a pressure nozzle 50 communicating with the fluid passage 49 is provided at a position facing the movable end 45A of the bimorph piezoelectric element 45.

This pressure guiding nozzle 50 is opened and closed by swinging the movable end 45A as shown by arrow B. Note that the fluid passage 49 communicates with an air pressure supply path 51 formed in the fixed portion 57, and a supply air pressure Ps is constantly applied thereto. Further, the sealed chamber 43 is provided with an output hole 53 that communicates with a pneumatic pressure output path 52 similarly formed in the fixing portion 57 . Note that the tips of the bimorph piezoelectric elements 44 and 45 close the nozzles 47 and 50, respectively, when no voltage is applied, and are displaced upwardly by applying a voltage to the input terminals 59 and 59, respectively. In addition, 54 in the figure is the closed room 4.
3 is a gasket for sealing, and 55 and 56 are O-rings for sealing the housing 41 and the fixed part 57, respectively.

Air pressure PO outputted from the switching valve 9 configured in this way is given to a pilot relay 10. The pilot relay 10 is an existing means for amplifying an input air pressure signal and converting it into a standard air pressure signal.

The output of this pilot relay 10 is led to an output port 11, and the air pressure there becomes the output air pressure to be finally extracted.

Further, the output of the pilot relay 10 is also guided to a pressure sensor 12. The pressure sensor 12 is a means for converting air pressure into an electric signal, and the output electric signal is amplified by the amplification means 5 and inputted to the positive terminal of the operational amplifier 4.

Next, the operation of this embodiment configured as described above will be explained.

When a current signal varying within 4 to 20 mA is input from terminals 2 and 3, it is converted into a voltage signal Va in input circuit 1. This signal Va is sent to an amplifying means 5 which is a value obtained by converting the current output air pressure into an electrical signal in a differential amplifier 4.
is compared with the output signal vb of. That is, operational amplifier 4
outputs a voltage value ε corresponding to the deviation (Va-Vb) between both signals, and waveform a in FIG. 5(a) shows the deviation signal ε which is the output of this operational amplifier 4.

This deviation signal ε is input to the comparator 6 and compared with the triangular waveform reference signal (waveform b in FIG. 5(a)) output from the reference waveform generating circuit 7. In the comparator 6, when the reference signal has a larger value than the deviation signal ε, the output becomes "H (on)", and when it is smaller, the output becomes "L (off)". In other words, in the output of the comparator 6, as shown in FIG. A pulse width modulated signal as shown in is obtained.The output of the knot circuit 14 is the inverted signal.

Therefore, in the switching valve 9, when the output pulse of the comparator 6 is H'', the nozzle 50 is "open".

The nozzle 47 is in the "closed" state, the supply air pressure Ps is applied to the sealed chamber 43, and the switching valve 9 is in the on state. Conversely, when the output pulse of the comparator 6 is L'', the nozzle 50
is "closed" and the nozzle 47 is "open", the supply air pressure Ps is cut off, and the air in the sealed chamber 43 flows out through the nozzle 47 into the atmospheric chamber 42 communicating with the atmosphere, and the switching valve 9 is opened. Turns off.

Therefore, when an on/off signal as shown in FIG. 5(b) is input from the comparator 6, the air pressure in the sealed chamber 43 changes, and the output air pressure Po in the air pressure output path
changes. That is, when the deviation signal ε is positive, the ON state of the switching valve 9 becomes longer than the OFF state, and the output air pressure PO from the air pressure output path 52 increases. Conversely, when the deviation signal ε is negative, the off state becomes longer and the output air pressure P
.

decreases. Note that the sealed chamber 43 has an output air pressure P.

It functions as a volume chamber to smooth the flow and alleviate pulsating flow caused by pulse width modulation.

Also, the deviation signal ε is near zero, that is, −60≦ε≦δ.

When this occurs, the deviation determining means 13 closes the AND gate circuits 15 and 16, so that voltage application to both piezoelectric elements 44 and 45 is cut off, and both nozzles 47 and 50 are closed. That is, the equilibrium pressure output is maintained in a state where the air consumption amount in the switching valve 9 is zero.

The output air pressure Po obtained in this way is the pressure sensor 1
2, which is converted into an electrical signal and fed to the operational amplifier 4 via the amplifying means 5. That is, this foot hack signal acts in the direction in which the deviation signal ε becomes zero. Such feedbank control makes it possible to obtain a stable output air pressure Po according to the human input signal.

〔Effect of the invention〕

As explained above, according to the electric-pneumatic converter of the present invention, the switching valve outputs an output by controlling the opening and closing of the pressure guiding nozzle through which the output air pressure Po is guided and the pressure guiding nozzle communicating with the atmosphere using a plate-shaped piezoelectric element. Since the air pressure Po is changed, the electrical-pneumatic pressure gain can be significantly increased compared to the electrical-pneumatic conversion method using nozzle back pressure.

Moreover, in the present invention, since the plate-shaped piezoelectric element is driven by a pulse width modulation signal, the effect of drift on the plate-shaped piezoelectric element is extremely small, and a high voltage power supply for compensating for drift is not required.

In addition, when the deviation signal between the input signal and the feedback signal is near zero, the operation of the plate-shaped piezoelectric element is stopped to maintain the balanced pressure output, so air consumption is small and compared to when the piezoelectric element is constantly vibrated. Thus, the life of the piezoelectric element can be extended.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a circuit diagram showing an example of the input circuit 1 in FIG. 1, and FIG. 3 is a circuit diagram showing an example of the reference waveform generation circuit 7 in FIG. 1. A circuit diagram, FIG. 4 is a sectional view showing the switching valve 9 of FIG. 1,
FIG. 5 is a signal waveform diagram showing the operation of the embodiment of FIG. 1. DESCRIPTION OF SYMBOLS 1... Input circuit, 4... Active amplifier, 6... Comparator, 7... Reference waveform generation circuit, 8...
・Pulse width modulation means, 9... Switching valve, 10... Pilot relay, 11... Output port, 12... Pressure sensor, 13... Deviation determination means, 44.45... Bimorph type Piezoelectric element, 47.50... pressure conducting nozzle.

Claims (1)

[Claims] A sealed chamber is provided with a first nozzle that communicates with the air pressure supply path, a second nozzle that communicates with the atmosphere, and an output hole, and when no voltage is applied, the tip of the nozzle closes the first nozzle and the voltage is reduced. A first plate-shaped piezoelectric element supported in a cantilever manner so that the tip opens a first nozzle when voltage is applied; the tip closes a second nozzle when voltage is not applied; and the tip closes the second nozzle when voltage is applied. a second plate-shaped piezoelectric element cantilevered so as to open a second nozzle; a pilot relay that converts an air pressure signal from the output hole into a standard air pressure signal; A pressure sensor converts the output pressure of this pilot relay into an electrical signal, and a pulse width modulation signal and its inverted signal corresponding to the deviation between the electrical signal from this pressure sensor and an external input signal are transmitted to the first and second switching valves, respectively. a pulse width modulation means for applying the pulse width modulation signal to the second plate-shaped piezoelectric element, and the pulse width modulation signal and its inverted signal to the first and second plate-shaped piezoelectric elements when it is detected that the deviation is substantially zero; An electric-pneumatic converter comprising: deviation determining means for stopping the supply of air.