JPH0445684B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electro-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 for the nozzle flapper, and the nozzle flapper, which is arranged so as to come into contact with the nozzle opening, is displaced in accordance with 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 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, with any of the above methods,
Since this method converts an electrical signal into nozzle back pressure, there was a problem in that it was not possible to obtain sufficient gain 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 includes plate-shaped piezoelectric elements 45 and 61 that are cantilever-supported in a sealed chamber 43 and whose tips swing when voltage is applied; The pressure conduction nozzle 50 opens when the first voltage H is applied due to the oscillating displacement of the piezoelectric element and closes when the second voltage L having a polarity different from that of the first voltage is applied, which connects the closed room and the atmosphere. Atmospheric control means 44, 61, 47 provided in the fluid passage 48 communicating with the air and closed when the first voltage is applied and opened when the second voltage is applied;
It has an output hole 53 led out from the sealed chamber to the outside, and a switch in which supply air pressure is applied from the pressure nozzle into the sealed chamber by applying a first voltage, and atmospheric pressure is brought into the sealed chamber by applying a second voltage. It has a valve 9, and converts an electrical signal into a pneumatic signal by applying a pulse-width modulated signal of voltage on both sides to the plate-shaped piezoelectric element of this switching valve to compensate for the deviation between the input signal and the feedback signal. .

[Effect]

In the switching valve, when the pressure guiding nozzle through which the supply air pressure Ps is introduced and the fluid path communicating with the atmosphere are controlled to open and close using a plate-shaped piezoelectric element and the atmosphere control means, the air pressure in the sealed chamber changes and the output air pressure Po increases. Change.

〔Example〕

Hereinafter, the present invention will be explained in detail together with examples.

FIG. 1 is a block diagram showing one embodiment of the present invention. Input circuit 1 connects input terminals 2 and 3 to 4~
This circuit inputs a 20mA current signal and converts it to a voltage signal, and also functions as a power supply circuit for other circuits. FIG. 2 shows a specific circuit of the input circuit 1, which includes an operational amplifier 23 and a transistor.
A constant current circuit 21 is configured from Tr1, resistor R3, and constant voltage source E1, and includes an operational amplifier 24 and a transistor.
A constant voltage circuit 22 is constituted by Tr2, resistors R1 and R2, and constant voltage source E2. 25 is an operational amplifier, R4 to R8 are resistors, and 26 is an output terminal.

The operational amplifier 4 receives the input signal Va from the input circuit 1.
and a feedback signal from the amplifying means 5, which will be described later.
It outputs the deviation from Vb as a voltage value,
Its output signal line extends to the inverting input terminal of comparator 6. Furthermore, the output signal line of a reference waveform generation circuit 7 that generates a stable triangular wave signal is connected to the non-inverting input terminal of the comparator 6, and the comparator 6 compares two input signal voltages and responds accordingly to the result. to a predetermined positive voltage (e.g. +5V) or a predetermined negative voltage (e.g. -
5V). That is, the comparator 6 and the reference waveform generation circuit 7 constitute a pulse width modulation means 8 for both-side voltage.

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 same figure, 3
1 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 R0 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 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 pressure 42 and a sealed chamber 43 in a housing 41, and bimorph piezoelectric elements 44 and 45 are mounted in a cantilevered state inside each chamber 42 and 43, respectively. An atmospheric hole 46 is bored in the atmospheric chamber 42.
As a result, the interior of the atmospheric chamber 42 is always in communication with the atmosphere. 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. This pressure guiding nozzle 47 is provided at a position facing the movable end 44A of the bimorph piezoelectric element 44, and as the movable end 44A swings as shown by arrow A, the pressure guiding nozzle 47 is opened and closed.

In the sealed chamber 43, the bimorph piezoelectric element 4
A fluid passage 4 is located at a position opposite to the movable end 45A of 5.
A pressure guiding nozzle 50 communicating with 9 is provided. This pressure guiding nozzle 50 is opened and closed by swinging the movable end 45A as shown by arrow B. In addition,
The fluid passage 49 communicates with an air pressure supply path 51 formed in the fixing part 57, where the air pressure is supplied.
Ps is always given. Also, in the sealed chamber 43, a pneumatic output path 5 formed in the fixed part 57 is also provided.
An output through hole 53 communicating with 2 is provided.
In the figure, 54 is a gasket for sealing the sealed chamber 43, and 55 and 56 are the housing 41 and the fixing part 5, respectively.
This is an O-ring that seals 7.

Bimorph piezoelectric elements 44 and 45 are driven in opposite directions by voltage application to input terminals 58 and 59. That is, by grounding the input terminal 59 and applying the output signal of the pulse width modulation means 8 to the input terminal 58, when the movable end 44A opens the pressure guiding nozzle 47, the movable end 45A closes the pressure guiding nozzle 50, and vice versa. When the movable end 44A closes the pressure guiding nozzle 47, the movable end 45A is driven to open the pressure guiding nozzle 50.

The air pressure Po output from the switching valve 9 configured as described above is applied to the pilot relay 10. 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 at the entrance/exit 1
1, and the air pressure here 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 compared in the operational amplifier 4 with the output signal Vb of the amplifying means 5, which is a value obtained by converting the current output air pressure into an electrical signal. In other words, the differential amplifier 4
Outputs Va−Vb. Waveform a in FIG. 5a shows the deviation signal Va-Vb which is the output of the operational amplifier 4.

This deviation signal Va-Vb is input to the comparator 6, and the reference waveform generating circuit 7 outputs a triangular waveform reference signal (waveform a in FIG. 5, waveform b).
compared to In the comparator 6, when the reference signal has a larger value than the deviation signal Va-Vb, the output becomes "H (positive)", and when it is smaller, the output becomes "L".
(negative)''. That is, at the output of the comparator 6, a pulse width modulated signal as shown in FIG. 5b is obtained.

As can be seen from the figure, when the deviation signal Va−Vb is near the zero point, the duty ratio of the output pulse of the comparator 6 is 1:1, and the deviation signal Va
-When Vb is positive, the “H” state becomes longer,
When it is negative, the "L" state becomes longer.

In the switching valve 9, when the output pulse of the comparator 6 is "H", the nozzle 50 is "open", and the nozzle 4
7 is in the "closed" state, 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", and the supply air pressure Ps is cut off, and the air in the sealed chamber 43 flows through the nozzle 47. The gas flows out into the atmospheric chamber 42 communicating with the atmosphere, and the switching valve 9 is turned off.

Therefore, when a pulse width modulation signal as shown in FIG. 5b 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 52 changes. That is, when the deviation signal Va−Vb is positive, the on state of the switching valve 9 becomes longer than the off state, and the pneumatic output path 5
The output air pressure Po from 2 increases. Conversely, when the deviation signal Va−Vb is negative, the off state becomes longer,
Output air pressure Po decreases.

Note that the sealed chamber 43 functions as a volume chamber that smoothes the output air pressure Po, and alleviates pulsating flow caused by pulse width modulation. Furthermore, since the output signal voltage of the pulse width modulation means 8 swings to both positive and negative sides, positive and negative voltages are alternately applied to the bimorph piezoelectric elements 44 and 45, respectively.
Polarization deterioration of the element is less likely to occur, and furthermore, the problem of drift, which occurs when the operating point shifts, does not occur.

This output air pressure Po is detected by the pressure sensor 12, and is converted into an electrical signal by the amplifying means 5.
The signal is fed back to the operational amplifier 4 via the amplifier 4. That is, this feedback signal acts in the direction in which the deviation signal Va-Vb becomes zero. Such feedback control makes it possible to obtain a stable output air pressure Po according to the input signal.

FIG. 6 is a sectional view showing another embodiment of the switching valve 9, and the same or corresponding parts as those of the switching valve shown in FIG. 4 are given the same reference numerals, and detailed explanation thereof will be omitted.

In this embodiment, a single bimorph piezoelectric element 61
This is used to switch fluids. Inside the sealed chamber 43 is a nozzle 50 through which the supply air pressure Ps is introduced.
and a nozzle 47 communicating with the atmosphere are provided so as to be spaced apart from each other and face each other, and a movable end 61A of a bimorph type piezoelectric element 61 supported in a cantilever is interposed between the two. Furthermore, an output hole 53 is bored in the upper part of the sealed chamber 43. In addition, 5
8 and 59 are input terminals to which the output pulse of the comparator 6 is applied; 62 is a bimorph piezoelectric element 61;
This is an insulating sealing material that maintains the base of the insulated state.

In the switching valve 9 configured as described above, when the output pulse of the comparator 6 is "H", the movable end 61A of the bimorph piezoelectric element 61 is displaced so as to close the nozzle 47 as shown in the figure. Therefore, the nozzle 50 is opened and the supply air pressure Ps is supplied to the sealed chamber 43. Conversely, when the output pulse of the comparator 6 is "L", the movable end 61A
is displaced so as to close the nozzle 50, and the nozzle 4
7 is released. Therefore, as soon as the supply air pressure Ps is cut off, the sealed chamber 43 is brought into communication with the atmosphere. From this operation, it can be seen that the output air pressure Po of this switching valve 9 has the same input/output relationship as that of the switching valve shown in FIG.

[Effects of the Invention] As explained above, according to the electro-pneumatic converter of the present invention, the pressure guiding nozzle through which the supply air pressure Ps is guided in the switching valve and the fluid passage communicating with the atmosphere are connected to the plate-shaped piezoelectric element and the atmospheric control device. Since the output air pressure Po is changed by controlling opening and closing by means and means, the electric-pneumatic pressure gain can be significantly increased compared to an electric-pneumatic conversion method using nozzle back pressure.

In addition, in the present invention, since the plate-shaped piezoelectric element is driven by a voltage on both sides with different polarities, that is, a pulse width modulation signal that swings positive and negative, the influence of drift on the plate-shaped piezoelectric element is extremely small, and the effect of drift on the plate-shaped piezoelectric element is extremely small. No high voltage power supply required. Furthermore, driving the piezoelectric element with a pulse width modulation signal having voltages on both sides has the effect of suppressing polarization deterioration of the piezoelectric element, which is effective in extending the life of the device.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention;
2 is a circuit diagram showing an example of the input circuit 1 in FIG. 1, FIG. 3 is a circuit diagram showing an example of the reference waveform generating circuit 7 in FIG.
5 is a signal waveform diagram showing the operation of the embodiment shown in FIG. 1, and FIG. 6 is a sectional view showing another example of the switching valve 9 shown in FIG. 1. DESCRIPTION OF SYMBOLS 1...Input circuit, 4...Operation 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, 44,
45... Bimorph type piezoelectric element, 47, 50... Pressure conduction nozzle.

Claims (1)

[Scope of Claims] 1. A plate-shaped piezoelectric element that is cantilever-supported in a sealed chamber and whose tip part swings when a voltage is applied.The plate-shaped piezoelectric element opens when a first voltage is applied due to the swinging displacement of the plate-shaped piezoelectric element, and the tip part swings when a first voltage is applied. a pressure-conducting nozzle that closes when a second voltage having a polarity different from that of the first voltage is applied; It has an atmosphere control means that opens when the second voltage is applied, and an output hole led out from the sealed chamber to the outside, and when the first voltage is applied, the pressure is supplied from the pressure nozzle to the sealed chamber. a switching valve that applies supply air pressure to the air and makes the inside of the sealed chamber atmospheric pressure by applying the second voltage; a pilot relay that converts the air pressure signal from the output hole into a standard air pressure signal; and an output of the pilot relay. a pressure sensor that converts pressure into an electrical signal; and a pulse width that applies a pulse width modulated signal having the first and second voltages to the switching valve corresponding to the deviation between the electrical signal from the pressure sensor and an external input signal. An electro-pneumatic converter, characterized in that it comprises modulation means.