JPH074401A - Electropneumatic converter and actuator system using electric-pneumatic converter - Google Patents

Abstract

PURPOSE:To provide an electric-pneumatic converter allowing electric-pneumatic conversion with accuracy for a long period of time. CONSTITUTION:In an electric pneumatic converter 20, a nozzle flapper mechanism 74 is provided with a flapper 24 and a discrete bimorph type piezoelectric element 80. The flapper 74 is abutted to a nozzle 72 by means of a spring member 82. Thus, in a normal state, no pulse application is required to the bimorph type piezoelectric element 80, exerting no mechanical action. In addition, the bimorph type piezoelectric element 80 is abutted to the flapper 74 only when a positive pulse is applied to the bimorph type piezoelectric element 80 to space the flapper 74 from the nozzle 72. In this case, electrostriction is prevented by applying positive and negative pulses to the bimorph type piezoelectric element 80 with the respective pulse widths made equal in sum to each other.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electro-pneumatic conversion device and an actuator system using the electro-pneumatic conversion device, which can convert an electric signal into an air output with high accuracy by using a nozzle flapper mechanism. The present invention relates to an electro-pneumatic conversion device capable of preventing the effects of creep, electric strain, etc. of a piezoelectric element even during long-term use, and an actuator system using the same.

[0002]

2. Description of the Related Art Conventionally, a valve is controlled based on the output of a control device. In these control valves, an operation device such as an electro-pneumatic positioner that feeds back the position of the stem of the valve to an electro-pneumatic conversion unit that converts an electric control signal into air pressure is usually used.

A conventional mechanism of such an electro-pneumatic converter is shown in FIG. That is, the movable iron piece is operated by driving the torque motor 2, the back pressure of the nozzle flapper 4 is adjusted, and the air pressure supplied to the external actuator 8 by the pilot relay 6 is adjusted. At this time, the position of the pilot relay 6 is detected by the position detection unit 10 and used as a feedback signal, and the torque motor 2 is controlled by a deviation signal from the control signal.

However, since the movable iron piece type torque motor 2 has a large mass, there is a problem that oscillation or hunting is likely to occur.

In addition, a microprocessor is used as a control device to achieve intelligentization. In this case, it is necessary to drive the torque motor with lower power consumption.

In order to solve such a problem, a bimorph type piezoelectric element has been used in place of the torque motor. This is because the electro-pneumatic conversion unit is further lightweight and has low power consumption.

An example using the bimorph type piezoelectric element is as follows:
It shows in FIG. That is, when the applied voltage is 0, the flapper 14 formed of the bimorph type piezoelectric element comes into contact with the nozzle 18 under the action of the spring 16 and constitutes a so-called non-bleed type. When a positive voltage is applied to the flapper 14, the flapper 14 is displaced toward the position A to separate the flapper 14 from the nozzle 18, as shown in FIG. By repeating this operation, it functions as a nozzle flapper mechanism.

[0008]

However, in the electro-pneumatic conversion section used in the above bimorph type piezoelectric element,
Even in the equilibrium state (applied voltage 0), the flapper 14
Under the action of the spring 16, it is forcibly curved toward the nozzle 18. The constant application of force in the bending direction causes the flapper 14 to creep as a result. In addition, as shown in FIGS. 8 and 9, since only one voltage (positive voltage) is applied and the applied voltage is constantly displaced in one direction, stress is applied to the flapper 14 at substantially the same position, causing creep. And the displacement amount d2 changes due to the influence of polarization.

Due to such a cause, the position of the flapper 14 in the equilibrium state in which the voltage is not applied is displaced, the conversion gain of the nozzle flapper mechanism is changed, and the entire system becomes unstable, and the control range may be narrowed. is there.

The present invention has been made in order to solve this kind of problem, and it is possible to accurately measure the electric power over a long period of time.
An object of the present invention is to provide an electro-pneumatic conversion device that performs air-conversion and an actuator system using the same.

[0011]

In order to achieve the above-mentioned object, the present invention provides an electro-pneumatic conversion device for changing the nozzle back pressure by a non-bleed type nozzle flapper mechanism to open and close a valve element. A flapper that changes the back pressure of the nozzle back pressure chamber by contacting with and separating from the nozzle and is constantly urged in the nozzle direction by an elastic member,
With respect to the flapper, only when a pulse of either positive or negative polarity is applied, a bimorph type piezoelectric element that abuts on the flapper and is displaced, and a control mechanism that applies a positive or negative pulse to the bimorph type piezoelectric element, It is characterized by including.

In the electro-pneumatic conversion device, it is preferable that the elastic member is arranged on the axis of the nozzle.

Further, it is more preferable that the drive signals, in which the pulses applied from the control mechanism to the bimorph type piezoelectric element are continuous, have the same amplitude and the sum of the positive and negative pulse widths is the same. .

Furthermore, the electro-pneumatic conversion device is used as a pilot valve of an actuator, one electro-pneumatic conversion device is on the fluid supply side of the actuator, and the other electro-pneumatic conversion device is on the fluid discharge side of the actuator. It can be used as an installed actuator system.

In this case, a detection device for detecting the fluid pressure acting on the actuator or the displacement amount of the actuator is provided, the output signal of the detection device is input to the control device, and the input signal externally input. Then, the bimorph type piezoelectric element is controlled based on the deviation signal.

Further, in the above actuator system, it is preferable that a fail safe device having a power source is provided in the control device and the power source is connected to an electro-pneumatic conversion device on a supply side or an exhaust side corresponding to the actuator system. is there.

More preferably, the power source is a battery or a capacitor.

[0018]

In the electro-pneumatic conversion device according to the present invention, since the flapper and the bimorph type piezoelectric element are separated, even if the flapper is a non-bleed type in which the flapper is always urged toward the nozzle side by the elastic member, the bimorph type No mechanical action is exerted on the piezoelectric element by the elastic member, and creep or the like does not occur during long-term use. In particular,
By disposing the elastic member on the axis of the nozzle, the flapper can prevent creep without generating a moment by the elastic member. Further, in the normal state (non-bleed state), the flapper is pressed against the nozzle by the elastic member, and it is necessary to separately apply a pulse to the bimorph type piezoelectric element in order to bring the flapper into contact with the nozzle. There is no. Therefore, it is possible to prevent electrical distortion and the like that occur when the pulse having only one polarity is continuously applied to the bimorph type piezoelectric element.

Further, the bimorph type piezoelectric element is constructed so that the flapper is displaced only when a pulse of one polarity is applied while being pressed against the tip of the nozzle. That is, when the pulse of the other polarity is applied, the flapper does not move. Therefore, in the non-bleed state, the drive signal composed of continuous pulses can be configured so that the sum of the pulse widths of positive and negative polarities and the same amplitude becomes the same, and this drive signal is transmitted to the bimorph type piezoelectric element. By applying, it is possible to prevent the occurrence of electrical strain due to polarization or the like.

If the electro-pneumatic conversion device is used as a pilot valve on the supply side and exhaust side of the actuator and feedback control is performed in particular, an actuator system can be constructed that operates accurately for a long period of time.

Further, in the above-mentioned actuator system, since a fail-safe device composed of a battery or a charging unit is provided as a power source, when the system is powered off or the like, a voltage is applied to the electro-pneumatic conversion device to drive it, and the actuator is driven. Since air can be supplied to or exhausted from the actuator and the actuator can be maintained in an appropriate state, the safety of the entire system can be further improved.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The electro-pneumatic converter according to the present invention and the actuator system using the same will be described below in detail with reference to the accompanying drawings.

First, the electro-pneumatic conversion device will be described, and subsequently, the actuator system (electro-pneumatic positioner) incorporating the electro-pneumatic conversion device will be described.

As shown in FIG. 1, the electro-pneumatic conversion device 20.
Is composed of a valve mechanism 22 and a nozzle flapper mechanism 24.

The valve mechanism 22 has a first chamber 30 and a second chamber 32 which communicate with the main body 26 through the hole 28.
A diaphragm 34 is provided in the first chamber 30, so that the upper half of the first chamber is the nozzle back pressure chamber 3
It becomes 6. A supply passage 38 communicating with a compressed air supply source (not shown) is connected to the nozzle back pressure chamber 36,
A pressure reducing valve 40 and a fixed throttle 4 are provided along the supply passage 38.
1 is provided. The pressure reducing valve 40 adjusts the elastic force of the first spring member 46 that biases the piston member 44 by screwing the knob 42. Piston member 4
The second spring member 50 is provided between the valve seat 4 and the valve seat 48, and the valve body 52 is provided by the third spring member 54 provided at the lower portion of the valve seat 48.
Is abutted on the shaft portion of.

Therefore, in the pressure reducing valve 40, when the pressure in the nozzle back pressure chamber 36 is higher than the pressure on the compressed air supply side, the cross-sectional area of the piston member 44 is larger than the cross-sectional area of the valve body 52, and therefore the upward direction. The piston member 44 is urged to move the valve body 52, which is urged by the third spring member 54, to follow the displacement, to be seated on the valve seat 48, and to block the communication with the compressed air supply side. On the other hand, when the pressure in the nozzle back pressure chamber 36 is lower than the pressure on the compressed air supply source side, the valve body 52 is separated from the valve seat 48 by the elastic force of the first spring member 46, and the nozzle back pressure chamber 36 communicates with the compressed air supply source side.

Next, the valve body 56 disposed in the first chamber 30 and the second chamber 32 comprises a flange portion 58 and a cylindrical portion 60, and the cylindrical portion 60 is axially displaced within the hole portion 28. The flange portion 58 is freely inserted, and is in contact with the diaphragm 34 by the elastic force of the spring member 62. Therefore, due to the displacement of the diaphragm 34, the cylindrical portion 60 of the valve body 56 is seated on or separated from the valve seat 64, and the supply passage 66 and the exhaust passage 68 communicating with the second chamber 32 are communicated.
The communication control is performed by the cylindrical portion 60.

On the other hand, the nozzle flapper mechanism 24 includes a nozzle 72 provided in communication with the nozzle back pressure chamber 36, a flapper 74 abutting against the end of the nozzle 72, and a support body 76 for movably supporting the flapper 74. A protrusion 78 mounted on the support 76 and formed on the lower surface of the flapper 74.
Type piezoelectric element 80 separated by a predetermined distance from
And a spring member 82 that constantly biases the flapper 74 toward the nozzle 72. The bimorph type piezoelectric element 80 is bent to the flapper 74 side when a positive voltage is applied, and is bent to the opposite side when a negative voltage is applied.

Now, an electro-pneumatic positioner 92 incorporating the electro-pneumatic conversion device 20 having such a structure will be described with reference to the block diagram of FIG.

The electro-pneumatic positioner 92 includes a power source section 94,
A microprocessor (hereinafter referred to as a μ processor) 98 to which a control signal is input from the power supply unit 94 via an A / D converter 96, and the power supply unit 94 and the μ processor 9
The communication I / F 100 connected to the No. 8 and the supply / exhaust electro-pneumatic converters 20a and 20b for driving the nozzle flapper mechanism 24 to operate the valve mechanism 22 based on the drive signal from the μ processor 98 are provided. Has been. In addition,
The electro-pneumatic converters 20a and 20b are respectively connected to a compression supply source and an exhaust port (not shown), and also connected to the external actuator 102 through a pipe line 104. The position detector 110 detects the amount of displacement of the stem 108 that controls the valve body 106 of the external actuator 102.
A position detection signal is input to the μ processor 98 via the / D converter 112, and signal processing is performed based on the deviation from the control signal.

A fail-safe section 114 is provided so as to be connected to the power supply section 94. The fail safe section 1
Reference numeral 14 denotes a charging unit 116 that charges a part of electric power of a control signal of the power supply unit 94 and an electro-pneumatic conversion device 20 when the power is cut off.
The control signals from the power supply monitoring unit 118 and the μ processor 98 that cause a current to flow through a and 20b cause the electro-pneumatic conversion device 20a,
Switch part 12 for selectively passing current to any of 20b
It consists of 0 and. The charging unit 116 may be replaced with a lithium battery or the like.

The electro-pneumatic positioner 9 thus constructed
2 is operated as follows. First, an external control signal is input to the μ processor 98 via the power supply unit 94 and the A / D converter 96. That is, the pressure of the pipe line 104 is increased to displace the stem 108 of the external actuator 102 (see FIG. 3A), and thereby the valve body 106.
A control signal is input so as to control. continue,
In the electro-pneumatic conversion device 20a, section C in FIG.
Then, positive and negative pulses having the same amplitude and different pulse widths as shown in FIG. 3B are applied as drive signals from the μ processor 98 to the bimorph type piezoelectric element 80 of the electro-pneumatic converter 20a. Therefore, when a positive pulse is applied to the bimorph piezoelectric element 80, as shown in FIG. 4, the bimorph piezoelectric element 80 abuts on the protrusion 78 of the flapper 74 and presses it upward, so that the flapper 74 is pressed. Separates the flapper 74 from the nozzle 72 against the elastic force of the spring member 82. Therefore, the nozzle back pressure chamber 3
At 6, the pressure drops and the diaphragm 34 is displaced in the Z1 direction. As a result, the spring member 62 causes Z
The valve body 56 having the flange portion 58 biased in one direction is also displaced in the Z1 direction. As a result, the cylindrical portion 60 of the valve body 56 is separated from the valve seat 64, and the supply passage 66 and the exhaust passage 68 are communicated with each other. Therefore, the conduit 10 shown in FIG.
4 can be supplied with compressed air from a compressed supply source.

When a negative pulse is applied to the bimorph type piezoelectric element 80, the bimorph type piezoelectric element 80 is separated from the protrusion 78 of the flapper 74 as shown in FIG. The flapper 74 is the spring member 82.
The abutting force is applied to the nozzle 72. Therefore,
The pressure of the nozzle back pressure chamber 36 rises, and the diaphragm 34 and the flange portion 58 of the valve body 56 move to the spring member 62.
It is displaced in the Z2 direction against the elastic force of. As a result, the communication between the supply passage 66 and the exhaust passage 68 is blocked by the cylindrical portion 60 of the valve body 56.

On the other hand, in the electro-pneumatic conversion device 20b, since the drive signal is not input, the bimorph type piezoelectric element 80 is not displaced, and the flapper 74 is pressed by the nozzle 72, so that the supply passage 66 and the exhaust passage 68 are formed. The cutoff state is maintained. That is, the exhaust from the external actuator 102 to the outside via the conduit 104 is blocked.

As described above, by applying the drive signal only to the electro-pneumatic conversion device 20a while changing the positive and negative pulse widths, in the section C, the pressure in the pipeline 104 is gradually increased to a predetermined pressure. (See FIG. 3 (a)). As a result, the compressed air supply source SUP in FIG.
Compressed air is supplied to the external actuator 102 via 04, and the valve body 106 is opened.

At this time, in the external actuator 102,
The displacement of the stem 108 is detected by the position detector 110, and A /
By feeding back the position detection signal to the μ processor 98 via the D converter 112, a deviation from the control signal is obtained in the μ processor 98, and the drive signal with the positive and negative pulse widths changed so as to eliminate the deviation is described above. It is output to the electro-pneumatic conversion device 20a (see FIG. 3).

In this way, while changing the positive and negative pulse widths, the external actuator 102 is electrically charged until a predetermined pressure is applied (the stem 108 is displaced to a predetermined position).
The air conversion device 20a is driven. Here, the drive signal is
As shown in FIG. 3B, the sums of positive and negative pulse widths of the same amplitude are set to be equal. Therefore, the pulse applied to the bimorph-type piezoelectric element 80 is not biased positively or negatively, and there is no possibility of causing a residual electric strain due to polarization of the bimorph-type piezoelectric element 80. In addition, the bimorph type piezoelectric element 8
Since the displacement direction of 0 is both positive and negative directions (Z1 direction, Z2 direction), creep or the like does not occur.

On the contrary, the stem 1 of the external actuator 102
08 is displaced in the opposite direction so that the external actuator 102
When reducing the pressure applied to the electro-pneumatic conversion device 20a, the electro-pneumatic conversion device 20a is shut off and the electro-pneumatic conversion device 20b is opened.
The operation in this case is the same as the above description, and therefore will be omitted.

Since the electro-pneumatic positioner 92 is provided with the fail-safe section 114, in the case of a power failure or an input break, the charging section 116 passes through the power monitoring section 118.
A voltage is applied to the electro-pneumatic conversion device 20b via the switch unit 120. Therefore, the electro-pneumatic conversion device 20b is opened, the pipe 104 communicates with the exhaust port, and the valve body 106 is closed. As a result, it is possible to prevent the valve body 106 from continuing to open.

In this way, the electro-pneumatic conversion device 2 of this embodiment is
In No. 0 (20a, 20b), the flapper 74 is formed separately from the bimorph type piezoelectric element 80 in the non-bleed type nozzle flapper mechanism 24. The bimorph type piezoelectric element 80 contacts the projection 78 of the flapper 74 only when a positive pulse is applied, and the flapper 74 is displaced. When a negative pulse is applied or when no pulse is applied, the bimorph type piezoelectric element 80 does not come into contact with the flapper 74 to act, and the flapper 74 causes the spring member 82 to operate.
Is abutted against the nozzle 72 by the elastic force of. Therefore, even if the positive and negative pulse widths are applied to the bimorph type piezoelectric element 80 while changing the pulse width, the flapper 74 causes the nozzle 7 to move the flapper 74 by the bimorph type piezoelectric element 80 only when the positive pulse is applied.
Flapper 74 by a negative pulse just separated from
Therefore, the flapper 74 is not pressed against the nozzle 72 by an excessive force.

Moreover, even if the negative pulse is applied to the bimorph type piezoelectric element 80 as described above, the state of the flapper 74 is the same as that when the positive and negative pulses are not applied. As shown in FIG. 3C, the sum of positive and negative pulse widths having the same amplitude can be equalized in the continuous drive signal, and the bimorph type piezoelectric element 80 does not generate electrical distortion due to the influence of polarization or the like.

Further, the spring member 82 is attached to the nozzle 72.
And the flapper 74 on the nozzle 72.
Are in contact with each other. In this case, since the flapper 74 is in the horizontal state, it is not necessary to apply positive and negative pulse widths to the bimorph type piezoelectric element 80 during non-bleeding.

Furthermore, the projection 78 of the flapper 74
By displacing the position of in the direction of the dashed arrow in Fig. 1,
The displacement amount of the flapper 74 by the bimorph type piezoelectric element 80 can be changed.

Furthermore, since the fail-safe section 114 is provided, the power supply monitoring section 118 detects an abnormal condition such as an input disconnection or a power failure when the power is being supplied from the outside, and the charging section 118 detects it. From 116 to the switch section 12 depending on the operating condition of the electro-pneumatic positioner 92 at that time.
A drive signal, that is, an opening signal can be output from 0 to the electro-pneumatic converters 20a and 20b.

In this embodiment, the external actuator 102 is of the single-acting type including the electro-pneumatic converters 20a and 20b, but as shown in FIG.
If it is a return type as in 02a, the electro-pneumatic converters 20a, 20c on the supply side and the electro-pneumatic converters 20b, 2 on the exhaust side.
An electro-pneumatic positioner is constructed by incorporating 0d.

Further, when the feedback control is performed, the displacement amount of the stem 108 is detected, but the pressure of the pipe line 104 may be detected and used.

[0047]

According to the electro-pneumatic conversion device of the present invention,
The following effects can be obtained.

That is, in the electro-pneumatic conversion device, the flapper and the bimorph type piezoelectric element are provided separately, so that even if the flapper is a non-bleed type in which the flapper is constantly urged toward the nozzle side by the elastic member, the bimorph type piezoelectric element is used. The elements include
No mechanical action is exerted by the elastic member, and creep or the like does not occur during long-term use. In particular, if the elastic member is arranged on the axis of the nozzle, the elastic member does not generate a moment with respect to the flapper and creep can be prevented.

In the normal state (non-bleed state), the flapper is pressed against the nozzle by the elastic member. Separately, in order to bring the flapper into contact with the nozzle, the bimorph type piezoelectric element is pulsed. Need not be applied. Therefore, it is possible to prevent electrical distortion or the like that may occur when only a pulse of one polarity is continuously applied to the bimorph type piezoelectric element.

Further, since the flapper is configured to be displaced only when the positive or negative polarity pulse is applied to the bimorph type piezoelectric element, the flapper is displaced when the other polarity pulse is applied. do not do. Therefore, a drive signal composed of continuous pulses can be configured so that the sum of positive and negative pulse widths having the same amplitude becomes the same, and by applying this drive signal to the bimorph type piezoelectric element, polarization etc. It is possible to prevent the occurrence of electrical distortion due to.

Further, by using the electro-pneumatic conversion device as a pilot valve on the supply side and exhaust side of the actuator, an actuator system that operates accurately for a long period can be constructed by performing feedback in particular. In the actuator system, since it has a fail-safe device composed of a battery or a charging unit as a power source, when the system is powered off or the like, a voltage is applied to the electro-pneumatic conversion device to drive it to supply air to the actuator or By exhausting the air, the actuator can be maintained in an appropriate state, so that the safety of the entire system can be achieved.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing an electro-pneumatic conversion device according to the present invention.

FIG. 2 is a schematic diagram of an electro-pneumatic conversion device according to the present invention.
It is a block explanatory view of an empty positioner.

FIG. 3 is a waveform diagram showing a pressure state of the positioner and an input signal to the electro-pneumatic conversion device in the electro-pneumatic positioner according to the present invention.

FIG. 4 is a vertical cross-sectional view showing an electro-pneumatic conversion device according to the present invention.

FIG. 5 is an explanatory view of a main part of another embodiment of the electro-pneumatic positioner according to the present invention.

FIG. 6 is a structural explanatory view of an electro-pneumatic positioner according to a conventional example.

FIG. 7 is a diagram showing a nozzle flapper mechanism according to a conventional example.

FIG. 8 is a waveform diagram showing an input signal of a nozzle flapper mechanism and a displacement state of the flapper according to a conventional example.

FIG. 9 is a diagram showing an influence of polarization of a nozzle flapper mechanism according to a conventional example.

[Explanation of symbols]

 20 ... Electro-pneumatic conversion device 22 ... Valve mechanism 24 ... Nozzle flapper mechanism 34 ... Diaphragm 56 ... Valve body 74 ... Flapper 80 ... Bimorph type piezoelectric element 82 ... Spring member 92 ... Electro-pneumatic positioner 98 ... Microprocessor 114 ... Fail-safe part

Claims (7)

[Claims] 1. In an electro-pneumatic conversion device that changes the nozzle back pressure by a non-bleed type nozzle flapper mechanism to open and close the valve body, etc., the nozzle back pressure chamber back and forth are brought into contact with and separated from the nozzle. A flapper that changes the pressure and is constantly urged in the nozzle direction by an elastic member, and a bimorph type that abuts on the flapper and displaces it only when a pulse of either positive or negative polarity is applied to the flapper. An electro-pneumatic conversion device comprising: a piezoelectric element; and a control mechanism for applying positive and negative pulses to the bimorph type piezoelectric element. 2. The electro-pneumatic conversion device according to claim 1, wherein the elastic member is arranged on the axis of the nozzle. 3. The electro-pneumatic conversion device according to claim 1 or 2, wherein the drive signals in which pulses applied from the control mechanism to the bimorph type piezoelectric element are continuous have the same amplitude and positive and negative, respectively. The electro-pneumatic conversion device is characterized in that the total sum of the pulse widths is the same. 4. An actuator system using the electro-pneumatic conversion device according to claim 1, wherein the electro-pneumatic conversion device is used as a pilot valve of an actuator, and one electro-pneumatic conversion device is used. An actuator system characterized in that the converter is arranged on the fluid supply side of the actuator and the other electro-pneumatic converter is arranged on the fluid discharge side of the actuator. 5. The actuator system according to claim 4, wherein a detection device for detecting a fluid pressure acting on the actuator or a displacement amount of the actuator is provided, and an output signal of the detection device is input to a control device, and an external device is provided. An actuator system is characterized in that a deviation signal from an input signal input from is obtained and a bimorph type piezoelectric element is controlled based on the deviation signal. 6. The actuator system according to claim 4 or 5, wherein the control device includes a fail-safe device having a power source, and the power source corresponds to the actuator system, and a supply-side or exhaust-side electro-pneumatic conversion device. An actuator system characterized by being connected to. 7. The actuator system according to claim 6, wherein the power source is a battery or a capacitor.