JPH023701A - Electric signal-pneumatic pressure conversion unit - Google Patents

Abstract

PURPOSE:To carry out the conversion of an electric signal to a pneumatic pressure signal easily and with high precision by constituting the piezoelectric strain element of a nozzle flapper from a ceramic member and a shim member and nipping only the shim member. CONSTITUTION:A shim member 32 is formed into T-figure form, and the hole parts 34a and 34b for screwing the tightening machine screws 12a and 12b are drilled at the prescribed positions of the T-figure shape, and a flapper is constituted by fixedly installing the piezoelectric ceramics members 36a and 36b onto the upper and under surfaces at other prescribed positions on the shim member 32. Therefore, the influence of the tightening force due to a fixed plate is eliminated, and the shift phenomenon can be reduced as little as possible. Therefore, the nozzle back pressure can be controlled correctly by a low voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electrical signal-pneumatic conversion unit for converting an electrical signal into a fluid pressure signal, in particular a pneumatic signal. The present invention relates to an electrical signal-to-pneumatic conversion unit in which a nozzle flapper is constructed of an electrostrictive element, and which is capable of converting a low-voltage electrical signal into a pneumatic signal as accurately as possible.

Conventionally, torque motors have been widely used as devices for converting electrical signals into pneumatic pressure.

In other words, according to this torque motor, current is supplied to the coils that make up the motor, and the rotational force corresponding to the current value is converted into a displacement amount, which is then converted into a pneumatic signal via the nozzle flapper, pilot valve, etc. When using such a torque motor to configure a control device such as an electro-pneumatic converter, the larger the force generated by the torque motor, the stronger it will be against the effects of mechanical vibrations, etc. Moreover, a product with stable performance can be obtained.

However, recently, there has been a demand for control equipment to be smaller and lighter, so how to make the torque motor smaller has become an important issue. In other words, the smaller the torque motor is, the smaller the force it generates in response to the current value, which inevitably makes it more susceptible to the mechanical vibrations mentioned above, and depending on the conditions of use of the control equipment, Using a torque motor itself would be technically impossible.

Therefore, the present inventor focused on an electrostrictive element and invented an electric signal-pneumatic conversion unit that converts an electric signal into a pneumatic signal by using this electrostrictive element, and patent application No. 5
Patent applications have been filed as No. 9-88178 and No. 60-23094.

That is, in these inventions, the electrostrictive element is a thin plate-like rectangular type, and a bimorph type is used in which one end is fixed as a fulcrum and the other end is used as a free end. In this case, when a voltage is applied to the electrode with one end of the electrostrictive element configured as described above fixed, the free end side changes slightly. Therefore, if the nozzle flapper is constructed from the electrostrictive element itself, changes in voltage can be easily converted into a nozzle back pressure, that is, an air pressure signal.

By the way, the following methods can be used to fix the electrostrictive element of the nozzle flapper configured as described above.

That is, as shown in FIG. 1, the nozzle flapper mechanism 2
A column 6 is integrally attached to the base 4 constituting the base 4.
is erected, and the electrostrictive element 8 is placed on this column 6. Then, it is fixed to a screw hole drilled in the column 6 with a tightening screw 12 via a fixing plate IO. On the other hand, a nozzle 14 is fixed to the base 4, and the tip of the nozzle 14 is connected to the electrostrictive element 8.
It is placed so that it is close to the

In this case, the electrostrictive element 8 has a configuration as shown in FIG. 2. That is, a shim member 16 made of a conductive material is formed into a rectangular shape, and piezoelectric ceramic members 18a and 18b are bonded to the upper and lower surfaces of the shim member 16 via an adhesive. As can be easily understood from the figure, the piezoelectric ceramic members 18a, 18b surround most of the area of the shim member 16. Therefore, the tightening screw 1 is
When attempting to fix the electrostrictive element 8 to the columnar body 6 in step 2, the electrostrictive element 8 is fixed between the fixed plate lO and the columnar body 6 in the order of the piezoelectric ceramic member 18a1, the shim material 16, and the piezoelectric ceramic member 18b. This led to him being pinched.

By the way, it is generally known that when a voltage is applied to the electrostrictive element 8, there is a relationship as shown in FIG. 3 between the applied voltage and the amount of displacement of the free end side. It is being That is, when a large voltage is applied, then lowered, and then raised again, a so-called hysteresis phenomenon appears. This phenomenon is particularly noticeable in bimorph electrostrictive elements. Moreover, even if the same voltage is applied, as time passes, curves B and B' will change from curves A and A' in Figure 3.
As shown in the curve, a phenomenon occurs in which the amount of displacement on the free end side shifts. This phenomenon tends to be exacerbated when the external ambient temperature changes.

Of course, the cause of such a phenomenon is largely due to the characteristics of the electrostrictive element itself, but on the other hand, the piezoelectric ceramic member 18a,
18b is fixed via an adhesive, or as shown in FIG.
7b, and tightening screws 12 are inserted into these holes 7a and 7b2.
When trying to hold the electrostrictive element 8 by the fixing plate 10 by loosely fitting the fixing screws 12a and 12b into the screw holes, the fixing plate lO may It is distorted as shown by the broken line and pressed against the corner of the electrostrictive element 8. Therefore, it has also been confirmed that this tightening effect promotes the shift phenomenon. Furthermore, when attempting precise control by applying as low a voltage as possible to the electrostrictive element 8, for example, a voltage around IOV, the amount of displacement generated in the electrostrictive element 8 becomes extremely small. As a result, it becomes necessary to perform control on the order of microns, so the tightening screws 12a and 12b. The tightening force must be carefully adjusted.

Moreover, when there are two tightening screws 12a and 12b as described above, it is virtually impossible to tighten them both equally, and on the other hand, if the tightening forces are uneven, the electrostrictive element will be affected unevenly. Uniform stress is applied.

In addition, in the above configuration, the piezoelectric ceramic member at the portion held between the fixed plates also expands and contracts due to the application of voltage, which changes the internal stress, which causes the shift phenomenon, making accurate control difficult. .

Therefore, a device for converting an electrical signal into a pneumatic signal based on this electrostrictive element at substantially such a low voltage as described above has not yet been developed.

[Object of the Invention] The present invention has been made in order to overcome the various disadvantages mentioned above, and when attempting to fix an electrostrictive element to a base, at least the piezoelectric ceramic member constituting the electrostrictive element is fixed to a base. Avoids being pinched between the body and the fixing plate, and therefore is not affected by the tightening force of the tightening screws.
An object of the present invention is to provide an electrical signal-to-pneumatic conversion unit that can easily and accurately convert an electrical signal into a pneumatic signal at low voltage.

[Means for achieving the object] In order to achieve the above object, the present invention provides an electrical signal-pneumatic conversion unit including a nozzle flapper mechanism that changes the nozzle back pressure according to the amount of displacement of the nozzle flapper.
An electrostrictive element that displaces the nozzle flapper in response to a change in an electric signal is formed by laminating a piezoelectric ceramic member and a shim material, and means for sandwiching only the shim material is provided, and the piezoelectric ceramic member is placed at the tip of the nozzle. It is characterized by being configured to be arranged so as to be separated by a predetermined distance.

[Embodiments] Next, preferred embodiments of the electrical signal-pneumatic conversion unit according to the present invention will be described in detail with reference to the accompanying drawings.

Components that are the same as those shown in FIGS. 1 to 4 are given the same reference numerals, and detailed explanation thereof will be omitted.

The present invention is particularly related to the shape of an electrostrictive element. That is, the shim material 32 constituting the electrostrictive element 30 is
It is formed into a letter shape. In this case, the shim material 32 is generally made of metal such as phosphor bronze or stainless steel, and has holes 34a and 34b into which the tightening screws 12a and 12b are screwed into predetermined T-shaped portions 33. is installed. Piezoelectric ceramic members 3fia, 36b are fixed to the upper and lower surfaces of the other predetermined portion 35 of the shim member 32 with an insulating material (not shown) in between. In this case, as can be easily seen from the figure, the piezoelectric ceramic member 36a136b does not cover at least the portions where the holes 34a and 34b are formed.

In the nozzle flapper mechanism having the above-described configuration, the shim material 32 is placed on the columns 6a, 6b, and the holes 34a, 3
The fixing plate 10 is placed on the fixing plate 4b, and the tightening screws 12a, 12b are screwed into the holes 34a, 34b of the electrostrictive element 30 through the holes drilled in the fixing plate 10 to fix them. At this time, as is easily understood, the piezoelectric ceramic member 3i3 is attached to the portion to be tightened by the tightening screws 12a and 12b.
a and 36b do not exist. Therefore, only the shim material 32 receives the tightening force. That is, the electrostrictive element 30
When fixing to the pillars (3a, 5b), it is necessary to adjust the tightening force as seen in the prior art.
There is no such thing. Moreover, when the piezoelectric ceramic members 36a and 36b are bonded to the shim material 32 via the insulating layer, the adhesive is not needed, so the amount of the adhesive is not affected when voltage is applied. will also be very small.

As a result, when a voltage is applied to the electrostrictive element 30 and an electrical signal is to be converted into a pneumatic signal, stable operation can be obtained without considering the tightening force. Particularly, when attempting to drive the electrostrictive element 30 with a low voltage, there is an advantage that precise control can be performed.

Next, an electric signal incorporating the electrostrictive element 30 according to the present invention -
A pneumatic signal converter will be briefly described.

The piezoelectric ceramic members 36a and 36b are electrically connected to one terminal of the controller 50, respectively. The other terminal of the controller 50 is electrically connected to the shim material 32. A pilot valve 52 is connected to the nozzle 14 , and the output side of the pilot valve 52 is branched and connected to a pneumatic signal-to-voltage conversion element 54 . The air pressure signal
The output side of the voltage conversion element 54 is introduced into the controller 50.

Note that a control signal S is introduced into this controller 50.

Therefore, when this control signal S is introduced into the controller 50, a predetermined voltage is applied from the controller 50 between the piezoelectric ceramic members 36a, 36b and the shim material 32, and the free end of the electrostrictive element 30 is Deflects due to voltage. This results in a change in the nozzle back pressure of the air drawn out of the nozzle 14, which is introduced into the pilot valve 52.

The output signal of this pilot valve 52 is introduced into a predetermined device to control the device.

On the other hand, the output signal of the pilot valve 52 is an air pressure signal -
is introduced into the voltage conversion element 54, which is then connected to the controller 50.
It is used as a feedback signal for

Furthermore, FIG. 7 shows an embodiment of a positioner that employs a voltage signal-pneumatic signal conversion mechanism.

Note that the same reference numerals are given to the same components as those used in the voltage signal-pneumatic signal conversion mechanism, and the description thereof will be omitted.

Therefore, in this embodiment, the output side of the pilot valve 52 is introduced into a control valve 60 to control this control valve 60, and the output side of this control valve 60 is branched to convert the amount of displacement into an electrical signal. It has been introduced into sensors that For example, a potentiometer is preferably used as this sensor. Therefore,
The output side of this potentiometer 62 is the controller 50
as a feedback signal.

Therefore, the signal output to the viroft valve 52 displaces the control valve 60, and the sensor output corresponding to the amount of displacement controls the controller 50 in feedback.

Furthermore, FIG. 8 shows another embodiment of the present invention. This embodiment is directed toward the electrostrictive element 30. That is, this electrostrictive element 30 has a shim material 32 having a simple rectangular shape. Piezoelectric ceramic member 3 of this shim material 32
The portion where 6a and 36b are not fixed is the columnar body 5a% 6
It goes without saying that the same effect as described above can be obtained by holding it between the b% fixing plates IO.

[Effects of the Invention] According to the present invention, only the portion of the shim material constituting the electrostrictive element is sandwiched as described above, and the nozzle back pressure is changed by the applied voltage. Therefore, in particular, it is not affected by the clamping force by the fixing plate, i.e.
It is possible to obtain an electrical signal-to-pneumatic conversion unit that can minimize the shift phenomenon and is not affected by the amount of adhesive. In particular, this conversion unit has the practical effect of being able to accurately control its nozzle back pressure with low voltage.

Although the present invention has been described above with reference to preferred embodiments, the present invention is not limited to these embodiments.
For example, in FIG. 5, the same effect can be obtained even if the pair of holes into which the tightening screws are inserted are not specifically provided and the holes are simply sandwiched between other clamping members, without departing from the gist of the present invention. Of course, various improvements and changes in design are possible within the scope.

[Brief explanation of the drawing]

Fig. 1 is a partially omitted front explanatory view of an electrical signal-to-pneumatic conversion unit according to the prior art, Fig. 2 is a plan view of an electrostrictive element incorporated in Fig. 1, and Fig. 3 is an electrostrictive element according to the prior art. 4 is a side view of the conversion unit shown in FIG. 1, FIG. 5 is a perspective view of the electrostrictive element according to the present invention, and FIG. 6 is a graph showing the electrostrictive element according to the present invention when FIG. 7 is an explanatory diagram of the state in which the electrostrictive element according to the present invention is incorporated into a signal-air pressure converter.
FIG. 8 is a perspective view showing another embodiment of the electrostrictive element according to the present invention. 12a, 12b... Tightening screw 30... Electrostrictive element 32... Shim material 34a, 34b...
Holes 36a, 36b...piezoelectric ceramic member 50.
... Controller 52 ... Pilot valve 54
...Air pressure signal-voltage conversion element 60...Control valve 62...Potentiometer FfG, 5 34a

Claims (1)

[Claims] (1) In an electrical signal-pneumatic conversion unit that includes a nozzle flapper mechanism that changes nozzle back pressure in accordance with the amount of displacement of the nozzle flapper, an electrostrictive element that displaces the nozzle flapper in response to changes in the electrical signal is connected to a piezoelectric ceramic member and shims. An electrical signal-pneumatic conversion unit characterized in that the unit is formed by laminating the shim material, is provided with means for sandwiching only the shim material, and is configured such that the piezoelectric ceramic member is disposed at a nozzle tip with a predetermined spacing. .