CA1142041A - Pneumatic converter - Google Patents
Pneumatic converterInfo
- Publication number
- CA1142041A CA1142041A CA000339778A CA339778A CA1142041A CA 1142041 A CA1142041 A CA 1142041A CA 000339778 A CA000339778 A CA 000339778A CA 339778 A CA339778 A CA 339778A CA 1142041 A CA1142041 A CA 1142041A
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- Canada
- Prior art keywords
- bellows
- nozzle
- converter
- pressure
- coupling plate
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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- Supply Devices, Intensifiers, Converters, And Telemotors (AREA)
- Transmission And Conversion Of Sensor Element Output (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A pneumatic converter for executing signal conversion by the use of a bellows unit comprising a bellows and a coupling plate to couple the two ends of the bellows with each other at a position disposed eccentrically from the center axis of the bellows. When fluid under pressure is admitted to the bellows via an inlet in one end, the bellows tries to expand but the coupling plate holds the ends together to cause, because of the eccentricity, one of the ends to become inclined. The extent of inclination is a measure of the pressure of the fluid.
A pneumatic converter for executing signal conversion by the use of a bellows unit comprising a bellows and a coupling plate to couple the two ends of the bellows with each other at a position disposed eccentrically from the center axis of the bellows. When fluid under pressure is admitted to the bellows via an inlet in one end, the bellows tries to expand but the coupling plate holds the ends together to cause, because of the eccentricity, one of the ends to become inclined. The extent of inclination is a measure of the pressure of the fluid.
Description
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The present invention relates to a pneumatic converter designed for converting a pressure signal to a proportional force or displacement signal or vice versa, and more particularly it relates to an improved pneumatic converter of the type which in-corporates the use of a bellows.
In general, when pressure is applied to a bellows, a proportional force or displacement is obtained from the free end thereo~ and a displacement (angle) or force can be converted to a pressure by the use of a bellows and a nozzle-flapper mechanism.
The pneumatic converter according to the present invention is of such a type.
According to the present invention, there is provided a pneumatic converter for converting a penumatic pressure to a mechanical displacement comprising a bellows having a first fixed end and a second movable end secured to said first end by a flexible coupling plate disposed within the bellows at a position displaced from the central axis of the bellows.
The prior art and the present invention will be better understood with reference to the accompanying drawings, in which:
Figure 1 illustrates the structure of an exemplary con-ventional converter in general use Figure l(A) being a front view and Figure l(B) a side view;
Figure 2 illustrates the structure of a pneumatic converter according to the present invention;
Figures 3 through 5 respectively show different examples where the converter of this invention is employed in a pressure indicator;
Figure 6 shows an example where the converter of this -i~ Jr ~
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invention is employed in a force-balance type feedback instrument;
Figure 7 illustrates the structure of another e~odiment of converter according to the present invention~
Figure 8 shows an example where this invention is used as a displacement-to-pressure converter, in which (A) is a front view, (B) is a vertical sectional view of (A), and (C) is a sectional view taken along the ~ la-.
- ~ ~ ~
line C-C in (A);
Figure 9 is an equivalent block diagram of the system shown in Figure 8;
Figure 10 shows an example where this invention is used as a displace-ment-to-force converter;
Figure ll shows an example where this invention is used as a current-to-pressure converter;
Figure 12 illustrates the actual structure of principal components in Figure 11;
Figure 13 is an equivalent block diagram of the system shown in Figure ll; and Figure 14 shows another example where this invention is used as a - current-to-pressure converter.
One of the known converters in general use for conversion of a pres-sure to a displacement ~angle) is illustrated in Figure 1, (A) being a front view and (B) a side view. Labelled as 21 is an L-shaped base; 22 is a bellows fixed at one end thereof to the base 21; and 23 is a movable plate whose one end is supported on the base 21 rotatably by means of a shaft 24. The free end of the bellows 22 is kept in contact with the middle portion of the ~ovable plate 23, and a coil spring 25 fixed at one end thereof is anchored to the other end of the plate 23, A pointer 26 has one end secured to the plate 23 by means of screws 27.
In the structure described above, since the free end 29 of the bellows 22 is bendable through 360 degrees, it becomes necessary for control-ling the direction of motion of the pointer 26 to provide a linear support fulcrum having, for example, a length ~ as illustrated. Moreover, a base mechanism is needed to secure the bellows 22, the coil spring 25 and so forth, hence complicating the construction with a resultant dimensional increase.
Consequently, a low-cost small structure is not attainable.
The object of the present invention resides in providing an improved pneumatic converter with an inexpensive, compact structure accomplished by a simple mechanism with a bellows unit which includes a coupling plate located in a bellows and serving to couple the two ends thereof with each other at a position deviating eccentrically from the center axis of the bellows.
In Figure 2 illustrating the structure of an embodiment according to this invention: labelled as 1 is a bellows into which an input pressure is introduced, and substantially disc-shaped bellows ends 2 and 3 are secured to the top and bottom, respectively, of the bellows 1. A coupling plate 4 composed of an elastic material is disposed at a position deviating slightly (by a distance e in this embodiment) from the centre axis of the bellows 1 and is held in such a manner that one edge thereof is anchored to the bellows end 2 while the other edge thereof is anchored to the bellows end 3. Labelled as 5 is a base to which the bellows end 3 is secured, and 6 is an inlet hole through which an input pressure Pin is introduced into the bellows 1.
The device described above operates as follows. Whe~ an input pressure P is introduced into the bellows 1, a force proportional to the effective area of the bellows 1 is generated in the axial direction thereof and is exerted to expand the bellows 1 in the axial direction. However, since the bellows ends 2 and 3 are coupled with each other by the coupling plate 4 with an eccentric deviation from the axis, the bellows énd 2 is caused to -~ z~
incline in the direction of the deviation with respect to the axis. Thus, it is rendered possible to obtain a pressure-to-displacement conversion mechanism by utilizing the displacement that results from such inclination.
In relation to the input pressure P, the inclination angle 0 of the - bellows is represented by the following equation:
Ae Kf + KB
in which ~: output inclination angle A: effective area of bellows 1 e: eccentric devia~ion Kf: rotational elastic constant of coupling plate 4 KB: rotational elastic constant of bellows 1 P: input pressure In the present invention, due to the provision of the coupling plate 4 in the bellows 1, the linear support fulcrum located outside of the bellows in the prior art is no longer needed thus reducing the dimensions.
Moreover, the coil spring can be eliminated as well since the coupling plate serves also as a spring, hence rendering unnecessary a complicated base construction to support the bellows, the coil spring and the external fulcrum mechanism. Thus the base structure is minimized dimensionally. Furthermore, because of the advantage that the support fulcrum can be located at an inner position beyond the diameter of the bellows~ the leverage can be increased easily. The entire construction is simplified since no external element exists with the coupling plate 4 alone provided in the bellows 1.
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Fi~lre 3 shows an example where the con-verter of this invention is employed in a pressure indicator, wherein a pointer 7 is attached directly to bellows end 2. The pressure indicator consists merely of a bellows, a coupling plate and a pointer which is a very simple and inexpensive structure.
Since there is no friction component, high operating stability is attainable.
In the pressure indicator of such a structure, the rigidity is great in the longitudinal direction of the coupling plate so that motion is effected only in the direction of thickness thereof.
In Figure 4 showing another example where the invention is employed in a pressure indicator, the coupling plate 4 is slightly longer than the bellows 1, which is thereby inclined asillustrated when the input pressure P
is zero. With increase of the input pressure, the bellows 1 is inclined in the opposite direction past its upright position. In this structure, both a plus (tensile) region and a minus (contractile) region are usable out of the allowable stress regions of the coupling plate 4' and the bellows 1, so that the maximum deflection angle attainable is approximately doubled as compared with the example of Figure 3.
In Figure 5 showing another example where the invention is employed in a pressure in~icator, labeled as 7' is a pointer which is supported near its lower end to a base 5 at a rotational fulcrum l. One end of a drive shaft 8 is secured to a bellows end 2, while the other end thereof is engaged with the rear end of the pointer 7' in a disengageable manner. This embodi-ment is advantageous in that, as the long pointer and the block-shaped bellows are constituted of separate members, the device can be stored conveniently prior to assembly and, in the case of breakage or the like, the pointer and
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The present invention relates to a pneumatic converter designed for converting a pressure signal to a proportional force or displacement signal or vice versa, and more particularly it relates to an improved pneumatic converter of the type which in-corporates the use of a bellows.
In general, when pressure is applied to a bellows, a proportional force or displacement is obtained from the free end thereo~ and a displacement (angle) or force can be converted to a pressure by the use of a bellows and a nozzle-flapper mechanism.
The pneumatic converter according to the present invention is of such a type.
According to the present invention, there is provided a pneumatic converter for converting a penumatic pressure to a mechanical displacement comprising a bellows having a first fixed end and a second movable end secured to said first end by a flexible coupling plate disposed within the bellows at a position displaced from the central axis of the bellows.
The prior art and the present invention will be better understood with reference to the accompanying drawings, in which:
Figure 1 illustrates the structure of an exemplary con-ventional converter in general use Figure l(A) being a front view and Figure l(B) a side view;
Figure 2 illustrates the structure of a pneumatic converter according to the present invention;
Figures 3 through 5 respectively show different examples where the converter of this invention is employed in a pressure indicator;
Figure 6 shows an example where the converter of this -i~ Jr ~
.
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invention is employed in a force-balance type feedback instrument;
Figure 7 illustrates the structure of another e~odiment of converter according to the present invention~
Figure 8 shows an example where this invention is used as a displacement-to-pressure converter, in which (A) is a front view, (B) is a vertical sectional view of (A), and (C) is a sectional view taken along the ~ la-.
- ~ ~ ~
line C-C in (A);
Figure 9 is an equivalent block diagram of the system shown in Figure 8;
Figure 10 shows an example where this invention is used as a displace-ment-to-force converter;
Figure ll shows an example where this invention is used as a current-to-pressure converter;
Figure 12 illustrates the actual structure of principal components in Figure 11;
Figure 13 is an equivalent block diagram of the system shown in Figure ll; and Figure 14 shows another example where this invention is used as a - current-to-pressure converter.
One of the known converters in general use for conversion of a pres-sure to a displacement ~angle) is illustrated in Figure 1, (A) being a front view and (B) a side view. Labelled as 21 is an L-shaped base; 22 is a bellows fixed at one end thereof to the base 21; and 23 is a movable plate whose one end is supported on the base 21 rotatably by means of a shaft 24. The free end of the bellows 22 is kept in contact with the middle portion of the ~ovable plate 23, and a coil spring 25 fixed at one end thereof is anchored to the other end of the plate 23, A pointer 26 has one end secured to the plate 23 by means of screws 27.
In the structure described above, since the free end 29 of the bellows 22 is bendable through 360 degrees, it becomes necessary for control-ling the direction of motion of the pointer 26 to provide a linear support fulcrum having, for example, a length ~ as illustrated. Moreover, a base mechanism is needed to secure the bellows 22, the coil spring 25 and so forth, hence complicating the construction with a resultant dimensional increase.
Consequently, a low-cost small structure is not attainable.
The object of the present invention resides in providing an improved pneumatic converter with an inexpensive, compact structure accomplished by a simple mechanism with a bellows unit which includes a coupling plate located in a bellows and serving to couple the two ends thereof with each other at a position deviating eccentrically from the center axis of the bellows.
In Figure 2 illustrating the structure of an embodiment according to this invention: labelled as 1 is a bellows into which an input pressure is introduced, and substantially disc-shaped bellows ends 2 and 3 are secured to the top and bottom, respectively, of the bellows 1. A coupling plate 4 composed of an elastic material is disposed at a position deviating slightly (by a distance e in this embodiment) from the centre axis of the bellows 1 and is held in such a manner that one edge thereof is anchored to the bellows end 2 while the other edge thereof is anchored to the bellows end 3. Labelled as 5 is a base to which the bellows end 3 is secured, and 6 is an inlet hole through which an input pressure Pin is introduced into the bellows 1.
The device described above operates as follows. Whe~ an input pressure P is introduced into the bellows 1, a force proportional to the effective area of the bellows 1 is generated in the axial direction thereof and is exerted to expand the bellows 1 in the axial direction. However, since the bellows ends 2 and 3 are coupled with each other by the coupling plate 4 with an eccentric deviation from the axis, the bellows énd 2 is caused to -~ z~
incline in the direction of the deviation with respect to the axis. Thus, it is rendered possible to obtain a pressure-to-displacement conversion mechanism by utilizing the displacement that results from such inclination.
In relation to the input pressure P, the inclination angle 0 of the - bellows is represented by the following equation:
Ae Kf + KB
in which ~: output inclination angle A: effective area of bellows 1 e: eccentric devia~ion Kf: rotational elastic constant of coupling plate 4 KB: rotational elastic constant of bellows 1 P: input pressure In the present invention, due to the provision of the coupling plate 4 in the bellows 1, the linear support fulcrum located outside of the bellows in the prior art is no longer needed thus reducing the dimensions.
Moreover, the coil spring can be eliminated as well since the coupling plate serves also as a spring, hence rendering unnecessary a complicated base construction to support the bellows, the coil spring and the external fulcrum mechanism. Thus the base structure is minimized dimensionally. Furthermore, because of the advantage that the support fulcrum can be located at an inner position beyond the diameter of the bellows~ the leverage can be increased easily. The entire construction is simplified since no external element exists with the coupling plate 4 alone provided in the bellows 1.
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Fi~lre 3 shows an example where the con-verter of this invention is employed in a pressure indicator, wherein a pointer 7 is attached directly to bellows end 2. The pressure indicator consists merely of a bellows, a coupling plate and a pointer which is a very simple and inexpensive structure.
Since there is no friction component, high operating stability is attainable.
In the pressure indicator of such a structure, the rigidity is great in the longitudinal direction of the coupling plate so that motion is effected only in the direction of thickness thereof.
In Figure 4 showing another example where the invention is employed in a pressure indicator, the coupling plate 4 is slightly longer than the bellows 1, which is thereby inclined asillustrated when the input pressure P
is zero. With increase of the input pressure, the bellows 1 is inclined in the opposite direction past its upright position. In this structure, both a plus (tensile) region and a minus (contractile) region are usable out of the allowable stress regions of the coupling plate 4' and the bellows 1, so that the maximum deflection angle attainable is approximately doubled as compared with the example of Figure 3.
In Figure 5 showing another example where the invention is employed in a pressure in~icator, labeled as 7' is a pointer which is supported near its lower end to a base 5 at a rotational fulcrum l. One end of a drive shaft 8 is secured to a bellows end 2, while the other end thereof is engaged with the rear end of the pointer 7' in a disengageable manner. This embodi-ment is advantageous in that, as the long pointer and the block-shaped bellows are constituted of separate members, the device can be stored conveniently prior to assembly and, in the case of breakage or the like, the pointer and
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the bellows are replaceable independently. Moreover, the design f~cilitates span adjustment, linearity adjustment and so on.
In Figure 6 showing an example where the invention is employed in a force-balance type feedback instrument: 9 is a feedback bellows; 11 is a rigid beam; 12 is a nozzle; and 13 is a pneumatic pressure amplifier. The stationary ends of an input bellows 1 and the feedback bellows 9 are secured to a base 5 respectively, while the free ends thereof are kept in contact with the rigid beam 11. The nozzle 12 is so disposed as to constitute a nozzle-flapper mechanism, in which a portion of the rigid beam 1] functions as a flapper. The pneumatic pressure amplifier 13 serves to amplifty the back pressure of the nozzle 12, and the amplifier outpwt is fed to the feedback bellows 9 while being transmitted as an output pressure Pout.
In the conventional device used in general heretofore, an input bellows 1 and a feedback bellows 9 are disposed at the two sides of a support fulcrum at the midpoint of a rigid beam 11. Accordingly, it is difficult or impossible to locate the input bellows 1 and the feedback bellows 9 close to each other due to the presence of the support fulcrwm7 and thus limits the achievable size reduction. Furthermore, there is the disad~antage of re-quiring mechanical components for the support fulcrum. However, in the e~ample of Figure 6, the fulcrum is located in the input bellows 1, and the function of the fulcrum mechan~sm is performed entirely by the coupling plate 4 alone, so that the construction is simplified to achieve smaller dimensions and lower production cost.
Figure 7 illustrates the structure of another embodiment according to the present invention, wherein a bellows end 2 and the coupling plate 4 ` ' ' , .
- - -are integrated with each other, ancl a recess 14 is formed therein to furnish flexibility. As a result, it becomes possible to prevent hysteresis error, temperature error or linearity error that may occur in the case of non-integration at the joints of the coupling plate 4 due to the unevenness of stresses when the two edges of the coupling plate 4 are secured to bellows ends 2 and 3 by welding or the like.
Figure 8 shows an example where this invention is used as a dis-placement_to_pressure converter, in which (A) is a front view, (B) is a vertical sectional view of (A), and (C) is a sectional view taken along the line C-C in (A)~ Labeled as 12 is a nozzle secured to a bellows end 2, and 15 is a flapper supported by a shaft 51 fixed on a base 5. One end of the flapper 15 is disposed opposite to the nozzle 12 to constitute a nozzle-flapper mechanism in cooperation with the nozzle, while the other end thereof receives an input displacement Din (angle). A pneumatic pressure amplifier 13 serves to amplify the back pressure of the nozzle 12 and generates an output, which is then fed to a bellows 1 while being transmitted as an out~
put pressure Pout. This embodiment operates in the following manner. Sup-posing that an input displacemen~ to reduce the gap between the flapper 15 and the nozzle 12 is applied to the flapper 15, the back pressure of the nozzle 12 increases and the pressure amplified by the pneuma~ic pressure amplifier 13 is introduced into the bellows 1, where a force proportional to the effective area of the bellows 1 is generated in the axial direction thereof. Although this force is exerted to expand the bellows 1 in the axial direction, since the bellows ends 2 and 3 are coup:Led with each other by the coupling plate 4 with an eccentric deviation from the center axis, the bellows end 2 is inclined in the direction of the deviation with respect to the axis, thereby causing inclination of the nozzle 12 to increase the gap between the noz le 12 and the flapper 15. Subsequent~y this gap is held at a balanced position in accordance with the input displacement, and the back pressure of the nozzle 12 at this time point is amplified by the pneumatic pressure am-plifier 13, which than generates an output pressure Pout proportional to the input displacement Din.
In Figure 9 showing a block diagram representing the system of Figure 8: Kl is the gain of nozzle-flapper mechanism; K2 is the gain of pneumatic pressure amplifier 13; AB is the effective area of bellows l; e is the eccentric deviation of coupling plate 4; k is the total elastic cons-tant (e.g. kg-mm/rad) of the displacement converter; and ~1 is the distance from support shaft 51 to nozzle 12. In this embodiment, a movable plate and so forth employed in the conventional device are no longer needed, and the noz le 6 is attached directly to the bellows end 2 to achieve a compact con-struction.
Figure 10 shows an example where this invention is used as a dis-placement-to-pressure converter, in which a communicating hole 121 is formed in the bellows end 2 so as to effect direct communication between nozzle 12 and bellows 1 with elimination of the pneumatic pressure amplifier 13 employed in the example of Figure 8. This embodiment is adapted for use in the case where a load has a small capacity, that is, when the output pneumatic pres-sure Pout need not be amplified much by the amplifier 13. In co~lparison with the example of Figure 8, this embodiment does not require -the pneumatic pressure amplifier 13 and a pipe for connecting the noz~le 12 with the am-~ z~
plifier 13, hence rendering ~he converter less expensive and smaller.
It is desirable that the rotational center of the bellows 1 and the center of the support shaft 51 are substantially aligned with each other.
However, an eccentric deviation may of course be given intentionally between the said two centers in the manner to improve the overall linearity charac--teristics of the entire device by compensating the linearity error of the bellows.
Figure 11 shows an example where this invention is used as a current-to-pressure converter;
Figure 12 illustrates the actual structure of the principal com-ponents in Figure 11; and Figure 13 is a block diagram representin~ the system of Figure 11.
Labeled as 16 is a force motor which is equipped with, in this example, a moving coil to convert a current input Ii of DC 4 to 20 mA to a proportional force, and 161 is a span adjustment screw inserted in the force motor 16. A
coupling plate 4 is disposed in a bellows 1 at a position slightly deviating (by a distance e) from the center axis of the bellows 1 and serves to couple bellows ends 2 and 3 with each other. Referring to Figure 11, labeled as ]1 is a rigid beam of which one end is connected to the force motor ]6, and the free end of the bellows 1 is connected to the middle portion of the rigid beam 11. A nozzle 12 constitutes a nozzle-flapper mechanism in cooperation with a portion of the other end of the beam 11. A pneumatic pressure am-plifier 13 serves to amplify the back pressure of the nozzle 12 and generates an output, which is then fed to the bellows 1 while being transmitted as an output pressure Pout. Labeled as 17 is a zero adjustment spring interposed _g_ between the beam 11 and a casing or the like, and 18 is a balance weight mounted on the beam 11. 1~1, K2 and K3 denote the transfer functions of force motor 16, nozzle-flapper mechanisms 11, 12 and pneumatic pressure amplifier 13; AB and An denote the effective areas of bellows 1 and nozzle 12; and e ~2' ~n and Q denote the distances from coupling plate 4 to the centers of .
bellows 1, force motor 16, nozzle 12 and zero ad;justment spring 17 respectively.
The above described structure operates as follows. When an input current I. flows in the force motor 16 to generate an upward force Fi, the ln beam 11 is thereby rotated counterclockwise about the coupling plate 4 serving as a support point, so that the gap between thebeam 11 and the nozzle 12 is decreased as a result to increase the back pressure of the nozzle 12. Such a back pressure change is amplified by the pneumatic pressure amplifier 13 and is transmitted as an output pressure Pout while being fed to the bellows 1. In response to the output pressure Pout, the bellows 1 generates a clock-wise moment to the coupling plate 4 and balances the same against the moment produced by the force Fi. In this example, a large leverage is attainable due to employment ofthe bellows 1 containing the coupling plate 4 therein, since the support fulcrum can be located in the extreme proximity of the center axis of the bellows 1. Consequently, there is no need to employ any ~0 complicated means such as a dual leverage mechanism or a vector lever, and thus the structure is rendered remarkably simple to ensure small dimensions, low production cost and high accuracy.
According to experimental data, the accuracy attained was ~0.1 percent in one mechanism with its leverage set to a ratio of 1:30.
Figure 14 shows another example where this invention is used as a current-to-pressure converter, in which a bellows end 2 and a coupling plate 4 are integrated with each other as i]lustrated, and a recess 14 is formed therein to furnish flexibility. As a result, it becomes possib]e to prevent hysteresis error, temperature error or nonlinearity error that may occur in the case o~ non-integration at the joints of the coupling plate 4 due to the ~evenness of stresses when the two edges of the coupling plate 4 are secured to bellows ends 2 and 3 by welding or the like. Any of such errors influences greatly the accuracy of the device particularly when the construction is reduced dimensional]y and the signal transferred in the converter becomes small in value.
Furthermore, a dcuble-tube nozzle 12' is employed in this embodiment to increase the loop gain. In the ordinary nozzle utilized generally, a high loop gain is not obtainable since a negative feedback occurs because of the nozzle injection force as shown by a dotted line in Figure 13. In this embodiment, however, such a problem is solved by using the double-tube nozzle 12' in which an inner tube 122' is disposed at a position slightly lower than an outer tube 121t by a distance d.
the bellows are replaceable independently. Moreover, the design f~cilitates span adjustment, linearity adjustment and so on.
In Figure 6 showing an example where the invention is employed in a force-balance type feedback instrument: 9 is a feedback bellows; 11 is a rigid beam; 12 is a nozzle; and 13 is a pneumatic pressure amplifier. The stationary ends of an input bellows 1 and the feedback bellows 9 are secured to a base 5 respectively, while the free ends thereof are kept in contact with the rigid beam 11. The nozzle 12 is so disposed as to constitute a nozzle-flapper mechanism, in which a portion of the rigid beam 1] functions as a flapper. The pneumatic pressure amplifier 13 serves to amplifty the back pressure of the nozzle 12, and the amplifier outpwt is fed to the feedback bellows 9 while being transmitted as an output pressure Pout.
In the conventional device used in general heretofore, an input bellows 1 and a feedback bellows 9 are disposed at the two sides of a support fulcrum at the midpoint of a rigid beam 11. Accordingly, it is difficult or impossible to locate the input bellows 1 and the feedback bellows 9 close to each other due to the presence of the support fulcrwm7 and thus limits the achievable size reduction. Furthermore, there is the disad~antage of re-quiring mechanical components for the support fulcrum. However, in the e~ample of Figure 6, the fulcrum is located in the input bellows 1, and the function of the fulcrum mechan~sm is performed entirely by the coupling plate 4 alone, so that the construction is simplified to achieve smaller dimensions and lower production cost.
Figure 7 illustrates the structure of another embodiment according to the present invention, wherein a bellows end 2 and the coupling plate 4 ` ' ' , .
- - -are integrated with each other, ancl a recess 14 is formed therein to furnish flexibility. As a result, it becomes possible to prevent hysteresis error, temperature error or linearity error that may occur in the case of non-integration at the joints of the coupling plate 4 due to the unevenness of stresses when the two edges of the coupling plate 4 are secured to bellows ends 2 and 3 by welding or the like.
Figure 8 shows an example where this invention is used as a dis-placement_to_pressure converter, in which (A) is a front view, (B) is a vertical sectional view of (A), and (C) is a sectional view taken along the line C-C in (A)~ Labeled as 12 is a nozzle secured to a bellows end 2, and 15 is a flapper supported by a shaft 51 fixed on a base 5. One end of the flapper 15 is disposed opposite to the nozzle 12 to constitute a nozzle-flapper mechanism in cooperation with the nozzle, while the other end thereof receives an input displacement Din (angle). A pneumatic pressure amplifier 13 serves to amplify the back pressure of the nozzle 12 and generates an output, which is then fed to a bellows 1 while being transmitted as an out~
put pressure Pout. This embodiment operates in the following manner. Sup-posing that an input displacemen~ to reduce the gap between the flapper 15 and the nozzle 12 is applied to the flapper 15, the back pressure of the nozzle 12 increases and the pressure amplified by the pneuma~ic pressure amplifier 13 is introduced into the bellows 1, where a force proportional to the effective area of the bellows 1 is generated in the axial direction thereof. Although this force is exerted to expand the bellows 1 in the axial direction, since the bellows ends 2 and 3 are coup:Led with each other by the coupling plate 4 with an eccentric deviation from the center axis, the bellows end 2 is inclined in the direction of the deviation with respect to the axis, thereby causing inclination of the nozzle 12 to increase the gap between the noz le 12 and the flapper 15. Subsequent~y this gap is held at a balanced position in accordance with the input displacement, and the back pressure of the nozzle 12 at this time point is amplified by the pneumatic pressure am-plifier 13, which than generates an output pressure Pout proportional to the input displacement Din.
In Figure 9 showing a block diagram representing the system of Figure 8: Kl is the gain of nozzle-flapper mechanism; K2 is the gain of pneumatic pressure amplifier 13; AB is the effective area of bellows l; e is the eccentric deviation of coupling plate 4; k is the total elastic cons-tant (e.g. kg-mm/rad) of the displacement converter; and ~1 is the distance from support shaft 51 to nozzle 12. In this embodiment, a movable plate and so forth employed in the conventional device are no longer needed, and the noz le 6 is attached directly to the bellows end 2 to achieve a compact con-struction.
Figure 10 shows an example where this invention is used as a dis-placement-to-pressure converter, in which a communicating hole 121 is formed in the bellows end 2 so as to effect direct communication between nozzle 12 and bellows 1 with elimination of the pneumatic pressure amplifier 13 employed in the example of Figure 8. This embodiment is adapted for use in the case where a load has a small capacity, that is, when the output pneumatic pres-sure Pout need not be amplified much by the amplifier 13. In co~lparison with the example of Figure 8, this embodiment does not require -the pneumatic pressure amplifier 13 and a pipe for connecting the noz~le 12 with the am-~ z~
plifier 13, hence rendering ~he converter less expensive and smaller.
It is desirable that the rotational center of the bellows 1 and the center of the support shaft 51 are substantially aligned with each other.
However, an eccentric deviation may of course be given intentionally between the said two centers in the manner to improve the overall linearity charac--teristics of the entire device by compensating the linearity error of the bellows.
Figure 11 shows an example where this invention is used as a current-to-pressure converter;
Figure 12 illustrates the actual structure of the principal com-ponents in Figure 11; and Figure 13 is a block diagram representin~ the system of Figure 11.
Labeled as 16 is a force motor which is equipped with, in this example, a moving coil to convert a current input Ii of DC 4 to 20 mA to a proportional force, and 161 is a span adjustment screw inserted in the force motor 16. A
coupling plate 4 is disposed in a bellows 1 at a position slightly deviating (by a distance e) from the center axis of the bellows 1 and serves to couple bellows ends 2 and 3 with each other. Referring to Figure 11, labeled as ]1 is a rigid beam of which one end is connected to the force motor ]6, and the free end of the bellows 1 is connected to the middle portion of the rigid beam 11. A nozzle 12 constitutes a nozzle-flapper mechanism in cooperation with a portion of the other end of the beam 11. A pneumatic pressure am-plifier 13 serves to amplify the back pressure of the nozzle 12 and generates an output, which is then fed to the bellows 1 while being transmitted as an output pressure Pout. Labeled as 17 is a zero adjustment spring interposed _g_ between the beam 11 and a casing or the like, and 18 is a balance weight mounted on the beam 11. 1~1, K2 and K3 denote the transfer functions of force motor 16, nozzle-flapper mechanisms 11, 12 and pneumatic pressure amplifier 13; AB and An denote the effective areas of bellows 1 and nozzle 12; and e ~2' ~n and Q denote the distances from coupling plate 4 to the centers of .
bellows 1, force motor 16, nozzle 12 and zero ad;justment spring 17 respectively.
The above described structure operates as follows. When an input current I. flows in the force motor 16 to generate an upward force Fi, the ln beam 11 is thereby rotated counterclockwise about the coupling plate 4 serving as a support point, so that the gap between thebeam 11 and the nozzle 12 is decreased as a result to increase the back pressure of the nozzle 12. Such a back pressure change is amplified by the pneumatic pressure amplifier 13 and is transmitted as an output pressure Pout while being fed to the bellows 1. In response to the output pressure Pout, the bellows 1 generates a clock-wise moment to the coupling plate 4 and balances the same against the moment produced by the force Fi. In this example, a large leverage is attainable due to employment ofthe bellows 1 containing the coupling plate 4 therein, since the support fulcrum can be located in the extreme proximity of the center axis of the bellows 1. Consequently, there is no need to employ any ~0 complicated means such as a dual leverage mechanism or a vector lever, and thus the structure is rendered remarkably simple to ensure small dimensions, low production cost and high accuracy.
According to experimental data, the accuracy attained was ~0.1 percent in one mechanism with its leverage set to a ratio of 1:30.
Figure 14 shows another example where this invention is used as a current-to-pressure converter, in which a bellows end 2 and a coupling plate 4 are integrated with each other as i]lustrated, and a recess 14 is formed therein to furnish flexibility. As a result, it becomes possib]e to prevent hysteresis error, temperature error or nonlinearity error that may occur in the case o~ non-integration at the joints of the coupling plate 4 due to the ~evenness of stresses when the two edges of the coupling plate 4 are secured to bellows ends 2 and 3 by welding or the like. Any of such errors influences greatly the accuracy of the device particularly when the construction is reduced dimensional]y and the signal transferred in the converter becomes small in value.
Furthermore, a dcuble-tube nozzle 12' is employed in this embodiment to increase the loop gain. In the ordinary nozzle utilized generally, a high loop gain is not obtainable since a negative feedback occurs because of the nozzle injection force as shown by a dotted line in Figure 13. In this embodiment, however, such a problem is solved by using the double-tube nozzle 12' in which an inner tube 122' is disposed at a position slightly lower than an outer tube 121t by a distance d.
Claims (8)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A pneumatic converter for converting a pneumatic pressure to a mechanical displacement comprising a bellows having a first fixed end and a second movable end secured to said first end by a flexible coupling plate disposed within the bellows at a position displaced from the central axis of the bellows.
2. The pneumatic converter as defined in claim 1, including an inlet for applying fluid pressure to the bellows means, and a means attached to a free end of the bellows for obtaining a dis-placement signal proportional to the fluid pressure.
3. The pneumatic converter as defined in claim 2, including a pointer having one end thereof anchored to the free end of the bellows.
4. The pneumatic converter as defined in claim 1, wherein the coupling plate is formed integrally with an end member closing one of the ends of the bellows.
5. The pneumatic converter as defined in claim 1, further comprising a nozzle located at the free end of the bellows, a flapper disposed opposite to the nozzle so as to constitute a nozzle-flapper mechanism in cooperation with the nozzle and dis-placeable in accordance with an input displacement, and an amplifier for amplifying the back pressure of the nozzle: wherein the output of said amplifier is transmitted as the output of the converter while being fed back partially to the bellows.
6. The pneumatic converter as defined in claim 1, further comprising a flapper displaceable in accordance with an input dis-placement, a nozzle located at the free end of the bellows and disposed opposite to the flapper in such a manner that the back pressure of the nozzle is introduced directly to the bellows via a communicating hole formed in the bellows, and a fluid source for supplying a fluid pressure to the bellows through a throttle:
wherein an output is obtained from a branch passage between the throttle and the bellows.
wherein an output is obtained from a branch passage between the throttle and the bellows.
7. The pneumatic converter as defined in claim 1, further comprising a rigid beam whose middle portion is kept in contact with the free end of the bellows, a current conversion element for applying to one end of the rigid beam a force proportional to an input current, a nozzle consituting a nozzle-flapper mechanism in cooperation with a portion of the other end of the rigid beam, and an amplifier for amplifying the back pressure of the nozzle:
wherein the output of said amplifier is transmitted as the output of the converter while being fed back partially to the bellows.
wherein the output of said amplifier is transmitted as the output of the converter while being fed back partially to the bellows.
8. The pneumatic converter as defined in claim 7, wherein the coupling plate is formed integrally with an end member closing one of the ends of the bellows and the nozzle is a double-tube type.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000339778A CA1142041A (en) | 1979-11-14 | 1979-11-14 | Pneumatic converter |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000339778A CA1142041A (en) | 1979-11-14 | 1979-11-14 | Pneumatic converter |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1142041A true CA1142041A (en) | 1983-03-01 |
Family
ID=4115603
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000339778A Expired CA1142041A (en) | 1979-11-14 | 1979-11-14 | Pneumatic converter |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1142041A (en) |
-
1979
- 1979-11-14 CA CA000339778A patent/CA1142041A/en not_active Expired
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