Note: Descriptions are shown in the official language in which they were submitted.
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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
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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
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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
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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
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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
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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-
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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
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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
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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
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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.
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