U.S. patent number 3,834,224 [Application Number 05/379,170] was granted by the patent office on 1974-09-10 for device for transducing force into pneumatic signal.
This patent grant is currently assigned to Toray Industries, Inc.. Invention is credited to Ryuya Itagaki, Sigeru Jinno, Tooru Sumi, Yoshiki Suzuki, Mitsuo Uchida.
United States Patent |
3,834,224 |
Uchida , et al. |
September 10, 1974 |
DEVICE FOR TRANSDUCING FORCE INTO PNEUMATIC SIGNAL
Abstract
A device for transducing a force into a pneumatic signal
comprises an air obstructing body composed of a rigid ball and
supporting disc against which a force to be transduced is applied,
and an air nozzle including an opening facing the rigid ball, the
air nozzle being connected to a compressed air supply unit.
Compressed air from the opening of the air nozzle flows away along
the surface of the rigid ball. As a result the above, the air
obstructing body moves upward or downward by the difference between
a compressed air force acting upon the rigid ball compressed and
the applied force to be transduced. When both forces balance, the
air obstructing body settles in an equilibrium position and at that
time, back air pressure of the nozzle has a relationship which is
proportional to the applied force to be transduced. Back air
pressure is measured by an air pressure measuring instrument
connected to the air nozzle as a pneumatic signal.
Inventors: |
Uchida; Mitsuo (Ibaraki,
JA), Jinno; Sigeru (Otsu, JA), Suzuki;
Yoshiki (Amagasaki, JA), Itagaki; Ryuya (Otsu,
JA), Sumi; Tooru (Otsu, JA) |
Assignee: |
Toray Industries, Inc. (Tokyo,
JA)
|
Family
ID: |
13418179 |
Appl.
No.: |
05/379,170 |
Filed: |
July 13, 1973 |
Foreign Application Priority Data
|
|
|
|
|
Jul 14, 1972 [JA] |
|
|
47-69976 |
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Current U.S.
Class: |
73/862.583 |
Current CPC
Class: |
G01L
1/02 (20130101) |
Current International
Class: |
G01L
1/02 (20060101); G01l 001/02 (); G01l 001/08 () |
Field of
Search: |
;73/141R ;137/82
;177/208 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Gill; James J.
Claims
What is claimed is:
1. Device for transducing force into pneumatic signal which
comprises:
1. means for supplying compressed air,
2. an air nozzle having an opening connected to said means for
supplying compressed air through an air tubing, the opening forming
an edge angle at a tip of the opening and the air tubing containing
an air restrictor,
3. an air obstructing body composed of a member having a curved
surface and a supporting disc, the member having the curved surface
facing said opening of said air nozzle and the supporting disc
contacting the opposite side of said curved surface, said body
having a member for transmitting an applied force to be transduced;
wherein said air obstructing body moves upward and downward by the
difference in force between a force acting upon the curved surface
by the compressed air from the air nozzle and the applied force to
be transduced, and
4. means for measuring back air pressure in said air nozzle,
wherein:
the radius of the opening of the air nozzle, the radius of
curvature of the curved surface, the radius of the supporting disc,
the air resistance of the air tubing and the edge angle of the
outer side of the opening of the air nozzle have the relationship
defined by the expressions of
R1/r = 1.about.10
R2 > r1
a/ao .gtoreq. 80
.theta. < 180
r .gtoreq. 1 where (r) is the radius of said opening, (R1) is the
radius of curvature of said curved surface, (R2) is the radius of
said supporting disc, (A) is the air resistance of said air
restrictor (Ao) is the air resistance of said air tubing and
(.theta.) is the edge angle of said opening.
2. A device as described in claim 1, wherein the member having a
curved surface is composed of a part of sphere.
3. A device as described in claim 1, the member having a curved
surface is a spherical ball.
4. A device as described in claim 1, wherein the projected area of
the supporting disc is circular.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a device for transducing a force
into a pneumatic signal. The invention provides a force to a
pneumatic transducing device which converts the amount of applied
force to be transduced into a corresponding air pressure value used
as a conventional industrial instrumentation technology pneumatic
signal.
Referring to the accompanying drawing, the following is a
description of one of the most popular transducing devices that has
been used for more than 20 years for a similar purpose as the
present invention.
In FIG. 1, the basic components comprise an air nozzle 1, an
opening 2, an air restrictor 3, air tubings 4, 5, 6 and 7, an air
bellows 8, an air pressure measuring instrument 9, an air supply
unit 10, a rod 11, a balancing beam 12 and a fulcrum 13. The air
nozzle 1 having an opening 2 for flowing compressed air is
connected to the air supply unit 10 through the air tubing 4 having
an air restrictor 3 therein. The air bellows 8 is connected to the
air pressure measuring instrument 9 through the air tubings 6 and
7, and is connected to the air nozzle 1 thhrough the air tubings 5
and 7. One end of the balancing beam 12 is rigidly connected to the
air bellows 8 by the rod 11, and the other end of the balancing
beam 12 is supported by the fulcrum 13. The balancing beam 12 is
placed adjacent the opening 2 of the air nozzle 1. The principle of
operation is as follows.
A force (F) to be transduced is applied on one end of the balancing
beam 12. When the force (F) increases, the balancing beam 12 tends
to incline around the fulcrum 13 in a direction to plug the
outcoming air flow from the air nozzle 1 (known as the so-called
"nozzle and flapper mechanism"), causing the back air pressure of
air nozzle 1 to increase to such an extent that a force produced by
the inflation of air bellows 8, with inside air pressure equal to
nozzle back air pressure, in the opposite direction to compensate,
or balance, the applied force (F) so that the balancing beam
movement settles at a new equilibrium position.
When the applied force (F) to be transduced decreases, the
balancing beam 12 and relating components act in reverse of the
above operation.
Such conventional transducing devices have some difficulties with
respect to the severe performance requirements often encountered in
industrial applications. Some of these are high measuring
accuracies, more reliable and stable operations, improved stability
under ambient temperature variations, adjustment free construction,
simplicity and compactness of mechanisms, and zero drift free
characteristics.
Careful observation during the performance evaluating test of the
typical conventional transducing device mentioned above reveals the
following points of consideration.
1. The angular displacement of one end of th balancing beam during
the full scale span range change of applied force was observed as
more than 100 to 200 .mu. (micron). This means the conventional
"force-balance" beam "moves" an amount that should not be ignored
from the standpoint of complete elimination of the undesirable
effects generally expected from a mechanism operating on the
deflection method.
2. The conventional device has many metal constructed parts, such
as bellows, springs andd hinges, each of which is subjected to the
influence of ambient temperature variations, etc.
3. The conventional device has many component parts, none of which
can be eliminated without sacrificing the guaranteed performance,
and each of which should be insured by accurate and elaborate
fabricating technology.
As a result, the overall performance characteristics can easily
deviate from the limits of specification performance by even
insignificant carelessness in assembly and adjustment.
4. One method of suppressing the undesirable results indicated
above is to adopt a relatively heavy order of force levels around
the balancing beam; the resulting larger dimensions of the main
component parts through miniaturization is the recent trend in
instrumentation technology.
Most of the above mentioned problems suggest we look over at the
basic conventional force balance mechanism traditionally used
during the past 20 years.
The invention we have developed solved most of those problems with
a minimum of component parts and with outstanding simplicity and
compactness.
The invention has no air bellows, balancing beam, fulcrums or
hinges. Nevertheless, the accuracy of force to air pressure
conversion performance was improved considerably.
BRIEF DESCRIPTION OF THE DRAWING
These and other objects are accomplished by the parts,
improvements, combinations and arrangements comprising the
invention, a preferred embodiment of which is shown and described
in detail herein.
Various modifications and changes in details of construction are
comprehended within the scope of the appended claims.
FIG. 1 is a principle illustration in cross-section of the device
for transducing the force into the pneumatic signal of the prior
art.
FIG. 2 is a schematic cross-sectional view illustrating one
embodiment of the present invention.
FIG. 3 is a schematic cross-sectional view illustrating the basic
system composition of the present invention.
FIG. 4 is a schematic cross-sectional view showing the force to air
pressure transducing element.
FIG. 5 is a graph relating to an applied force to be measured and
the pneumatic signal output.
FIG. 6 is a graph relating to output air pressure change/supply air
pressure change and a radius of supporting disc/radius of the rigid
ball.
FIG. 7 is a schematic illustration of some variations of the
supporting disc. FIGS. 8, 9 and 10 are graphs relating to
hysteresis, linearity or error and a radius of the rigid
ball/radius of the opening.
FIGS. 11, 12 and 13 are graphs relating to hysteresis, linearity or
error and radius of the opening.
FIGS. 14, 15 and 16 are graphs relating to hysteresis, linearity or
error and edge angle of the opening.
FIG. 17 is a graph relating to output air pressure change and an
air resistance of the air restrictor/an air resistance of the air
tubing.
DETAILED DESCRIPTION OF THE INVENTION
Referring to FIG. 2, a force (F) to be transduced is applied
downward on the lower end of the vertical rod 25 which is connected
with circular suspension ring 21 by an over-load safety spring 24.
Force (F) is conveyed in sequence from vertical rod 25, circular
suspension ring 21, and supporting disc 22 to air obstructing ball
23.
On the other hand, compressed air is supplied from air supply unit
28 through capillary air restrictor 26 and air reservoir chamber 27
to air outflow nozzle 29.
The difference of the force (F) to be transduced and a force
developed in the opposite direction by a static back pressure
within the nozzle opening and an outcoming air flow causes the air
obstructing ball 23 to move upward or downward, depending on
whether the sign of the difference of the forces is plus or minus,
until the air ostructing ball 23 reaches an equilibrium
position.
In this state, the air pressure between air nozzle 29 and air
restrictor 26 shows an exact one-to- one correspondence with the
force to be transduced, and can be used as a measured pneumatic
signal of force (F).
Eventually, the change in the amount of force to be transduced can
be converted to the corresponding change in output air pressure at
the output air tubing 30 and measured by the air pressure measuring
instrument 31.
Further detailed explanation of the invention follows.
FIG. 3 shows the basic system composition of the invention, and
FIG. 4 shows the force to air pressure transducing element, the
most essential part of the invention.
Each component part is shown as: compressed air supply unit 1, air
tubing 2, air restrictor 3, air reservoir 4, air nozzle opening 5,
air obstrucing body 6 composed of rigid ball 6A and supporting disc
6B, air pressure outlet 7, air tubing 8, pneumatic signal
indicating instrument 9 and the applied force to be transduced
(F).
Referring to FIG. 3, compressed air is supplied from a compressed
air supply 1 and passed through air restrictor 3 and air tubing 2,
reaching air reservoir 4 and flowing out to the atmosphere through
nozzle opening 5.
In the upper outside position of the central vertical axis of air
reservoir 4, the air obstructing body 6 is placed for free
movement, especially in a vertical direction.
The air obstructing body 6 is composed of a rigid ball 6A and a
supporting disc 6B with one side of rigid ball 6A facing closely
the nozzle opening 5 and a supporting disc 6B is contacted with
rigid ball 6A on the other side of the nozzle opening 5.
The air obstructing body 6 reaches a certain equilibrium position
depending on the relationship between two forces oppositely
exerted. One force is developed on one side of rigid ball 6A by the
outflowing air from the air nozzle opening 5, and the other force
to be transduced is exerted on the supporting disc 6B.
When a force to be transduced changes the outgoing flow rate of
air, a corresponding change results, with air restrictor 3 causing
an air reservoir pressure change.
Consequently, the air pressure in the air reservoir 4,
by indicating instrument 9 through air tubing 8, has a reproducible
relation with force (F) to be transduced.
The edge shape of the end of the air nozzle opening 5 assures
stable and smooth air.
The data from observations made during a performance evaluating
test of the invention using the actual prototype shown in FIGS. 3
and 4 are explained as follows.
Referring to FIG. 5, a force to be transduced as a pneumatic output
signal relation is shown. The scale unit of the abscissa axis is in
grams and that of the ordinate axis is in percentage. Each
dimension of this example is as follows. The radii of nozzle
opening, ball and supporting disc are 5.1 mm, 5.1 mm and 14.75 mm
respectively. Compressed air pressure is 1.6 kg/cm.sup.2 G. 100
percent of output pneumatic signal corresponds to 1.0 kg/cm.sup.2
G. FIG. 5 shows that the invention assures highly linear conversion
characteristics. An interesting dimensional relationship exists
between the radii of the supporting disc and rigid ball and the
ratio of output air pressure change and supply air pressure change
under constant applied force. FIG. 6 shows this relationship as
observed in the test using the prototype shown in FIGS. 3 and
4.
This data indicates that the effects of the variation in supply air
pressure on the measured value of output could be neglected when
the radius ratio of supporting disc to ball exceeds 1.5.
Generally, it is desirable to select a supporting disc having a
larger projection area in the perpendicular plane against the
central axis of air outflow nozzle than the ball has.
In the case explained above, the air obstructing body was composed
of a complete sphere and a disc. However, another experiment
indicated that the rigid ball need not be completely spherical in
shape although the side facing against the air nozzle should have a
spherical surface.
Similarly, the supporting disc need not necessarily be completely
circular in shape. In this case, the projection area of the
component parts of the air obstructing body should be defined as
the value giving maximum projection diameter considered as having
complete circular cross sectional shapes.
FIG. 7 shows some variations of supporting disc shapes tested in
the experiments. The typical data relating to displacement of the
air obstructing body observed in the experiments shows displacement
of the air obstructing body to be less than 20 .mu., and
reproducibility of the output signal better than .+-. 0.12 percent
and the effect of ambient temperature variation of .+-. 30.degree.
C on the output signal variation to be better than .+-. 0.2
percent.
The dimensional relation of the radius of a spherical air
obstructing body and the air nozzle opening, using the prototype
shown in FIGS. 3 and 4, was observed with regard to several
performance characteristics.
FIGS. 8, 9 and 10 show the manner by which the radius ratio of
spherical air obstructing body to air nozzle opening affects the
performance characteristics with regard to hysteresis, linearity,
and error caused by variations in the supply of air pressure
respectively.
FIGS. 8, 9 and 10 illustrate that the performance error could be
suppressed within 1 percent of full scale span if the range in
ratio falls between 1 and 10.
Better performance characteristics can be obtained when the radius
of air nozzle opening is selected as more than 1.75 mm and the
ratio of the radius of ball to air nozzle opening is also selected
within the range of 1.5 -5.0 . Then the three performance
parameters mentioned above show better than .+-. 0.25 percent of
full scale span.
The three performance parameters explained above, (hysteresis,
linearity and error caused by variation in supply of air pressure)
also depend on the dimension of the radius of the air nozzle the
relationship of which are shown in FIGS. 11, 12 and 13.
This data indicates that in order to maintain the performance error
at less than 1 percent of full scale span, then it is necessary to
select the dimension of radius of air nozzle of at least 1 mm. By
selecting the diameter in a proper value, performance better than
.+-. 0.25 of full scale span was obtained.
AS to the relation of the edge angle (.theta.) of the air nozzle,
shown in FIG. 4, to the performance characteristics, experimental
results are shown in FIGS. 14, 15 and 16.
The abscissa axis of these figures express the angle (.theta.) of
the edge shape of the air nozzle.
This data indicates that when the value of (.theta.) exceeds
180.degree. the performance characteristics suddenly show a steep
increase in errors and near the 180.degree. value the data suggests
unstable performance.
Consequently, the desirable edge angle is less than
180.degree..
A relation also exists between performance characteristics and the
air path resistivity of the air restrictor 3 (abbreviated as
resistance (A)), and the air path resistivity of the air path
beginning from the air restriction outlet via the air reservoir to
the air nozzle opening (abbreviated as resistance (Ao).
FIG. 17 shows this relation using the prototype shown in FIGS. 3
and 4. Abscissa axis is the ratio of (A) vs. r,in logarithmic
scale, and ordinate axis is output signal error readings in
kg/cm.sup.2.
These data were plotted at each (.sup.A /Ao) value by changing air
supply pressure by 0.4 kg/cm.sup.2 from the stationary value, and
the force to be measured in four cases, namely Og, 10g, 20g, 25g,
25g. The radii of spherical obstructing body, air nozzle, and
supporting disc were 5.6 mm, 5.1 mm, and 7.5 mm, respectively. Air
supply pressure was 1.6 kg/cm.sup.2 G. FIG. 17 indicates that below
an (.sup.A /Ao) ratio value of 80,the output signal showed unstable
performance with considerable errors. These results suggest that
the ratio value should be more than 80 for the purpose of the
invention.
In this experiment, the changing amount of air supply was selected
as 0.4 kg/cm.sup.2 based on the certain criteria popular in the
industrial instrumentation field: (A) can be properly selected by
adjusting air restricting element.
* * * * *