Pressure transducer

A pressure transducer having two through holes extending in one direction and a additional two through holes in another direction in a detection block such that they cross each other. The transducer has a pressure receiving portion located in the center of the detection block and surrounded by the through holes, and a retaining portion located around the periphery of the detection block and surrounding the pressure receiving portion. The pressure receiving portion is connected to the retaining portion through parallel upper and lower thin wall portions which are formed continuously between the upper wall of the through holes and the upper surface of the detection block, and between the lower wall of the through holes and the lower surface of the detection block.

BACKGROUND OF THE INVENTION 
The present invention relates to a pressure transducer wherein through 
holes are bored in a detection block portion such that easily-deformable 
parallel thin portions are formed between the upper and lower hole walls 
of the through holes and the upper and lower surfaces of the detection 
block portion. 
When a tunnel is excavated in soft ground by a shield excavator while the 
amounts of excavated earth and exhausted earth are balanced, earth 
excavated by the rotary cutter of the excavator is packed into a chamber 
separated by bulkheads, and it is detected whether or not the earth 
pressure in the chamber is exactly equal to the static earth pressure at a 
facing which keeps the facing stable. An earth pressure cell employed for 
this purpose must be able to deliver a correct mean stress constantly even 
when it receives a concentrated eccentric load owing to the presence of 
pebbles and the like. A similar ability is also needed, and actually tried 
to be sought, in various fields of technology, such as when an 
investigation is made of the forces on the inside of a silo for the 
purpose of designing and controlling the silo. 
The inventor of the present application has suggested several types of load 
converters which can meet the aforementioned requirements, some of which 
will be described hereinafter. 
One is the constitution wherein parallel flat plates are formed by boring a 
through hole having a square sectional shape in a detection block. This 
structure is shown in Japanese Patent Application published under No. 
124169/1979. 
Another is the improved constitution wherein a through hole is provided by 
cutting off the section between two small round holes and connecting them 
instead of having a square hole, in view of such inconvenience as in 
preparation of the parallel flat-plates by a through hole of square 
section. This is not only very easy to prepare but also capable of 
fulfilling a function equivalent to the function of the aforesaid parallel 
flat plates. This is disclosed in my co-pending U.S. patent application 
Ser. No. 433,109 filed Oct. 6, 1982. 
In order to facilitate the understanding of the present invention, an 
outline of the invention disclosed in the aforementioned co-pending U.S. 
application is explained with reference to FIG. 1. 
In FIG. 1, a detection block 1b is formed in the shape of a chest with 
rounded in surfaces as illustrated, and small round holes 3 are formed at 
upper and lower positions in the direction perpendicular to the 
longitudinal direction of the block. Extended through holes 2 are formed 
with their upper ends having a larger distance between them than that 
between the lower ends thereof, by connecting two round holes 3 together 
through a connection passage 4. A pressure receiving portion 5 located at 
the middle of the longitudinal detection block 1b, which is held between 
the two through holes 2 thus prepared, and retaining portions 6 located on 
both sides of the pressure receiving portion 5 are connected together by 
upper and lower parallel thin wall portions 7 formed between each of the 
upper and lower round holes 3 and the upper and lower surface of the 
detection block 1b against which the upper and lower round hole portions 3 
confront. A pressure receiving plate 1a is formed above the pressure 
receiving portion 5 in a unitary structure, while a circular base 1c 
supporting the retaining portions 6 in a built-in beam manner is formed 
below the portions 6, and an opening 8 is formed in the base 1c. When the 
pressure receiving plate 1a is loaded in the axial direction, the pressure 
receiving portion 5 in the middle of the detection block 1b is displaced 
in the vertical direction so that its center of gravity moves parallel. 
Therefore, the displacement and the force applied can be determined by a 
displacement detection device or a force detection device provided 
underneath, and in addition, since compression and tension strains are 
generated in the parallel thin portions 7 which are each bent, strain 
outputs can be obtained by attaching four strain gages to the portions 7 
and forming them into a Wheatstone bridge. 
However, since the parallel thin portions located at four upper and lower 
portions are configured so that they extend in the same, single direction, 
the characteristics thereof and the results obtained are influenced by the 
direction of the load and differ in accordance with whether the direction 
of the load is the same as that direction or is perpendicular thereto. 
Although it may be possible to improve the transducer by changing the 
linear format of the detection block 1b to cross-shaped format, such a 
change in format configuration still provides an opening 8 formed in 
either case between the detection block 1b and the base member 1c, and 
this brings about another disadvantage that the detection of the load 
transduced into liquid pressure of a liquid enclosed inside the circular 
base member 1c is impossible and the formation of an explosion-proof 
terminal box wherein an inactive gas is enclosed is also impossible with 
the structure of the known transducer. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide an improved load 
transducer which permits the elimination of the disadvantages of the known 
transducers. 
Another object of the invention is to provide a load transducer which has 
improved eccentric load characteristics. 
A further object of the invention is to provide a new load transducer in 
which the deformation of the structural body of the transducer is not 
transmitted to the detection portions thereof. 
Another object of the present invention is to provide a load transducer 
wherein linearity and non-hysterisis characteristics, which are 
indispensable to a pressure gage, are guaranteed. 
In the load transducer according to the present invention, two through 
holes are bored in each of two different directions in a detection block 
in such a manner that they cross each other. The load transducer has a 
pressure receiving member or portion located in the center of the 
detection block and surrounded by the through holes, and a retaining 
member or portions located around the periphery of the detection block and 
surrounding the pressure receiving portion. The pressure receiving portion 
and the retaining portion are connected to each other by upper and lower 
parallel thin wall portions which are formed continuously between the 
upper and lower hole surfaces of each through hole, and the upper and 
lower surfaces of the detection block. This structure attains the objects 
of the invention described above. 
The pressure receiving portion of the detection block may have a shape of a 
square pyramid with a narrower base, or may have a shape of a square 
pillar by arranging the four through holes vertically. 
A tubular protective housing may be connected to the base of the detection 
block with an annular gap formed between the inner surface of the housing 
and the outer surface of the detection block. The detection block has an 
annular recess to form a pressure receiving plate. A sealing material, 
such as cold-vulcanized silicone rubber, is provided between the periphery 
of the pressure receiving plate and the protective housing so as to seal 
the annular gap. 
It is preferred that the detection block has an annular thin portion 
adjacent to the base so that the deformation of the structural body of the 
transducer is not transmitted to the detection portion thereof. 
The detection block may have a recess at its one end opposite to the 
aforesaid pressure receiving plate so that the recess may include therein 
a liquid. The fluctuations of the liquid pressure can be indicated by a 
Bourdon tube. 
Other objects and features of the present invention will become more 
apparent from the following description of the preferred embodiments of 
the invention, which will be made with reference to the accompanying 
drawings.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
In FIGS. 2-4 illustrating one embodiment of the present invention, 
particularly FIG. 2 which is given to facilitate comparison with the 
structure of FIG. 1, a substantially cylindrical detection block 1b is 
provided with two through holes 2 bored in each of two different 
directions in the block such that they cross each other. The detection 
block has an annular recess 1d to form an integral end pressure receiving 
portion (hereinafter pressure receiving plate portion) 1a. Accordingly, 
while the through holes in the structure of FIG. 1 extend in a single 
direction, on the other hand, the through holes in the apparatus of the 
present invention extend in two different directions which virtually cross 
each other, as illustrated. Similarly, the parallel thin portions 7 
connect the central pressure receiving portion 5 of the detection block 1b 
to the retaining portion 6 in the upper and lower parts of the detection 
block 1b. The thin portions 7 in the upper part of detecting block 1b are 
formed at the annular exposed surface surrounding the connection to 
pressure receiving plate portion 1a in the annular recess 1d . As is 
apparent from FIG. 2, the thin portions, which are simply parallel in the 
structure of FIG. 1, are in a continuous square formation. Further, the 
part equivalent to, or corresponding to, the opening 8 in the structure of 
FIG. 1 is not provided in the structure of the present invention. The 
boring and cutting of the through holes and portions 5, 6, 7 can be 
readily formed precisely without substantial labor or difficulty. 
FIG. 3 illustrates the hole structure of the embodiment of FIG. 2 which is 
obtained by the four crossing through holes 2. The cross-sectional shape 
of each through hole 2 is not limited in any way to that shown in FIG. 3 
in which two round hole parts 3, connected together with a connection hole 
part 4, extend in cross section in one direction, and can be modified to 
any other desirable configurations. For instance, the connection hole part 
4 may be provided along the center line connecting two round hole parts 3 
as shown in FIG. 5A, or may take the shape of a continuous hole formed by 
a plurality of round holes partly overlapping each other as shown in FIG. 
5B. In the illustrated embodiment, the shape of the central pressure 
receiving portion 5 surrounded by the four through holes 2 is that of a 
square pyramid with a narrower base. This could also be formed as a square 
pillar by arranging the four through holes into a vertical configuration. 
Furthermore, the pressure receiving planar portion 1a which is formed 
integrally with detection block 1b can be formed in the shape of a 
threaded rod in an appropriate manner when the principle of the invention 
is applied to a load gage. In this way, appropriate alterations can be 
applied according to various uses thereof. 
FIG. 4 illustrates a practical example of a structure on the basis of the 
constitution shown in FIG. 2. The pressure transducer has a protective 
tube 9 which is welded onto the base portion 1c so that a certain annular 
gap is formed between the tube 9 and the side surface of the pressure 
receiving plate portion 1a, and a plurality of bolt holes 10 are provided 
in part of the base portion 1c which projects in the shape of a flange so 
as to make it possible to mount the device on various apparatuses, and a 
cover 13 having a receptacle 12 for a lead cable 11 is fitted to the base 
portion 1c by bolts 14. The annular gap between the pressure receiving 
plate portion 1a and the inner surface of the protective tube 9 is sealed 
at the periphery of the pressure receiving plate portion 1a with a soft 
elastic sealing material 15, which preferably is an injection molded piece 
of cold-vulcanized silicone rubber, so that the linearity and 
non-hysterisis characteristics which are material and indispensable to a 
pressure gage are guaranteed, and a complete sealing is ensured. 
In the illustrated embodiment, the section in which the detection block 1b 
and the base portion 1c are connected is formed into a circular thin wall 
as indicated by reference numeral 16, so that the deformation of the 
structural body of the pressure transducer is not transmitted to the 
detection portion or is minimized if transmitted thereto. For the purpose 
of detecting strain in the lower parallel thin wall portions 7 by means of 
strain gages, four strain gages 17 combined into a Wheatstone bridge are 
attached thereto, so that a compression strain can be detected by strain 
gages attached to the side of the retaining portion 6, and tension strain 
can be detected by strain gages attached to the central pressure receiving 
portion 5. The strain gages 17 are connected to the lead cable 11 through 
the intermediary of a terminal board 18, the terminal board 18 being held 
by a retainer member 19 which fits in a seat inside the base portions 1c 
and held by bolts 20. 
FIG. 6 illustrates a calibration line in the direction of the pressure 
applied to the device, which shows an excellent linearity and almost no 
hysterisis. 
FIG. 7 shows the eccentric load characteristics of the device in which the 
strain outputs indicate a nearly fixed value irrespective of the 
eccentricity of the load acting point. 
FIG. 8 shows a pressure transducer in accordance with another embodiment of 
the invention. In the modified transducer, the pressure on the pressure 
receiving plate portion 1a is transmitted to the central pressure 
receiving portion 5 and further to a liquid 21 enclosed inside the 
circular base portion and a cover 13, and the fluctuations of the liquid 
pressure thereof are indicated directly by a Bourdon tube 22. The other 
structure will be understood from the foregoing description and from the 
drawing, any further description will not be made. 
As will be apparent from the foregoing, the pressure transducer according 
to the present invention provides further improvements in the eccentric 
load characteristics, in particular, while maintaining an ease of 
preparation which is relatively effective for mass production. Further, 
the present invention is excellent also in the sense that, after various 
transducing elements are arranged in a compartment formed in the space 
below the detection block 1b, they can be sealed up and separated from the 
surrounding space, or that detection through liquid-pressure conversion 
can be conducted by enclosing a liquid space, as in the embodiment of FIG. 
8. 
Although the present invention has been described with reference to the 
preferred embodiments, many modifications and alterations can be made 
within the spirit of the invention.