U.S. patent application number 15/868979 was filed with the patent office on 2018-05-17 for method of producing ultrasonic flowmeter, ultrasonic flowmeter produced by the method and fluid controller having the ultrasonic flowmeter.
The applicant listed for this patent is ASAHI ORGANIC CHEMICALS INDUSTRY CO., LTD.. Invention is credited to Hidenori EBIHARA, Syunichirou HAGIHARA.
Application Number | 20180136022 15/868979 |
Document ID | / |
Family ID | 50788436 |
Filed Date | 2018-05-17 |
United States Patent
Application |
20180136022 |
Kind Code |
A1 |
HAGIHARA; Syunichirou ; et
al. |
May 17, 2018 |
METHOD OF PRODUCING ULTRASONIC FLOWMETER, ULTRASONIC FLOWMETER
PRODUCED BY THE METHOD AND FLUID CONTROLLER HAVING THE ULTRASONIC
FLOWMETER
Abstract
An ultrasonic flowmeter includes a measurement pipe through
which a fluid flows, and two ultrasonic transceivers provided on
outer side portions of the measurement pipe so as to be spaced
apart from each other in an axis direction. In the method of
producing the ultrasonic flowmeter, fabricating the measurement
pipe in advance is fabricated, and then is set in a mold as an
insert. Two transmitting bodies are formed by insert molding on the
outer side portions of the measurement pipe so as to be spaced
apart from each other in the axis direction, so that the two
transmitting bodies are integral with the measurement pipe. The two
ultrasonic transceivers are mounted on the two transmitting bodies,
respectively.
Inventors: |
HAGIHARA; Syunichirou;
(Miyazaki, JP) ; EBIHARA; Hidenori; (Miyazaki,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ASAHI ORGANIC CHEMICALS INDUSTRY CO., LTD. |
Miyazaki |
|
JP |
|
|
Family ID: |
50788436 |
Appl. No.: |
15/868979 |
Filed: |
January 11, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
14061254 |
Oct 23, 2013 |
9903744 |
|
|
15868979 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
Y10T 137/7722 20150401;
B29C 45/14409 20130101; G01F 15/18 20130101; G01F 1/662 20130101;
Y10T 29/49005 20150115; G01F 1/66 20130101; B29C 2045/14147
20130101 |
International
Class: |
G01F 1/66 20060101
G01F001/66; B29C 45/14 20060101 B29C045/14 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 24, 2012 |
JP |
2012-234890 |
Claims
1. A method of producing an ultrasonic flowmeter, said ultrasonic
flowmeter comprising a measurement pipe configured for a fluid to
flow through, said measurement pipe having outer side portions
spaced apart from each other in an axis direction of the
measurement pipe; and two ultrasonic transceivers provided on the
outer side portions of the measurement pipe, said method
comprising: forming said measurement pipe of fluorine resin by
extrusion molding in advance; setting said measurement pipe in a
mold as an insert; forming two transmitting bodies of the same
material as said measurement pipe by insert molding on the outer
side portions of said measurement pipe so as to be spaced apart
from each other in the axis direction of said measurement pipe, so
that said two transmitting bodies are integral with said
measurement pipe, said two transmitting bodies surrounding a
circumference of said measurement pipe; and mounting said two
ultrasonic transceivers on said two transmitting bodies,
respectively.
2. The method to claim 1, wherein an arithmetic mean roughness Ra
of an inner peripheral surface of said measurement pipe satisfies a
relation of 0 .mu.m<Ra.ltoreq.0.2 .mu.m.
3. The method according to claim 2, wherein an inner diameter D of
said measurement pipe satisfies a relation of 0.5
mm.ltoreq.D.ltoreq.10 mm.
4. The method according to claim 1, wherein a flow passage or a
joint is formed by insert molding on at least one of an upstream
side and a downstream side of said measurement pipe in the axis
direction of the measurement pipe so as to be integral with said
measurement pipe.
5. The method according to claim 1, wherein a flow passage is
formed by insert molding on at least one of an upstream side and a
downstream side of said measurement pipe in the axis direction of
the measurement pipe so as to be integral with said measurement
pipe, and a joint is formed by insert molding on the flow passage
on at least one of the upstream side and the downstream side of
said measurement pipe.
6. The method according to claim 1, wherein said setting comprises
inserting said measurement pipe inside the mold.
7. The method according to claim 1, wherein said forming the
transmitting bodies further includes injecting molding for the
transmitting bodies into the mold to form molded portion; and
removing the measurement pipe and the molded portions, which are
integral with each other when the molding material is solidified,
from the mold.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a continuation of U.S.
application Ser. No. 14/061,254 filed Oct. 23, 2013, and claims
priority from Japanese Application Number 2012-234890, filed Oct.
24, 2012. The disclosures of all of the above-listed prior
applications are hereby incorporated by reference herein in their
entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
[0002] The present invention relates to a method of producing an
ultrasonic flowmeter, an ultrasonic flowmeter produced by the
method, and a fluid controller having the ultrasonic flowmeter,
which ultrasonic flowmeter is used in fluid transportation in
various industries such as chemical works, semiconductor
manufacture field, food processing field and biotechnology field,
which propagates an ultrasonic vibration through a fluid and
measures a flow velocity or flow rate of the fluid from a
difference between ultrasonic wave propagation time from an
upstream side of the flow and ultrasonic wave propagation time from
a downstream side of the flow. The present invention particularly
relates to a method of producing an ultrasonic flowmeter, an
ultrasonic flowmeter produced by the method, and a fluid controller
having the ultrasonic flowmeter, which ultrasonic flowmeter is
suitable for measuring a micro flow rate and the flow rate of a
slurry fluid or especially the CMP slurry fluid used in the
semiconductor field.
2. Description of the Related Art
[0003] Ultrasonic flowmeters for measuring a flow velocity or flow
rate of a fluid flowing in a measurement pipe from a difference in
ultrasonic wave propagation time are generally classified into two
types.
[0004] In a first type of ultrasonic flowmeter, flow passages are
connected to both ends of a linear measurement pipe so that the
flow passages are at generally right angle to the measurement pipe,
and ultrasonic transceivers are disposed on an upstream side and a
downstream side of the measurement pipe so that the ultrasonic
transceivers face each other across the measurement pipe. In the
ultrasonic flowmeter, an ultrasonic wave transmitted from the
upstream ultrasonic transceiver is propagated through a fluid in
the measurement pipe and received by the downstream ultrasonic
transceiver. Instantaneously after that, an ultrasonic wave
transmitted from the downstream transceiver is propagated into the
fluid in the measurement and received by the upstream ultrasonic
transceiver (see Japanese Unexamined Patent Publication Nos.
2000-146645, 2006-337059, 2007-58352, etc.). In the process, a
difference between the ultrasonic wave propagation time from the
upstream ultrasonic transceiver to the downstream ultrasonic
transceiver and the ultrasonic wave propagation time from the
downstream ultrasonic transceiver to the upstream ultrasonic
transceiver is used to measure the flow velocity of the fluid in
the measurement pipe and measure the flow rate.
[0005] In a second type of ultrasonic flowmeter, two ultrasonic
transceivers are disposed on transmitting bodies mounted on outer
peripheral portions of a linear measurement pipe, respectively. In
the ultrasonic flowmeter, an ultrasonic wave transmitted from one
of the ultrasonic transceivers is propagated into a fluid in the
measurement pipe through the transmitting body and a wall of the
measurement pipe, propagated obliquely with respect to a flowing
direction of the fluid in the measurement pipe while being
reflected on the pipe wall of the measurement pipe, and received by
the other ultrasonic transceiver. Instantaneously after that, the
transmitting side and the receiving side are switched, and,
similarly to above, an ultrasonic wave transmitted from one of the
ultrasonic transceivers is received by the other ultrasonic
transceiver (see Japanese Unexamined Patent Publication Nos.
2005-188974, 2008-275607, 2011-112499, etc.). In the process, like
the first type of the ultrasonic flowmeter, a difference between
the ultrasonic wave propagation time from the upstream ultrasonic
transceiver to the downstream ultrasonic transceiver and the
ultrasonic wave propagation time from the downstream ultrasonic
transceiver to the upstream ultrasonic transceiver is used to
determine the flow velocity of the fluid in the measurement pipe
and measure the flow rate
[0006] In the first type of the ultrasonic flowmeter, bent portions
are formed on both end portions of the measurement pipe. Therefore,
especially in a case where a fluid flowing in the measurement pipe
is a slurry, the slurry is deposited and fixed to the bent
portions, and propagation of the ultrasonic vibration is hindered,
thus causing a problem that accurate measurement of the flow rate
is not possible. On the contrary, the second type of the ultrasonic
flowmeter has an advantage that the above-mentioned problem is
unlikely to happen since it is not necessary to form bent portions
on both end portions of the measurement pipe.
[0007] However, in the second type of the ultrasonic flowmeter, it
is necessary to provide the transmitting bodies on the outer
peripheral portion of the measurement pipe. In a case where the
transmitting bodies fabricated in a process different from the
measurement pipe fabricating process are later mounted to the
measurement pipe by an adhesive, welding, etc., it is likely that
positions of the transmitting bodies with respect to the
measurement pipe and a distance between the transmission bodies
vary depending on proficiency of an operator, thus causing
deterioration of measurement accuracy. Further, factors such as an
amount of adhesive applied, drying time of the adhesive, uniformity
of application of the adhesive, etc., cause variation in
performance of the ultrasonic flowmeter, and therefore need to be
controlled in order to ensure performance of the ultrasonic
flowmeter. In addition, in a case where a small-diameter
measurement pipe is used, a problem occurs that it is difficult to
assemble the measurement pipe and the transmitting bodies. It is
not necessary to use an adhesive when the measurement pipe and the
transmitting bodies are formed integrally with each other by
injection molding. However, it is necessary to provide a draft in
an inner diameter of the measurement pipe, which makes a flow
velocity of a fluid in the measurement pipe non-constant.
Therefore, forming the measurement pipe and the transmitting bodies
integrally with each other is not suitable especially for
fabricating a small-diameter measurement pipe. As a result, when
fabricating the transmitting bodies and the measurement pipe
integrally with each other, cutting work is often used.
[0008] However, with the cutting work, it is especially difficult
to fabricate a measurement pipe having a small pipe diameter, and
it is also difficult to control quality of an inner peripheral
surface of the measurement pipe. Further, microasperity is formed
on the inner peripheral surface of the measurement pipe, and
microscopic bubbles are thus easily adhered to the inner peripheral
surface of the measurement pipe. Surfaces of the microscopic
bubbles reflect an ultrasonic vibration, thereby causing a decrease
in output signal strength and deterioration of measurement accuracy
especially in the second type of the ultrasonic flowmeter in which
the ultrasonic vibration is propagated while being reflected within
the measurement pipe.
[0009] In order to solve the problem of the microscopic bubbles
inside the measurement pipe, Japanese Unexamined Patent Publication
No. 2012-42243 suggests a straight-pipe type ultrasonic flowmeter
in which, as shown in FIG. 10, a measurement portion 103 provided
in a measurement space 102 of a housing 101 includes a straight
pipe member 104 for measurement through which a fluid for
measurement flows, and a pair of transducers 105 disposed on an
outer periphery of the pipe member 104 at a given interval in an
axis direction. A diameter-reduced portion or a bubble-crushing
portion 106 is provided on a downstream side of the pipe member
104, thereby crushing small bubbles, which are generated when a
flow rate is small and are likely to gather near an inner wall
surface. However, pressure drop is caused by the diameter-reduced
portion provided as the bubble-crushing portion 106, and foreign
matters are likely to be adhered to and deposited on the
diameter-reduced portion. Further, it becomes difficult for
regular-sized bubbles to pass through due to the diameter-reduced
portion, which can cause deterioration of measurement accuracy.
[0010] Accordingly, it is an object of the present invention to
solve the problems of the prior art and to provide an ultrasonic
flowmeter with high measurement accuracy, in which transmitting
bodies for ultrasonic transceivers to be mounted thereon are formed
integrally with a measurement pipe.
[0011] In a first aspect, according to the present invention there
is provided a method of producing an ultrasonic flowmeter including
a measurement pipe through which a fluid flows, and two ultrasonic
transceivers provided on outer side portions of the measurement
pipe so as to be spaced apart from each other in an axis direction,
which includes steps of: fabricating the measurement pipe in
advance; setting the measurement pipe in a mold as an insert;
forming two transmitting bodies by insert molding on the outer side
portions of the measurement pipe so as to be spaced apart from each
other in the axis direction, so that the two transmitting bodies
are integral with the measurement pipe; and mounting the two
ultrasonic transceivers on the two transmitting bodies,
respectively.
[0012] In the method of producing the ultrasonic flowmeter, the
measurement pipe fabricated in advance is arranged as the insert in
the mold, and the transmitting bodies are formed by insert molding
on the outer side portions of the measurement pipe so that the
transmitting bodies are integral with the measurement pipe.
Therefore, it is possible that the measurement pipe and the
transmitting bodies are fabricated in different processes, and it
is easy to improve smoothness of an inner peripheral surface of the
measurement pipe. Thus, the above method can be easily applied to a
measurement pipe having a small diameter. Further, in the above
ultrasonic flowmeter production method, it is not necessary to
integrate the measurement pipe with the transmitting bodies by
using an adhesive. Therefore, a problem that performance of the
ultrasonic flowmeter can be varied due to use of an adhesive is
avoidable, and fabrication of the measurement pipe having a small
diameter can be easier. It is also possible to form the
transmitting bodies accurately at predetermined positions on the
outer side portions of the measurement pipe with almost no
variation. As a result, it can be easier to ensure a certain level
of measurement accuracy without depending on proficiency of an
operator.
[0013] In the ultrasonic flowmeter production method, the
measurement pipe is preferably fabricated by extrusion molding.
Since the inner peripheral surface of the measurement pipe
fabricated by extrusion molding has a small surface roughness, it
is possible to prevent microscopic bubbles from being adhered to
the inner peripheral surface of the measurement pipe. Also, when
extrusion molding is used, unlike injection molding, no draft is
needed in the inner peripheral surface of the measurement pipe,
thus preventing influence of the draft on measurement. Therefore,
the above method makes it easier to fabricate a measurement pipe
having a small diameter and can be applied to fabrication of a
measurement pipe having a wide range of diameters. Further, when
the measurement pipe is fabricated, heat is applied once.
Therefore, when insert molding is carried out by using the
measurement pipe, excellent thermal stability and productivity are
obtained because the measurement pipe is heated once when the
measurement pipe is fabricated. The arithmetic mean roughness Ra of
the inner peripheral surface of the measurement pipe more
preferably satisfies a relation of 0 .mu.m<Ra 0.2 .mu.m. When
the arithmetic mean roughness of the inner peripheral surface of
the measurement pipe is within the above range, adhesion of
microscopic bubbles to the inner peripheral surface of the
measurement pipe can be prevented effectively.
[0014] Preferably, an inner diameter D of the measurement pipe
satisfies a relation of 0.5 mm.ltoreq.D.ltoreq.10 mm.
[0015] Also, the measurement pipe and the transmitting bodies are
preferably made of a same material, and the measurement pipe and
the transmitting bodies are more preferably made of a fluorine
resin.
[0016] In the above-mentioned ultrasonic flowmeter production
method, a flow passage or a joint may be formed by insert molding
on at least one of an upstream side and a downstream side of the
measurement pipe so as to be integral with the measurement
pipe.
[0017] In a second aspect, according to the present invention,
there is provided an ultrasonic flowmeter produced by the
above-mentioned ultrasonic flowmeter production method.
[0018] In a third aspect, according to the present invention, there
is provided a fluid controller including the ultrasonic flowmeter
described above, and a control part controlling an instrument in
accordance with an output from the ultrasonic flowmeter.
[0019] In the ultrasonic flowmeter production method according to
the present invention, the measurement pipe and the transmitting
bodies are formed by insert molding so as to be integral with each
other. Therefore, the transmitting bodies can be formed, integrally
with the measurement pipe, at accurate positions of the outer side
portions of the measurement pipe without needing proficiency of an
operator and use of an adhesive, thereby improving measurement
accuracy of the ultrasonic flowmeter. Further, smoothness of the
inner peripheral surface of the measurement pipe can be improved,
thereby making it easier to restrain adhesion of microscopic
bubbles to the inner peripheral surface of the measurement pipe. As
a result, the ultrasonic flowmeter with high measurement accuracy,
which is unlikely to be affected by the microscopic bubbles, can be
achieved.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0020] The above and other objects, features and advantages of the
present invention will be described below in more detail based on
embodiments thereof with reference to the accompanying drawings, in
which:
[0021] FIG. 1 is a longitudinal sectional view showing an overall
configuration of a first embodiment of an ultrasonic flowmeter
produced by a method of producing an ultrasonic flowmeter according
to the present invention;
[0022] FIG. 2 is a longitudinal sectional view showing a first
variation of the ultrasonic flowmeter shown in FIG. 1;
[0023] FIG. 3 is a longitudinal sectional view showing a second
variation of the ultrasonic flowmeter shown in FIG. 1;
[0024] FIGS. 4A to 4D are explanatory views showing steps of the
ultrasonic flowmeter production method according to the present
invention;
[0025] FIGS. 5A and 5B are explanatory views for explaining
influences of microscopic bubbles adhered on an inner peripheral
surface of a measurement pipe of the ultrasonic flowmeter;
[0026] FIG. 6 is a longitudinal sectional view showing a second
embodiment of an ultrasonic flowmeter according to the present
invention;
[0027] FIG. 7 is a longitudinal sectional view showing a third
embodiment of an ultrasonic flowmeter according to the present
invention;
[0028] FIG. 8 is an overall configuration diagram of a fluid
controller using the ultrasonic flowmeter produced by the
ultrasonic flowmeter production method according to the present
invention;
[0029] FIG. 9 is a schematic view showing an overall configuration
of experimental equipment for studying an influence of the surface
roughness of the inner peripheral surface of the measurement pipe
of the ultrasonic flowmeter on measurement accuracy and output
signal strength; and
[0030] FIG. 10 is a partial cross-sectional side view showing an
example of a conventional ultrasonic flowmeter.
DETAILED DESCRIPTION OF THE INVENTION
[0031] While embodiments of an method of producing an ultrasonic
flowmeter according to the present invention, an ultrasonic
flowmeter produced by the method, and a fluid controller having
such an ultrasonic flowmeter will be described with reference to
the drawings, the present invention should not, of course, be
limited thereto.
[0032] First, an overall configuration of an ultrasonic flowmeter
10 produced by a method of producing an ultrasonic flowmeter
according to the present invention will be described with reference
to FIG. 1.
[0033] The ultrasonic flowmeter 10 includes a measurement pipe 1
through which a fluid to be measured flows in a filled state, a
pair of transmitting bodies 2 constituted by a first transmitting
body 2a and a second transmitting body 2b, and ultrasonic
transducers 3 serving as ultrasonic transmitter-receivers that are
attached on the pair of transmitting bodies 2, respectively.
[0034] A surface roughness of an inner peripheral surface 1a of the
measurement pipe 1 is smaller than that of an inner peripheral
surface of a measurement pipe fabricated by cutting work, so that
microscopic bubbles are less likely to be adhered to the inner
peripheral surface 1a of the measurement pipe 1. More specifically,
an arithmetic mean roughness Ra of the inner peripheral surface 1a
of the measurement pipe 1 is smaller than that of an inner
peripheral surface of a measurement pipe fabricated by cutting work
(normally, about 0.4 .mu.m), in other words, the arithmetic mean
roughness Ra of the inner peripheral surface 1a of the measurement
pipe 1 is within a range of 0 .mu.m<Ra<0.4 .mu.m, preferably
0 .mu.m<Ra.ltoreq.0.2 .mu.m, and more preferably 0
.mu.m<Ra.ltoreq.0.02 .mu.m. It is preferred that the measurement
pipe 1 is fabricated by extrusion molding in order to reduce the
surface roughness of the inner peripheral 1a and smooth the inner
peripheral surface 1a. A material used for forming the measurement
pipe 1 is preferably a synthetic resin such as perfluoroalkoxy
fluorocarbon resin (PFA), polyvinylidene fluoride (PVDF), polyvinyl
chloride (PVC) or polypropylene (PP), etc., because a synthetic
resin is suitable for extrusion molding. However, a material for
the measurement pipe 1 is not particularly limited as long as the
measurement pipe 1 can propagate an ultrasonic wave, and the
measurement pipe 1 may be made of metal such as duralumin,
aluminum, aluminum alloy, titanium or stainless steel (SUS).
Although an outer diameter and an inner diameter of the measurement
pipe 1 are not particularly limited, it is preferred that a pipe
wall thickness of the measurement pipe 1 is small in order to
facilitate propagation of an ultrasonic vibration. Further, it is
preferred that the inner diameter D of the measurement pipe 1
satisfies a relation of 0.5 mm.ltoreq.D.ltoreq.10 mm. The reason is
why the measurement pipe 1 having the inner diameter of 0.5 mm or
more can be used as an insert and a pipe usable for such a
measurement pipe 1 can be produced without a special production
method, so it is versatile and easily available. Also, in a
measurement pipe having an inner diameter of 10 mm or less, an
influence of adhesion of the microscopic bubbles is especially
great. Therefore, when an ultrasonic flowmeter is manufactured by
using the ultrasonic flowmeter production method according to the
present invention, an effect of preventing adhesion of the
microscopic bubbles on the inner peripheral surface 1a of the
measurement pipe 1 is greatly beneficial.
[0035] The first transmitting body 2a and the second transmitting
body 2b of the pair of transmitting bodies 2 are provided on outer
side portions of the measurement pipe 1 so as to be spaced apart
from each other in an axis direction of the measurement pipe 1, and
are fused at fused portions 4 so as to be integral with the
measurement pipe 1. Preferably, as in the embodiment shown in FIG.
1, each of the first transmitting body 2a and the second
transmitting body 2b has a substantially conical shape, a diameter
of which is increased towards a bottom face side from a cone point
side, and inner peripheral surfaces of through holes of the first
transmitting body 2a and the second transmitting body 2b, which
surround a circumference of the measurement pipe 1, are fused at
the fused portions 4 so as to be entirely integral with the outer
peripheral surface of the measurement pipe 1. Further, the first
transmitting body 2a and the second transmitting body 2b are
disposed opposite to each other so that the cone point sides
thereof are positioned closer to each other and the bottom face
sides are farther from each other. On the bottom face sides, the
first transmitting body 2a and the second transmitting body 2b have
end faces extending in a direction perpendicular to the axis
direction of the measurement pipe 1.
[0036] However, a shape of the transmitting body 2 is not limited
to the shape described in the embodiment shown in FIG. 1. For
example, in the embodiment shown in FIG. 1, each of the
transmitting bodies 2 (the first transmitting body 2a and the
second transmitting body 2b) has a substantially conical shape, and
the inner peripheral surfaces of the through holes, which surround
a circumference of the measurement pipe 1, are fused at the fused
portions 4 so as to be entirely integral with the outer peripheral
surface of the measurement pipe 1. However, as shown in FIG. 2, it
is also possible that the diameter of the through hole on the
bottom face side is increased so as to be larger than the diameter
of the through hole on the cone point side and that the fused
portion 4 is formed only at a part of the inner peripheral surface
of the through hole on the cone point side while the remaining part
of the inner peripheral surface of the through hole is separated
from the outer peripheral surface of the measurement pipe 1. In
this case, it is preferred that at least one third of the inner
peripheral surface of the through hole of each of the transmitting
bodies 2 is integrally fused so that an ultrasonic wave is easily
propagated in the measurement pipe 1 from each of the transmitting
bodies 2. Further, each of the transmitting bodies 2 may have a
non-conical shape such as a semispherical shape in which a planar
portion is arranged so as to be perpendicular to the axis direction
of the measurement pipe 1, or a shape of a column extending
obliquely to the axis direction of the measurement pipe 1 as shown
in FIG. 3. Also, each of the transmitting bodies 2 does not have to
surround an entire circumference of the measurement pipe 1, and may
be provided only in a part of the entire circumference of the
measurement pipe 1 as shown in FIG. 3.
[0037] A material for the transmitting bodies 2 is not particularly
limited as long as it is possible to form the transmitting bodies 2
by insert molding. For example, transmitting bodies 2 may be made
of a synthetic resin such as perfluoroalkoxy fluorocarbon resin
(PFA), polyvinylidene fluoride (PVDF), polyvinyl chloride (PVC) or
polypropylene (PP), or may be made of metal such as duralumin,
aluminum, aluminum alloy, titanium or stainless steel (SUS).
However, the transmitting bodies 2 are preferably made of the same
material as the measurement pipe 1 in order to realize good
propagation capability of an ultrasonic vibration.
[0038] The ultrasonic transducers 3 used as ultrasonic transceivers
are not particularly limited as long as the ultrasonic transducers
3 can generate ultrasonic waves. For example, the ultrasonic
transducer 3 may be an ultrasonic transducer which is fabricated by
using a piezoelectric material such as lead zirconate titanate
(PZT) and generates an ultrasonic wave by extending and contracting
in an axis direction when voltage is applied. The ultrasonic
transducers 3 are mounted on the transmitting bodies 2,
respectively, so that an ultrasonic wave generated by one of the
ultrasonic transducers 3 is propagated to the other ultrasonic
transducer 3 through a fluid in the measurement pipe 1. In the
embodiment shown in FIG. 1, each of the ultrasonic transducers 3
has a doughnut shape or a shape of a disk with a hole, and the
axial end faces of the ultrasonic transducers 3 are bonded to the
end faces of the transmitting bodies 2 on the bottom face side,
respectively, by an adhesive or the like. The inner diameter of the
ultrasonic transducer 3 is substantially equal to the diameter of
the through hole of each of the transmitting bodies 2 on the bottom
face side, and an inner peripheral surface of the ultrasonic
transducer 3 are separated from the outer peripheral surface of the
measurement pipe 1. However, the shape of the ultrasonic transducer
3 is not limited to the shape of the disk with the hole, and may
be, for example, a semicircular shape or a sector shape.
[0039] Next, the procedure for producing the ultrasonic flowmeter
10 shown in FIG. 1 according to the ultrasonic flowmeter production
method of the present invention will be described with reference to
FIGS. 4A to 4D. First, as shown in FIG. 4A, the measurement pipe 1
is fabricated in advance so that the inner peripheral surface
thereof has an arithmetic mean roughness Ra (0 .mu.m<Ra<0.4
.mu.m) smaller than that of the measurement pipe fabricated by
cutting work. The arithmetic mean roughness Ra of the inner
peripheral surface of the measurement pipe 1 is preferably within
the range of 0 .mu.m<Ra.ltoreq.0.2 .mu.m, and more preferably,
the range of 0 .mu.m<Ra.ltoreq.0.02 .mu.m, so that it is less
likely that the microscopic bubbles are adhered to the inner
peripheral surface of the measurement pipe. It is particularly
preferable that the measurement pipe 1 is fabricated by extrusion
molding because the measurement pipe 1 having the inner peripheral
surface 1a of the arithmetic mean roughness of 0
.mu.m<Ra.ltoreq.0.2 .mu.m can be easily fabricated.
[0040] Next, after a straight pin is inserted into the measurement
pipe 1 fabricated in advance as shown in FIG. 4B, the measurement
pipe 1 with the straight pin 5 inserted therein is set in the mold
6 as an insert, as shown in FIG. 4C, and then a material for
forming the transmitting bodies 2 is injected into the mold 6, thus
carrying out insert molding. Insert molding may be carried out by
compression molding of the material for the transmitting bodies 2,
instead of injection molding. When the molding material is cooled
so that the molded portions 7 are solidified integrally with the
measurement pipe 1, the measurement pipe 1 and the molded portions
7 formed to be integral with each other are taken out of the mold
6, and runner portions 7a are removed from the molded portions 7 by
cutting, thereby forming the transmitting bodies 2.
[0041] After the pair of transmitting bodies 2 is thus formed by
insert molding at predetermined positions on the outer side
portions of the measurement pipe so as to be integrally with the
measurement pipe 1 in a state where the pair of transmitting bodies
2 are spaced apart from each other by a predetermined distance in
the axis direction of the measurement pipe 1, the ultrasonic
transducers 3 are mounted on the end faces of the transmitting
bodies 2, respectively, by an adhesive or the like, thereby
fabricating the ultrasonic flowmeter 10 shown in FIG. 1.
[0042] In a case where the measurement pipe 1 and the pair of
transmitting bodies 2 are integrated with each other by using an
adhesive, an amount of the adhesive applied, drying time of the
adhesive, uniformity of application of the adhesive, and so on
affect performance of the ultrasonic flowmeter 10, and proficiency
of an operator affects yield. Therefore, in order to avoid
variation of the performance of the ultrasonic flowmeter, the
amount of the adhesive applied, drying time of the adhesive, and so
on have to be controlled, thereby causing a cost increase.
Moreover, there has been a problem that assembly is more difficult
when the size of the ultrasonic flowmeter is smaller and the
diameter of the measurement pipe 1 is smaller. In contrast,
according to the ultrasonic flowmeter production method of the
present invention, it is not necessary to use an adhesive to
integrate the measurement pipe 1 and the pair of transmitting
bodies 2 with each other, and therefore the problem stated above is
avoidable. Further, when a fluorine resin such as PFA and PVDF is
used as the material for the measurement pipe 1, adhesion by use of
an adhesive is not suitable for fixing the pair of transmitting
bodies 2 to the measurement pipe 1 and use of the method of
producing the ultrasonic flowmeter according to the present
invention is more suitable.
[0043] According to the ultrasonic flowmeter production method of
the present invention, the measurement pipe 1 is fabricated in
advance in a different process and therefore the surface roughness
of the inner peripheral surface of the measurement pipe 1 can be
easily reduced, thereby easily producing the ultrasonic flowmeter
in which the microscopic bubbles are less likely to be adhered to
the inner peripheral surface of the measurement pipe 1. The
ultrasonic flowmeter production method according to the present
invention is especially effective in the case where the measurement
pipe 1 is fabricated from a fluorine resin such as PFA and PVDF,
because a surface tension of a fluorine resin such as is large and
the bubbles are thus easily adhered to the inner surface of the
measurement pipe 1. Further, according to the ultrasonic flowmeter
production method of the present invention, the pair of
transmitting bodies 2 can be formed at predetermined positions on
the outer side portions of the measurement pipe 1 without depending
on proficiency of an operator and with almost no variation, because
the measurement pipe 1 and the pair of transmitting bodies 2 are
formed to be integrally with each other by insert molding.
Therefore, the ultrasonic flowmeter 10 with high measurement
accuracy can be provided easily.
[0044] In particular, when the measurement pipe 1 is fabricated by
extrusion molding, the measurement pipe 1 having the inner
peripheral surface of the arithmetic mean roughness Ra of 0.02
.mu.m or less can be fabricated easily. In addition, in the case
where the measurement pipe 1 is fabricated by extrusion molding, no
draft is needed in the inner peripheral surface of the measurement
pipe 1 unlike the case where the measurement pipe 1 is fabricated
by injection molding. When a draft is provided in the inner
peripheral surface of the measurement pipe 1, the flow velocity of
the fluid in the measurement pipe 1 changes depending on a
location, which influences measurement, and the influence is even
larger especially in the measurement pipe 1 having a small
diameter. In the case of the measurement pipe 1 having the inner
diameter of 5 mm or less and the length of 30 mm or more, it is
especially difficult to fabricate the measurement pipe 1 by
injection molding. However, by fabricating the measurement pipe 1
by extrusion molding, such a problem is prevented and the
measurement pipe 1 having the small diameter can be fabricated
easily. This makes it possible to produce the ultrasonic flowmeter
with high measurement accuracy, which hardly causes adhesion of the
microscopic bubbles to the inner peripheral surface of the
measurement pipe 1 and makes it possible to measure a micro flow
rate. Further, in the case where the measurement pipe 1 is
fabricated by extrusion molding, the measurement pipe 1 has
excellent thermal stability and productivity when insert molding is
carried out by using the measurement pipe, because the measurement
pipe 1 is heated once when the measurement pipe 1 is
fabricated.
[0045] Although the measurement pipe 1 and the pair of transmitting
bodies 2 can be formed to be integral with each other by injection
molding, it is difficult to design a mold and control forming
conditions especially in the case of the measurement pipe 1 having
a small diameter (the measurement pipe 1 having the inner diameter
of 2 mm or less) because it is necessary to reduce the surface
roughness of the inner peripheral surface of the measurement pipe 1
in order to restrain adhesion of microscopic bubbles. However, when
the measurement pipe 1 is fabricated by extrusion molding, the
measurement pipe 1 having the small surface roughness can be easily
fabricated and the problem stated above does not occur.
[0046] Next, the operation of the ultrasonic flowmeter 10 produced
as stated above will be described.
[0047] In the ultrasonic flowmeter 10, when a voltage pulse or a
voltage having no frequency component is applied from a converter
(not shown) to the ultrasonic transducer 3 located on the upstream
side along the fluid flow direction, the ultrasonic transducer 3
generates a vibration in a direction along the thickness (i.e., in
a direction of voltage application) and in a diameter direction
(i.e., in a direction perpendicular to the direction of the voltage
application) of the ultrasonic transducer 3. The end faces on the
bottom face side, i.e., the axial end face, of the transmitting
body 2 is fixedly secured to the axial end face of the ultrasonic
transducers 3 and a voltage is applied between both axial end faces
of the ultrasonic transducers 3, so that the ultrasonic vibration
in the direction along the thickness, which has a large energy of
the ultrasonic vibration, is propagated to the end face of the
transmitting body 2 on the bottom face side. The ultrasonic
vibration thus propagated to the transmitting body 2 is further
transmitted to the fluid in the measurement pipe 1 through the
transmitting body 2 and the pipe wall of the measurement pipe 1 and
is propagated in the fluid inside the measurement pipe 1 while
being repeatedly reflected on the outer peripheral surface of the
measurement pipe 1. Thereafter, the ultrasonic vibration is
propagated, through the transmitting body 2 located on the
downstream side in opposed relation, to the ultrasonic transducer 3
fixed to the transmitting body 2 located on the downstream side,
and is converted into an electric signal, which is outputted to the
converter.
[0048] When the ultrasonic vibration is transmitted from the
upstream ultrasonic transducer 3 to the downstream ultrasonic
transducer 3 and received by it, the transmitting and receiving
sides are instantaneously switched in the converter, and a voltage
pulse or a voltage having no frequency component is applied from
the converted to the downstream ultrasonic transducer 3. Then,
similarly to the upstream ultrasonic transducer 3, the ultrasonic
vibration is generated and propagated to the fluid in the
measurement pipe 1 through the transmitting body 2. This ultrasonic
vibration is again received by the ultrasonic transducer 3 fixed to
the transmitting body located on the upstream side in opposed
relation and is then converted into an electric signal, which is
outputted to the converter. In the process, the ultrasonic
vibration is propagated against the flow of the fluid in the
measurement pipe 1. Therefore, the propagation velocity of the
ultrasonic vibration in the fluid is lower than when the ultrasonic
vibration transmitted from the upstream ultrasonic transducer 3 is
received by the downstream ultrasonic transducer 3, and the
propagation time is longer.
[0049] In the converter, the propagation time of the ultrasonic
vibration from the upstream ultrasonic transducer 3 to the
downstream ultrasonic transducer 3 and the propagation time of the
ultrasonic vibration from the downstream ultrasonic transducer 3 to
the upstream ultrasonic transducer 3 are measured, and a flow
velocity and a flow rate are computed based on a difference between
the propagation times. Thus, highly accurate measurement of a flow
rate can be achieved.
[0050] Microscopic bubbles adhered to the inner peripheral surface
1a of the measurement pipe 1 of the ultrasonic flowmeter 10 reflect
ultrasonic waves on the surfaces of the microscopic bubbles. As
shown by an arrow A in FIG. 5A, the ultrasonic vibration that is
not affected by the microscopic bubbles is propagated in the
measurement pipe 1 while being repeatedly reflected on the outer
peripheral surface of the measurement pipe 1. However, as shown by
arrows B in FIG. 5A, when microscopic bubbles are adhered to the
inner peripheral surface 1a of the measurement pipe 1, the
ultrasonic vibration, which has been propagated from the ultrasonic
transducer 3 on the transmitting side to the transmitting body 2
and the measurement pipe 1, is reflected on a boundary between the
measurement pipe 1 and the microscopic bubbles, i.e., near the
inner peripheral surface 1a of the measurement pipe 1, thereby
disturbing propagation of the ultrasonic vibration to the fluid in
the measurement pipe 1, or the ultrasonic vibration, which is
propagated in the fluid in the measurement pipe 1, is reflected on
a boundary between the fluid in the measurement pipe 1 and the
microscopic bubbles, thereby disturbing entrance of the ultrasonic
vibration into the ultrasonic transducer 3 on the receiving side.
As a result, an amount of ultrasonic waves that reach the
ultrasonic transducer 3 on the receiving side can be reduced,
thereby causing a reduction of signal strength. As shown in FIG.
5B, the ultrasonic vibration that is not affected by the
microscopic bubbles is propagated in the measurement pipe 1 while
being repeatedly reflected on the outer peripheral surface of the
measurement pipe 1 as indicated by an arrow A. On the other hand,
as indicated by an arrow B, when the microscopic bubbles are
adhered to the inner peripheral surface 1a of the measurement pipe
1, the ultrasonic vibration is reflected on a boundary surface
between the microscopic bubbles and the surrounding area thereof,
thereby making differences among propagation passages of the
ultrasonic vibration and affecting the propagation time. As a
result, measurement accuracy can be deteriorated.
[0051] By producing the ultrasonic flowmeter 10 according to the
ultrasonic flowmeter production method of the present invention,
the surface roughness of the inner peripheral surface 1a of the
measurement pipe 1 of the ultrasonic flowmeter 10 can be easily
reduced, thereby becoming smoothed. Therefore, it is possible to
restrain adhesion of microscopic bubbles on the inner peripheral
surface 1a of the measurement pipe 1, thus avoiding a reduction of
signal strength and deterioration of measurement accuracy due to
the microscopic bubbles.
[0052] The ultrasonic flowmeter and the ultrasonic flowmeter
production method according to the present invention have been
described, using the ultrasonic flowmeter 10 of the first
embodiment shown in FIG. 1 as an example. However, application of
the present invention is not limited to the configuration of the
ultrasonic flowmeter 10 of the first embodiment. In the ultrasonic
flowmeter 10 of the first embodiment shown in FIG. 1, the outer
peripheral surface of the measurement pipe 1 and the inner
peripheral surfaces of the through holes of the transmitting bodies
2 are fused integrally with each other at the fused portions 4.
However, the transmitting bodies 2 may be provided, by any other
way, on the outer side portions of the measurement pipe 1 so as to
be integral with the measurement pipe 1. For example, like an
ultrasonic flowmeter 10' of a second embodiment shown in FIG. 6, an
outer measurement pipe portion 8 having a pair of transmitting
bodies 2 may be formed by insert molding on outer side portions of
the measurement pipe 1, and an outer peripheral surface of the
measurement pipe 1 and an inner peripheral surface of the outer
measurement pipe portion 8 may be fused to be integral with each
other at the fused portion 4. In the ultrasonic flowmeter 10 of the
first embodiment, the measurement pipe 1 and the pair of
transmitting bodies 2 are formed to be integral with each other by
insert molding. However, like an ultrasonic flowmeter 10'' of a
third embodiment shown in FIG. 7, an inlet flow passage 9a and an
outlet flow passage 9b may be formed to be integral with the
measurement pipe 1 on the upstream side and the downstream side of
the measurement pipe 1, respectively. Further, a joint portion 9c
and/or a holding portion 9d for holding the ultrasonic flowmeter
10'' on a housing (not shown) may be provided on the inlet flow
passage 9a and the outlet flow passage 9b formed by insert
molding.
[0053] FIG. 8 shows a fluid controller 20 having used the
ultrasonic flowmeter according to the present invention.
[0054] The fluid controller 20 includes an ultrasonic flowmeter 21,
and a fluidic element 22 for adjusting a flow rate, a flow
velocity, a pressure and so on of a fluid, and an electric
component 25 that processes an output signal from the ultrasonic
flowmeter 21 and performs control. As the ultrasonic flowmeter 21,
an ultrasonic flowmeter produced by the method of producing the
ultrasonic flowmeter according to the present invention is used,
such as the ultrasonic flowmeter 10 of the first embodiment shown
in FIG. 1, the variations of the ultrasonic flowmeter 10 shown in
FIGS. 2 and 3, the ultrasonic flowmeter 10' of the second
embodiment shown in FIG. 6, or the ultrasonic flowmeter 10'' of the
third embodiment shown in FIG. 7.
[0055] For example, an electric-driven or air-driven pinch valve
may be used as the fluidic element 22. However, the fluidic element
22 is not limited to the electric-driven or air-driven pinch valve
as long as the fluidic element 22 is an instrument for adjusting a
flow rate, a flow velocity, a pressure and so on of a fluid.
[0056] The electric component 25 includes an amplifier part 23 that
amplifies an output signal from the ultrasonic transducer 3 of the
ultrasonic flowmeter 21 (i.e., ultrasonic flowmeter 10, 10' or
10''), and a control part 24 that performs control based on the
signal amplified by the amplifier part 23, so that the electric
component 25 can control the operation of the fluidic element 22
based on a control signal from the control part 24 and perform
fluid control.
[0057] Since the ultrasonic flowmeter 21 according to the present
invention is used in the fluid controller 20, it is possible to
measure a flow rate of a fluid with high accuracy, thereby
achieving accurate fluid control.
[0058] FIG. 9 shows experimental equipment for confirming an
influence of adhesion microscopic bubbles due to surface roughness
on measurement accuracy and signal strength. In the experiment, air
32 was supplied into a tank 38 filled with pure water 31 degassed
by a degasifier 33, and bubbling was performed for 30 minutes.
Thus, pure water containing microscopic bubbles was prepared. While
adjusting a flow rate by using a valve 35, the pure water
containing the microscopic bubbles was supplied by a pump 34 from
the tank 38 to an ultrasonic flowmeter 36, and output signals from
the ultrasonic flowmeter 36 (specifically, the ultrasonic
transducer on the receiving side thereof) was observed by using an
oscilloscope 37. In the experiment, a size of the measurement pipe
of the ultrasonic flowmeter 36 was unified to a length of 40 mm, an
outer diameter of 3 mm, and an inner diameter of 2 mm, and a
square-wave voltage pulse having a frequency of 600 kHz and an
amplitude of .+-.5 V was applied to an ultrasonic transducer on a
transmitting side.
[0059] Under the conditions stated above, a peak-to-peak voltage
Vp-p of an output signal from an ultrasonic transducer on a
receiving side when a conventional ultrasonic flowmeter having a
measurement pipe and transmitting bodies fabricated integrally with
each other by cutting work was used as the ultrasonic flowmeter 36
was compared with a peak-to-peak voltage Vp-p of an output signal
from the ultrasonic transducer on the receiving side when the
ultrasonic flowmeter 10, 10', or 10'' according to the present
invention was used as the ultrasonic flowmeter 36. The inner
peripheral surface of the measurement pipe fabricated integrally
with the transmitting bodies by cutting work had an arithmetic mean
roughness Ra of 0.4 .mu.m, and, when an ultrasonic flowmeter using
the measurement pipe fabricated by cutting work was used as the
ultrasonic flowmeter 36, an output signal from the ultrasonic
flowmeter was 40 to 75 mVp-p. On the other hand, the inner
periphery 1a of the measurement pipe 1, fabricated by extrusion
molding and used in the ultrasonic flowmeter 10, 10', or 10'', had
the arithmetic mean roughness Ra of 0.2 .mu.m, and an output signal
from the ultrasonic flowmeter 10, 10', or 10'' using the
measurement pipe 1 was 100 to 170 mVp-p. This confirmed that the
strength of the received signal was enhanced, and an influence of
the microscopic bubbles was reduced. In addition, an effect of
improvement in measurement accuracy was also achieved.
* * * * *