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JPS63274860

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DESCRIPTION JPS63274860
[0001]
This invention relates to a method for appropriately determining the surface shape of an
ultrasonic lens used in ultrasonic flaw detection and the like. (Conventional technology and its
problems) In performing ultrasonic flaw detection, it is necessary to make an ultrasonic wave
into a focused wave using an ultrasonic lens and to focus it on a target point of the inspection
material itself. In this case, the ultrasonic waves focused by the ultrasonic lens are refracted
when they enter from inside to outside of the material to be inspected. For this reason, in order
to obtain a focused wave that is actually focused at the target point, it is necessary to determine
the surface shape of the ultrasonic lens (and thus its focusing characteristics) while taking into
consideration such refraction and the like. FIG. 9 is an explanatory view of a conventional
method for determining the surface shape of an ultrasonic lens in such a position. In the figure,
an ultrasonic wave US is emitted from a probe 2 provided with an ultrasonic transducer (not
shown) and an ultrasonic lens 3. The ultrasonic waves uS are focused waves by the action of the
ultrasonic lens 3. And, in this example, a round bar 1 immersed in water (not shown) is assumed
as a material to be inspected to be subjected to ultrasonic flaw detection, and ultrasonic waves
are applied to a target point A inside the round bar 1. Consider the case of focusing. At this time,
the probe 2 is disposed such that its central axis U intersects perpendicularly with the axis V of
the round rod 1 and the central axis U passes through the target point A. Under this
arrangement, the surface shape of the ultrasonic lens 3 is determined as follows. First, consider a
plane PA which includes the central axis U and which is perpendicular to the axis 1 of the round
rod 1. Then, the radius of curvature r (FIG. 10) of the surface 4 of the ultrasonic lens 3 is set so
that each of the sound rays SL of the ultrasonic wave US which travels on the plane PA from the
probe 2 pass through the target point A. It is decided. However, the refraction angle of the sound
ray SL on the surface of the round rod 1 is determined based on Snell's law. As described above,
the surface shape of the ultrasonic lens 3 can be determined with relatively high accuracy only
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by the sound ray analysis on the plane PA because of the geometric symmetry in the case of the
arrangement as shown in FIG. It is because it is expensive. By the way, such a surface shape
determination method is premised on making the central axis U of the probe 2 perpendicular to
the axis V of the material to be inspected. However, in fact, there are not a few cases where flaw
detection is performed (that is, oblique incidence is made) by setting the angle between the
central axis U of the probe 2 and the axis 3 of the test material as an angle other than vertical. At
this time, geometrical symmetry as shown in FIGS. 9 and 10 is lost. For this reason, if the surface
shape of the ultrasonic lens 3 is determined based only on the conventional two-dimensional
analysis (that is, sound ray analysis on the plane PA), the focusing error becomes large, and the
focusing degree of the ultrasonic waves decreases. There is a problem of doing it.
And as a result, S / N of ultrasonic flaw detection will also fall. In order to solve this problem, it is
conceivable to determine the surface shape of the ultrasonic lens 3 based on three-dimensional
sound ray analysis. However, when performing three-dimensional sound ray analysis, a large
number of Another problem arises that the operation has to be performed. And such a problem is
a problem that occurs not only in the above case but also when the geometric symmetry of the
shape of the test material itself is low, etc., and an ultrasonic lens is used for applications other
than ultrasonic flaw detection It is also a common problem if you (Object of the Invention) The
present invention is intended to overcome the above-mentioned problems in the prior art, and
relates to the spatial positional relationship between an object to be irradiated with an ultrasonic
wave and an ultrasonic lens, and the geometry of the object itself. An object of the present
invention is to provide a method of determining the surface shape of an ultrasonic lens that can
increase the focusing degree of ultrasonic waves with a relatively small amount of calculation
even when the target symmetry is low. (Means for achieving the object) In order to achieve the
above object, the present invention is characterized in that the ultrasonic wave generated outside
the target object is made incident as the focusing wave to the inside of the object, and the inside
of the object is In focusing the ultrasonic wave on a predetermined target point, as a method of
determining the surface shape of the ultrasonic lens used when making the ultrasonic wave into
a focusing wave, ■ super emitted from the central point of the ultrasonic lens A first step of
determining an arrangement position and an arrangement attitude of the ultrasonic lens so that a
sound ray of a sound wave passes through the target point, and specifying a sound ray from the
central point as a reference sound ray; A second step of assuming a value of a predetermined
shape parameter representing the shape of the surface of the acoustic lens; and a field where the
surface shape of the ultrasonic lens is configured according to the assumed value of the shape
parameter The position of each intersection point of each sound ray of ultrasonic waves
respectively emitted from a predetermined number of minute sound sources assumed on the
surface of the ultrasonic lens and the reference sound ray on a predetermined projection plane A
third step of calculating a sum of positional deviations between each of the intersection points
and the target point; and repeating the second and third steps while sequentially changing the
value of the shape parameter; A fourth step of adopting the value of the shape parameter with
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which is the smallest as the actual shape parameter value of the ultrasonic lens, thereby
determining the surface shape of the neck ultrasonic lens. (Embodiment) FIG. 1 is a flow chart
showing the procedure of an ultrasonic lens surface shape determination method according to an
embodiment of the present invention.
Further, in FIG. 2, when performing ultrasonic flaw detection using the cylindrical material 8
immersed in water (not shown) as the inspection material, the surface shape of the ultrasonic
lens is determined according to the procedure shown in FIG. It is a conceptual diagram of a case.
And FIG. 3 is a figure which projected the sound ray of the ultrasonic wave shown in FIG. 2 on xy
plane perpendicular | vertical to the central axis of a cylindrical material. The procedure for
determining the surface shape of the ultrasonic lens will be described below with reference to
these figures. However, for the purpose of clarifying the features of the invention, in the
ultrasonic flaw detection of FIG. 2, a plano-concave lens 7 having a cylindrical surface 6 as shown
in FIG. 4 is used. Further, the case where the radius of curvature R in the I-I cross section passing
through the center point R8 of the surface 6 will be described. A, Determination of the lens 1 ·
and the foundation First, the cylindrical material 8 to be inspected for internal defects (Fig. 2). A
target point Z at which the ultrasound US should be focused inside of FIG. 3). Set Next, when the
ultrasonic wave is made to enter the inside of the cylindrical material 8, an incident point Po
which is an incident center position is determined. This incident point P. The target point Z along
the direction of the central axis 2 of the cylindrical material 8. Are set at positions separated by a
predetermined distance l. Also, as shown in FIG. 3, a target point Z. And incident point P. The
directions of the X-axis and the y-axis are determined such that the projection of the line segment
connecting the X-axis and Y-axis into the x-y plane is parallel to the X-axis. Next, the sound ray a
of the ultrasonic wave emitted from the central point R8 of the ultrasonic lens 7. But the incident
point P. , And enters the inside of the cylindrical material 8 and this acoustic ray a. The
placement position and the placement posture of the ultrasonic lens 7 are determined so that the
target point Z0 passes through the target point Zo. In this process, the angle of refraction of
sound rays at the surface of the cylindrical material 8 is determined based on Snell's law. Further,
the distance between the center point R6 of the ultrasonic lens 7 and the surface of the
cylindrical member 8, the diameter of the ultrasonic lens 7, and the like are determined in
advance. Furthermore, sound ray a specified as described above. Is rat in the following process! !
It is treated as "ray". This reference sound line a. Is a sound ray of the ultrasonic wave from the
center point of the ultrasonic lens 7 and therefore has nothing to do with the value of the
curvature radius R of the surface 6 of the ultrasonic lens 7. Therefore, even if the radius of
curvature R is changed in the following process, this reference sound ray a. Is unchanged. B,
Calculation of shape parameter temporary and total of positional displacement amount As
described above, reference sound ray a. Is determined, and an arbitrary value (for example, R =
25 m) is assumed as the radius of curvature R as the shape parameter of the surface 6. Next, on
this surface 6, it is assumed that n minute sound sources R (i = 1.2, ..., n) arranged at equal
intervals on an arc passing through the center point R8. The sound ray a H (i = 1. 2..., N) of the
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ultrasonic wave emitted from the lens is calculated by using Snell's law.
Also, each sound line a. And the reference sound line a. Find the position of the intersection point
c, (i = 1.2..., N) on the x-y projection plane PI of and. Then, the snow intersection C1 and the
target point Z. Which positional deviation Δx− (i = 1.2..., N) on the x−y projection plane P1 is
obtained. This misregistration mother ΔX is the target point Z. Assuming that the X coordinate
of X is Xo, and the X coordinate of the intersection point C, is X, it is defined as the absolute
value of these differences 1xo-x, l. However, when the intersection C1 can not be obtained, or
when the intersection C8 is positioned outside the cylindrical member 8, the positional deviation
amount ΔX is not calculated. By the way, this positional deviation amount ΔX indicates only the
deviation between the intersection point C1 and the target point 2 ° in the X axis direction, but
the reference sound ray a. And the X axis are parallel, there is no positional deviation in the y
axis direction between the intersection point C · and the target point 7 °. Further, since the
positional deviation in the direction of the central axis 2 of the cylindrical material 8 is in
proportion to Δxi, it can be said that the smaller the ΔX, the smaller the positional deviation in
the central axis Z direction. Therefore, the I3-dimensional positional deviation amount between
the intersection point C1 and the target point Zo is sufficiently expressed only by the positional
deviation amount ΔX · in the X-axis direction. Then, the above processing is repeated for all the
n small sound sources R, and the sum ΣΔX of the positional deviation amount ΔX obtained by
the calculation is calculated. Also, the sum Σ is the sum of i. This sum ΣΔX is the target point Z,
as is apparent from its definition. It is four that reflects the degree of focusing of the ultrasonic
waves in Determination of C0 Surface Shape In this way, after the sum ΣΔXi of positional
displacement amounts when the curvature radius R of the surface 6 is 25 am, a new value (for
example, R = 30 tnts) is assumed as the curvature radius R Then, in the same procedure as
described above, the sum of the amounts of deviation when the curvature radius R is 301 RM is
obtained. In this manner, repetitive processing is performed to obtain the sum of displacement
amounts for various values of the radius of curvature R (for example, 25 m to 60 M). Then, the
radius of curvature R such that the sum of the positional displacement amounts is minimum is
adopted as the actual radius of curvature of the surface 6, thereby determining the surface shape
of the ultrasonic lens 7. The above method does not use the premise that the central axis U of the
ultrasonic lens is perpendicular to the axis 2 of the material to be inspected. For this reason, the
target point Z also when these axes are not perpendicular to one another and are inclined at an
arbitrary angle. The surface shape of the ultrasonic lens 7 can be determined so that the degree
of focusing of the ultrasonic waves at the point.
The same applies to the case where the symmetry of the shape of the test material is low. That is,
in the above case, originally, three-dimensional analysis is required, but if the surface shape is
determined as in the above-mentioned embodiment, evaluation of the degree of focusing is
simple and accurate. Thus, the surface shape of the ultrasonic lens can be determined with a
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relatively small amount of calculation. FIG. 5 is a figure which shows the example of an
experiment which detects the artificial defect provided in the inside of a sample by ultrasonic
flaw detection. In this figure, this sample 9 is a cylindrical material having an outer diameter of
123 s + and an inner diameter of 83.6 m, and the artificial defect 10a provided on the inner wall
of the welded portion 9a has a depth of 1/3 of the thickness of the welded portion 9a. Have.
Further, another artificial defect 10b having a depth of 1/2 of the thickness of the welded
portion 9a is also provided on the inner wall opposite to this. The positions of these artificial
defects 10a and 10b in the circumferential direction are 90 ° and 270 ′ ′, respectively, and
the position of the ultrasonic wave emitted from the probe 2a is a half depth of the thickness of
the welded portion 9a ( Focusing at the target point), the reflection intensity of the ultrasonic
wave from this position is measured by the probe 2b. FIG. 6 is an ultrasonic wave when the
surface shape of the ultrasonic lens incorporated in the probe 2a, 2b of FIG. 5 is determined by
the method shown in the above embodiment (curvature radius R = 30 m) It is a graph which
shows angular distribution of reflective intensity of. 7 and 8 show the case where parallel
ultrasonic waves are incident without using an ultrasonic lens (without a lens), and the case of
using an ultrasonic lens having an inappropriate surface shape (curvature) It is a graph which
each shows angular distribution of the reflective intensity of the ultrasonic wave of radius R = 50
m). The horizontal axis represents the circumferential position (angle) of the artificial defects 10a
and 10b, and the vertical axis represents the reflection intensity. In these graphs, when the
ultrasonic lens whose surface shape is determined by the method described in the above
embodiment is used (FIG. 6), the positions where the artificial defects 10a and 10b are provided
(position 90 ° in the circumferential direction, The reflection intensity of the ultrasonic wave at
270 ") is extremely large compared to that at the position without the artificial defects 10a and
10b, and as a result, the S / N is also sufficiently large. This is because the ultrasonic wave
emitted from the probe 2a is sufficiently focused at the target point. On the other hand, when an
ultrasonic lens is not used (FIG. 7) and when an inappropriate ultrasonic lens is used (FIG. 8),
focusing of the ultrasound at the target point is not sufficient. Not only the degree of focusing at
the point is reduced, but also the ultrasonic waves that are not focused become noises, making it
difficult to specify the circumferential position of the artificial defects 10a and 10b, and the S / N
also decreases.
As described above, in the ultrasonic lens configured according to the present invention, the S /
N can be made sufficiently large as compared with the conventional method. By the way, the
method of determining the surface shape of the ultrasonic lens according to the present
invention is not limited to the above-described embodiment, and the following modifications are
possible. {Circle over (3)} In this embodiment, a cylindrical material is used as a target object on
which ultrasonic waves are incident, but the present invention is also effective when an object
having an arbitrary shape is used. The surface of the ultrasonic lens is not limited to a cylindrical
surface, and may be various curved surfaces, for example, a spherical surface. Of course, the
invention is not limited to the aspect of ultrasonic flaw detection (reflection method, transmission
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method, etc.), and can be applied to ultrasonic lenses other than those for ultrasonic flaw
detection. (2) As the shape parameter, not only the radius of curvature but, for example, in the
case of a parabolic lens or the like, the eccentricity of the objective surface may be used as a
parameter. The position may be adopted, and the degree of convergence may be evaluated by the
magnitude of the sum Σ (Xo-X). (Effects of the Invention) As described above, in the method of
determining the surface shape of the ultrasonic lens according to the present invention, attention
is paid to the intersection of the reference sound ray and another sound ray, and the positional
deviation between this intersection and the target point By using the sum of the two as a
parameter of the degree of focusing, even when the spatial relationship between the object on
which the ultrasonic wave is to be incident and the ultrasonic lens and the geometrical symmetry
such as the shape of the object itself are relatively low, It is possible to obtain a method of
determining the surface shape of the ultrasonic lens that can increase the degree of focusing of
the ultrasonic wave with a small amount of calculation.
[0002]
Brief description of the drawings
[0003]
FIG. 1 is a flow chart showing the procedure of the method for determining the surface shape of
an ultrasonic lens according to an embodiment of the present invention, and FIGS. 2 and 3 show
the surface shape of an ultrasonic lens used for ultrasonic flaw detection. 4 is a schematic view of
an ultrasonic lens for determining the surface shape in this embodiment, and FIG. 5 is a layout of
an experimental example for detecting an artificial defect by ultrasonic flaw detection. FIGS. 6 to
8 are graphs showing the results of the experiment shown in FIG. 5, and FIGS. 9 and 10 are
explanatory views of a conventional method for determining the surface shape of the ultrasonic
lens.
6 ... surface of ultrasonic lens, 7 ... ultrasonic lens, ao ... reference sound ray, al, a2, ..., fa line, C1,
C2 '' intersection point, Ro ... of ultrasonic lens Center point, R, R2, ..., Ro ... Minute sound source,
Zo ... Target point
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