Inner Profile Measurement and Flaw Inspection of Pipes and

Inner Profile Measurement and Flaw Inspection of Pipes and
10th IMEKO TC14 Symposium on
Laser Metrology for Precision Measurement and Inspection in Industry
Braunschweig, GERMANY, 2011, September 12-14
Inner Profile Measurement and Flaw Inspection of
Pipes and Tubes
T. Wakayama, T. Yoshizawa, Saitama Medical University,
Non-profit organization 3D Associates
Abstract:
Inner profile measurement is an important matter in such fields as mechanical engineering
including car and aircraft
plant.
industries, and heavy industry relating to jet engines and power
In addition, we can find many applications in medicine and/or surgery related field.
Here we describe recent development of our measurement principle for inner diameter and
profile of pipes and/or tubes.
The key device in this technique is a ring beam device which
consists of a conical mirror and a laser diode (LD). And the fundamental principle is based on
optical sectioning without using any contact type stylus. The optically sectioned profile of an
inner wall of a pipe-like object is analyzed to give the inner profile in addition to the inner
diameter. This optical instrument with simple and small configuration has been under
development for practical uses. In our experimental works up to now, the availability of this
instrument has been evaluated in many cases. This ring beam device consisting of a conical
mirror and a LD is assembled in a glass pipe and the beam emitted from the LD is deformed,
after reflected by the top of the conical mirror, into a disk-like circular light sheet. We show
measurement result of pipes, and, at the same time, report a few examples that are
developed for practical purposes. Both the ring beam device and a miniaturized CCD camera
are fabricated into a glass tube for easier practical applications. We have already reported the
fundamental principle of this measurement system and showed some applications. Here we
report our trial to extend our technique to checking defects and flaws on the inner wall of
pipe-like objects.
1. Introduction
Damage and cracks due to fatigue of gas and water tubes are pointed to be a social problem
world-widely. And check and inspection of pipes and sewers are required to prevent serious
disasters. Therefore speedy and simple inner profile measurements of pipes have been
concerned from the viewpoint of safety managements to avert various accidents. Besides
these social concerns, there are different requests for measuring the inner diameter and/or
inner profile of pipes, especially, in automobile industry (various pipes and manifolds in
10th IMEKO TC14 Symposium on
Laser Metrology for Precision Measurement and Inspection in Industry
Braunschweig, GERMANY, 2011, September 12-14
addition to engines, for example). The inner surface of engine blocks or other castings is
strongly required to be inspected. In addition to these industrial necessities, there are different
requests for checking inner profiles of human organs such as tracheae, large bowels and
stomach in medicine and oral cavity in dental field. Most of methods hitherto in use [1] are
classified into contact methods with any kind of mechanical stylus or touching probe. However,
contact methods are not appropriate for inner profile measurement because of long
measurement time and fear of damage. In this situation it is strongly demanded to inspect
inner profile by using optical methods. Conventionally bore-scopes and endoscopes have
been utilized, but these are useful merely for visual examination by naked-eyes. Some optical
methods have been proposed which incorporates a rotating mirror or prism to scan the inner
surface. One technique using a rotating mirror is well-known that was used for checking the
inner wall of sewers in London [2]. And another principle using a DOE and a conical mirror is
reported [3]. However, to realize similar and simple system, we have proposed an idea for
inner profile measurement using a ring beam device consisting of a conical mirror, a laser
diode, and a CCD camera in 2006 [4].The fundamental technique is based on optical
sectioning, and, in the previous paper, we suggested possibility of inspection of defects as
well as inner profile measurement of pipes Now, in this paper, our recent instrument with
smaller size is also shown. This instrument, as small as a cigarette, is incorporated with the
ring beam device and a small CMOS camera. The optically sectioned profile is analyzed to
calculate the inner profile. In this experiment, a bore of an engine block is used to measure
the inner profile and to find flaws of inner surface.
2. Principle
2.1 Inner profile measurement
Figure 1 shows fundamental principle for inner profile measurement. A laser beam from the
LD (laser diode) hits the apex of the conical mirror, and then the beam reflects and spreads to
form a ring beam like a disk. When this disk-like beam comes to the inner wall of the pipe, we
can observe optically sectioned profile, i.e. peripheral cross section of the pipe. This profile is
captured by a CCD/CMOS camera. According to the principle of triangulation, the inner
diameter of the profile can be expressed as
r = l tanφ
(1),
Here, r means the radial length AR, l is the length of base line from the conical mirror to the
lens of CMOS camera. The angle φ is angular separation between OR and OA. In the
previously papers [3,4], we have discussed alignment between the conical mirror and the
10th IMEKO TC14 Symposium on
Laser Metrology for Precision Measurement and Inspection in Industry
Braunschweig, GERMANY, 2011, September 12-14
camera, and we checked error caused by
A
misalignment. From he practical viewpoint,
we should
sample
note the same profile is given
regardless of the device position, that is the
ring beam device is not necessary to be
r
centered. Here, just to be sure, we show the
influence of refraction index of a cylindrical
glass. The ray from the LD is traced as is
φ
shown in Fig. 2. Then, optically sectioned
profile is to be captured by the camera using
dashed
lines.
However
the
profile
l
R
O camera
is
observed through the glass tube. Actually,
sample
the light may be refracted by the cylindrical
glass. In this case, the light proceeds as is
Fig. 1: Fundamental principle of inner
Fig.1
diagram of inner profile
profileSchematic
measurement
measurement by a triangulated method
shown by solid lines. In Fig.2, r1, r2 and r3
indicate the radiuses from the conical
mirror to inner wall of glass, outer wall of
A’
that and inner wall of sample, respectively.
Here, ∆r means the error of the radius
between RA’ and the real radius RA.
According to geometrical calculations, the
A
n1
r3
n2
r2
n1
r1
error of the radius can be expressed as
r sin (α + φ )
∆r = 2
cos φ cos α
sample
∆r
(2)
α
lens
φ
R
Here, α indicates the angle based on
Snell’s law. The α is given by the index of
air n1, glass n2 and the angle α
⎛ n1
⎞
cos φ ⎟⎟
⎝ n2
⎠
α = sin −1 ⎜⎜
l3
l2
l1
l
(3).
Fig.2
Fig. 2:
f
f
Influence of glass pipe
Influence of index of cylindrical glass
This error ∆r may not be negligible if we
measure a small size tube, but usually we need not to be nervous about this.
At any rate we can observe an optically sectioned profile and this profile is captured by using
a camera. According to the principle of triangulation, the radial length at the circular angle θ
is given by the next expression
10th IMEKO TC14 Symposium on
Laser Metrology for Precision Measurement and Inspection in Industry
Braunschweig, GERMANY, 2011, September 12-14
r (θ ) = AR = l tan (θ )
(4).
Here the radius r (θ ) can be determined from the intensity distribution which becomes
Gaussian distribution along the radial direction r (θ ) . It should be noted that our method
doesn’t need to align the camera and the ring beam device at the center of the pipe.
2.2 Construction of the probe
L
conical mirror
wide-angle lens
D
LD
CMOS sensor
ring beam device
miniature camera
Fig. 3: Inner structure of a probe
Fig. 4: Appearance of a probe with 10mm
diameter
We have developed a few sizes of compact inner profile measuring instruments. Figure 3
shows construction of one sample instrument and a picture of appearance. The ring beam
device are built in together with a laser diode (with 650nm wave length), and a miniature
camera. Each component should be adjusted precisely to be good in alignment. In this case,
a miniature camera with a wide-angle lens and a 1/4 CMOS sensor is incorporated. The ring
beam device and the miniature camera are jointed inside the cylindrical glass. The power of
LD is supplied through a hairline enameled wire. In addition, we are developing another
optical instrument using a transparent electrode instead of a metal wire.
Now we have various kinds of proto-type instruments with the diameter from 5mm to 120mm.
additionally we have such an extremely small size probe as 3mm in diameter.
2.3 Experimental examples
We led the compact inner profile measuring instrument on
a linear stage and moved along the guide rail inside the
tube. Figure 5 shows a TV component (electron gun)
which has too steep inner surface and grooves to check
by a contact-type stylus. The optically sectioned profiles
are shown in Fig.9 where optical sections are obtained by
TV’s component
Fig.Fig.7
5: Sample
(TV gun )
10th IMEKO TC14 Symposium on
Laser Metrology for Precision Measurement and Inspection in Industry
Braunschweig, GERMANY, 2011, September 12-14
every 10mm. On the basis of these
captured
optical
sections,
inner
profiles of this sample are analyzed
as shown in Fig. 10. The 3D
expression of the result from every
(a) 0mm
(a) 0̊
30 deg. angle are shown from (a) to
(d) in Fig.10.
Currently we are trying to move this
instrument to practical applications in
industry. In fact, a few companies are
checking availability of this prototype
(b) 10mm
(b) 30̊
system for their own purposes. One
example shown in Fig. 13 is under trial
use for checking the inner diameter of
a bore (80 mm in diameter) of an
engine block. Now we are checking
accuracy
(c) 20mm
(c) 60̊
of
this
probe
using
a
reference gage (Mitutoyo Corp.). One
gage assured to be 25.000+ 0.002
mm is measured 25.05 + 0.002 mm.
At
present,
we
experimental
are
repeating
testing
using
three-size probes mainly
(d) 30mm
(d) 90̊
Fig. 7:Optically
Cross sections
Fig.8
sectioned
10 mm
profileatofevery
TV component
Fig.8:
3D representation
Fig.9 Three
dimensional of
profile
profile ofinner
TV component
for
car
industry
and
heavy
engineering industry. In our trial,
defects or flaws on the inner surface
are proved to be detected by our principle. Figure 9
shows one example that is commercially manufactured
for practical use. Here let’s show another example of
measurement result on an irregular shape object in
Fig.10 (a). One profile of this object is shown in (b), and
the total inner appearance is expressed in (c). This may
Fig. 9: Commercialized probe
(with 25mm diameter)
truth. In addition to profile measurement, checking of defects and flaws on the inner wall of the
look like outer surface, but inner surface is shown in
pipe has been proved possible. In Fig. 14 an aluminum cylindrical sample.
10th IMEKO TC14 Symposium on
Laser Metrology for Precision Measurement and Inspection in Industry
Braunschweig, GERMANY, 2011, September 12-14
In addition to profile measurement, checking of defects and flaws on the inner wall of the pipe
has been proved possible. In Fig. 14 an aluminum cylindrical sample with original
(b)
(a)
Fig.10:
(c)
Measurement of an irregular object (a), inner profile (b), and total inner
surface (c)
marks due to fabrication process and intentionally scratched flaw. The scratched mark is
easily detected as is observed in Fig.15, and even the faint taint caused by drawing process is
found at the bottom of the figure.
Fig. 11: Sample: (Aluminum cylinder)
Fig. 12 Detection of flaws
3. Conclusions
We have developed a compact measuring instrument to know inner profiles of pipe-like
objects. The instrument is so simple as consists of a ring beam device with a conical mirror
and a miniature camera. The ring beam from this device brings optical section of the inner
wall, and the section data captured by the miniature camera are used to calculate the inner
profile. At the same time, we are trying to inspect defects and flaws on the inner surface of the
sample. At this moment, various samples are inspected and measured. We are now trying to
apply this principle to industrial measurement and, in the future, we expect to find applications
in medical field.
10th IMEKO TC14 Symposium on
Laser Metrology for Precision Measurement and Inspection in Industry
Braunschweig, GERMANY, 2011, September 12-14
References
[1] T. Yoshizawa Ed.: Handbook of Optical Metrology: Principles And Applications, CRC Press,
New York, (2009)
[2] T.A. Clarke, The development of an optical triangulation pipe profiling instrument, [Optical
3-D Measurement Techniques III.], Pub. Wichmann, 331-340 (1995).
[3] P.S. Zavyalov, Yu. V. Chugui et al.: Photonics in Measurement 2004, pp.433-443
VDI
Verlag (2004)
[4] T. Yoshizawa, M. Yamamoto, T. Wakayama: Proc. SPIE Vol.6382 (2006) pp.63820D1-5
[5] T. Wakayama, H. Takano, T. Yoshizawa: Proc. SPIE Vol.6762
(2007) pp.67620D1-5
[6] T. Wakayama, T. Yoshizawa: Proc. SPIE Vol.7066
(2008) pp.70660D1-6
[7] T. Yoshizawa, T. Wakayama: Proc. SPIE Vol.7855
(2010) pp.78550B1-8
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