U.S. patent application number 09/747251 was filed with the patent office on 2002-06-27 for fixture for eddy current inspection probes.
Invention is credited to Givens, Glenn D., O'Connell, James P., Traxler, Joseph A..
Application Number | 20020079889 09/747251 |
Document ID | / |
Family ID | 25004285 |
Filed Date | 2002-06-27 |
United States Patent
Application |
20020079889 |
Kind Code |
A1 |
Givens, Glenn D. ; et
al. |
June 27, 2002 |
Fixture for eddy current inspection probes
Abstract
A fixture for use with eddy current inspection probes
facilitates inspection of airfoil leading and trailing edges. The
fixture includes a fixture body having a hole formed in one side
thereof for receiving a probe and a V-groove formed in another side
thereof for receiving a workpiece surface. A clamp arm is pivotally
mounted to the fixture body, and a spring is disposed between the
clamp arm and the fixture body. The spring biases one end of the
clamp arm towards the fixture body so that a workpiece can be
clamped between the clamp arm and the fixture body.
Inventors: |
Givens, Glenn D.; (Milford,
OH) ; O'Connell, James P.; (Fairfield, OH) ;
Traxler, Joseph A.; (Hamilton, OH) |
Correspondence
Address: |
PATRICK R. SCANLON
PIERCE ATWOOD
ONE MONUMENT SQUARE
PORTLAND
ME
04101
US
|
Family ID: |
25004285 |
Appl. No.: |
09/747251 |
Filed: |
December 21, 2000 |
Current U.S.
Class: |
324/240 ;
324/262 |
Current CPC
Class: |
G01N 27/9006
20130101 |
Class at
Publication: |
324/240 ;
324/262 |
International
Class: |
G01N 027/82; G01R
033/00 |
Claims
What is claimed is:
1. A fixture for use with an eddy current inspection probe, said
fixture comprising: a fixture body having a hole formed therein for
receiving said probe; and a clamp arm pivotally mounted to said
fixture body, said clamp arm being spring-biased so that a
workpiece can be clamped between said clamp arm and said fixture
body.
2. The fixture of claim 1 further comprising a first guide wheel
rotatively mounted to said fixture body, and a second guide wheel
rotatively mounted to said clamp arm.
3. The fixture of claim 2 wherein said first and second guide
wheels have axes of rotation that are substantially parallel to one
another.
4. The fixture of claim 1 wherein said fixture body has a V-groove
formed therein for receiving a workpiece surface.
5. The fixture of claim 4 wherein said V-groove is defined by
intersecting planar surfaces formed on said fixture body.
6. The fixture of claim 5 wherein said hole defines a central axis
and a first one of said planar surfaces is oriented at a
predetermined angle with respect to said central axis.
7. The fixture of claim 6 further comprising a first guide wheel
rotatively mounted to said first planar surface, and a second guide
wheel rotatively mounted to said clamp arm.
8. The fixture of claim 1 wherein said fixture body includes a pair
of flanges extending outwardly from one side thereof, and said
clamp arm is pivotally mounted to said fixture body between said
flanges.
9. The fixture of claim 8 further comprising a pivot pin extending
between said flanges and through said clamp arm.
10. The fixture of claim 1 further comprising a set screw threaded
into said fixture body for engaging said probe.
11. A fixture for use with an eddy current inspection probe, said
fixture comprising: a fixture body having a hole formed in one side
thereof for receiving said probe and a V-groove formed in another
side thereof for receiving a workpiece surface, said V-groove being
aligned with said hole; a clamp arm pivotally mounted to said
fixture body, said clamp arm having first and second ends; and a
spring disposed between said second end of said clamp arm and said
fixture body for biasing said first end of said clamp arm towards
said fixture body.
12. The fixture of claim 11 further comprising a first guide wheel
rotatively mounted to said fixture body, and a second guide wheel
rotatively mounted to said first end of said clamp arm.
13. The fixture of claim 12 wherein said first and second guide
wheels have axes of rotation that are substantially parallel to one
another.
14. The fixture of claim 11 wherein said V-groove is defined by
intersecting planar surfaces formed on said fixture body.
15. The fixture of claim 14 wherein said hole defines a central
axis and a first one of said planar surfaces is oriented at a
predetermined angle with respect to said central axis.
16. The fixture of claim 15 further comprising a first guide wheel
rotatively mounted to said first planar surface, and a second guide
wheel rotatively mounted to said first end of said clamp arm.
17. The fixture of claim 11 wherein said fixture body includes a
pair of flanges extending outwardly from one side thereof, and said
clamp arm is pivotally mounted to said fixture body between said
flanges.
18. The fixture of claim 17 further comprising a pivot pin
extending between said flanges and through said clamp arm.
19. The fixture of claim 11 further comprising a set screw threaded
into said fixture body for engaging said probe.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates generally to eddy current inspection
and more particularly to fixtures for facilitating the use of hand
held eddy current inspection probes.
[0002] Eddy current inspection is a commonly used technique for
nondestructively detecting discontinuities or flaws in the surface
of items made of electrically conductive material, including many
gas turbine engine components. Eddy current inspection techniques
are based on the principle of electromagnetic induction in which
eddy currents are induced within the component under inspection by
application of alternating magnetic fields. Known eddy current
probes include absolute probes, which contain a single inductive
coil, and differential probes, which have a drive coil and a sense
coil. In the case of a differential probe, eddy currents are
induced in the component under inspection when the probe is moved
into proximity with the component by alternating magnetic fields
created in the drive coil. The eddy currents produce a secondary
magnetic field that is detected by the sense coil, which converts
the secondary magnetic field into an electrical signal that may be
recorded and/or displayed for analysis. As the eddy current probe
is passed over the component, the presence of cracks and other
discontinuities or deformations in the component will produce
changes in the magnitude of the induced eddy current as compared to
the magnitude of the induced eddy current in areas that do not have
such anomalies. This results in corresponding variations in the
magnitude of the signal output by the sense coil. Hence, the output
signal, specifically the amplitude of the output signal variations,
is an indication of the condition of the component. An eddy current
machine operator may then detect and size flaws by monitoring and
analyzing the output signals.
[0003] Rotor blades are used in the compressor and turbine sections
of gas turbine engines for interacting with the gas stream flow of
the engine. Rotor blades typically include a shank having a
dovetail for mounting the blade to a rotor disk and an airfoil that
extends radially outwardly from the shank and into the gas stream.
The airfoil includes a pressure side and a suction side joined
together at a leading edge and at a trailing edge. Rotor blades are
ordinarily formed as a one-piece casting of a suitable superalloy,
such as a nickel-based superalloy, which has acceptable strength at
the elevated temperatures of operation in the gas turbine
engine.
[0004] During engine operation, the leading and trailing can be
susceptible fatigue cracking because of the high temperatures and
pressures to which the blades are exposed. Furthermore, the
trailing edges can experience cracking during the blade
manufacturing process because they are very thin compared to the
rest of the airfoil. Thus, it is common to frequently subject rotor
blade leading and trailing edges to eddy current inspection before
and after service.
[0005] This is typically accomplished with a hand held eddy current
probe, wherein an operator moves the probe by hand along the
leading or trailing edge of the rotor blade airfoil. However, this
can often be a difficult procedure to perform because of probe
normalization and "lift-off" variables. In other words, it is
difficult for a human operator to maintain the probe at the proper
angle and in constant contact while moving the probe over the
surface being inspected. If either probe angle is altered or
lift-off occurs, then the inspection integrity can become
compromised. Accordingly, it would be desirable to have a means for
maintaining probe angle and contact during eddy current
inspections.
BRIEF SUMMARY OF THE INVENTION
[0006] The above-mentioned need is met by the present invention,
which provides a fixture for use with eddy current inspection
probes. The
[0007] The inspection fixture 10 comprises a fixture body 14 of a
generally rectangular block shape having four sides and two ends. A
hole 16 for receiving the eddy current probe 12 is formed in a
first side of the fixture body 14, about midway between the two
ends thereof. The hole 16 extends perpendicularly from the first
side of the fixture body 14 to a second side, opposite to the first
side. A set screw 18 is threaded into the fixture body 14 at a
first end thereof. The set screw 18 extends perpendicularly to the
probe hole 16 so as to engage the probe 12. Thus, tightening the
set screw 18 against the probe 12 will retain the probe 12 in the
hole 16. Loosening the set screw 18 will allow the probe 12 to be
removed. A knurled knob 20 is provided to facilitate tightening and
loosening of the set screw 18.
[0008] A pair of flanges 22 extend outwardly from the second side
of the fixture body 14, adjacent to the second end thereof (i.e.,
the end opposite the set screw 18). The flanges 22 are spaced apart
in a yoke configuration to define a channel 24 therebetween. Each
flange 22 forms a planar edge 26 on the side closest to the first
end of the fixture body 14. These edges 26 define a first planar
surface of the fixture body 14. The fixture body 14 also includes a
second planar surface 28 formed on the second side thereof,
adjacent to the first end. The first and second planar surfaces 26,
28 intersect to define a V-groove 30 for receiving an airfoil edge
of a blade 32 to be inspected. As shown in FIG. 1, the trailing
edge of the blade 32 is being inspected; however, the inspection
fixture could also be configured to be inspect the leading
edge.
[0009] The V-groove 30 is aligned with the probe hole 16 so that
the probe 12 is properly positioned with respect to the blade edge
when the blade edge is received in the V-groove 30. The second
planar surface 28 is oriented at a predetermined angle with respect
to the central axis of the probe hole 16 (and thus with respect to
the longitudinal axis of the probe 12). As will be explained below,
this angle determines the orientation of the probe 12 when the
blade edge is received in the V-groove 30.
[0010] A clamp arm 34 is disposed in the channel 24 between the two
flanges 22. The clamp arm 34 is pivotally mounted to the fixture
body 14 by a pivot pin 36 that extends between the two flanges 22
and through the clamp arm 34 at a point approximately midway
between the two ends thereof. The clamp arm 34 is a relatively
long, narrow member having a first end that extends beyond the
flange edges 26 and a second end that extends beyond the second end
of the fixture body 14. A spring 38 disposed in the channel 24
extends between the fixture body 14 and the clamp arm 34 for
biasing the clamp arm 34. Specifically, the spring 38 engages the
clamp arm 34 between its second end and the pivot pin 36 so as to
bias the clamp arm first end towards the second planar surface 28
on the fixture body 14. Inward manual pressure exerted on the
second end of the clamp arm 34 will pivot the clamp arm 34 against
the spring pressure and widen the gap between the second planar
surface 28 and the first end of the clamp arm 34.
[0011] A slot 40 is formed in the second planar surface 28, near
the first end of the fixture body 14. A first guide wheel 42 is
mounted in the slot 40 for rotation about a first axle 44. Another
slot 46 is formed in the clamp arm 34, near the first end thereof.
A second guide wheel 48 is mounted in the second slot 46 for
rotation about a second axle 50. Thus, when the inspection fixture
10 is mounted on the blade 32, the first guide wheel 42 contacts a
first side (either the suction or pressure side) of the blade 32,
and the second guide wheel 48 contacts the other side of the blade
32. The two axles 44, 50 are disposed in a common plane. More
specifically, the axles 44, 50 are both perpendicular to the blade
edge when the inspection fixture 10 is mounted on the blade 32.
Thus, the guide wheels 42, 48 will smoothly guide the fixture 10
and probe 12 along the blade 32 while the blade edge is being
scanned. Furthermore, the fixture body 14 is preferably, but not
necessarily, made of a self-lubricating plastic material such as
the material sold under the trademark DELRIN.RTM., to avoid
metal-to-metal contact with the blade 32 during inspections.
[0012] In operation, the eddy current probe 12 is first placed in
the probe hole 16 and secured with the set screw 18. The probe 12
is positioned in the hole 16 so that its end is aligned with the
V-groove 30 situated at the end of the hole 16. Many commercially
available hand held eddy current probes are provided with a notch
in the end for engaging the surface to be inspected. In this case,
the probe would be positioned in the hole 16 so that the probe
notch was aligned with the V-groove 30.
[0013] Once the probe 12 is properly set in the fixture 10, the
second end of the clamp arm 34 is pressed toward the fixture body
14 to open a gap between the first and second guide wheels 42, 48.
The fixture 10 is then placed on the blade 32 so that the blade
edge to be inspected is situated in the V-groove 30 and the first
guide wheel 42 contacts a first side of the blade 32. In this
position, the probe 12 will be properly oriented with respect to
the blade edge because of the predetermined angle between the
second planar surface 28 and the central axis of the probe hole 16.
The clamp arm 34 is then released so that the spring 38 will bias
the clamp arm 34 toward with the blade 32 such that the second
guide wheel 48 contacts the opposite side of the blade 32. The
blade 32 is thus clamped between the first and second guide wheels
42, 48. At this point, the probe end will be in contact with the
blade edge and oriented at the proper angle thereto. The inspection
fixture 10 can then be moved by hand spanwise over the length of
the blade edge with the guide wheels 42, 48 rolling over the
respective blade airfoil surfaces. With this arrangement, an
operator can easily maintain the probe 12 against the blade edge
and with the proper orientation over the entire scan length. The
inspection fixture 10 provides complete and repeatable coverage of
airfoil edges and assures inspection integrity by minimizing
operator dependency and reducing lift-off variables.
[0014] The inspection fixture 10 can be used to inspection either
the leading or trailing edges of rotor blade airfoils, although the
geometry may vary from application. That is, fixtures used for
inspecting leading edges may require a different fixture geometry
(particularly the angle of the second planar surface 28 with
respect to the probe axis and the distance between first guide
wheel 42 and the V-groove 30) than fixtures used for inspecting
trailing edges. Furthermore, the inspection fixture 10 is not
limited to use with rotor blades; it can also be used in the
inspection of the leading and trailing edges of other types of
airfoils, such as stator vanes.
[0015] The foregoing has described a spring loaded, wheel guided
fixture for eddy current probes that targets a predetermined
inspection zone with minimal variation. While specific embodiments
of the present invention have been described, it will be apparent
to those skilled in the art that various modifications thereto can
be made without departing from the spirit and scope of the
invention as defined in the appended claims.
* * * * *