Method for adjustment of transducer position to compensate...

Details Method for adjustment of transducer position to compensate... Method for adjustment of transducer position to compensate...

1999-09-27

2001-02-06

Raevis, Robert (Department: 2856)

Measuring and testing

Instrument proving or calibrating

Apparatus for measuring by use of vibration or apparatus for...

C073S001840, C073S001860

Reexamination Certificate

active

06182494

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention generally relates to ultrasonic testing of objects and, more particularly, is concerned with a method for adjustment of transducer position to compensate for ultrasonic testing beam alignment errors.
As depicted diagrammatically in
FIG. 1
, a prior art ultrasonic immersion testing system
10
typically involves the use of an immersion tank
12
for holding an object
14
immersed in a coupling fluid
16
and a manipulator
18
positioned on the tank
12
such that the pointing direction
20
of the manipulator
18
intersects the object
14
at known coordinates. The manipulator
18
mounts a transducer
22
which also is immersed in the coupling fluid
16
and generates an ultrasonic beam
24
toward the object
14
to be inspected or tested.
Ultrasonic immersion testing requires that the ultrasonic beam
24
intersect a surface
14
a
of the test object
14
at a defined angle. For
20
most volumetric inspections, the ultrasonic beam
24
should be parallel to a normal vector
26
from the object surface
14
a
at the point of intersection
28
of the beam
24
with the surface
14
a
. However, in most ultrasonic immersion systems, small angle errors E will be present between the positions of the manipulator
18
and transducer
22
of the system
10
causing the pointing direction
20
of the manipulator
18
and the direction of the ultrasonic beam
24
from the transducer
22
to be offset or diverge from one another such that the ultrasonic beam
24
will not be parallel with the normal vector
26
at the point of intersection
28
of the ultrasonic beam
24
with the surface
14
a
of the object
14
.
Ultrasonic immersion systems capable of scanning complex shape objects use information collected from computer-generated descriptions of the object or from “teach and learn” scanner applications to orient the transducer. These systems typically use simplified geometric algorithms to position the transducer for evaluation of the object. These systems, however, cannot correct for position and angle offsets that are associated with the transducer and the manipulator. These offsets can lead to errors in the positioning and orienting of the transducer which can reduce the detection capability of the ultrasonic evaluation.
The small errors in the transducer alignment relative to the manipulator pointing direction can lead to larger angle errors between the ultrasonic beam and the surface normal vector. The significance of the positioning errors are increased by the surface curvature of complex shape objects. Errors in the location of intersection between the ultrasonic beam and the surface of the object will lead to increased errors in the alignment of the ultrasonic beam relative to the surface normal vector at the point of incidence.
This additional alignment error limits the use of contour following methods on complex shape objects. Objects with small radii of-curvature will have larger angle alignment errors for the same beam position errors. To use contour following methods to scan complex shape objects, these positioning errors caused by misalignment of the ultrasonic beam must be minimized.
Consequently, a need exists for an innovation which will provide a solution to the aforementioned misalignment error problem without introducing any new problems in place thereof.
BRIEF SUMMARY OF THE INVENTION
The present invention provides a transducer position adjustment method designed to satisfy the aforementioned need. The adjustment method of the present invention corrects the transducer position so as to thereby compensate for ultrasonic beam translation and rotation alignment errors. The method requires no modification in the computer software and geometric algorithms used by the ultrasonic immersion system. Therefore, the method can be used to compensate for alignment errors with any generic contour-following ultrasonic testing scanner.
In an embodiment of the present invention, therefore, a method is provided for adjustment of transducer position relative to an object to compensate for ultrasonic testing beam alignment errors. The transducer position adjustment method comprises the steps of providing a manipulator of an ultrasonic immersion testing system having a pointing direction and supporting a transducer generating an ultrasonic beam, providing a calibration body defining a target thereon, immersing the transducer of the manipulator and the calibration body in a coupling fluid in an immersion tank of the ultrasonic immersion testing system, setting the manipulator initially at a first position such that the pointing direction of the manipulator is aligned with the target of the calibration body at known coordinates, and adjusting the manipulator subsequently to a second position such that the ultrasonic beam of the transducer is br ought into alignment with the target of the calibration body at the known coordinates for initiating an inspection of a test object after replacing the calibration body with the test object.
More particularly, the calibration body is provided with a generally block-like configuration and a top surface. The target of the calibration body is in the form of a recess defined in the bottom surface of the calibration body. The recess of the calibration body has a flat bottom. The setting of the manipulator includes defining the first position by a first angle and a second angle. The first angle is defined between the manipulator pointing direction and a positive Z axis of the ultrasonic immersion testing system. The second angle is defined between the manipulator pointing direction and an X axis in the plane of the X axis and a Y axis of the ultrasonic immersion testing system. The adjusting of the manipulator includes defining the second position by the first angle and the second angle and scanning the calibration body with the ultrasonic beam of the transducer to align the ultrasonic beam of the transducer with the target of the calibration body.


REFERENCES:
patent: 4170891 (1979-10-01), Elsner
patent: 5381383 (1995-01-01), Burfeindt

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