Note: Descriptions are shown in the official language in which they were submitted.
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METHOD AND APPARATUS FOR SCANNING AN OBJECT
TECHNICAL FIELD
[0001] The present disclosure relates to the field of non-destructive
testing. More specifically, the present disclosure relates to a method and an
apparatus for scanning an object.
BACKGROUND
[0002] Mechanical scanning of regularly shaped objects, such as for
example flat or slightly curved objects, is well documented and widely used. A
structure of an object is typically mapped by software using a grid, for
example
a rectangular grid, in which a length and a width of each rectangular pixel of
the grid is identical. The grid is typically aligned with main axes of a
scanner,
designated axes x and y, and a scanning motion is obtained by moving a
probe, for example an ultrasonic probe, along one axis or along a combination
of axes (for instance x) and repeated after indexing along a perpendicular
direction by moving one or a set of axes (for instance y), while maintaining a
distance between the probe and the structure surface. Some systems use a
plurality of such probes.
[0003] Trigger signals are generated to initiate ultrasonic pulse
generation and data acquisition when the probe reaches positions set by the
grid. Encoder signals of the main scanning axis (for example x) are monitored
by an encoder counter that generates the trigger signals at required probe
positions. The probe is indexed in a perpendicular direction by a distance
dictated by dimensions of the pixels on the grid at the end of the scanning
motion. The scanning motion is then repeated for a new index position.
[0004] Three-dimensional (3D) ultrasonic scanning has been
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achieved in the past based on input of 3D computer-aided design (CAD) files.
Motion of a 3D probe is obtained by inversed kinematics allowing moving a
probe at constant distance and orientation with regards to a single surface of
a
scanned object. A virtual axis, composed of a motion control input/output,
amplifier drive, motor and encoder, is calibrated to move synchronously with
the 3D probe motion as the 3D probe follows a scanned surface. The encoder
of this virtual axis represents movements along a single surface and is
monitored during 3D movements of real axes. Trigger pulses are generated at
equal distances traveled by the encoder of the virtual axes, providing a way
to
generate trigger pulses representing a travel over a complex surface.
[0005] Transmission scanning is achieved by adding a second,
receiving probe facing an exit surface, opposite from a first emitting probe
facing the scanned surface. The receiving probe follows the emitting probe,
which is controlled in three dimensions as expressed hereinabove. A constant
orientation and distance is maintained between the emitting and receiving
probes. In controlling movement of the emitting and receiving probes, no
consideration is given to the exit surface.
[0006] Currently available techniques are not well-suited for scanning
of complex shapes, especially for those presenting curved surfaces defined in
a 30 space. Needs exist for scanning complex objects, in particular for non-
destructive testing purposes.
[0007] Therefore, there is a need for techniques that enable efficient
scanning of complex shapes.
SUMMARY
[0008] According to the present disclosure, there is provided a
method of scanning an object. Two virtual, orthogonal axes are positioned on a
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surface of the object. A scanning path of a probe is controlled as a function
of
the two virtual, orthogonal axes.
[0009] According to the present disclosure, there is also provided an
apparatus for scanning an object. The apparatus comprises a movable
support, a probe and a controller. The probe is mounted on the movable
support. The controller is operably connected to the movable support and to
the probe. The controller is configured to calculate a position of two
virtual,
orthogonal axes on a surface of the object and to control a scanning path of
the probe as a function of the two virtual, orthogonal axes.
[0010] The foregoing and other features will become more apparent
upon reading of the following non-restrictive description of illustrative
embodiments thereof, given by way of example only with reference to the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] Embodiments of the disclosure will be described by way of
example only with reference to the accompanying drawings, in which:
[0012] Figure 1 is a flowchart showing operations for scanning an
object;
[0013] Figure 2 is a schematic view of a phased array probe;
[0014] Figure 3 is a schematic view of the phased array probe of
Figure 2 combining some of its array elements to form three
(3) equivalent probes;
[0015] Figure 4 is a block diagram of a scanning apparatus
representing an information flow within the apparatus;
[0016] Figure 5 is a flowchart showing operations for generating
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scanning positions from a computer assisted design file;
[0017] Figures 6A and 6B provide an illustration of transmission mode
when the effect of refraction within an object is considered (6A) or not (6B);
[0018] Figure 7 is an example of a triangulation representing an
imported surface;
[0019] Figure 8a is an example of a parametric space obtained from
isomorphic triangulation of a single surface;
[0020] Figure 8b is an example of a parametric space obtained from
isomorphic triangulation of entry and exit surfaces;
[0021] Figure 9 is an example of an apparatus for scanning an object
in pulse-echo mode;
[0022] Figure 10 is an example of an apparatus for scanning an
object in through-transmission mode; and
[0023] Figure 11 is an image of a real-life object along with a
scanning result of the real-life object.
DETAILED DESCRIPTION
[0024] Like numerals represent like features on the various drawings.
[0025] Various aspects of the present disclosure generally address
one or more of the problems of scanning of complex shapes, including without
limitations curved shapes and those shapes presenting surfaces defined in a
three-dimensional (3D) space.
[0026] The following terminology is used throughout the present
disclosure:
[0027] = Probe: a physical device capable of sending and/or receiving a
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signal towards an object under test.
[0028] Scanning path: a series of consecutive positions of a scanner
probe.
[0029] Pulse: a brief signal emitted by a probe.
[0030] Isomorphic triangulation: mapping of a surface into a plurality
of adjoining triangles using a constant arrangement of
triangles of variable dimension and angles, in which the
number of adjacent triangles attached to each vertex enclosed
within the boundaries of the surface remains constant
throughout the whole surface of an object.
[0031] Rectangular grid: tessellation of a surface into a rectangular
mosaic.
[0032] Mesh size: smallest length or depth of a rectangle in a
rectangular grid.
[0033] Parametric space: mathematical representation of a surface,
for example as a rectangular grid.
[0034] Virtual axis: mathematical representation of an axis on a
parametric space, for example axes of a rectangular grid.
[0035] Contour: broad perimeter fully enclosing a scanned object.
[0036] Pulse-echo mode: signal acquisition mode of a probe in which
a pulse is emitted by the probe and a reflected signal is
acquired by the same probe.
[0037] Transmission mode: signal acquisition mode in which a pulse
is emitted by an emitting probe and acquired by a receiving
probe after transmission through an object.
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[0038] Entry surface: surface of an object receiving a pulse from a
probe.
[0039] Exit surface: surface of an object from which a pulse, received
at an entry surface, exits after transiting through the object.
[0040] Couplant material: a medium present between a probe and a
surface of a scanned object, including without limitation water,
air, or another fluid.
[0041] Controller: a processor, a computer, a combination of
processors and/or computers, possibly including a memory, an
interface, and similar components, the controller may be hard-
wired for carrying a function or may comprise programmable
code for carrying a function.
[0042] Movable support: mechanical device capable of moving under
control of a controller while supporting a probe or a plurality of
probes.
[0043] Command: a control signal sent from a first component to a
second component for initiating an action of the second
component.
[0044] Multi-axis: a mechanical device capable of moving in
translation or in rotation along more than one axis.
[0045] Phased array of probes: a plurality of probes grouped in a
manner allowing production of a predetermined pattern of
pulses.
[0046] Non-destructive testing: a material evaluation technique that
does not cause damage to an object under test.
[0047] C-Scan image: an image constructed by retrieving information
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from ultrasonic signals resulting from ultrasonic scanning of an
object, the ultrasonic signals being recorded at each position
on a rectangular grid applied on a scanned object.
[0048] In an embodiment, the present disclosure presents a method
of scanning an object. Without limitation, the object may comprise one or more
curved surfaces. Two virtual, orthogonal axes are positioned on a surface of
the object. A scanning path of a probe is controlled as a function of the two
virtual, orthogonal axes.
[0049] In another embodiment, the present disclosure presents an
apparatus for scanning an object. The apparatus comprises a movable
support, a probe and a controller. The probe is mounted on the movable
support. The controller is operably connected to the movable support and to
the probe. The controller is configured to calculate a position of two
virtual,
orthogonal axes on a surface of the object and to control a scanning path of
the probe as a function of the two virtual, orthogonal axes.
[0050] The disclosed method and apparatus can be used for various
applications, including without limitation for non-destructive testing
purposes.
[0051] Referring now to the drawings, Figure 1 is a flowchart showing
operations for scanning an object. In Figure 1, a sequence 100 comprises a
plurality of operations that may be executed in variable order, some of the
operations possibly being executed concurrently, some of the operations being
optional. Operation 110 comprises defining a rectangular grid by isomorphic
triangulation of a surface of an object. A parametric space of the surface of
the
object is defined in operation 120 by positioning two virtual, orthogonal axes
on
axes of the rectangular grid. At operation 130, a scanning path of a probe is
controlled as a function of the two virtual, orthogonal axes. Without
limitation,
the probe may be an ultrasonic probe including for example an immersible
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probe or an air coupled probe, an eddy current probe, a laser probe, a hybrid
probe, and the like. Operation 130 involves moving the probe along a scanning
path that can include a plurality of successive probe positions corresponding
to
a plurality of positions of the two virtual, orthogonal axes on the
rectangular
grid. In a variant, a distance between two nearest probe positions corresponds
to a mesh size of the rectangular grid.
[0052] The parametric space can be based on surfaces extracted
from a computer aided design (CAD) file representing the object.
Alternatively,
a curvature and a contour of a surface of the object can be manually defined
by an operator, following which the rectangular grid can be defined within the
contour of the object.
[0053] The probe can operate in pulse echo-mode or in transmission
mode. In the pulse-echo mode, the probe emits pulses that are reflected on the
surface of the objet and the same probe detects an echoic signal. In
transmission mode, the probe is an emitting probe facing an entry surface of
the object and a second, receiving probe faces an exit surface of the object,
moving in synchrony with the scanning path of the emitting probe to detect a
signal resulting from transmission of an emitted pulse through the object. Of
course, either the echoic signal or the transmitted signal both result from an
originally emitted pulse. The echoic or transmitted signal is distorted when
compared to the originally emitted pulse. Analysis of the amplitude, time of
flight and other characteristics of the echoic or transmitted probe can
provide
an understanding of characteristics of the object, including beneath its
surface.
[0054] Instead of moving a single probe operating in pulse-echo
mode or a single pair comprising a single emitting probe paired with a single
receiving probe, the sequence 100 may comprise moving a phased array of
pulse-echo probes, or moving synchronized phased arrays of emitting and
receiving probes along the scanning path.
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[0055] Figure 2 is a schematic view of a phased array probe. Figure 3
is a schematic view of the phased array probe of Figure 2 combining some of
its array elements to form three (3) equivalent probes. Referring at once to
Figures 2 and 3, a phased array probe 700 faces a surface 504 of an object
604. In a first variant, array elements 702 are controlled in a manner that
combines their aim to steer or focus a beam 706 impinging on the surface 504.
Steering of the beam 706 can comprise focusing ultrasounds at a desired
depth under the surface 504 of the object 604 or at a desired angle on the
surface 504. The phased array probe 700 can focus on each position of the
rectangular grid, one point at a time. In this case, the phased array probe
700
is used and operated as a single virtual probe 708. In a second variant,
subsets 704, 714 and 724 of the array elements 702 are grouped, for example
in groups of eight (8) elements, to form distinct virtual probes 708, 718 and
728
that steer beams 706, 716 and 726 to impinge on various points of the surface
504. For a given position of the phase array probe 700, through electronic
control of the array elements 702 to adjust a focal law for each element group
704, 714 and 724 based on the curvature of the surface 504, more than one
point of the surface 504 are concurrently covered.
[0056] Figure 4 is a block diagram of a scanning apparatus
representing an information flow within the apparatus. An apparatus 200 for
scanning an object comprises a plurality of components, some of which are
optional. The various components of the apparatus 200 may be implemented
as stand-alone modules or can alternatively be combined in one or more
modules, the modules being realized as printed circuit boards, electronic
circuits, processors, computers, and like devices. The apparatus 200 as shown
on Figure 4 is for illustration purposes. The apparatus 200 comprises a
movable support (shown on later Figures), one or more probes 202, for
example an ultrasonic probe, mounted on the movable support, and a
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controller. The controller comprises a computer 204, an encoder monitoring
module 216 and an ultrasonic data acquisition unit 226. The controller is
operably connected to the movable support and to the probe 202. The
controller is configured to calculate position information 211 related to two
virtual, orthogonal axes on the surface 504 of an object 604 to be scanned and
to control a scanning path of the probe 202 as a function of the two virtual,
orthogonal axes. The computer 204 has module 206 that calculates a position
of the two virtual, orthogonal axes on the surface of the object as a function
of
known scanning positions 208 that may be obtained, for example, from a CAD
file or from a prior analysis of the object. The computer 204 provides
positioning commands 210 to a motion controller 212, which converts them to
a voltage applied to motors, for example servo motors (not shown), for
continuously moving the movable support, and the probe 202, along
consecutive positions of the scanning path on the surface 504 of the object
604. The computer stores control parameters 229 provided to the ultrasonic
data acquisition unit 226. Generally, the computer 204 comprises executable
code to perform or to control the various operations of the sequence 100 of
Figure 1.
[0057] The encoder
monitoring module 216 receives probe position
information 218 from encoders 222 of a mechanical scanner 220 operably
connected to the movable support. The encoder monitoring module 216 also
receives the position information 211 related to the two virtual, orthogonal
axes. The position information 211 is a function of positions of each
individual
axis of the apparatus 200 and comprises a combination of positions of all axes
involved in the displacement of the probe 202. Within the encoder monitoring
module 216, an encoder monitoring process 217 analyses the position
information 211 related to the two virtual, orthogonal axes and the probe
position information 218 to generate pulse commands 224 that are sent to the
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ultrasonic data acquisition unit 226.
[0058] A variant of the apparatus 200 using stepper motors (not
shown) to move the movable support can be contemplated. With stepper
motors, the probe position information 218 becomes unnecessary since the
positioning commands 210 bring the movable support to a desired position
directly, without a need for positional feedback. With stepper motors, each
one
of successive voltage pulses results in a predetermined advance of the
movable support. A nearly continuous movement is obtained by generating a
rapid train of pulses. A displacement amount of the movable support
corresponding to each pulse being set by configuration of the apparatus 200,
the encoder monitoring module 216 can therefore use the positioning
commands 210 directly as a substitute for the position information 218.
[0059] Having received the pulse commands 224, the ultrasonic data
acquisition unit 226 forwards the pulse commands 224 to the probe 202 that
generate pulses from the pulse commands 224. The same probe or another
probe 202 detects signals reflected by or transmitted through the object and
forwards signal information 228 to the ultrasonic data acquisition unit 226.
The
ultrasonic data acquisition unit 226 then forwards the detected signal
information 228 to the computer 204.
[0060] Having initiated a pulse sent by the probe 202 and having
received and stored signal information 228 resulting from the probe, the
computer 204 controls generation of a next pulse as the probe 202 passes at a
desired location on the surface 504 of the object 604. After a pulse has been
generated, the computer 204 determines when a next pulse is generated by
selecting a physical axis to be monitored. This process can be illustrated by
considering a simple case of a probe motion that involves movements of
physical axes X and Y in a scanning path forming a circular motion of the
probe around a scanned object, in a plane defined by the axes X and Y. The
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circumference of this circular scanning path defines a total linear
displacement
of the probe over 360 degrees in the plane. Assuming that a minimum
inspection coverage requirement for the object impose generation of a pulse
command every time the probe moves by one (1) mm along this
circumference, based on an encoder signal of one of axes X or Y, a decision is
made for each upcoming position to determine whether the position of the X or
Y axis is to be monitored. This determines when to generate a pulse
command. A linear movement of 1 mm along the circumference of the circular
scanning path involves a different amplitude of movement for the X and Y
axes. In some areas, there is very little movement along the X axis and most
of
the 1 mm movement takes place on the Y axis. The opposite occurs in other
areas of the circular scanning path. It may be observed that monitoring a
single
one of axes X and Y does not provide sufficient information to define a circle
and, in some cases, the movement along that single monitored axis can be too
small or null. Consequently, a new axis is selected at each new upcoming
probe position.
[0061] To determine when
the next pulse is generated, after having
selected the physical axis to be monitored, the module 206 calculates a next
position information 211 of the two virtual, orthogonal axes on the surface of
the object. Of course, a variant in which successive values of position
information 211 are calculated at once is within the scope of the present
disclosure. For example, the module 206 can calculate at once a full
displacement along a given virtual axis, for a fixed position on another
virtual
axis. A sequence described herein, in which one value of the position
information 211 is calculated before each pulse generation, is for
illustration
purposes and does not limit the present disclosure. The encoder monitoring
process 217 uses this next position information 211 of the two virtual,
orthogonal axes and uses updated probe position information 218 to generate
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a new pulse command 224 forwarded toward the probe 202. A series of
consecutive positions of the two virtual, orthogonal axes forms the scanning
path of the probe 202.
[0062] In a variant, available positions of the two virtual, orthogonal
axes on the surface of the object can be constrained to map on a mesh of a
rectangular grid defined by isomorphic triangulation of the surface of the
object. In the same or other variant, a distance between two nearest positions
of the pairs of virtual, orthogonal axes on the surface of the object
correspond
to a maximum desired distance between scanned locations on the object.
[0063] Regardless, the computer 204 may create an image (shown
on a later Figure) of the object based on an analysis of a series of detected
signal information 228. The image can be stored in memory (not shown) or
forwarded to a display (not shown). The image can be used for example to
detect flaws of the object that may not be visible from its surface.
[0064] The motion controller 212 of the movable support receives the
positioning commands 210 for moving the probe (or probes) 202. In turn, the
encoders 222 detect movements 221 of the probe 202 and provide the probe
position information 218 to the encoder monitoring module 216. Because the
movable support may be a multi-axis movable support, the motion controller
212 may comprise a plurality of axis controllers 214 and the mechanical
scanner 220 may comprise a plurality of encoders 222. Each encoder 222
tracks a position of a motor axis. The axis controllers 214 and the encoder
monitoring module 216 both monitor signals from the encoders 222. The axis
controllers 214 use positional information to adjust voltages applied to motor
axes in order to control the axis displacement speed and smoothness and
further to minimize differences between desired and attained positions during
and at the end of a displacement event.
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[0065] The positioning
commands 210 may comprise a plurality of
commands for moving the multi-axis movable support about a plurality of
mechanical axes (shown on later Figures) and the encoders 222 of the
mechanical scanner 220 may detect movements of the probe 202 about the
plurality of mechanical axes. Consequently, the probe position information 218
may comprise information about the position of the probe 202 in the plurality
of
mechanical axes.
[0066] Motor voltage and
encoder signals are exchanged 230
between the plurality of axis controllers 214 and corresponding encoders 222,
providing feedback in order to ensure smooth motion of the probe 202. In
particular, voltage applied to the various motors is impacted by information
received from the encoders 222.
[0067] The probes 202
may comprise an emitting probe positionable
facing an entry surface of an object being scanned and a receiving probe
positionable facing an exit surface of the object. When such a pair of probes
202 is used, the controller provides positioning commands 210 and acts upon
probe position information 218 of both probes to control a synchronized
scanning path of the emitting probe and of the receiving probe. In a variant,
relative positions of the emitting and receiving probes may be mechanically
fixed, in which case synchronized motion of the probes is inherently obtained.
A variant showing an emitting probe and a receiving probe is shown on a later
Figure.
[0068] In another
variant, the phased array 700 forming a plurality of
virtual probes 708, 718 and 728 can be mounted on the movable support and
configured to concurrently inspect a plurality of positions of corresponding
pairs of virtual, orthogonal axes on the surface of the object. The module 206
of the computer 204 calculates positions of the pairs of virtual, orthogonal
axes
on the surface of the object as a function of known scanning positions 208 of
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each of the virtual probes 708, 718 and 728 of the phased array 700. The
encoder monitoring process 217 analyses the information 211 related to each
pair of virtual, orthogonal axes and the probe position information 218 of
each
corresponding virtual probes 708, 718 and 728 to generate pulse commands
224 addressed to each respective virtual probes 708, 718 and 728.
[0069] Various embodiments of the method and apparatus for
scanning an object, as disclosed herein, may be envisioned. The following
paragraphs present non-limiting features that may be present in some
embodiments and not in other embodiments.
[0070] The scanning apparatus and method for disclosed herein can
be used for ultrasonic scanning of complex shapes presenting curved surfaces
defined in a 3D space. The method and apparatus allow inspection of a
complex shaped structure, typically a composite material shaped for
aerospace applications, using one or multiple ultrasonic probes moved using a
combination of linear and rotational mechanical axes. The ultrasonic probes
can operate in pulse-echo or through-transmission mode. By respecting a
maximum distance between each probe position along the structure surface, a
C-Scan image of the structure can be produced based on data resulting from
reflection or transmission of ultrasonic pulses. This process involves mapping
a 3D surface of the object on a rectangular grid defined in a parametric
space,
where each adjacent elements of the 3D surface of the object forming a mesh
of the grid are separated by a maximum distance corresponding to a desired
inspection coverage and overlap. In this manner, a maximum distance
between points of entry and exit of the ultrasonic waves along the surface can
be controlled by defining a mesh size of the grid.
[0071] Therefore, mapping of surfaces of a 3D structure into a
parameterized space defined by two (2) virtual orthogonal axes can define a
synchronized movement of multiple mechanical axes supporting one or more
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probes along the surface. This can be used for inspection from a single side,
in
a pulse-echo mode, or from both sides of the structure, in a through-
transmission mode. Controlled movement of the probes along virtual axes
defined in a parametric space can adopt a jogging 'mode, follow absolute
parametric positions, form an automated scan, and the like. Trigger pulses can
be generated at equidistant positions of a parametric axis defined on a curved
surface, using mechanical axes of the scanner without the need for an
additional motor/drive. C-Scan images can be generated at a controlled
resolution. A decision process can select a proper axis or axes that need to
be
monitored to generate equidistant trigger pulses.
[0072] The disclosed method and apparatus for 3D ultrasonic
scanning can be applied to a pulse-echo inspection by following a single
structure surface or, in transmission by following two opposing surfaces of a
structure. Mapping of the surfaces can be achieved manually if the structure
can be defined as the repetition of a curve along another curve, as in the
case
of a swept surface, for example a revolution or extrusion surface. Mapping of
the surfaces can alternatively be based on a CAD drawing. The former case is
referred to as "2.5D" scanning or "contour following scanning", while the
latter
case is referred to as "3D scanning".
[0073] In the case of manual surface mapping (2.50), the mapping
applies to contour following scanning and comprises a definition of the
external
surface that needs to be covered by the ultrasonic inspection using an
ultrasonic probe. A curvature of the surface is defined by positioning the
probe
in front of the surface contour and by adjusting the orientation of the
ultrasonic
probe until the ultrasonic echo returning from the surface of the material is
optimized. This happens when the ultrasonic signal impinges perpendicularly
on the surface. Using the sound velocity in a medium between the probe and
the surface, for example in water, this gives a position and orientation of a
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point of the surface within limits of the ultrasonic scanner. This operation
is
repeated at different probe positions until a sufficient number of points have
been defined to represent the curvature of the structure. In the case of a
curve
that is repeated cyclically on the object, coverage of a single repeatable
pattern is sufficient. This operation is performed on the entry surface of the
ultrasonic waves for pulse-echo scanning, and on both the entry and the exit
surfaces of ultrasonic waves for transmission scanning. The points acquired on
the surface are used in a process that generates a continuous contour within
the limits defined by the acquired points using interpolation processes, for
example a spline. Once the contour has been defined, the extent of the
material along an axis perpendicular to the contour, for example on an
extrusion axis, is defined to map the entire surface. The 2.5D surface is
defined in a 2D parametric space with a set of orthogonal vectors (-11,V),
where
the curve obtained by ultrasonic measurements defines an axis of the
parametric space (e.g. 14) and the curve along which the latter is repeated
defines the second axis of the parametric space (e.g. 13).
[0074] In the case of
automated surface mapping (3D), a file including
a CAD drawing representing the surfaces of the structure to be inspected can
be used to map the surface for a 3D inspection. Figure 5 is a flowchart
showing operations for generating scanning positions from a computer
assisted design file. A flowchart 300 comprises a plurality of operations that
may be executed in variable order, some of the operations possibly being
executed concurrently, some of the operations being optional. Software code
implemented in the computer 204 is executable to perform or control
performance of the operations of the flowchart 300. Surfaces from a CAD file
302 are converted 304 into a step file 306 prepared for 3D scanning software.
Surfaces that need to be covered by the ultrasonic inspection, including a
single surface for pulse-echo mode or two opposed, entry and exit surfaces for
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transmission scanning, are selected 308 and converted into a parametric
space defined by the two orthogonal vectors (ii,) using advanced triangulation
processes. The objective of the triangulation is to create a rectangular
parametric surface out of the 3D surface(s) of the structure. This allows to
create C-Scan images from the acquired data, which is properly arranged on a
rectangular grid.
[0075] A first triangulation 310 is performed on the imported surfaces,
producing a triangulated surface file 312, from which four corners of a
rectangular parametric surface, for example natural corners of the structure,
are defined 314 based on the geometry of the surface to inspect. If
transmission of ultrasound pulses is to be performed through the thickness of
the structure, the corners of the entry and exit surface are defined in an
orderly
manner to associate the corners of each side for an optimal ultrasonic
transmission. These corners define four boundaries of the parametric surfaces.
A rectangular isomorphic triangulation is then calculated 316 on the output of
the triangulation of the surfaces.
[0076] Figure 7 is an example of a triangulation representing an
imported surface. An object 604 has been subjected to triangulation. Triangle
vertices located on boundaries 402 of the surfaces of the object 604 define
limits of the parametric surface. A position of each triangle vertex, such as
404,
that is inside the boundaries of the surfaces is calculated in order to obtain
smooth isoparametric curves.
[0077] Figure 8a is an example of a parametric space obtained from
isomorphic triangulation of a single surface. Figure 8b is an example of a
parametric space obtained from isomorphic triangulation of entry and exit
surfaces. Both Figures 8a and 8b show a mesh size 502 of a rectangular grid.
While Figure 8a only shows one surface 504, Figure 8b shows that the surface
504 is an entry surface facing an exit surface 506. Examples of orthogonal
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vectors (ii) defining the parametric space are displayed on Figure 8a; though
not shown, the vectors 01,0 are also definable on the entry and exit surfaces
504 and 506 of Figure 8b.
[0078] Returning to Figure 5, if transmission of ultrasound pulses is to
be performed through the thickness of the structure of the object 604, three
(3)
options are available for the isomorphic triangulation 316. A selection point
318
provides one of these options. In a first case, for each point of the entry
surface 504, an equivalent point is defined on the exit surface 506. This
allows
to fully cover both surfaces. This optimal coverage allows detection of flaws
inside a volume enclosed between the entry and exit surfaces 504 and 506, as
well as detection of bonding flaws between core material and bonded layers on
the entry and exit surfaces 504 and 506. Alternatively, in a second case, for
each point of the entry surface 504, a nearest point is found on the exit
surface
506. This nearest point of the exit surface 506 is associated to that point of
the
entry surface 504. This option minimizes a distance travelled by the
ultrasonic
waves inside the structure of the object 604. In that case, the entry surface
504
is fully covered while the exit surface 506 is not necessarily fully covered.
Detection can be made of bonding defects between a layer present at the entry
surface 504 and core material of the object 604 while maintaining optimal
ultrasound transmission through the volume of the object 604. A third case
may be used in certain applications such as for inspection of honeycomb
structures. In such a case, pulses are directed so that they impinge the
structure in parallel to an alignment of a core of the honeycomb so that
transmission is made through the material. This is achieved by associating
points of the entry and exit surface so that they are aligned in parallel to
the
core arrangement. A variant may further impose a constant transmission
angle.
[0079] A smoothing, or fit 320, performed for example as a B-Spline,
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is performed on the surface defined by the rectangular isomorphic
triangulation
to ensure a parametric surface that is sufficiently smooth to minimize jerking
of
the mechanical axes resulting from sudden changes in the local curvature of
the parametric surface. This parameterization operation defines smooth axis
displacements and an increased inspection speed. For two (2) surfaces, the
parametric space is defined so that a given position of one surface is linked
to
a single position on the opposing surface. The output of this process is a
parametric space 322 defined by the two orthogonal vectors (71,).
[0080] The probe 202 can move over a 3D space around a 2.5D
surface or 3D a surface. For the case of the transmission mode, a selection
324 determines whether or not the effect of refraction is used to adjust
angles
of emitting and receiving probes.
[0081] Figures 6A and 6B provide an illustration of transmission mode
when the effect of refraction within an object is considered (6A) or not
(613). If
the object 604 is known or assumed to be made of an isotropic material, the
refraction effect is considered (Figure 6A) and angles a, j3 of an emitting
probe
202e and of a receiving probe 202r are adjusted in for aiming at corresponding
entry and exit points on the object 604 while considering the refraction
occurring within the object 604. If the refraction effect is not considered
(Figure
6B), the probes 202e and 202r are simply oriented to aim at each other and at
and the entry and exit points on the object 604.
[0082] In another variant, an optimal angle for a probe used in pulse-
echo mode can be set based on a desired refraction angle inside the object
604. In yet another variant, the receiving probe 202r can be replaced by a
second emitting probe 202e, both emitting probes operating in pulse-echo
mode, and optimal angles for each emitting probe can be determined.
[0083] A desired distance between the probe 202 and the surface of
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21
the object 604 is input by another user input 326. The sound velocity of the
couplant material and the sound velocity of the object 604 are used to
calculate the probe angle using Snell's law of refraction. For transmission
scanning, a distance between the exit surface and the receiving probe is also
input by another user input 326. Also in the case of transmission scanning
using ultrasonic pulses, two options can be selected for determining probe
angles. In a first option, sound velocity of the material forming the object
604
under test is used to calculate an angle of a probe on the entry surface
(emitting probe 202e, shown on a later Figure) and of a probe on the exit
surface (receiving probe 202r, also shown on a later Figure). The probe angles
are chosen to allow entire coverage of the entry and exit surfaces,
considering
the wave refraction occurring at the interface between the couplant material
and the entry surface of the object 604 under test, as well as at the
interface
between the couplant material and the exit surface of the object 604. In a
second option, an angle used to align the emitting probe 202e and the
receiving probe 202r is calculated so that it provides complete coverage of
the
entry and exit surface.
[0084] Inverse
kinematics 328 define the scanning path that follows
the surface of the object, for pulse-echo scanning, or follows the entry
surface
for the emitting probe 202e and the exit surface for the receiving probe 202r
in
transmission scanning. The inverse kinematics 328 apply the selection 324 in
the case of transmission mode. The inverse kinematics 328 additionally apply
the distance between the probe or probes and the surface or surfaces,
determined at 326. These parameters and the parametric space 322 are used
in the inverse kinematics 328 to define two orthogonal, virtual axes (U,V)
330.
The virtual axes (U,V) 330 define simultaneous movements of the emitting and
receiving probes 202e and 202r, in the case of transmission scanning, or
defines the movement of the probe 202 for pulse-echo scanning. As mentioned
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hereinabove, pulse-echo can be performed on both sides of the object 604
using two (2) emitting probes, in which case the virtual axes (U,V) 330 define
simultaneous movement of both emitting probes. Scanning positions 332 of the
probe 202 follow the two orthogonal, virtual axes (U,V) 330 while applying at
least a minimum inspection coverage parameter 334.
[0085] 3D scanning is performed in the parametric space (ra) by
moving the mechanical axes simultaneously using the virtual axes (U,V). The
resolution of the scan within axes (U,V) is defined in order to respect the
minimum inspection coverage parameter 334 defining a maximum distance
between two (2) adjacent scanned locations on the surface. Coordinates of the
scanning positions 332 where data is desired to be recorded are defined in
order to obtain a rectangular grid, providing a constant number of scanning
points to record along the virtual axis U for all positions along the virtual
axis V.
The distance between 2 consecutive scanning positions 332 is not necessarily
constant but is selected according to the maximum allowable distance.
[0086] Referring again to Figure 4, emitting ultrasonic pulses and
recording detected ultrasonic signal information 228 at the calculated
scanning
positions 332 involves generating trigger pulse commands 224 when the probe
202 reaches proper coordinates. This is achieved by monitoring the probe
position information 218 related to one or multiple axes during scanning
movement (e.g. along the U virtual axis). Since multiple mechanical axes are
involved in the 3D motion of the probe 202, a process determines which
encoder 222 is desired to be monitored during the probe 202 displacement.
More than one axis can be monitored during a scanning movement but only
one encoder 222 is used at a time. Thus, the encoder 222 that needs to be
monitored can change between two adjacent scanning position 332 at a given
index position during probe 202 movement along the scanning axis (e.g. along
the U virtual axis). For each scanning position 332 where detected ultrasonic
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signal information 228 is desired to be recorded and where trigger pulses are
desired to be generated, the probe position information 218 for the axis to be
monitored is calculated and the encoder monitoring module 216 generates the
pulse commands 224 at the proper scanning position 332. This is re-calculated
for each index position (e.g. along the V virtual axis).
[0087] The computer 204 records detected ultrasonic signal
information 228 based on the trigger pulse commands 224 and a C-Scan
image is generated. Generally, each pulse generates one signal information
element defining one pixel. Because each pixel of the scanned rectangular grid
do not necessarily have the same dimensions, sizing tools (length, surface,
etc.) applied to the C-Scan image are adapted to take true dimensions of each
pixel into account.
[0088] Figure 9 is an example of an apparatus for scanning an object
in pulse-echo mode. A probe 202 operating in pulse-echo mode is mounted on
a movable support 602 and faces a surface of the object 604 being scanned by
the scanning apparatus 200. The object 604, the probe 202 and at least a
lower extremity of the movable support 602 are immersed within a water basin
600. The object 604 is mounted on a support 606 that is itself fixedly mounted
on a frame 608 of the water basin 600. Immersing the object 604 in water is
one of many options. The scanning apparatus 200 can alternatively make use
of a water jet or bubbler system to provide a local water column for wave
propagation between the probe 202 and the object 604, of make use of air
coupled probes 202 designed to emit and receive ultrasonic waves in air. In
the example of Figure 9, the probe 202 emits ultrasonic pulses that travel
through water and impinge on the surface of the object 604. The pulses
penetrate at least in part through a depth underneath the surface of the
object
604 before being reflected and detected again by the probe 202. A reflection
from an opposite surface of the object 604 may occur if nothing within the
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object material interferes with the transmission of the ultrasonic wave, or
attenuates the transmitted ultrasonic waves down to an undetectable level, and
if the wave hits the opposite surface at an angle that allows reflection back
towards the probe 202. However, a flaw, for example a crack, a void, a
porosity, an inclusion, a delamination, and the like, if present inside the
object
604, may reflect of diffract the wave, depending on its composition,
orientation
and size, resulting in the probe 202 receiving a reflected or a diffracted
wave or
receiving no response to a given pulse. The movable support 602 moves
longitudinally, laterally and vertically along axes x, y and z, and can thus
reach
various positions around the object 604. The probe 202 is held by a head 610
mounted on the movable support. The head 610 rotates about a vertical axis r1
in order to allow facing a tip 612 of the probe in a normal axis with the
surface
of the object 604. The head 610 also rotates about a horizontal axis r2 in
order
to raise or lower the tip 612 of the probe 202 without moving the movable
support 602. Considering at once Figures 4 and 9, the movable support 602
forms a five (5) axis support capable of moving up or down, longitudinally,
laterally and, considering two rotational axes of the head 610, provides five
(5)
axes x, y, z, r1 and r2, under control of the positioning commands 210. The
movements 221 of the probe 202 are detected over five (5) dimensions. Other
configurations involving more or less degrees of freedom, including without
limitation mutually perpendicular rotational axes, are also contemplated.
[0089] Figure 10 is an
example of an apparatus for scanning an
object in through-transmission mode. An emitting probe 202e is supported by a
movable support 602e having a head 610e. A receiving probe 202r is
supported by a movable support 602r having a head 610r. In one embodiment,
the two movable supports 602e and 602r and their respective heads 610e and
610r are synchronized so that the emitting probe 202e is normal to an entry
surface 504 of the object 604 while the receiving probe 202r is co-aligned
with
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an emission path of the emitting probe 202e, facing an exit surface 506 of the
object 604. In another embodiment, angles of the emitting and receiving
probes 202e and 202r with regards to the entry and exit surfaces of the object
604 can be set according to the selection 324 and to the principles introduced
in the foregoing description of Figures 5 and 6. If the refraction effect is
to be
considered, the angle of the emitting probe 202e is adjusted based on the laws
of refraction (Snell's law) in order to obtain a propagation path inside the
object
604 that goes from the entry point to its corresponding exit point on the
opposite surface. The same principle applies to the receiving probe 202e. The
ultrasound wave traveling through the object 604 comes out at the exit point
at
an angle given by Snell's law. The receiving probe 202r points to the exit
point
at the angle calculated by the refraction law. In a variant, a synchronized
but
mechanically variable relationship between the two movable supports 602 and
602r may allow preserving a fixed distance between the emitting probe 202e
and the entry surface of the object 604 while, at the same time, preserving a
fixed distance between the receiving probe 202r and the exit surface of the
object 604. A mechanically fixed relationship between the two movable
supports 602 and 602r maintains a fixed distance between the emitting and
receiving probes 202e and 202r. Amplitudes, shapes and frequencies of
transmitted signals received by the receiving probe 202r are affected by the
shape and thickness of the object 604, by what is present inside the object,
for
example flaws such as cracks, voids, porosity, inclusions, delaminations, and
the like, such flaws impacting the ultrasonic waves in terms of attenuation,
refraction, diffraction, loss of transmission due to total or partial
reflection, and
the like.
[0090] Because of varying shapes of the object 604 being scanned,
the emitting probe 202e is not necessarily normal with the exit surface 506.
[0091] It may be observed that a definition of an entry or exit surface
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of the object 604 is not a feature of the object 604 but is to be considered
in
relation to a position of the emitting and receiving probes 202e and 202r. As
the movable supports 602e and 602r rotate 180 degrees about a vertical axis
of the object 604, the entry surface becomes and exit surface, and vice-versa.
[0092] Figure 11 is an image of a real-life object along with a
scanning result of the real-life object. The object 604 of preceding Figures
is
shown at the top of Figure 11. The same object 604 is reproduced at the
bottom of Figure 11, an image 620 being superimposed on the object 604.
Though Figure 11 is two-dimensional, a C-Scan image can actually be
projected on a 3D representation of the structure based on 3D surfaces
defined in a CAD file. The image 620 has been created by the computer 204
based on the detected signal information 228 obtained in pulse-echo mode
from one probe 202 having moved through the scanning path. Features of the
image 620 represent depths of echoes returning from pulses having
propagated underneath the entry surface of the object 604, revealing an inner
structure of the object 604.
[0093] Those of ordinary skill in the art will realize that the
description
of the method and apparatus for scanning an object are illustrative only and
are not intended to be in any way limiting. Other embodiments will readily
suggest themselves to such persons with ordinary skill in the art having the
benefit of the present disclosure. Furthermore, the disclosed method and
apparatus may be customized to offer valuable solutions to existing needs and
problems of scanning objects that have complex shapes.
[0094] In the interest of clarity, not all of the routine features of the
implementations of the method and apparatus are shown and described. It will,
of course, be appreciated that in the development of any such actual
implementation of the method and apparatus, numerous implementation-
specific decisions may need to be made in order to achieve the developer's
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specific goals, such as compliance with application-, system-, and business-
related constraints, and that these specific goals will vary from one
implementation to another and from one developer to another. Moreover, it will
be appreciated that a development effort might be complex and time-
consuming, but would nevertheless be a routine undertaking of engineering for
those of ordinary skill in the field of non-destructive testing having the
benefit of
the present disclosure.
[0095] In accordance with the present disclosure, the components,
process operations, and/or data structures described herein may be
implemented using various types of operating systems, computing platforms,
network devices, computer programs, and/or general purpose machines. In
addition, those of ordinary skill in the art will recognize that devices of a
less
general purpose nature, such as hardwired devices, field programmable gate
arrays (FPGAs), application specific integrated circuits (ASICs), or the like,
may also be used. Where a method comprising a series of operations is
implemented by a computer or a machine and those operations may be stored
as a series of instructions readable by the machine, they may be stored on a
tangible medium.
[0096] Systems and modules described herein may comprise
software, firmware, hardware, or any combination(s) of software, firmware, or
hardware suitable for the purposes described herein. Software and other
modules may reside on servers, workstations, personal computers,
computerized tablets, personal digital assistants (PDA), and other devices
suitable for the purposes described herein. Software and other modules may
be accessible via local memory, via a network, via a browser or other
application or via other means suitable for the purposes described herein.
Data
structures described herein may comprise computer files, variables,
programming arrays, programming structures, or any electronic information
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storage schemes or methods, or any combinations thereof, suitable for the
purposes described herein.
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