The invention relates to a method for inspecting the interior
of a material, comprising of moving at least one sensor at a substantially constant
distance along a surface of the material. Such a method is known, for instance from
American patent 6,948,369
Materials or material connections, such as welds, can be
inspected using ultrasonic waves or ultrasound. After activation an ultrasonic transducer
then transmits an ultrasonic wave beam which penetrates into the material for inspecting,
and is partially reflected again. The wave reflections are received by the ultrasonic
transducer and converted into an electrical signal. Changes in the structure of
the material or material transitions can be detected by analysing these signals.
The ultrasonic transducer thus has both a transmitting and a receiving function.
By displacing the ultrasonic wave beam in controlled manner
over a determined surface the material for inspecting can be inspected in a particular
area. When a determined surface or area is scanned by the ultrasonic wave beam and
the measurement data relating to the inspected surface or area are displayed graphically,
this is referred to as making a scan. A device which makes it possible to scan a
determined surface or area systematically using an ultrasonic wave beam is therefore
called a scanner.
A problem occurring in the ultrasonic inspection of materials
or connections is that ultrasonic waves are greatly damped in the air, whereby only
weak reflections are detected. Use is therefore often made for ultrasonic inspections
of a bath in which the material for inspection is arranged. The medium in the bath,
usually water, conducts the ultrasonic waves well, whereby strong and readily detectable
reflections occur. Such inspections are however often laborious and time-consuming.
The costs of a bath, which usually has to have considerable dimensions to also allow
inspection of larger objects, are moreover relatively high. For many objects an
ultrasonic inspection in a bath is not practically feasible at all.
An ultrasonic scanner is therefore described in the above
American patent 6,948,369
with which inspections can be carried out in the open air, so without
here immersing the objects for inspecting in a bath. This known scanner, which is
particularly intended for checking the quality of welded connections, is provided
with an ultrasonic transducer which is arranged at the top of a reverse-conical
housing. The form of the housing corresponds to the form of an ultrasonic wave beam
which is transmitted by the transducer and which is focussed at a determined depth
in the material for inspecting. The underside of the housing, which is intended
for placing on the material for inspecting, has a cylindrical form and is provided
with a collar placed therearound. This collar serves to support the scanner over
a greater surface area. The space in the housing between the transducer and the
underside is filled with a liquid such as water. The conical part of the space is
closed with a membrane situated some distance above the surface of the material.
The space between the membrane and the surface of the material is connected to a
source of contact fluid, for instance water.
The scanner is connected to an element to be fixed to the
material, for instance a magnet or a great weight, and is displaced manually or
by means of a mechanism in a square pattern over the surface of the material for
inspecting. A second transducer herein detects and transmits the displacements to
a central processing unit, in which the reflections received by the first transducer
are also processed and optionally displayed graphically. In this manner so-called
A-scans, B-scans and/or C-scans of the welded connections can be made.
This known method has a number of drawbacks. In the first
place the movement of the scanner over the material is not very uniform due to the
square progression thereof. This results in a jerky movement, whereby there is the
danger of the scanner coming off the material for inspecting. Carrying out the movement
manually results in further unevenness. In practice it is not readily possible to
manually displace such a scanner in regular manner over the surface. When use is
however made of a mechanism for the movement, the costs of the installation to be
used in inspection then increase sharply. In addition, the material for inspecting
comes into contact with the liquid which is introduced into the space between the
membrane and the collar, whereby it must be dried or cleaned after inspection.
The invention now has for its object to further develop
a method of the type described in the preamble such that the above described drawbacks
do not occur, or at least do so to lesser extent. According to a first aspect of
the invention, this is achieved in such an inspection method in that the at least
one sensor performs a substantially uniform movement along the surface. This reduces
the risk of the position of the sensor changing relative to the material surface
due to jolting, whereby the direction and distance of the wave beam could vary and
the detection would become less reliable. Due to the uniform movement performed
by the sensor according to the invention the acceleration forces are low, so that
the sensor can be moved along the surface at relatively high speed. Scanning therefore
takes only a short time, whereby the method is very suitable to be performed manually.
The at least one sensor preferably performs a composite
movement along the surface, whereby a relatively large surface area can be covered.
A rapid and simple manner of covering a large area in a short time is to have the
sensor perform a rotation movement and a translation movement. The sensor hereby
moves as it were in a spiral shape along the surface.
According to a second aspect of the invention, the at least
one sensor comprises an ultrasonic transducer, and a medium which conducts the ultrasonic
waves well is placed between the at least one sensor and the surface. This medium
can be a liquid but it is also possible to envisage the use of a gel.
In order to ensure a stable and uniform movement of the
sensor it is recommended that the readily conductive medium is held immobile on
the surface, and the at least one ultrasonic transducer is moved through or along
the medium. The readily conductive medium is here advantageously kept clear of the
surface so that the material does not have to be dried or cleaned after the inspection.
The invention also relates to a device with which the above
described inspection method can be performed. From the above stated
American patent 6,948,369
is already known a device for inspecting the interior of a material, which
is provided with at least one sensor and means for moving the at least one sensor
at a substantially constant distance along a surface of the material. An inspection
device according to the present invention is distinguished from this known device
in that the moving means are adapted to cause the at least one sensor to perform
a substantially uniform movement along the surface. This in turn results in the
advantages described above with reference to the method.
Due to the uniform movement the acceleration forces in
particular are low, whereby the device will not vibrate, or hardly so, during scanning.
The device can thus be held in stable manner against the material for inspecting,
whereby better measuring results can be obtained. The sensor can hereby be moved
at higher speed so that the inspection requires less time and it is easier to hold
the device by hand in a fixed position on the material for inspecting during this
The moving means are preferably adapted here to cause the
at least one sensor to perform a composite movement, in particular a rotation movement
and translation movement, along the surface.
A structurally simple embodiment is herein achieved when
the moving means comprise an element rotatable about an axis, wherein the at least
one sensor is arranged eccentrically relative to the axis. The sensor thus performs
a circular movement around the rotation axis.
The moving means preferably comprise a translatable element
in which the rotatable element is accommodated. A combination of the two movements
is thus achieved in simple manner.
When the moving means comprise a motor which drives the
rotatable element and/or the translatable element via at least one transmission,
the movements are combined with simple means, while the costs of the device can
be low through the use of a single motor.
According to another aspect of the invention, the at least
one sensor comprises an ultrasonic transducer and the inspection device further
comprises a medium which conducts ultrasonic waves well and which is placed between
the at least one sensor and the surface.
This readily conductive medium is preferably arranged in
a chamber to be held immobile on the surface, and the at least one ultrasonic transducer
is movable through or along the chamber. In this manner a very uniform movement
of the transducer can be guaranteed, this movement being stabilized by the chamber
with the conductive medium. Direct contact between the medium and the surface of
the material is moreover avoided due to the chamber, so that no medium is lost and
the material does not have to be dried or cleaned. Finally, it is simple in this
manner to determine the position of the ultrasonic transducer relative to the material.
Only the position of the transducer relative to the medium chamber has to be measured
for this purpose, since this chamber does not move relative to the material for
inspecting. When, in addition to the ultrasonic reflections, the position of the
ultrasonic transducer is thus also determined, this information can be processed
and displayed using signal and data processing equipment. A common form of presentation
of these measurement data is a so-called C-scan, wherein a determined reflection
pattern in a surface is displayed graphically using colours. A determined condition
in or on a material, such as for instance a weld connection, can hereby be displayed
as a colour indication.
When the movements of the transducer are provided by a
translatable and a rotatable element, a structurally simple device is obtained if
the translatable element is mounted slidably on the chamber.
In order to obstruct the radiation from and to the transducer
as little as possible at least a wall of the chamber to be held on the surface preferably
has a window permeable to ultrasonic waves. In the ultrasonic window the wall consists
of a material which causes few ultrasonic reflections and thereby disrupts the reflected
ultrasonic signal as little as possible. The material of the window can consist
of a solid, a rubber-like material, a foil or of other materials. A minimal absorption
and reflection of the ultrasonic waves is achieved when the window is a membrane.
In order to keep the reflection of the window itself as
low as possible the window can enclose a non-right angle with a line connecting
the at least one ultrasonic transducer and the surface. By placing the window such
that the ultrasonic wave beam is not incident on the window perpendicularly but
at an angle, reflections from the window, which are undesirable, can be directed
such that they do not reach the ultrasonic transducer, or at least do so with less
intensity. The measurement is thus disrupted as little as possible by reflections
from the window.
In order to also be able to use the inspection device in
the case of components which do not run flat under the device, for instance components
with a bent edge, it can preferably be provided with means for deflecting waves
transmitted by the at least one ultrasonic transducer. The device can thus detect
a material for inspecting as it were "round the corner". These deflecting means
can comprise a mirror which is placed in the chamber or can be connected thereto.
The invention is now elucidated on the basis of two embodiments,
wherein reference is made to the accompanying drawing, in which corresponding components
are designated with reference numerals increased in each case by 100, and in which:
- Fig. 1 shows a partly cut-away perspective view of a first embodiment of the
inspection device in use for detecting an internal fault in a material;
- Fig. 2 shows a partly cut-away perspective view of a second embodiment of the
inspection device; and
- Fig. 3 shows a cross-sectional view of the embodiment of fig. 2 in use for inspecting
a material with upright edge.
A device 1 (fig. 1) for inspecting the interior of a material
2 comprises a sensor 3, in the shown example an ultrasonic transducer, and means
4 for moving this transducer 3 at a substantially constant distance along a surface
5 of material 2. Transducer 3 transmits an ultrasonic wave beam 29 which is focussed
at a determined depth in the material 2 for inspecting and also receives reflections
of wave beam 29. Moving means 4 are adapted to cause transducer 3 to perform as
uniform a composite movement as possible along surface 5, in this case a circular
rotation movement according to arrow C and a translation movement according to arrow
For this purpose moving means 4 comprise firstly an element
6 which is rotatable about an axis A and in which the transducer 3 is received eccentrically
relative to axis A. Transducer 3 is herein per se also rotatable in element 6 by
means of bearings 7. Transducer 3 is connected via a cable 8 to a control and processing
unit (not shown here). This unit is adapted to analyse the reflected ultrasonic
signals, process and present them in diverse ways, as figures or graphically. The
unit is also adapted to control the movements of transducer 3 and for activation
Cable 8 is placed through a cable guide 9 in rotatable
element 6 and attached non-rotatably at 10 to a housing 11 enclosing moving means
4. During rotation of rotatable element 6 the cable 8 will bend between guide 9
and transducer 3. For this purpose a flexible mechanical coupling (not shown here),
for instance a bellows coupling, can also be arranged between transducer 3 and cable
8. It is otherwise also possible to envisage transducer 3 being received fixedly
in rotatable element 6 and a rotatable electrical connection, for instance an inductive
connection or a connection with slide contacts, being arranged between transducer
3 and cable 8 or somewhere in cable 8.
In addition, moving means 4 comprise a translatable element
12 in which rotatable element 6 is received via bearings 13. This translatable element
12 here takes the form of a carriage which bears the greater part of inspection
device 1, including housing 11. It is however also possible to envisage carriage
12 being accommodated slidably in housing 11, whereby this housing 11 can function
as a handle.
Arranged among other parts on carriage 12 is a motor 14,
which also forms part of moving means 4. This motor 14 has an output shaft 15 which
drives rotatable element 6 via a first transmission. The same shaft 15 also drives
translatable element 12 via a second transmission. Motor 14 or rotatable element
6 is provided with an angular displacement sensor (not shown here) for measuring
the angle through which the rotatable element 6 is rotated.
The first transmission is formed simply by a toothed wheel
16 which is connected to rotatable element 6 and which engages in a toothed wheel
17 on motor shaft 15. The second transmission is formed by a toothed wheel 18 which
engages in toothed wheel 17 on motor shaft 15 and which is connected via a shaft
19 to a smaller toothed wheel 20. This toothed wheel 20 co-acts with a gear rack
21 which is in turn attached to a fixed part of inspection device 1.
The fixed part of device 1 is formed by a chamber 22 filled
with a medium 23 which readily conducts the ultrasonic waves of transducer 3. This
medium 23 can be a liquid such as water, but a gel can also be envisaged. This chamber
22 here has a bent upper edge 24 around which an edge 25 of carriage 12 engages
so that carriage 12 is mounted slidably on chamber 22. Seals (not shown here) are
of course provided between carriage 12 and chamber 22 to prevent leakage of medium
23 out of chamber 22.
Chamber 22, which is thus closed on the top side by carriage
12, has a peripheral wall 26 and an end wall 27. In this end wall 27, which is placed
on the surface 5 of the material 2 for inspecting, is formed a window 28 which is
well permeable to the ultrasonic wave beam 29 from transducer 3. This window 28
can for instance be a membrane. In order to preclude as far as possible disruptive
reflections from window 28 reaching transducer 3 the window can, as stated, enclose
a non-right angle with a line L connecting transducer 3 and surface 5. Window 28
could also be given a spherical form. Window 28 is detachable, and can be replaced
with another window if desired.
The above described inspection device 1 now operates as
follows. Device 1 is first placed with the bottom wall 27 of medium chamber 22 onto
surface 5 of a material 2 for inspecting, at a location where an irregularity is
suspected, for instance a subsurface crack, or at the position of for instance a
welded connection. Motor 14 is then started and transducer 3 activated. Transducer
3 will now continuously transmit an ultrasonic wave beam 29 which penetrates the
material 2 through chamber 22 and window 28. When wave beam 29 encounters an irregularity
30, it is reflected. If there are no irregularities in material 2 the wave beam
is reflected by the opposite surface 31. Because the propagation speed of ultrasonic
wave beam 29 in material 2 is known, the depth at which the beam 29 was reflected
can be determined from the time which has elapsed between transmitting and receiving
of wave beam 29. This depth can be displayed graphically.
While transducer 3 transmits its wave beams 29 and receives
reflections, it is set into an uniform movement relative to the stationary chamber
22 by motor 14, the transmissions, carriage 12 and rotatable element 6. This uniform
movement forms a combination of a circular rotation C around axis A and a linear
translation as according to arrow T. The resulting movement is thus spiral, whereby
wave beam 29 can cover a relatively large surface area of material 2. The position
of transducer 3 is given at every moment by the angular displacement sensor. Because
the movement is very uniform and device 1 itself is held immobile, the accelerations
are slight and transducer 12 can be moved very quickly. An image of the interior
of material 2 is thus obtained in a short time by coupling the reflections to the
positions of transducer 3.
In an alternative embodiment of inspection device 101 (fig.
2) the window 28 is removed and an auxiliary chamber 132 is mounted against wall
127 on the underside of chamber 122. Accommodated in this auxiliary chamber 132
is a mirror 133 with which the direction of the ultrasonic wave beam 129 from transducer
103 can be deflected, in the shown embodiment through a right angle. Auxiliary chamber
132 is provided with its own window 134 which is formed in a side wall 135 thereof.
In the shown embodiment the mirror 133 takes a spherical form, whereby it also serves
to focus wave beam 129. With this embodiment of device 101 a material 102 having
an upright part 136 (fig. 3) can be inspected. This embodiment is generally suitable
for performing measurements at locations which are difficult to access, such as
in corners or in the vicinity of obstacles. And although auxiliary chamber 132 is
described here as a separate component for later mounting, device 101 could also
be provided with a single, continuous medium chamber 122 in which a mirror 133 could
The above described inspection device can have a very compact
form and is thereby suitable for use as hand tool. The device can thus be used at
locations where space is limited, such as for instance between components of car
bodywork or in aircraft where materials must be checked at specific locations -
for instance at the position of spot welds or rivets. The free surface of the material
for inspecting required for placing of the device thereon can be small because the
wall with the window, which comes into contact with the materials for inspecting,
can be given a small form. Since the control and processing unit is also portable,
the entire inspection device can be used on location.
Although the invention is described above on the basis
of a number of embodiments, it can be varied in numerous ways. A different type
of sensor could for instance also be used instead of an ultrasonic transducer, for
instance an eddy-current sensor, a laser, a thermal sensor or the like. A medium
chamber is of course not necessary in every type of sensor. It is also possible
to apply more than one sensor, and combinations could be made of different types
of sensor. Nor is the movement of the sensor limited to a combination of a circular
rotation and a linear translation. Other cyclical movements, such as elliptical
movements, can also be envisaged, while the translation movement could also run
along a curved path. In addition to the conductive medium in the chamber, use could
further also be made of a contact medium between the wall of the chamber in which
the window is situated and the material surface. Undesired damping of the ultrasonic
waves is hereby limited as much as possible. Finally, it must also be remembered
that, where terms such as "top" and "bottom" are used in the text, these must be
seen in relation to the shown figures. In reality however, the inspection device
according to the invention can be used in any desired position.
The scope of the invention is therefore defined solely
by the following claims.