Contact ultrasonic transducer head

A contact ultrasonic transducer head assembly. A stationary housing is adapted to be fitted to a remotely operated manipulator. A movable assembly slidably received by the stationary housing has a plurality of independently suspended ultrasonic transducers mounted thereon. A position encoder mounted in the movable assembly monitors movement within the stationary housing. A limit switch is used to electrically disable the remotely operated manipulator when the movable assembly slides a predetermined distance into the stationary housing to prevent damage to the transducers or the surface being inspected.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention generally relates to ultrasonic inspection devices 
and in particular to inspection devices which are placed in direct contact 
with the work under inspection. 
2. General Background 
Ultrasonic examination of work such as pressurized water reactor vessels is 
typically performed from the inside of the vessel. During such 
examinations, ultrasonic transducers are manipulated by a remotely 
operated apparatus to scan predetermined areas of the reactor vessel. The 
examination is accomplished by generating an ultrasonic sound wave which 
is acoustically coupled to the vessel being inspected. The sound wave 
travels through the material of the vessel at a rate determined by the 
acoustic velocity of the material. 
The acoustic velocity is a product of the material's density and 
elasticity. Reflections or echos of the sound wave occur whenever the 
velocity of the propagated sound wave is altered. The magnitude of the 
echo is related to the acoustic impedance of the reflecting material 
interface or, in the case of a flow, its size and orientation in relation 
to the size and orientation of the transmitted sound wave. Two methods of 
coupling the transmitted sound wave from the transducer to the vessel 
under inspection are generally used. In one, known as the immersion 
method, the transducer is submersed in water and placed a set distance, 
generally several inches, from the vessel wall. The sound waves are 
transmitted from the transducer, through the water, and into the vessel 
wall. Reflected sound waves are received by the transducer and 
electronically processed to determine the location of the reflection. A 
second method of inspection, the contact method, places the ultrasonic 
transducers in direct contact with the vessel under inspection. The sound 
is coupled to the vessel by a thin film of water. The transducer may be 
attached to a remotely operated manipulating system such as an automated 
reactor inspection system (ARIS) which controls the positioning of the 
transducer head inside the reactor vessel. As far as is known, previous 
applications of the contact method of inspection have involved the use of 
rigid plates specifically contoured for each geometric configuration 
examined in the vessel. A problem with this method is that several 
different plates would be required for a typical vessel inspection. 
Normally, the entire inspection tool must be removed from the vessel to 
change the inspection plate. Removal of the inspection tool to change out 
the inspection plate is impractical as such examinations are usually 
critical path. Ultrasound systems of which the inventors are aware include 
the following. 
U.S. Pat. No. 4,489,729 entitled "Ultrasound Imaging System" is aimed at 
general applicatins for the medical field and discloses the use of a 
plurality of transducers, range signal means, timing means, energizing 
means for the transducers, means for listening for an ultrasonic wave, 
means for selecting a sequence of firing transducers, and means for 
producing an output representative of the received ultrasound signals. 
U.S. Pat. No. 4,210,028 entitled "Method and Apparatus for Ultrasonically 
Measuring Concentrations of Stress" is aimed at vessel inspections and 
discloses an ultrasonic transducer array, means for measuring the time of 
flight of the acoustic waves within the object of interest, and means for 
determining from the time of flight measurements any variations in the 
acoustic velocity of the acoustic waves within the object of interest. 
U.S. Pat. No. 4,096,755 entitled "Ultrasonic Inspection Apparatus" is aimed 
at inspection of aircraft fuselage components and discloses a carriage 
movable over a surface to be ultrasonically inspected, alternate 
transmitting and receiving ultrasonic transducers mounted on the carriage, 
means for causing each of the transmitting transducers to generate a burst 
of sound in the surface, separate detectors for each of the receiving 
transducers for detecting a shift in phase in the sound received by its 
associated receiving transducer due to a defect in the surface and for 
momentarily indicating a shift in phase indicative of a defect, a single 
master indicator for all transducers, and means for actuating the master 
indicator. 
U.S. Pat. No. 4,252,022 entitled "Detection, Characterization and Studying 
of Flaws in Work by Acoustic Imaging" relates to acoustical holography and 
discloses a method of studying flaws in work having an irregular surface 
comprising generating and focusing acoustic energy on or near the 
irregular surface, scanning the surface with the focused acoustic energy, 
receiving resulting acoustic energy from echoes from flaws, and 
controlling the reception to reduce the effects of differences in the 
irregular surface. 
U.S. Pat. No. 4,523,468 entitled "Phased Array Inspection of Cylindrical 
Objects" is aimed at pipe inspection and discloses a method of 
ultrasonically locating defects in an object with first and second 
transducer arrays comprising actuating at least one transducer of each 
array and causing the remaining transducers to assume a reflected 
receiving mode, measuring an ultrasonic wave travel time between 
transmission and receipt, determining the spatial relationship between the 
transmitting and receiving transducer, and determining the location of the 
defect from the measured travel time and relative spatial relationship of 
the transducers. 
U.S. Pat. No. 4,604,897 entitled "Multitransducer Ultrasonic Transducer 
With Transducers of Different Sizes" discloses the use of probes of 
different sizes and control means for selectively activating successive 
groups of transducers. 
U.S. Pat. No. 4,582,065 entitled "Ultrasonic Step Scanning Utilizing 
Unequally Spaced Curvilinear Transducer Array" discloses an assembly for 
use in a medical diagnostic system comprising a plurality of individual 
ultrasonic transducer elements and a mounting structure defining a curved 
array face for disposing the transducer elements in a convex curvilinear 
array. 
The known art does not address the problem of variations in the water path 
distance in immersion testing. The use of several contact heads shaped to 
match the contour of the portion of the vessel under examination, a time 
consuming and impractical process, is also not addressed in the area of 
contact testing. 
SUMMARY OF THE INVENTION 
The present invention solves the aforementioned problem in a 
straightforward manner. What is provided is a contact head which holds a 
plurality of transducers. The head assembly is mounted on a remotely 
operated tool capable of manipulating the head throughout a reactor 
vessel. Each transducer is fitted into an individual transducer holder and 
is mounted on an independent suspension system capable of contouring to 
irregular surfaces as well as conforming to surface contours ranging from 
flat to a thirteen inch radius. The transducers are contained in a larger 
transducer holder which is mounted on a movable assembly. The movable 
assembly is slidably mounted to a stationary housing which is mounted on a 
remotely operated tool. This movability gives the contact head the ability 
to stay in contact with the vessel wall during inspection regardless of 
minor geometric variations in the vessel. The movable assembly is provided 
with wear pads which support the load of the movable assembly against the 
reactor vessel wall. This allows the suspension system of the transducers 
to function independently and minimize wear on the transducers. 
In view of the above, it is an object of the present invention to provide a 
contact head assembly with the ability to carry all transducers required 
to do a full reactor vessel inspection.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to the drawings, it is seen that the invention is generally 
referred to by the numeral 10. Contact ultrasonic transducer head 10 is 
generally comprised of stationary housing 12 and movable assembly 14. 
Stationary housing 12, best seen in FIG. 1-2, is adapted to be connected to 
a remotely operated tool by providing mounting plate 16 at the rear 
thereof. In the preferred embodiment, mounting plate 16 is adapted to be 
mounted to a manipulator such as the ARIS II or III manipulator 18 shown 
in FIG. 1. However, it should be understood that mounting plate 16 may be 
adapted to fit any suitable manipulator. As seen in Figure 1, stationary 
housing 12 is illustrated as being cylindrical and attached to mounting 
plate 16 by any conventional means such as screws 20. Mounting plate 16 is 
adapted to slidably receive tubular shaft 22 through which electrical 
connections to movable assembly 14 are run. Sealing means such as O-ring 
24 may be used to prevent fluid leakage betwen mounting plate 16 and shaft 
22. Transducer head assembly 10 may be mounted on ARIS manipulator 18 by 
extending shaft 22 into the manipulator and terminating it at the control 
system therein (not shown) where all electrical connections are made. With 
this direct connection to the control system, transducer head assembly 10 
may be rotated 360 degrees by the manipulator to maintain proper alignment 
for complex vessel geometries. As seen in FIGS. 2 and 3, stationary 
housing 12 is provided with flange 26 around its forward internal edge 
which serves as a means of retaining movable assembly 14 within stationary 
housing 12. 
Movable assembly 14, seen in FIGS. 2 and 3, has its main body portion 28 
sized to be slidably received within stationary housing 12 and is 
cylindrical in shape. Tubular shaft 22 extends through rear plate 30 and 
provides a path for electrical connections from ARIS manipulator 18 into 
transducer head assembly 10. Tubular shaft 22 terminates interior of 
movable assembly 14 and may be attached to interior plate 32 or formed 
integrally therewith. Transducder mounting plate 34 may be integral with 
interior plate 32 or attached thereto by any suitable means such as 
screws. In the preferred embodiment, transducer mounting plate 34 is 
adapted to receive nine (9) separate transducers. As shown in FIG. 4, 
transducers 36 are preferrably arranged in a 3.times.3 array. Each 
transducer 36 is fitted into an individual transducer holder 38. The four 
corner transducer holders 38 c, d, e, f are each mounted in corner 
transducer gimbals 40 c, d, e, f that allow the corner transducers 38 c, 
d, e, f to rotate on two separate axes independent of each other. Each 
corner transducer gimbal 40 c, d, e, f is held in place by two pistons 
(not shown) at a right angle to the gimbal to provide one of the 
rotational directions to the transducer. Each piston is loaded with a 
compression spring to allow movement of the transducer between its first 
normal flat position and second rotated position in response to movement 
across uneven surfaces. Side transducers 36 b, g, h, i are mounted in side 
transducer holders 38 b, g, h, i respectively that allow the respective 
side transducers to rotate on one axis. Each side transducer holder is 
held in place with two pistons which are spaced apart substantially 180 
degrees around the transducer holder. Each piston is loaded with a 
compression spring to allow movement of the transducer between a first 
normal flat position and a second rotated position during movement across 
uneven surfaces. In addition, a plunger 42, seen in FIG. 3, is used to 
provide additional load distribution on each of side transducers 36 b, g, 
h, i. Each plunger 42 is biased toward its respective transducer by a 
spring 44. Center transducer 36a is mounted in center transducer holder 
38a which is held in place by four pistons, one located at each corner of 
transducer holder 38a. Each piston is loaded with a compression spring to 
allow movement of center transducer 36a between a first flat position and 
second rotated position during movement across an uneven surface. This 
provides for rotation on two separate axes. Although each separate 
suspension system is not fully illustrated, pistons 46 and spring 48 are 
illustrative of the general arrangement of the transducer suspension 
system described above. 
Transducer mounting plate 34 is provided with means for allowing the 
suspension system of the transducers to function independently of 
manipulator pressure on the surface being inspected and minimizing 
transducer wear. As seen in FIGS. 3 and 4, a plurality of wear pads 50, 
eight in the preferred embodiment, are attached to transducer mounting 
plate 34 by any conventional means such as screws. Wear pads 50 extend 
forward of transducer mounting plate 34 slightly less than transducers 36 
to allow contact of the transducers with the surface being inspected while 
wear pads 50 continue to support the load of transducer head assembly 10. 
Transducer head assembly 10 is provided with means for monitoring the 
extent of telescopic travel of movable assembly 14 within the stationary 
housing 12. As seen in FIG. 3, position encoder 52 is mounted in movable 
assembly 14. Chain 54 is anchored at its first end on mounting plate 16, 
engaged on a sprocket on position encoder 52, and anchored on its second 
end to take-up sprocket 56 which is spring loaded. Take-up sprocket 56 
keeps chain 54 in tension so that any movement of movable assembly 14 
within stationary housing 12 is detected by encoder 52 and relayed to the 
proper indicating means. 
Means for electrically disabling the manipulator to prevent damage to 
transducer head assembly 10 or the surface being inspected as a result of 
excess pressure against the surface being inspected is also provided in 
the form of limit switch 58. Limit switch 58 is mounted in movable 
assembly 14 and has a plunger 60 which extends towards mounting plate 16. 
When movable assembly 14 slides completely into stationary housing 12, 
plunger 60 contacts mounting plate 16 and is forced into limit switch 58, 
which electrically disables manipulator 18 to prevent it from exerting 
excess pressure against the surface being inspected. Sliding of movable 
assembly 14 forward within stationary housing 12 may be accomplished by 
the use of pressurized air or hydraulic fluid supplied from manipulator 
18. As seen in FIGS. 2 and 3, electrical connections to and from 
transducers 36, position encoder 52, and limit switch 58 are provided by 
wiring harness 62 which extends through tubular shaft 22 into manipulator 
18. 
In the preferred embodiment, mounting plate 16 has tubular shaft 22 
extending therethrough for mounting on an ARIS II or III manipulator. 
However, the mounting plate and tubular shaft may be adapted to be mounted 
on any suitable manipulator. It is also pointed out that the transducer 
mounting arrangement allows for interchangeability of transducers and 
provides a minimum of a twenty-five (25) percent scan overlap for each 
transducer. 
Because many varying and differing embodiments may be made within the scope 
of the inventive concept herein taught and because many modifications may 
be made in the embodiment herein detailed in accordance with the 
descriptive requirement of the law, it is to be understood that the 
details herein are to be interpreted as illustrative and not in a limiting 
sense.