Test head holder in a test system carrier, preferably for ultrasonic test heads

In a test system carrier for non-destructive testing of a workpiece, a test head holder including means for moving a test head of the test system carrier and means for pressing the test head against a surface of the workpiece, the test head pressing means including a compressed air cylinder having a piston, a gimballed support body coupled to the piston for supporting the test head, the piston being actuatable to press the test head substantially perpendicularly against the surface of the workpiece.

The invention relates to a test head holder in a test system carrier, 
preferably for ultrasonic test heads. For testing reactor pressure vessels 
in nuclear power plants, tests of the vessel material are required at 
periodic intervals; particularly the material of the welded seams and the 
thermally affected zones adjoining those seams must be checked. Remotely 
controllable testing instruments (manipulators) are preferably used for 
this purpose. Such testing instruments are predominantly equipped with 
ultrasonic test heads. Starting from one of the surfaces (inside or 
outside) of the vessel, the testing instruments test the volume of the 
material of the vessel wall as well as particularly highly stressed zones 
near the surface such as the inside edges of the coolant nozzle bores. 
These tests are performed primarily as comparative tests, it being 
therefore necessary that repeated tests be made with high reproducibility 
of the guidance and movement of the test heads. In special cases, such as 
curved test tracks in the vicinity of the nozzles, for example, it is 
necessary that the test heads perform rotary movements besides the 
movements in the longitudinal and transverse directions. These movements 
place stringent requirements on the test head holders. Unevenness of the 
test surface and changes of the spacing between the test head guidance 
plane and the test surfaces must not produce major deviations from the 
predetermined test head positions. In general, only a limited amount of 
space is available for the tests between the vessel and the shielding wall 
surrounding it. The determining part for the above-mentioned conditions is 
the holder which connects the test head per se to the testing device 
(manipulator). 
All the heretofore known holders use springs as contact pressure means, 
with the typical distance-dependent force changes such as are known from 
spring diagrams, note, for example, the German Published Prosecuted 
Application DT-AS 2 153 397. In these conventional devices it is necessary 
to exchange the springs to vary the contact pressure. 
In order to keep the force variations small, either the lever arms or the 
springs must be made longer, wherby considerable space is lost. 
It is therefore an object of the invention of the instant application to 
overcome the aforedescribed shortcomings of the devices of this general 
type and to provide a device by which test heads, especially ultrasonic 
test heads, can be pressed against the surface to be tested with a 
constant force which is adapted to the structure of the surface, 
equalizing unevennesses without varying the contact pressure. Lateral 
displacement from the prescribed position when running over unevennesses 
is to be avoided. In addition, the holder should have an overall height as 
small as possible and occupy only a small area parallel to the test 
surface. The deviations from the prescribed positions due to the 
unavoidable bearing clearances should be kept as small as possible for the 
different movements, particularly for the rotary movement. 
With the foregoing and other objects in view, there is provided, in 
accordance with the invention, in a test system carrier for 
non-destructive testing of a work piece, a test head holder comprising 
means for moving a test head of the test system carrier and means for 
pressing the test heads against a surface of the work piece, the test-head 
pressing means comprising a compressed-air cylinder having a piston, a 
gimballed support body coupled to the piston for supporting the test head 
the piston being actuatable to press the test head substantially 
perpendicularly against the surface of the work piece. 
The advantages obtainable with the invention are seen primarily in the fact 
that the test head holder according to the invention can be used equally 
well for inside tests (immersion technology) as well as for outside tests 
(flow technology). The contact pressure of the test heads is produced for 
each test head by a separate compressed-air cylinder. The contact pressure 
can be varied by remote control by means of a reducing valve at the 
compressor or control unit. This is advantageous, for example, for testing 
surfaces with weld seams (inside overlay welding) only by the flow 
technology, i.e., with high flowing-water pressure and correspondingly 
high contact pressure. 
In accordance with another feature of the invention, linear guide means are 
provided for guiding the gimballed support body in stroke direction of the 
piston, in a manner that the cylinder and piston are relieved of lateral 
forces exerted by the test head on the gimballed support body as the test 
head is slidingly moved over the surface of the work piece. 
In accordance with an additional feature of the invention, the piston has a 
piston rod, and means are provided for fastening the support body to the 
piston rod. 
In accordance with a further feature of the invention, the guiding means is 
in the form of two axially parallel linear guides having guide rods, each 
slidably secured to a guide body, the cylinder being rigid with the guide 
bodies and disposed axially parallel to the guide rods and intermediate 
the thereto. 
In accordance with yet another feature of the invention, there is provided 
a compressed-air source, and supply lines connecting the compressed-air 
source to the cylinder, the volume of the cylinder being smaller than the 
volume of the supply lines and the volume of the compressed-air source. 
This is done so that the contact pressure is subjected only to minor, 
negligible changes when the stroke changes. This is particularly important 
when testing with the flow technology or technique and with high 
flowing-water pressure and correspondingly high contact pressure. Equally 
important in this regard is the precise lateral guidance. 
In accordance with yet an additional feature of the invention, in order to 
prevent loss of coupling when moving over surfaces with a coarse 
structure, there is provided a test holder for ultrasonic test heads with 
flowing-water coupling of a test head to a workpiece having depressions, 
comprising means for increasing the contact pressure of the test head to 
the workpiece, means for increasing the flowing-water pressure and means 
for filling-in the depressions in the workpiece with water so as to 
maintain coupling between the test head and the workpiece. 
In accordance with yet a further feature of the invention, there is 
provided separate means for supplying compressed-air to force the piston 
in opposite piston stroke directions. 
In accordance with still another feature of the invention, there are 
provided means for spring-biasing the piston in one piston stroke 
direction, and means for supplying compressed air to force the piston 
against the biasing means in opposite piston stroke direction. 
The compact construction of the test head holder according to the invention 
makes it possible to mutually align several test heads closely together in 
a row and even two or more rows closely together without limiting the 
mobility of the individual test heads. This is of particular importance 
for volume tests in thick vessel walls by means of tandem test head 
arrangements. If two or more parallel rows of test heads are used, the 
expensive and deadline-menacing test times are shortened and the required 
high testing standards are nevertheless maintained. For this purpose, 
there is provided, in accordance with still an additional feature of the 
invention, a multiplicity of test heads forming a test head row supported 
by a carrier arm in mutual alignment, each test head having a pneumatic 
drive unit and including means for equally pressing the multiplicity of 
test heads against the surface of the workpiece, the pressing means 
including a compressed air supply hose common to all of the test heads, 
and including linear guide means for guiding the gimballed support bodies 
in stroke direction of the respective piston in a manner that the 
respective cylinder and piston are relieved of lateral forces exerted by 
the test heads on the respective gimballed support body as the test heads 
are slidingly moved over the surface of the workpiece. 
In accordance with still a further feature of the invention, a plurality of 
test head rows are structurally connected in parallel to each other to 
form a test head network. 
The pneumatic system makes it possible, in addition, to lift the test heads 
of the test surface by remote control. Thereby, unnecessary wear of the 
runners or sliding surfaces of the test heads can be avoided when the test 
device executes large movements, without testing per se taking place. For 
this purpose, single-acting pneumatic cylinders with return springs 
suffice, for which reason the invention provides that the pistons can be 
acted upon unilaterally against the force of a return spring. If the test 
heads must overcome low obstacles (e.g. blisters, ledges etc.), then the 
test heads can be lifted quickly and in a programmed manner ahead of the 
obstacle through the use of double-acting pneumatic cylinders, which can 
be acted upon from either side. 
In accordance with a concomitant feature of the invention, a multiplicity 
of test heads forming a test head row are supported by a carrier arm in 
mutual alignment, each test head having a pneumatic drive unit and 
including first means for equally pressing less than all of the 
multiplicity of test heads against the workpiece and second means for 
equally pressing at least one test head of the balance of the multiplicity 
of test heads against the workpiece, the first and second pressing means 
each including a separate common compressed air supply hose connected to a 
separate control valve, the separate control valve being connected to a 
compressed-air source. 
Other features which are considered as characteristic for the invention are 
set forth in the appended claims. 
Although the invention is illustrated and described herein as embodied in 
test head holder in a test system carrier, preferably for ultrasonic test 
heads, it is nevertheless not intended to be limited to the details shown, 
since various modifications and structural changes may be made therein 
without departing from the spirit of the invention and within the scope 
and range of equivalents of the claims.

Referring now to the figures of the drawing and first, particularly to 
FIGS. 1 to 3 thereof, there is shown a test head 1 mounted by means of two 
mutually aligned pins 2 with a swivel axis a* in a rectangular gimbal 
frame 3, which is closed on itself. The gimbal frame 3, in turn, is 
mounted by means of two mutually aligned pins 4 with the tilting axis b* 
in a holding bracket 5 (see also FIG. 5). The holding bracket 5 is 
connected to the crosspiece 7 by two countersunk screws 70, shown in 
broken lines. Two guide rods 6 are firmly pinned in the crosspiece 7 and 
slide in the guide bushings 8 of a guide body 9. The guide bushings 8 must 
run freely and are therefore advantageously constructed as ball bushings. 
Between the guide bushings 8, which can generally also be called guide 
inserts, the guide body 9 carries a pneumatic cylinder 10 with a piston 
100 (see FIG. 2), the piston rod 11 of which is bolted tightly to the 
crosspiece 7. Compressed air feed for pressing the test head 1 against a 
test surface 17 is affected through an upper hose connection 12; the test 
head 1 is lifted off the test surface 17, in a double-acting piston, by 
the application of pressure through the lower hose connection 13, which is 
omitted when a single-acting piston is employed. In a single-acting piston 
100, on the other hand, the return spring 101, shown in broken lines (see 
FIG. 2) must be provided. The return spring 101 is braced with one end 
against the piston 100 and with the other end against a shoulder 102 of 
the cylinder 10. The cylinder 10 has compressed-air control openings 121. 
The guide body 9 of the holder is adjustably fastened on the carrier arm 15 
of the otherwise non-illustrated test system carrier (manipulator) with a 
clamping piece 14 by means of two screws 140. Flowing water from the water 
hose 16 is forced between the test head 1 and the test surface 17. The 
flowing water, together with the contact pressure from the pneumatic 
cylinder 10, effects a so-called "floating" and thereby permits easy 
sliding of the test head on rough and uneven surfaces, such as welded 
overlay seams and the like. During inside testing of a vessel filled with 
water (immersion technology), this flowing-water method is also required 
for very rough surfaces in order to obtain the "floating effect". In a 
test head chain (FIGS. 6a and 6b) and in a test head network arrangement 
(FIG. 7), the test heads 1a, 1b, 1c, etc. are supplied with compressed air 
through a common supply hose, all cylinders 10a, 10b, 10c, etc. exerting 
the same contact pressure on all the test heads 1a, 1b, 1 c, etc. due to 
pressure equalization. 
If individual cylinders of a test head chain are each supplied with 
compressed air through a separate supply hose, as will be explained 
hereinafter in further detail, it is possible to lift off and press down 
the test head 1c individually, for example, without affecting the other 
test heads 1a and 1b. 
According to FIGS. 6a and 6b, several test heads (in the embodiment shown, 
the three test heads 1a, 1b and 1c) are each structurally combined with 
one support body formed of elements 2, 3, 4 and 5; one pneumatic drive 
unit 10a, 10b, 10c, respectively, as well as one rectilinear guide 8, 9, 
respectively, to form a test head row or test head chain. To this end, the 
just-mentioned members are fastened to the carrier arm 15 in alignment 
with one another. The separate pressing-down and lifting-off of the test 
head 1c is accomplished by means of separate compressed-air lines p2 and 
a2', as in FIG. 8c, for single-acting compressed-air cylinders, or p2, b2' 
and a2', as in FIG. 8d, for double-acting compressed-air cylinders. First, 
however, FIGS. 8a to 8d will be explained in principle, showing the 
required simple pneumatic circuits (with symbols in accordance with German 
Standards DIN 243000), where 
Q=source of compressed air (e.g. compressor) 
D=adjustable regulating valve (pressure-reducing valve), 
M=manometer (pressure indication) 
Sp=storage tank (employed here as an indication that between D and V the 
volume is substantially larger than that between cylinders 10a to c and V) 
V, v1, v2=control valves 
A, b=consumer connections 
P=pressure line generally 
p1, p2, poo, po=specific pressure lines 
R=venting line (relief opening) 
F=return springs for valves V, V1, V2. 
In FIGS. 8a and 8c, single-acting cylinders with return springs are shown. 
The valves V, V1 and V2 are electrically actuatable 3/2-way valves with 
return spring, 3/2 means a compressed-air valve with two switching 
positions represented by two square boxes within the rectangular valve and 
2+1=3 inlets and outlets. These valves operate as follows: When the magnet 
is not energized (position shown), the pressure line P is shut off and the 
consumer connection A is vented through R. With the magnet energized (the 
box on the left-hand side containing the arrow is moved to the right-hand 
side), the pressure line P is connected to the consumer connection A, so 
that the pistons are driven out. This position is effective only as long 
as the magnet is energized. After the magnet voltage is removed, the valve 
V is automatically returned to the switching position shown. 
In FIGS. 8b and 8d, double-acting cylinders are shown. The valves V, V1 and 
V2 are electrically operated 4/2-way valves with return springs. 4/2 means 
a compressed-air valve with two switching positions and 2+2=4 inlets and 
outlets. These valves operate as follows: With the magnet non-energized 
(position shown), the pressure line P is connected to the consumer 
connection B (return position of the pistons) and the consumer connection 
A is vented through R. With the magnet energized (left-hand box shifted to 
the right-hand side), the pressure line P is connected to the consumer 
connection A, so that the pistons are driven out, and the consumer 
connection B is now vented through R. This position is effective only as 
long as the magnet is energized. After the magnet voltage is removed, the 
valve V is automatically returned to the switching position shown. 
In FIGS. 8a and 8b, all of the cylinders 10a and 10c are controlled by a 
common valve V. With the valve V switched on, pressure equalization 
between all cylinders up to the pressure regulating valve D is effected. 
In FIGS. 8c and 8d, the cylinders 10c can be controlled, separately from 
the cylinders 10a and 10b2, by a valve V2 of their own. Control of the 
cylinders 10a to 10b2 is effected by the valve V1. Here, too, the pressure 
is equalized between all switched-on cylinders (either 10a to 10b2 or 10a 
to 10c) up to the pressure-regulating valve D. 
The meaning of the other symbols is as follows: 
poo=pressure line between D and SP 
po=pressure line between SP and the branching point A 
p1, p2=pressure line between Z and, respectively, V1 and V2. 
Furthermore, in FIGS. 8a and 8c: 
a, a1=main consumer lines 
a1, a2, a3, a4=consumer lines between a and 10a or 10b1 or 10b2 or 10c 
a11, a12, a13=consumer lines between a1 and 10a or 10b1 or 10b2, 
respectively, 
a2'=separate consumer line between V2 and 10c 
In FIGS. 8b and 8dm there are in addition: 
a, b, a1, b1=main consumer lines, 
b1, b2, b3, b4=consumer lines to the one piston side of 10a or 10b1 or 10b2 
or 10c, respectively, 
a1, a2, a3, a4=consumer lines to the other piston side of 10a or 10b1 or 
10b2 or 10c, respectively, 
b11, b12, b13=consumer lines between b1 and the one piston side of 10a or 
10b1 or 10b2, respectively; and 
a2', b2'=separate consumer lines between V2 and the one or the other piston 
side of the cylinder 10c. 
The circuit diagram according to FIG. 8d shows a pneumatic circuit 
corresponding to FIGS. 6a and 6b, however, two cylinders 10b1 and 10b2 are 
shown, as aforementioned, instead of the one cylinder 10b according to 
FIGS. 6a and 6b. In both cases, the cylinder 10c is the separately 
acted-upon cylinder. In general, test head chains can be formed with n+1 
cylinders (n=1, 2, 3 . . . ), where at least one thereof can always be 
separately controllable. Separate control can also be realized for 
single-acting pneumatic cylinders, as shown in FIG. 8c. 
In the test head network according to FIG. 7, the corresponding 
compressed-air control circuit is not shown. However, it should be 
understood that one of the circuits according to FIGS. 8a to 8d can be 
used analogously and that, if the circuits according to FIGS. 8c and 8d 
are used properly, individual compressed-air cylinders 10a to 10c or 10a' 
to 10c' can be actuatable separately. In this way, individual test heads 
1a to 1c or 1a' to 1c' can be seatable or liftable off, separated from the 
other test heads. The test head network can be thought of here as produced 
by two test head chains, as shown in FIGS. 6a and 6b by increasing the 
number of test heads per chain from three to four, the carrier arms 15 and 
15' being mounted on a common non-illustrated holder.