Abstract:
An inspection device ( 300 ) has an ultrasonic transducer ( 304 ) encased in a couplant block ( 302 ) mounted in a housing ( 328 ). The housing ( 328 ) has a pair of encoders ( 340, 342 ) mounted thereto. The transducer ( 304 ) is mounted to scan perpendicular to the contact surface ( 306 ) of the block ( 302 ). A coupling block with a PTFE layer on the contact surface is also provided.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a device for inspecting components. More specifically, the present invention relates to a device for the ultrasound scanning of composite aircraft components. 
       BACKGROUND OF THE INVENTION 
       [0002]    Non-visible areas of materials, such as the interiors of components, welds and composite materials can be analysed using ultrasonic testing. This type of non-destructive testing (NDT) utilises the reflection of sound waves to detect faults and features which would otherwise be very difficult to detect without destroying the component. Ultrasonic testing is a common technique in the aerospace sector to test the integrity of materials at manufacture and during service. 
         [0003]    Scanners tend to be of the portable type (i.e. more suited to in-service scanning) or non-portable type (specifically for production). 
         [0004]    A feature of ultrasonic testing is that a couplant is required to aid transmission of the ultrasonic energy to the test specimen because the acoustic impedance mismatch between air and solids (i.e. such as the test specimen) is large. This mismatch causes reflection of the sound waves and a loss in scan quality if a couplant is not used. Couplants generally take the form of water or gel or a deformable solid such as a low acoustic loss elastomer. 
         [0005]    Another feature of ultrasonic testing is that the ultrasonic transducer needs to be correctly orientated (usually perpendicularly orientated) with respect to the entity or fault to be detected. In laminar composite materials, these faults exist in a primarily parallel orientation to the surface of the workpiece. As such, correct orientation of the scanner with its scanning direction perpendicular to the surface of the workpiece is important. 
         [0006]    Traditionally, ultrasonic testing has been limited in terms of inspection speed as the operation had to be carried out on a point-by-point basis. Improvements have led to the development of array scanning, or “paintbrush” scanning which permits a continuous scan over a surface to produce a two dimensional image of the desired region of the test component. Such equipment however is bulky and limited to use in a production (as opposed to service) environment and is not considered portable. 
         [0007]    A problem is that low acoustic loss elastomers have a relatively high coefficient of friction making it difficult to move them across a surface to be scanned. Generally speaking, lower friction materials generally do not have the desired acoustic properties. 
         [0008]    It is an aim of the invention to provide an improved inspection device. 
       SUMMARY OF THE INVENTION 
       [0009]    According to the present invention there is provided an ultrasonic scanner for scanning a workpiece comprising:
       an ultrasound transducer,   a solid coupling component defining a transducer contact surface for contact with the transducer and a workpiece contact surface for contact with a workpiece to be scanned,   in which the solid coupling component at least partially surrounds the transducer to locate the transducer relative to the workpiece contact surface.       
 
         [0013]    Advantageously, the interface between the transducer and the coupling component acts to orient the transducer correctly with respect to (e.g. normal to) the surface to be scanned. 
         [0014]    According to a second aspect of the invention there is provided a coupling component for an ultrasonic scanner comprising a body constructed from an elastomeric polymer and comprising a layer of low friction material at least partially covering the body to form a workpiece contact surface with a coefficient of friction less than 0.5. 
         [0015]    Advantageously, a layer of low friction material assists the coupling component in moving across the surface of a workpiece. 
         [0016]    By “coefficient of friction” we mean coefficient of friction as measured in the standard way for polymers—i.e. against polished steel. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    An example scanner will now be described in detail with reference to the accompanying figures in which: 
           [0018]      FIG. 1   a  is a perspective view of a first scanner in accordance with the present invention, 
           [0019]      FIG. 1   b  is a perspective view of the scanner of  FIG. 1   a,    
           [0020]      FIG. 1   c  is a side view of the scanner of  FIG. 1   a  in use, 
           [0021]      FIG. 2   a  is a perspective view of a second scanner in accordance with the present invention, 
           [0022]      FIG. 2   b  is a side view of the scanner of  FIG. 2   a  in use, 
           [0023]      FIG. 3   a  is an exploded perspective view of a third scanner in accordance with the present invention, 
           [0024]      FIG. 3   b  is a perspective view of the scanner of  FIG. 3   a,    
           [0025]      FIG. 3   c  is a top view of the scanner of  FIG. 3   a  in use, 
           [0026]      FIG. 3   d  is a side view of a part of the scanner of the scanner of  FIG. 3   a , and 
           [0027]      FIGS. 4   a - 4   c  are perspective views of low friction coating methods of a fourth scanner in accordance with the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0028]    Referring to  FIGS. 1   a  to  1   c , a scanner  100  comprises a couplant block  102  and an ultrasound array  104 . The couplant block  102  is constructed from a low acoustic loss elastomer, and is generally cuboid shaped. The block  102  defines a workpiece contact surface  106 . An array receiving formation  108  in the shape of a cuboidal recess is defined in the block  102  and is open to an insertion orifice  110 . 
         [0029]    The ultrasound array  104  is of the type well known in the art and is generally cuboidal, comprising a port  112  for connection of a data line  114 . The array  104  is capable of emitting and receiving ultrasound in order to scan a component as will be described below. The array has a scanning direction  116 . 
         [0030]    The scanner  100  is assembled by sliding the array  104  into the array receiving formation  108  through the insertion orifice  110 . The array receiving formation  108  is dimensioned to the approximate external dimensions of the array  104 , and as such can support the array  104  in a desired position. It is desirable that the scanning direction  116  is perpendicular to the contact surface  106  and as such the receiving formation is oriented with this in mind. 
         [0031]    A small amount of couplant liquid (e.g. water or a gel) may be added to the orifice  110  to aid transmission of ultrasound energy across the array-couplant boundary and also to aid insertion and removal of the array  104 . 
         [0032]    Referring to  FIG. 1   c , a workpiece  10  comprises a stiffener  12  comprising a flange  14  projecting at 90 degrees to a base  16 . The flange  14  joins the base  16  at a pair of opposing fillet radii  18  of 2 degrees radius. 
         [0033]    The flange  14  comprises a defect  20  for detection. 
         [0034]    To detect the defect  20 , the scanner  100  is positioned on the flange  14  with the contact surface  106  fully abutting the flange  14 . As such the scanning direction  116  is perpendicular to the flange  14 . This provides the optimum orientation between the array  104  and the defect  20  for detection and analysis. Data is collected via the line  114  and analysed appropriately. 
         [0035]    The scanner  100  may also be used to detect faults in the base  16 . 
         [0036]    A fine water spray mist (not shown) is also applied to the scanner and workpiece to reduce friction and increase the efficiency of transmission of ultrasound between the two components. 
         [0037]    Turning to  FIGS. 2   a  and  2   b , a scanner  200  is shown. Components similar to the scanner  100  are numbered  100  greater. 
         [0038]    The couplant block  202  is generally cuboid and comprises an arcuate surface  218  opposite the contact surface  206 . The arcuate surface makes the scanner  200  more comfortable to hold in a user&#39;s hand. 
         [0039]    The couplant block defined a recess  220  in which a rotary encoder  222  is positioned. The rotary encoder  222  comprises an encoder wheel  224  and an encoder data line  226 . The encoder  222  is used to determine the distance travelled by the scanner  200 . 
         [0040]      FIG. 2   b  shows the scanner  200  in use. Compared to the scanner  100 , the scanner  200  uses contact between the encoder wheel  224  and the flange  14  to determine the distance travelled by the scanner  200  over the flange  14 . The scanner  200  may also be used to detect faults in the base  16 . 
         [0041]    Referring to  FIGS. 3   a  to  3   c , a scanner  300  is shown. Components similar to the scanner  100  are numbered  200  greater. 
         [0042]    The scanner  300  comprises a housing  328  constructed from a plastics material. The housing  328  is generally C-shaped comprising a base portion  330 , a first arm  332  and a second arm  334 . Each arm  332 ,  334  defines an encoder mounting arrangement  336 ,  338  respectively. The housing is ergonomically shaped to be comfortably received in a user&#39;s hand. 
         [0043]    The scanner  300  comprises a first encoder  340  and a second encoder  342  each similar to the encoder  222 . The encoders  340 ,  342  are mounted to the housing  328  via the encoder mounting arrangements  336 ,  338 . The encoder mounting arrangements  336 ,  338  are arranged to allow the encoders  340 ,  342  to move in use but remain resiliently biased towards the workpiece to main contact therewith. Allowing the encoders  340 ,  342  to move relative to the housing  228  allows the scanner  300  to traverse uneven surfaces with greater effectiveness, as contact is maintained between the contact surface  306  and the workpiece  10 . 
         [0044]    In use, the housing  328  fits around the couplant block  302  as shown in  FIG. 3   b . The housing  328  is shaped to retain the couplant block  302  as the first arm  332  and the second arm  334  are tapered inwardly. The arms  332 ,  334  therefore retain the tapered couplant block  302 . 
         [0045]    As shown in  FIG. 3   c , the scanner  300  is moved in direction D along the flange  14  of the workpiece  10 . Throughout most of the scanning operation both encoders  340 ,  342  contact the flange  14 , however approaching the ends one of the encoders  340 ,  342  will lose contact. Under these circumstances, the distance travelled over the flange  14  is determined from a single encoder. In this way, the scanner  300  is capable of scanning the entire length of a workpiece  10 . The scanner  100  may also be used to detect faults in the base  16 . 
         [0046]      FIG. 3   d  shows a side view of the couplant block  302  of the scanner  300 . As can be seen, the couplant block  302  comprises a chamfered end portion  344  of angle A. The end portion  344  therefore allows scannig of flanges  14  at angles of less than 90 degrees to the base  16 . 
         [0047]      FIG. 4   a  shows a scanner  400  comprising a couplant block  402  and a transducer  404 . The scanner  400  comprises a plurality of flexible self-adhesive PTFE (polytetrafluoroethylene) strips  406 . The strips are adhered to the base of the couplant block  402  to provide a low friction layer between the couplant block and a workpiece (not shown). 
         [0048]    It has been shown that although PTFE does not generally exhibit favourable acoustic properties for the propagation of ultrasonic waves, using a thin layer of PTFE in the order of 0.05 to 0.2 mm does not significantly inhibit the performance of the scanner. 
         [0049]    Turning to  FIG. 4   b  and alternative arrangement is shown whereby the strips of PTFE tape  406  are overlapped. 
         [0050]    Turning to  FIG. 4   c , a PTFE sheath  408  is provided which conforms substantially to the exterior profile of the couplant block  402 . As such an even layer of PTFE is provided which eliminates any effects that may be caused by having the edges of the PTFE tape  406  in the scanning field.