Abstract:
A flexible array probe is disclosed suitable for use in the non-destructive testing and inspection of test pieces with varying cross-sectional geometries. Array elements—such as, but not limited to, eddy current sensors, piezoelectric sensor elements, and magnetic flux leakage sensors—are mounted on thin alignment fins and coupled together with pairs of pivot mechanisms along the axis of desired rotation. The pivot mechanisms allow rotation in exactly one dimension and force the flexible array probe to align its elements orthogonally to the surface of the structure under test. Alignment and coupling fixtures are also disclosed.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit and priority of U.S. Provisional patent application Ser. No. 60/939,171 filed on May 21, 2007 entitled FLEXIBLE ARRAY PROBE FOR THE INSPECTION OF A CONTOURED SURFACE WITH VARYING CROSS-SECTIONAL GEOMETRY, the entire disclosure of which is included herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to array probes for non-destructive testing and inspection, and more particularly, to a flexibly eddy current or ultrasonic array probe assembly which can be applied and used to inspect contoured surfaces of varying cross-sectional geometry. 
     Any discussion of the related art throughout this specification should in no way be considered as an admission that such art is widely known or forms part of the common general knowledge in the field. 
     Although much of the discussion in the present disclosure speaks specifically to eddy current array probes, it is not limited in this regard. The flexible array probe of the present invention is well suited to any surface coupling array probe, such as, but not limited to, eddy current sensors, piezoelectric sensor elements—such as, but not limited to, ultrasonic transducers and bond testing probe elements—and magnetic flux leakage sensors—such as, but not limited to, Hall Effect sensor elements—devices. 
     Eddy current inspection is commonly used to detect flaws in manufactured components, such as tubes or billets. An inspection coil, typically referred to as an eddy current probe, is positioned near a piece to be inspected and driven with high frequency alternating electrical currents which, in turn, create an alternating magnetic field near the surface of the test piece. This magnetic field induces eddy currents in the conductive surface of the test piece which are sensed and measured by the eddy current probe. If a flaw or defect is present on the surface of the test piece, the flow of eddy currents will be altered, and this change will be readily detected by the eddy current probe. The amplitude and position of these current changes can then be analyzed and recorded, for example through visual inspection by a test operator or processed through an automated alarm algorithm, to determine the size and location of the defect or flaw. Eddy current array systems comprise of a plurality of inspection coils (or other types of eddy current sensors well known to those skilled in the art) arranged in such a way as to be conducive to a particular inspection task. 
     Eddy current inspection of contoured surfaces has long been a challenge in non-destructive testing and inspection. Some manufacturing processes—for example, billet rolling systems—can produce items with cross-sectional geometries defined only within a certain tolerance range. This variation on the shape of the test surface can make certain key aspects of eddy current inspection problematic. Maintaining a constant liftoff—the height at which an eddy current sensor is positioned above a test surface—for example can become extremely difficult using a solid, inflexible eddy current array probe. Similarly, it is critical that the axis of each eddy current sensor be held orthogonal to the surface under test. Using an eddy current array probe which holds its elements in fixed positions, this can be impossible to achieve while testing parts with varying geometry. 
     U.S. Pat. No. 4,543,528 to Baraona describes a flexible probe assembly which attempts to address these problems. Baraona&#39;s array probe uses a plurality of independent test heads—each housing at least one array element—fixed to each other with flexible bands. A two point coupling and alignment fixture—referred to as an “urging mechanism”—is also provided. 
     While Baraona&#39;s flexible array probe provides a reasonable solution to the problem of inspecting a convex surface, it holds a number of limitations. The range of motion (rotation) of each element in the array is limited by the rigidity of the flexible bands and by the spacing of the test heads. To achieve a useful probe curvature, array elements must either be spaced a distance apart or multiple elements placed on each test head. Both options significantly limit the usefulness of the flexible array probe. Baraona&#39;s probe and alignment fixture also make a poor showing of maintaining orthogonal coil orientation along sharply curved surfaces. Due to the nature of the design, each test head is allowed a degree of mobility against those directly adjacent to it, and the two point alignment fixture is not suited to support or align the critical center array elements. Furthermore, the design as presented is only suitable for testing convex surfaces. 
     Accordingly it would be advantageous to provide a robust flexible array probe which provides a large degree of flexibility while maintaining a tight element arrangement. Further, it would also be advantageous if the flexible array probe inherently tended to align its elements orthogonally to the surface of a structure under test. It would also be advantageous if the flexible array probe were conducive to measuring test pieces with variations in their cross-sectional geometry while maintaining a consistent eddy current sensor liftoff and orientation for every element in the array. It would further be advantageous if the probe were conducive to coupling to multiple curve shapes, including, but not limited to, convex, concave, and S-shaped surfaces. 
     SUMMARY OF THE DISCLOSURE 
     It is the object of the present disclosure to overcome the problems associated with prior art. The present disclosure does this by introducing a novel flexible array probe comprising thin array element mounting fins coupled together by pairs of pivot mechanisms located along the desired axis of rotation. The pivot mechanism pairs allow the elements of the array to rotate in exactly one dimension, while preserving a tight element arrangement and inherently aligning the elements orthogonally with the surface of the structure under test. In this way, the resulting flexible array probe will be pliant enough to respond to variations in the cross-sectional geometry of a structure under test—such as, but not limited to, variations directly relating to the manufacturing process of the structure under test—without the need for any mechanical adjustment. 
     Accordingly it is the object of the present disclosure to provide a robust flexible array probe built with pivot mechanisms which allow a large degree of flexibility while maintaining a tight probe element arrangement. 
     It is also an object of the present disclosure that the flexible array probe inherently, through use of the pivot mechanisms, align its elements orthogonally to the surface of a structure under test. 
     It is further an object of the present disclosure that the flexible array probe be conducive to measuring test pieces with variations in their cross-sectional geometry while maintaining a consistent probe element liftoff and orientation for every element in the array. 
     It is further an object of the present disclosure that the probe be conducive to coupling to multiple curve shapes, including, but not limited to, convex, concave, and S-shaped. 
     It is further an object of the present disclosure to provide a method and fixture of the alignment and coupling of the flexible array probe. 
     Other features and advantages of the present invention will become apparent from the following description of the invention which is provided below in relation to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A-1B  are perspective drawings illustrating the assembly of the flexible array probe of the present disclosure using the cylindrical tab/slot pivot mechanism; 
         FIG. 2A  is a perspective drawing illustrating the assembly of the flexible array probe of the present disclosure using the spacer element pivot mechanism; 
         FIG. 2B  is a perspective drawing illustrating the assembly of the flexible array probe of the present disclosure using the spacer element pivot mechanism along with space element alignment slots; 
         FIG. 3  is a perspective drawing illustrating the assembly of the flexible array probe of the present disclosure using the chain pivot mechanism; 
         FIG. 4  is a perspective drawing illustrating an alternate embodiment of the flexible array probe of the present disclosure which makes use of multiple probe element housings per probe fin; 
         FIG. 5  is a perspective drawing illustrating the completely assembled flexible array probe of the present disclosure; 
         FIG. 6  is a perspective drawing illustrating the flexible array probe of the present disclosure being applied to a convex surface; 
         FIG. 7  is a perspective drawing illustrating the flexible array probe of the present disclosure being applied to a concave surface; 
         FIG. 8  is a perspective drawing illustrating the flexible array probe of the present disclosure mounted into an alignment and coupling fixture; 
         FIG. 9  is a perspective drawing illustrating an alternate embodiment of the flexible array probe of the present disclosure which uses mounted support magnets to couple and align to a structure under test; 
         FIG. 10  is a perspective drawing illustrating a plurality of flexible array probes as described by the present disclosure arranged into a large test system; 
         FIG. 11  is a cutaway assembly drawing illustrating an alternate embodiment of the flexible array probe of the present disclosure wherein the degree of flexibility within the probe can be adjusted after assembly; 
         FIG. 12  is a cutaway assembly drawing illustrating a single wire assembly method for the flexible array probe of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure describes a flexible eddy current array probe comprising a plurality of thin array element mounting fins (referred to herein as “probe fins”) coupled together with sets of pivot mechanisms thereby allowing probe elements fixed to the probe fins to rotate in exactly one dimension. In this way, a flexible array probe of any size and shape can be realized. The details of the different types of pivot mechanisms used and the construction of the flexible array probe are discussed in detail below. 
     Although the present disclosure speaks specifically to an eddy current array probe, it is not limited in this regard. Indeed, the devices and methods of the present disclosure are well suited to any surface coupling array probe, such as, but not limited to, eddy current sensors, piezoelectric sensor elements, and magnetic flux leakage sensors devices. 
       FIGS. 1A and 1B  illustrate the assembly of the preferred embodiment of the present disclosure. Both figures are intended to show the same assembly process from different angles. Probe fins  101  are fixed with probe element housings  102  in appropriate locations, contingent on the size and shape of the array required. Depending on the material used and construction method, the probe fins  101  and the probe element housings  102  may be built as one solid piece. In the exemplary flexible array probe depicted in  FIGS. 1A and 1B , eddy current sensor elements  103  are secured in the probe element housings  102 . 
     Cylindrical tabs  104  and matching cylindrical slots  106  are molded on or machined into probe fins  101 . Holes are drilled through each slot/tab pair, and wire  105  is drawn through. In a later assembly step (illustrated in  FIG. 5  and discussed in detail below), the probe fins  101  are pulled together, and the wires  105  pulled to the desired tension, trimmed, and sealed against the outermost probe fins  101 . 
     A preferred embodiment, as illustrated in  FIGS. 1A and 1B , shows a pair of holes drilled through each slot/tab pair and consequently a pair of wires  105  running through each slot/tab pair. However, the disclosure is not limited in this regard. More or fewer holes and wires may be used depending on the degree of flexibility or stiffness required for an application. It should also be noted that while cylindrical tabs  104  and corresponding cylindrical slots  105  are used in the exemplary flexible array probe depicted in  FIGS. 1A and 1B , the present disclosure is not limited in this regard. Indeed, tab and corresponding slot elements can take a plurality of geometric shapes, including, but not limited to, spherical. 
       FIG. 2A  illustrates an alternate embodiment of the present disclosure. The design is identical to the preferred embodiment except that the cylindrical slots  106  and tabs  104  of  FIGS. 1A and 1B  are replaced with spacer elements  204 . These spacer elements  204  can be made of any material suitable to the application—for example, but not limited to, copper, plastic, rubber, or carbide as well as self lubricating materials such as Polyetheretherketone (commonly termed PEEK in the industry) and Acetal—and can be sized to provide a significantly larger range of element spacing that the cylindrical slot/tab pivot mechanism of the preferred embodiment can allow. While the spacer elements  204  depicted in  FIG. 2  are spherical, the methods of the present disclosure are not limited in this regard. Spacer elements  204  can take a plurality of geometric shapes, such as, but not limited to, cylindrical, square, and trapezoidal.  FIG. 2B  represents an alternate embodiment of the present disclosure wherein spacer element alignment slots  206  are provided on the surface of the probe fins  201 , providing an alignment means for spacer elements  204 . Such an alternative embodiment is well suited for use with spacer elements  204  made from a rigid material, such as, but not limited to, plastic or copper. 
       FIG. 3  illustrates another alternate embodiment of the present disclosure. In this embodiment, the probe fins  301  are fixed with mounting posts  305  along the desired axis of rotation, and fixed to link elements  306 . The link elements  306  are then coupled together with posts  307  to form a chain assembly  304 . In this embodiment, a pair of these chain assemblies  304  is used; one along each side of the array assembly. This embodiment provides a very robust flexible array probe and can be used to create a flexible array probe which retains its shape after manipulation—two features which can be of great benefit to a manual inspection processes. 
     It should be noted that while the exemplary flexible array probe illustrated in  FIG. 3  depicts mounting posts  305  securing probe fins  301  to link elements  306 , the present disclosure is not limited in this regard. Indeed, a plurality of securement methods can be used to affix said link elements  306  to said probe fins  301 , including, but not limited to, epoxy, mounting screws, and multiple support post systems, so long as the individual link elements  306  are not permitted to rotate with respect to the individual probe fins to which they are secured. 
       FIG. 4  illustrates a third alternate embodiment wherein each of the probe fins  401  is fixed with multiple probe element housings  402  and consequently probe elements  403 .  FIG. 4  depicts the cylindrical tab/slot pivot mechanism as used in the preferred embodiment, but this embodiment is not limited in this regard. Indeed, any of the three pivot mechanisms (cylindrical slot/tab, spacer ball, or chain) can be used with this multiple probe element housing technique. 
       FIG. 5  illustrates a completely assembled flexible array probe built using the preferred embodiment of the present disclosure. A plurality of probe fins  501  are brought together using the tab/slot pivot mechanism illustrated in  FIG. 1  and held together using the sets of wires also show there. For the final product the wires are pulled to the desired tension, trimmed, and then fixed in place using epoxy  504 . While epoxy  504  is depicted in this and subsequent figures, other methods of securement may be used, including, but not limited to, clamps, clips, mounting screws, and stop sleeves. Wear shoes  505  made from a hard, low friction material such as, but not limited to carbide, may be added to the mating surface of the flexible array probe to protect and extend the life of the probe. 
     Within this assembly, the probe element housings  502  are brought together into a tight array, flexible in exactly one dimension. It should be noted that while the exemplary probe shown in  FIG. 5  (and used in many of the other figures) is a 3×5 array probe, an array probe of any dimension can be realized using the methods of the present disclosure. 
       FIG. 6  illustrates the flexible array probe of the present disclosure  601  coupled to a convex surface  602 .  FIG. 7  illustrates the flexible array probe of the present disclosure  701  coupled to a concave surface  702 . In both cases, the array probes ( 601  and  701 ) have conformed to the geometry of the contoured structure under test ( 602  and  702 ) and orientated their elements with a uniform lift off and orthogonal to the surface of the structure under test. With the pivoting mechanisms (the cylindrical tabs  104  and slots  106  of  FIGS. 1A and 1B , the spacer balls  204  of  FIG. 2 , or the chain structure  304  of  FIG. 3 ) in place, each of the probe fins is pulled into correct alignment by those directly adjacent to it, forcing the entire probe structure  601  and  701  to inherently conform to the surface geometry of the structure under test  602  and  702 . 
     It should be noted that while the preferred embodiment of the present disclosure makes use of probe housing elements, the methods of the present disclosure are not limited in this regard. Indeed, the methods of the present disclosure can be used to realize a flexible array probe wherein probe elements are fixed directly to probe fins. 
       FIG. 8  illustrates an alignment and coupling fixture suitable for use with the flexible array probe of the present disclosure. The flexible array probe  801  is coupled to a contoured structure under test  802  by mounting frame  803 . Adjustable posts  806  along with fixed posts  807  secure the end points of flexible array probe  801  against the contoured structure under test  802 . A pressing mechanism  804 —designed to approximate the shape of the structure under test—is mounted on an adjustable post  805  at the critical measurement point. The contact surface  808  of the pressing mechanism  804  can either be made from a hard material—such as, but not limited to, plastic or steel—to provide a ridged contact surface to hold the flexible array probe  801  to a reasonably well-known shape, or an elastomeric material—such as, but not limited to, rubber or silicone—to the flexible array probe  801  to conform to a wider array of test structures. 
     The alignment posts  806  and  805  are adjustable in two dimensions and can be used to fit the flexible array probe  801  to a wide range of surface sizes and shapes. The pressing mechanism  804  can also be constructed to any shape—such as, but not limited to, a convex or concave curve, a flat wedge, or a complex S-shape—in order to match the structure under test  802  and can be built to any size to allow direct coupling with as many or as few elements of the flexible array probe  801  as required by the application. 
     Mounting bars  810  and  811  are provided so the entire structure—the probe and the alignment and coupling fixture together—can be mounted into a large automated test system or installed on a production line. 
     It should be noted that while the alignment and coupling fixture depicted in  FIG. 8  makes use of pressing mechanism  804  to accurately couple the flexible array probe  801  against the contoured structure under test  802 , the methods of the present disclosure are not limited in this regard. Indeed, within many inspection operations the flexible array probe  801  would be sufficiently coupled to the contoured structure under test  802  by the force applied through alignment posts  806  and  807  alone. Within such an inspection operations, a coupling structure such as pressing mechanism  804  would be unnecessary and therefore not included within the alignment and coupling fixture. 
     It should also be noted that while the exemplary alignment and coupling fixture depicted in  FIG. 8  makes use of an L-shaped mounting frame  803 , the methods of the present disclosure are not limited in this regard. While the exemplary mounting frame  803  is well suited for coupling the flexible array probe of the present disclosure to a rounded bar structure—that is, a structure with flat surfaces, each orthogonal with respect to the other, on either side of the curved inspection area—it should be well understood by those skilled in the art that other shaped mounting frames could be employed to effectively couple the flexible array probe of the present disclosure to other types of structures, such as, but not limited to, tubes and rails. 
     The inventors also contemplate an alignment and coupling fixture wherein alignment posts  805  and  807  are spring loaded within alignment tracks  809 , such that the flexible array probe will remain under constant tension as it is applied to a structure under test  802 . 
       FIG. 9  illustrates a simpler method for aligning and coupling the flexible array probe  901  to a ferromagnetic contoured structure under test  902  suitable for spot checking or any otherwise non-automated inspection. A plurality of alignment magnets  903  are mounted onto the individual probe fins and used hold the entire flexible array probe  901  in place. Using an alignment method of this type, the flexible array probe  901  can easily and quickly be moved to different locations on the test piece and adjusted by hand during an inspection. It should be noted that while  FIG. 9  shows alignment magnets  903  mounted on only the two outermost probe fins, more alignment magnets  903  may be used depending on the requirements of the application, including an embodiment wherein each probe fin was fixed with its own set of alignment magnets  903 . 
       FIG. 10  illustrates a plurality of flexible array probes  1001  as described by the present disclosure mounted in place around a billet  1002  which has a rounded square cross-section. In this way, the flexible array probe of the present invention can be used as part of a large test system to provide full coverage of a complex part. 
       FIG. 11  is a cutaway assembly drawing depicting an alternate embodiment of the flexible array probe of the present disclosure wherein the tension of the one or more wires  1106  coupling the probe fins  1101  to each other can be adjusted after assembly. In this way, life cycle changes in wire tension, which can be detrimental the an inspection operation&#39;s effectiveness and accuracy, can be easily corrected without disassembly of the probe. 
     A first wire securement element  1108  fixes a first end of wire  1106  to the first probe fin  1101   b.  The wire  1106  is then drawn through each of the probe fins  1101  and spacer elements  1102 , and a second wire securement element  1105  fixes a second end of wire  1106  to the end of a tension adjustment screw  1103 . The tension adjustment screw  1103  is secured within a threaded slot  1104  within housing element  1107 . Housing element  1107  is then further secured against the last probe fin  101   a.  By manipulating the tension adjustment screw  1103  within the threaded slot  1104  the tension of the wire  1106  can be adjusted, providing an operator means to maintain flexibility of the flexible array probe of the present disclosure as is optimal for a given inspection operation. 
     As previously mentioned in the discussion of  FIG. 5 , the securement elements  1105  and  1008  can take a plurality of forms dependant on the needs of the inspection operation. Such forms include, but are not limited to, epoxy, clamps, clips, mounting screws, and stop sleeves. Further, while the cutaway assembly drawing depicted in  FIG. 11  shows a single wire  1106  and a single tension adjustment screw  1104  for ease of explanation, the methods of the present disclosure are not limited in this regard. Indeed, a plurality of such wires and adjustment elements would likely be used in most flexible array probe assemblies. 
     It should also be noted that while the exemplary probe in  FIG. 11  depicts the tension screw housing element  1107  as a separate element affixed to probe fin  1101   b,  the methods of the present disclosure are not limited in this regard. Indeed, in many practical applications of the methods of the present disclosure, such a housing element would be integrated into probe fin  1101   b.    
       FIG. 12  is a cutaway assembly drawing illustrating a single wire assembly technique for a flexible array probe built according to the methods of the present disclosure. A single long wire  1203  is drawn through a plurality of probe fins  1201  via multiple holes  1202  in each probe fin  1201 . Said long wire  1203  is treaded through each probe fin multiple times such as to effectively draw the plurality of probe fins together. 
     Although the present invention has been described in relation to particular embodiments thereof, many other variations and modifications and other uses will become apparent to those skilled in the art. It is preferred, therefore, that the present invention not be limited by the specific disclosure herein.