Abstract:
Disclosed is an ECA probes assembly capable of providing reliable and durable ECA inspections of dovetail slots without the use of an external guiding mechanism. The design combines a novel universal probe manipulator with a probe support suited for a wide range of probe supports which fit a rage of turbine disks. The probe support embodies a rigid yet expandable core, exerting a force pushing the array probe against the inner cavity of the dovetails. The pushing force is strategically located in critical areas of the dovetail leading to array probe to be self-guiding into the dovetail, and to provide optimum performance with consistent and stable lift-off.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit and priority of U.S. Provisional patent application Ser. No. 61678857 filed Aug. 2, 2012 entitled AN NDT ASSEMBLY WITH A UNIVERSAL MANIPULATOR FOR INSPECTING DOVETAIL OF DIFFERENT SIZES, the entire disclosure of which is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to an assembly used for a non-destructive inspection or testing (NDI/NDT) device, particularly it relates to an assembly for inspecting dovetail slots in turbo machine rotor disk by using eddy current array probes. 
       BACKGROUND OF THE INVENTION 
       [0003]    Eddy current array (ECA) inspection is commonly used to detect flaws in surfaces of manufactured metal components such as turbine engine components. During this type of inspection, electro-magnetic induction is used to induce eddy currents in the component being inspected. A plurality of sensors inside an ECA probe separately generates alternating magnetic fields, which induces the eddy currents in the component while the probe is moved near the component. When flaws are present in the component, the flow of eddy currents is altered. The altered eddy currents produces changes in a secondary magnetic field which are detected by the array of sensors inside the ECA probe. An ECA acquisition unit monitors variations of secondary magnetic fields to produce readings for each of the ECA probe sensors which are typically representative of the flaw size. A complete scan of the dovetail is typically achieved by moving the probe along the entire dovetail length while acquiring ECA readings and position information in order to construct a cscan image representative of the actual condition of whole inspected surface of the dovetail. 
         [0004]    The reliability and accuracy of the measurement depend on the ECA probe being properly positioned in the dovetail in order to maintain, for all inspections, a relatively constant sensor to part distance (Lift-off). Another important aspect is the ability to track the position of the probe in the dovetail slot in order to accurately reconstruct the cscan image. 
         [0005]    Past solutions to produce a reliable cscan image from an ECA scan of a dovetail slot were not adapted for the deployment of a versatile, portable and reliable product. For example, U.S. Pat. No. 7,800,364 describes a solution where the probe manipulator itself provides a precise position reference to the probe using the adjacent dovetail slots as reference. Such a solution requires an important redesign for every dovetail design and in thus not adapted for a product with large deployment. 
         [0006]    Other solutions provided patents such as U.S. Pat. No. 5,315,234, U.S. Pat. No. 5,442,286, U.S. Pat. No. 6,339,326, U.S. Pat. No. 6,545,467, U.S. Pat. No. 6,563,307 and U.S. Pat. No. 6,812,697 use conformable probe supports and some actuation mechanism to expand the probes and force the sensors onto the dovetail inner surfaces. In this case, one drawback is the frequent probe damage that occurs when the ECA probe moves near part edges which causes excessive strain on the probe. Another drawback is the need for automation in order to expand the probes in the dovetail slot, which typically requires the use of a robot to conduct the inspection. 
         [0007]    Therefore there is an unmet need for a solution to provide a portable and reliable ECA probe and manipulator system easily adaptable to multiple turbine disk designs. 
       SUMMARY OF THE INVENTION 
       [0008]    The present disclosure provides a method and design of a novel ECA probes assembly capable of providing reliable and durable ECA inspections of dovetail slots without the use of an external guiding mechanism. 
         [0009]    The design combines a novel universal probe manipulator with a probe support suited for a wide range of probe supports which fit a rage of turbine disks. The probe support embodies a rigid yet expandable core, exerting a force pushing the array probe against the inner cavity of the dovetails. The pushing force is strategically located in critical areas of the dovetail leading to the array probe to be self-guiding into the dovetail, and to provide optimum performance with consistent and stable lift-off through the entire surface of the dovetail. 
         [0010]    Advantages of the invention include the use of the same probe manipulator for a wide range of probe supports fitting rages of turbine disk designs. 
         [0011]    Advantages of the invention also include the use of probe support perfectly optimally suited for the usage of a flexible printed circuit ECA probe for dovetail inspections without the drawback of existing solutions, i.e., durability problems, the required use of a robot to conduct the scans, etc. 
         [0012]    In addition, advantages of the invention also include the significantly improved performance in the areas close to dovetail edges by providing a more stable and snuggly fit between the probe and the cavity surface in these critical areas. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a cross-sectional view of the ECA probe and probe support illustrating how the probe support of the invention can fit into the inspected dovetail slot to provide self-guiding properties centering and pushing the probe against the inner surface of the dovetail slot. 
           [0014]      FIG. 2  is a perspective view of the self-guiding probe assembly of the invention. 
           [0015]      FIG. 3  is a cross sectional view of the self-guiding probe assembly of the invention. 
           [0016]      FIG. 4  is an isometric view of the universal probe assembly, providing elaboration on the manipulator. 
           [0017]      FIG. 5  is an exploded view of the various components of the universal manipulator. 
           [0018]      FIG. 6  is a perspective view illustrating the universal dovetail probe manipulator attached on a turbine disk. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0019]    Referring to  FIGS. 1 and 2 , a first aspect of the invention is the self guiding properties of a ECA probe assembly  100 . By opposition to the prior art probe of U.S. Pat. No. 7,800,364 which relies on the manipulator itself for precisely guiding the plurality of sensors of the ECA probe in a dovetail  13  of a rotor disk  15 , new probe assembly  100  of the invention uses the profile of dovetail  13  for precisely maintaining the lift-off distance within some defined limits. 
         [0020]    For probe assembly  100  of the preferred embodiment (illustrated on  FIG. 1  in contact with dovetail  13  and in  FIG. 2 , perspective view, not in contact with dovetail  13  and in a downward motion  4 ), lift-off is controlled by pushing a thin ECA probe  120 , which preferably comprises groups of sensors, with each group consisting of any number of individual sensors and is preferably manufactured using a form of mat or sheet with flexible backing, such as flexible printed circuit board technologies, being attached (either permanently or using re-attachable means) to a probe support  110 , which is made out of rigid but flexible material (such as ABS, PEEK, Delrin, etc.). In order to make probe  120  re-attachable, an adhesive material can be applied between probe  120  and probe support  110 . ECA probe  120  is attached to probe support  110  in such a way that ECA probe  120  does not experience movement relative to probe support  110 . In this way the locations of each of the plurality of sensors in the cross section of probe assembly  100  can be known to an encoder system  354  (not shown, refer to  FIG. 5 ). Because of the shape of dovetail  13 , probe support  110  is correspondingly Ω-shaped to be able to fit into and out of dovetail  13 . Probe support  110 &#39;s flexibility is exploited by forming pivot points  112  at some strategic locations. Manufacturing probe support  110  to leave a relatively thin layer of material at pivot points  112 , where the probe support  110  is meant to bend, forms a naturally spring loaded shape  114 , which forces contact between ECA probe  120  and dovetail slot  13  at all inspected areas  150 ,  152 ,  154  (Shown in  FIG. 1 , not shown in  FIG. 2 ). Shown also in  FIG. 1  is a ball bearing assembly  202  as part of probe support  110 , which will be explained in  FIG. 3   
         [0021]    Probe support  110 ′s rigidity and pre-defined pivot point  112  make it possible to control spring loaded shape  114 ′s movement  160  in order to obtain the same pressure and movement on both sides of ECA probe  120 . Another unique aspect of the invention is to provide almost uniform movement  160  along the whole length of ECA probe  120 , even if ECA probe  120  is not completely inserted in the dovetail. This property is important to obtain better inspection performances near the part edges compared to prior art solutions, such as U.S. Pat. No. 5,315,234, U.S. Pat. No. 5,442,286, U.S. Pat. No. 6,339,326, U.S. Pat. No. 6,545,467, U.S. Pat. No. 6,563,307 and U.S. Pat. No. 6,812,697, and to provide longer probe life by eliminating most of the strains in the probe itself caused by the use of a soft compressed body to provide the probe pressure on the inspected component. 
         [0022]    The location of pivot points  112  is determined by considering the mechanical tolerances of dovetail  13  (which are typically of the order of +/−0.05 mm) and the positions of the inspected areas in dovetail  13 , in order to minimize the possible lift-off variations between ECA probe  120 &#39;s elements and the inspected surface. Probe  120 &#39;s thickness (typically about 0.15 mm) and preferably some protective low friction tape (typically 0.07 5mm thick Teflon) is also considered when probe support  110  is designed. Therefore, even if dovetail  13 &#39;s shape is not perfectly constant from other dovetails, the inspected surface can be used to guide probe  120  during the inspection. 
         [0023]    Referring now to  FIG. 3 , which is a cross section of  FIG. 2 , shows how probe assembly  100  can be attached to a manipulator arm  310  in order to take full benefit of the self guiding properties of probe assembly  100 . Probe assembly  100  is connected to manipulator arm  310  using a link system  200 , allowing independent movement of the probe assembly  100  in an up direction  1002 , a down direction  1004 , a right direction  1012 , a left direction  1010  and an angular direction  1020 . Link system  200  comprises a central portion  204 , which interconnects two ball joint assemblies  202  and  206  (or equivalent mechanical system). Ball joint assembly  206  is preferably integrated into a small detachable coupling component  208  which makes it possible for the user to easily separate probe assembly  100  from manipulator arm  310 . For example, the connection between probe assembly  100  and manipulator arm  310  can be achieved using a set screw  210 . 
         [0024]    Typically, ball joint assembly  202 &#39;s position in probe support  110  on the X, Y plane is in the center of the areas defined by  150 ,  152  and  154  (not shown, refer to  FIG. 1 ). Typically, ball joint assembly  202 &#39;s position in the probe support  110  on the Z Axis is located in the center of the probe support  110 . Ball joint assembly  202  is preferably located here in order to avoid inducing torque in probe assembly  100  when it is pushed in or pulled out of dovetail  13  (not shown, refer to  FIG. 1 ). 
         [0025]    Now looking at  FIG. 4 , a universal probe manipulator  300  is shown with probe assembly  100  attached. Manipulator  300  includes a center portion  350 , a swivel base  360  and arm  310 . Center portion  350  and base  360  are attached in order to allow a rotational degree of freedom  1100 . Center portion  350  and arm  310  are also attached in order to allow a translation degree of freedom  1110 . 
         [0026]      FIG. 5  provides an exploded view on the sub-components of manipulator  300 . Arm  310  comprises a rectilinear rack  314 , a shaft  312  and a handle  316 . Center portion  350  comprises encoder system  354  to connect with rectilinear rack  314 , a linear bearing  352  to provide translational degree of freedom  1110  (not shown, refer to  FIG. 4 ), buttons  356  to remotely operate the acquisition system with common operations (such as start/stop and save data) and a scanner interface cable  358 . Swivel base  360  comprises a handle  362 , a pivot system  364 , which allows rotational degree of freedom  1100  (not shown, refer to  FIG. 4 ), and contact shoes  366 . Linear bearing  352  is affixed to swivel base  360  via pivot system  364  so that, when swivel base  360  is pushed snuggly against a disk face  502  (shown in  FIG. 6 ), a predetermined degree of freedom of movement is allowed between shaft  312  and swivel base  360  in a plane that is parallel to the axial direction and perpendicular to disk face  502 . 
         [0027]    Now looking at  FIG. 6 , which illustrates manipulator,  300  and probe assembly  100  during the inspection of dovetail slot  13 . Both contact shoes  366  are in contact with disk face  502  during the inspection. This contact between contact shoes  366  and disk face  502  is possible due to the rotational degree of freedom  1100  (not shown, refer to  FIG. 4 ). Contact shoes  366  are typically made out of rubber or similar material in order to provide a smooth and stable contact with disk face  502 . Contact shoes  366  are also wide enough to contact to disk face  502  with various disk designs with different dovetail shapes and sizes. Base  360  is U shaped in order to completely retract probe  120  from dovetail  13  during the inspection so that dovetail  13  can be scanned completely in one scan while contact shoes  366  are sitting on disk face  502 . The width of the U shape for base  360  is large enough to allow the required rotational degree of freedom  1100  (not shown, refer to  FIG. 4 ) to cover Z Axis dovetail angle a found on most turbine disk design. 
         [0028]    Dovetail  13  can be fully inspected in one scan either by scanning while pushing probe assembly  100  in dovetail  13  or by scanning while pulling probe assembly  100  out of dovetail  13  using translation movement  1110  (not shown, refer to  FIG. 4 ), this position in the Z axis is recorded by encoder system  354  and transmitted to the ECA acquisition unit (not shown) through cable  358 . A mapping of the information recorded using ECA probe assembly  100  along dovetail  13  length can then by displayed by the acquisition unit (not shown). Inspection of dovetail  13  by pulling the probe is typically preferred as the action of pulling the probe naturally forces shoes  366  in contact with disk face  502 . 
         [0029]    While Prior art solution (such as U.S. Pat. No. 7,800,364) did require a specific probe and manipulator design for each turbine disk design, the combined use of self-guiding probe assembly  100  and manipulator  300  with rotational degree of freedom  1100  and contact shoes  366  to sit on disk face  502  makes it possible to use the same probe manipulator  300  for a wide range of turbine disk designs. As for the probe, it is typically required to redesign only the probe support  110  in order to adapt to a dovetail design.