Abstract:
A hand held non-destructive testing device has a frame which supports an NDI sensor and incorporates means for translation across a surface to be inspected with position registration and resilient means for maintaining the sensor and the translation means in intimate contact with the surface. An ergonomic handle is mounted to the frame for manually controlled translation of the frame incorporates a plurality of control means for control of the sensor in scanning of the surface under inspection.

Description:
DEVELOPMENT UNDER GOVERNMENT CONTRACT 
   This invention was made with Government support under contract number N00014-04-C-0182 awarded by the United States Navy Office of Naval Research. The government has certain rights in this invention. 

   REFERENCE TO RELATED APPLICATIONS 
   This patent application is related to copending application Ser. No. 11/163,834 filed Nov. 1, 2005 entitled “FLEXIBLE HAND HELD MR SCANNING ARRAY FOR CRACKS/FLAWS” having a common inventor and a common assignee with the present application, the disclosure of which is incorporated herein by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates generally to the field of non-destructive inspection (NDI) of structures and more particularly to a hand held positioning and control device for imaging arrays such as Magnetoresistive (MR) scanning arrays. 
   2. Description of the Related Art 
   Non-destructive inspection (NDI) of aerospace structures to detect flaws may be performed by various techniques that include X-ray radiography, ultrasonics, acoustic emissions, and eddy currents. Current imaging scanners are typically operated using mechanical positioning means which require significant mechanical and structural support. Currently there is no hand held device that can rapidly scan along a row of fasteners to inspect the subsurface condition of the structure. 
   Eddy current inspection devices are commonly used for NDI of electrically conductive components. Eddy current inspection devices typically use one or more excitation coils to generate an alternating magnetic field, which in turn induces eddy currents in the component, and typically use a pickup coil to detect the magnetic field generated by the eddy currents. When an eddy current encounters an internal flaw of the component, the eddy current flows around the flaw and the resulting magnetic field generated by the eddy current is changed. The pickup coil indirectly detects this change which gives information regarding the location and size of the flaw within the component. 
   Magnetoresistive (MR) sensors are known for low frequency performance permitting deep feature/flaw detection in metallic structure at sensitivities considerably above those provided by conventional eddy current techniques. Exemplary NDI systems employing MR are disclosed in U.S. Pat. No. 6,150,809 to Tiernan et al. which uses two parallel sheets of conductors to create the magnetic field and uses a giant magnetoresistive (GMR) sensor positioned between the sheets to detect the magnetic field signals generated by eddy currents and application Ser. No. 10/923,519 entitled EDDY CURRENT INSPECTION DEVICE, having a common assignee with the present invention, the disclosure of which is incorporated herein by reference. 
   Eddy current inspection using MR sensors is applicable to scanning of specific structural elements on an aircraft, containing rows of rivets or other fasteners. It is therefore desirable that an imaging scanner be mounted in a structure for operation by hand to allow a technician to accurately yet conveniently perform inspection of the desired structure. 
   SUMMARY OF THE INVENTION 
   A system incorporating the present invention provides a non-destructive testing device having a frame incorporating means for translation across a curved surface to be inspected with resilient means for maintaining a non-destructive inspection (NDI) sensor and the translation means in intimate contact with the surface. An ergonomic handle mounted to the frame for manually controlled translation of the frame incorporates at least one control means for control of the sensor in scanning of the surface under inspection. 
   In an exemplary embodiment, an excitation coil with a plurality of conductor ribbons is attached to a flexible membrane. The frame supports the membrane and provides the means for translation across a surface to be inspected and resilient means for maintaining the entire membrane surface with the excitation coil and the translation means in intimate contact with the surface. A magnetoresitive (MR) array is supported within the frame adjacent the membrane to be in close proximity to the surface. The MR array detects the magnetic fields resulting from eddy currents created by the excitation coil for identification of cracks or other features of interest in the surface under inspection. 
   Flexibility of the membrane and excitation coil allows inspection of curved surfaces not possible with rigid excitation devices. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other features and advantages of the present invention will be better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein: 
       FIG. 1  is an isometric external view of an embodiment of the invention; 
       FIG. 2  is a flow chart of exemplary operational sequence for NDI using the controls provided by the embodiment of the invention disclosed in  FIG. 1   
       FIG. 3  is a schematic diagram of the elements of the present invention for an embodiment using an MR scanning array; 
       FIG. 4  is an isometric cutaway view of the embodiment of  FIG. 1  showing structural details for the MR scanning array application; and, 
       FIG. 5  is an exemplary printed circuit board housing the MR array for use with the disclosed embodiment of the invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The present invention provides the capability to scan the surface of a structure using a hand held NDI device with integral controls.  FIG. 1  shows details of an exemplary embodiment. A housing  10  encloses the elements of the scanner, which will be described for an exemplary embodiment in greater detail subsequently. Wheels  12  are mounted to a frame of the housing for translating the scanner in a desired direction by the operator. A position encoder  14  such as an encoder wheel, optical sensor or track ball is mounted from the frame of the housing intermediate the wheels for continuous position registration. Manual operation of the sensing device is enhanced with a “mouse” like handle  16  mounted to the frame. Integral control buttons  18   a  and  18   b  and scroll wheel  20  provide for control of the sensor and operational functions of the complete unit. The mouse handle is shaped ergonomically so that an operator can easily cause the device to glide across the surface of the aircraft being inspected. 
   For the embodiment shown, connecting ribbon cable  22  operably provides power and data communication between the sensor and external electronics while an additional cable  24  provides connection to the control elements and position encoder. Those skilled in the art will recognize alternative cabling arrangements as may be most desirable for the type of scanner employed. 
   For operation of the functions typically required in NDI scanner operation, the controls provided by the present invention allow the operator to conduct the entire inspection using the controls on the hand held device. As shown in the flow chart of  FIG. 2  for an exemplary NDI control sequence, the operator places the device in position for scanning, for example, a row of fasteners  202 . By “clicking” the right control button  204 , the position defined by the position encoder is reset. By clicking the left control button  206 , entry of scan data is initiated. The device is then translated along the fastener row  208 . Data from the position encoder and the scanning array are transferred  210  to a computer terminal such as a portable personal computer for data storage, manipulation and visualization. Upon completion of the scan, the operator again clicks the left control button  212  to terminate the scanning. The control wheel is then operable to scroll through the acquired data  214  which is presented on the computer monitor with position from the encoder and visual image from the scanning array presented. If additional scanning is desired  216 , the left button is again “clicked” while if a new scan is desired  218 , the right button is clicked resetting the scan position. 
   While an exemplary format for use of the controls is presented herein, the use of mouse type control inputs allows the functionality of the control buttons to be software programmable for a plurality of functions. 
   An embodiment of the present invention for one type of scanner particularly suited to the features of the invention, a magnetoresistive (MR) array, is shown schematically in  FIG. 3 . A rigid frame  26  provides for transferring downward pressure exerted by the operator, as represented by arrows  28 . The frame incorporates resilient structural elements  30  providing spring loads, so that pressure is always applied when the operator presses downward on the mouse handle to intimately position the scanner with respect to the surface under inspection. For the embodiment shown, the displacement range of the resilient elements allows for various radii of curvature in the surface of the item being inspected to be accommodated, while maintaining continuous and total contact between the surface being inspected and a flexible excitation coil  32 . The coil, with its conducting ribbons  34  perpendicular to the plane of the drawing in  FIG. 3  is shown in a gently curved configuration. The coil is embedded in or mounted on a flexible membrane or pad  36  of rubber or other nonconductive substrate. In an exemplary embodiment medium soft closed cell blended neoprene sponge identified by product number CCNS SCE  41  is employed as the membrane. The surface under inspection  38  is the shape which defines the curved shape of the coil through intimate contact between the coil and membrane and the surface. 
   As shown in  FIG. 4 , the resilient elements of the frame are provided by the wheel bogeys  40  urging the wheels into intimate contact with the surface under inspection by springs  42  reacting against receivers on the frame. The sensing surface, in the example present in the drawings the membrane, is mounted to the lower surface of the bogeys intermediate the wheels. The diameter of the wheels is predetermined to maintain the intimate contact of the membrane and the excitation coil mounted thereto with the surface undergoing inspection. 
   As shown schematically in  FIG. 3  and a physical embodiment in  FIG. 4 , sensor array  44  is contained in housing  10 . The array is supported by a resilient mount  46  shown as piston or block  48  constrained within a cylinder or channel  50  and loaded by a spring  52 . For purposes of description herein, the scan motion is left and right in the configurations shown in  FIG. 3  for circumferential scanning as represented by double arrow  54  at the bottom of the figure. Wheels  12  support the housing with respect to the surface under inspection and protrude coincident with or slightly beyond the coil, so that the coil is in contact with the surface as well as the wheels themselves. 
   The sensor array is mounted to a printed circuit (PC) board, the edge of which is adhesively bonded or otherwise affixed to the excitation coil to assure close contact of the array with the surface under investigation. Block  48  to which the PC board is mounted is urged downward by spring  52  reacting against the frame. Guide rods  56  are employed to retain the block and mounted array in a substantially parallel or tangential orientation with respect to the surface under investigation. The connectors for the array receive ribbon cables  58  for interconnection to a terminal connector  60  mounted on internal element  62  for further connection to the external power and data cable. Power for the excitation coil is provided through connector  64 , which for the embodiment shown is attached to slider block  48  which acts as the array holder/fixture. 
   The scanning MR array is shown in  FIG. 5 . For the embodiment disclosed, the array employs 32 elements 65 oriented along the lower edge of a printed circuit board  66 . Multiple connectors  68  provide external connection to the elements through integral wiring on the PC board. Giant Magnetoresistive sensors (GMR) are employed in the embodiment disclosed. Inter-sensor spacings of 0.020 inch and 0.031 inch have been employed in exemplary devices employing the invention. 
   Alternative embodiments employ anisotropic magnetoresistive (AMR) sensors in staggered arrays and the invention disclosed herein is applicable for use with spin dependent tunneling (SDT) MR sensors for alternative inspection applications. 
   The embodiment of the invention disclosed with an imaging array of MR sensors provides for inspection of curved surfaces, such as those commonly found on aircraft fuselages and wings. The excitation coil is flexible, and is attached to a piece of flexible material, such as a dense foam rubber. The density and flexibility of this material, to which the coil is affixed, ensures that the coil remains in intimate contact with the top surface of the component undergoing inspection. Downward pressure applied by the operator during the scanning ensures that this contact is continuous, and uninterrupted, and over the entire surface of the coil. 
   The entire unit is ergonomically constructed, permitting easy hand scanning. As the unit is scanned in the direction indicated, the downward pressure exerted by the operator keeps the flexible membrane mounted excitation coil in contact with the surface of the item being inspected. The MR array is maintained in contact with the surface via the spring which pushes down on the block to which the array PC board is mounted. The array is linearly oriented perpendicular to the plane of  FIG. 3  with the sensors sensitive to the field in the direction normal to the surface of the item being inspected. As the unit is scanned over the surface employing the controls as previously described, the field values are recorded, and their image is displayed on a computer monitor. 
   For the embodiment shown, the orientation and configuration of the scanning head created by the flexible membrane, coil and PC board mounted sensors is such that scanning in an axis directed along the circumference of the curved surface, the full sensor array is always seated such that it is in contact along its full length with the surface being inspected, being above that surface by the thickness of the excitation coil, which is very thin, and a thin insulating layer which may be created using mylar tape or similar material. The configuration shown in the  FIG. 3  permits scanning for cracks that are parallel to the circumferential direction. 
   Having now described the invention in detail as required by the patent statutes, those skilled in the art will recognize modifications and substitutions to the specific embodiments disclosed herein. Such modifications are within the scope and intent of the present invention as defined in the following claims.