Abstract:
An inspection apparatus for nondestructive inspection/evaluation. The inspection apparatus may include a probe, and sensor, and a biasing spring. The probe may have a first end and a second, free end defining an opening. The sensor may be received in the opening. The biasing spring may be received in the opening in between the first end of the probe and the sensor to urge the sensor away from the first end of the probe. The probe may include a gimbal joint or ball and socket type joint and a spindle, where the joint provides for deflection of the probe relative to the spindle. A blocking pin for limiting the range of movement of the sensor retains part of the sensor in the opening. The sensor may have a position extending out of the opening, and a position where an end of the sensor is substantially flush with the end of the probe.

Description:
GOVERNMENT RIGHTS 
     This invention was made with Government support under Contract No. FA8650-08-C-5213 awarded by the Department of Defense. The Government has certain rights in this invention. 
    
    
     FIELD 
     The present disclosure relates to nondestructive inspection/evaluation (NDI/NDE), and more particularly to sensors used in NDI/NDE that detect defects in structures and parts. 
     BACKGROUND 
     Increases in the complexity of aerospace structures have made NDI/NDE, which terms are used interchangeably herein, more and more difficult to apply successfully and cost-effectively. Often, a region of a particular structure requires inspection, but is inaccessible for the application of conventional NDE methods. In some cases such inspection requirements of regions with limited access have prompted part removal to improve access, or expensive redesigns altogether. Conventional tools include extenders and manipulation arms to reach into limited access areas and to aid probe placement on or near limited access areas of aircraft. Such areas may be cavities or obstructed areas, and include, for example, the interior of aircraft wings. 
     When in operation, certain sensors for detection of defects in a surface are preferably seated on the surface, or at least require maintaining no more than a maximum clearance from the surface. When a sensor, for example an eddy current sensor, is not completely seated on the surface, which may be referred to as “lift-off,” the result may be a reduced sensitivity to small cracks. 
     A sensor may be applied to a surface that is not completely flat and require movement of the probe along the surface, or may be mounted to a rotating end of a probe for NDE in limited access areas. Either case may result in lift-off. For the rotating application, if the probe end is not exactly perpendicular to the surface to be inspected, the rotating path of the sensor will be eccentric; although the sensor may be flush with the surface at one point along the path, at an opposite point on the path there will be lift-off. Accordingly, apparatus is needed that addresses lift-off to provide adequate sensitivity for detection of defects over the full range of motion of the sensor. 
     SUMMARY 
     In accordance with an embodiment, an inspection apparatus may include a probe, and sensor, and bias means. The probe may have a first end and a second, free end defining an opening. The sensor may be received in the opening. The bias means may be received in the opening in between the first end of the probe and the sensor to urge the sensor away from the first end of the probe. 
     In accordance with another embodiment, an inspection apparatus may include a probe, a sensor, bias means, and means for limiting the range of movement of the sensor. The probe may have a longitudinal axis, a first end, and a second, free end having a surface and defining an opening, and may include a gimbal joint or ball and socket type joint disposed between the first end and the second, free end of the probe. The probe may further include a spindle having a proximal end and a distal end, with the distal end being operatively connected to the joint. The sensor may have a first end and a second end and be received in the opening, where the sensor has a range of movement relative to the probe. The bias means may be received in the opening in between the first end of the probe and the first end of the sensor to urge the sensor away from the first end of the probe. The means for limiting the range of movement of the sensor may retain part of the sensor in the opening. The sensor may have an extended position with the second end of the sensor extending away from the surface of the second, free end of the probe a predetermined distance, and a retracted position with the second end of the sensor substantially flush with the surface of the second, free end of the probe. 
     In accordance with another embodiment, a method performing an inspection is provided. The method includes providing a probe having a longitudinal axis and including a first end and a second, free end defining an opening, with bias means first inserted in the opening and then a sensor inserted in the opening. The sensor is urged away from the first end of the probe using the bias means, and the probe is rotated about the longitudinal axis. 
     Other aspects and features of the present disclosure, as defined solely by the claims, will become apparent to those ordinarily skilled in the art upon review of the following non-limited detailed description of the disclosure in conjunction with the accompanying figures. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The following detailed description of embodiments refers to the accompanying drawings, which illustrate specific embodiments of the disclosure. Other embodiments having different structures and operations do not depart from the scope of the present disclosure. 
         FIG. 1  is a side view of an example of a manipulator arm for NDE including a scanner with a probe in accordance with an embodiment of the present disclosure. 
         FIG. 2  is a perspective view of an exposed interior of a wing illustrating application of the exemplary manipulator arm of  FIG. 1 . 
         FIG. 3  is a front end perspective view of an example of a scanner including a probe in accordance with an embodiment of the present disclosure. 
         FIG. 4  is a side view of an example of a probe in accordance with an embodiment of the present disclosure. 
         FIG. 5  is a side perspective view of the exemplary probe of  FIG. 4 . 
         FIG. 6  is another side perspective view of the exemplary probe of  FIG. 4 . 
         FIG. 7  is a bottom perspective view of the exemplary probe of  FIG. 4 . 
         FIG. 8  is a side perspective view of the exemplary scanner including a probe of  FIG. 3 . 
         FIG. 9  is an example of a high frequency eddy current impedance plane display that may result from application of the exemplary probe of  FIG. 4 . 
     
    
    
     DESCRIPTION 
     The following detailed description of embodiments refers to the accompanying drawings, which illustrate specific embodiments of the disclosure. Other embodiments having different structures and operations do not depart from the scope of the present disclosure. Like reference numerals may refer to the same element or component in the different drawings. 
     Certain terminology is used herein for convenience only and is not to be taken as a limitation on the embodiments described. For example, words such as “proximal”, “distal”, “top”, “bottom”, “upper,” “lower,” “left,” “right,” “horizontal,” “vertical,” “upward,” and “downward” merely describe the configuration shown in the figures or relative positions. The referenced components may be oriented in any direction and the terminology, therefore, should be understood as encompassing such variations unless specified otherwise. 
       FIG. 1  shows an example of a device  40  for performing NDE in a limited access area, which may be referred to as extended reach NDE, limited access NDE, surgical NDE, or the like. The device  40  may include an articulating manipulator arm  42  with an end effector  44  provided at the distal end. In the embodiment shown, the end effector includes a scanner  46  and a probe  48 . The probe  48  may include, for example, an eddy current sensor, a magnetic sensor, an ultrasonic sensor, or the like. For the embodiment shown, starting at the proximal end of the arm  42  may be operator handles  50 , control knobs and switches  52 , and a main shaft  54  with a proximal end mounted to the handles  50 . A multi-axis elbow joint  60  may be mounted to the distal end of the main shaft  54 , and a pivoting shaft  62  may be mounted to the multi-axis elbow joint  60 . To provide an additional degree of articulation a wrist joint  64  may be mounted to the distal end of the pivoting shaft  62 . A slider ball  70  may be provided on the main shaft to bear against the wall of the enclosure that contains the area to be inspected as the main shaft  54  extends through an access hole. The slider ball  70  provides a location for an operator to steady the arm  42 . Control cables  72  may extend from the control knobs and switches  52  to the multi-axis elbow joint  60  and to the wrist joint  64 . A video camera  74  may be mounted near the distal end of the main shaft  54  for situational awareness to aid the operator in placement of the distal end of the device  40  and the probe  48 . 
       FIG. 2  shows a section of an aircraft wing  76  with an internal wall  78  cut away to expose the example NDE device of  FIG. 1  in use. The device  40  extends through the access hole  80  into the enclosure  82 , which is large enough for the distal end of the manipulator arm  42  and the end effector  44  to pass through, which in one embodiment is approximately three inches in diameter. A support bracket  83  is mounted in the opening  80 . This embodiment of a support bracket  83  is semi-circular and defines a semi-circular opening to receive the slider ball  70 . Levers may be rotated to turn bolts that extend through holes that are used to mount an access panel, which has been removed. In this example, the probe  48  is being used to detect defects in a structure or part, which may also be referred to as a target, which as shown is metal around fasteners  84  in stringers  86 , specifically the metal around the bolts and nuts that are on the inboard side of the stringers  86 . Other locations of inspection and other types of materials and structures or parts may be inspected as well. The pivoting shaft  62  is pivoted with the multi-axis elbow joint  60  to position the probe  48  behind the stringer  86  to be inspected, and the wrist joint  64  is pivoted to align the probe  48  with a bolt. Monitors  90 ,  92  are provided to assist the operator/inspector. One monitor  90  displays a high frequency eddy current impedance plane display, discussed in detail below and the other monitor  92  shows video. 
       FIG. 3  is an end perspective view of the end effector  44 , which includes an embodiment of a probe  48  mounted to the scanner  46 . In this embodiment the probe  48  may include an eddy current sensor  100 , including a coil of wire. The scanner  46  may be a micro eddy current rotating scanner, which may include a motor. It is not necessary for other embodiments of the device  40  or the probe  48  that the scanner  46  be a rotating type. The distal end of the scanner  46  may include lights  102 , for example LEDs, to illuminate the enclosure and the target to be inspected, and a camera lens  104  to provide an image to a video camera in the scanner  46 . Another video camera could also be mounted in proximity of the probe  48  to provide additional situational awareness. A knob  106  has a threaded bolt (not shown) on it that may be loosened to remove the scanner  46  from the wrist joint  64 . The other end of the threaded bolt may bear against a cylinder to which the scanner  46  is attached. 
       FIGS. 4-7  show an embodiment of the probe  48  with an embodiment of an eddy current sensor  100 . The probe  48  may include a spindle  110 , a central member  112  mounted to the spindle  110 , and a housing  114  mounted to the central member  112 . In this embodiment, the housing  114  is translucent. The sensor  100  may be received in an opening which may be a bore  120  in the housing  114  or be otherwise slidably mounted to the housing  114 . The central member  112  may be mounted to the spindle  110  with a set screw  122  ( FIG. 6 ). The housing  114  may be cylindrical, may encase the sides of the central member  112 , and extends distally below the bottom of the central member  112 . Below the distal end of the central member  112  the housing  114  may define a substantially cylindrical opening  124  and have a cylindrical wall  126 . The cylindrical wall  126  may be of adequate thickness to receive the sensor  100  in the bore  120  in the wall  126 , as shown, or other configurations may be provided to attach the sensor  100  to the probe  48 . In the example shown of inspecting the metal around a fastener  84 , the opening  124  in the housing  114  is large enough to receive the end of the fastener  84  that protrudes from the structure. 
     A spring  130 , such as a coil spring as schematically shown, a leaf spring, compressible and resilient material, or other biasing means may be provided in between the proximal end of the bore  120  and the proximal end of the sensor  110 , and urges the sensor  100  distally such that the sensor  100  may extend out of the bore  120  past the distal surface  132  of the housing  114 . The spring loading increases the probe&#39;s compliance to the surface of the structure under inspection. Seating of the eddy current sensor  100  over the fastener  84  so that the sensor  100  lies as flat as possible on the structure is generally desirable for conducting a proper inspection. The sensor  100  is retained in the bore  120  with a pin  134  that extends laterally through an opening  136  in the housing wall  126  and passes through a slot  138  in the sensor  100 . The proximal side  140  of the slot  138  is blocked by the pin  134  as the spring  130  urges the sensor  100  to withdraw from the bore  120 . The proximal side  140  of the slot  138  is located such that the sensor  100  may extend a predetermined distance X from the bore  120  below the distal surface  132  of the housing  114 . 
     In addition, a joint  142  may be provided in the spindle  110  at the connection to the central member  112 . The joint  142  may be, for example, a gimbal joint, a ball and socket type joint, or the like, and in the embodiment of a probe  48  described herein, may allow for a deflection of, for example, at least approximately 12 degrees, with a preferred angle of at least 15 degrees between the spindle  110  and the longitudinal axis of the probe  48 . Joint deflection may be greater with other embodiments, and particularly in embodiments where the sensor  100  can extend a greater predetermined distance X from the bore  120  below the distal surface  132  of the housing  114  than in the exemplary embodiment described herein. 
     The joint  142  may be designed to transfer scan rotation through an angle as needed, but to return to a zero angle position when the end is free, which may be referred to as self-aligning. This self-aligning may be accomplished in a variety of ways, for example in a ball and socket type joint, using a non-spherical ball and socket that pulls slightly out and extends an inner spring when an angle away from the longitudinal axis of the probe  48  is created. The spindle  110  and joint  142  rotate during scanning, as does the rest of the probe  48 . 
     In one exemplary embodiment, the inside diameter of the housing  114  is 0.5 inches, the housing wall  126  thickness distally from the central member  112  is 0.112 inches, the radius from the longitudinal axis of the probe  48  to the longitudinal axis of the sensor  100  is 0.183 inches, and the predetermined distance X that the sensor  100  may extend past the distal surface  132  of the housing  114  is 0.008 inches. 
     The probe materials may include, for example, for the central member  112 , spindle  110 , spring  130 , and pin  134 , metals such as steel, stainless steel, or other steel alloy. The housing  114  may be molded plastic or other nonconductive material, which may be translucent to facilitate assembly and visualization of a fastener during scanning. The sensor  100  may be made of materials as known to one of ordinary skill in the art. 
       FIG. 8  shows a detail view of the end effector  44  in use. Angle θ is the predetermined deflection angle that the joint  142  provides. As shown, the joint  142  allows a deflection of approximately 15 degrees between the spindle  110  and the longitudinal axis Y-Y of the probe  48 . The distance that the sensor  100  can extend past the distal surface  132  of the housing  114  makes this relatively high degree of deflection possible. When the probe  48 , and the sensor  100  with it, rotates when the housing  114  is not parallel to the target surface, there will be one point on the path of rotation where the distal surface  132  of the housing  114  is closest to the target, preferably with the sensor  100  touching the target surface, and a point on the opposite side of the path of rotation where the distal surface  132  of the housing  114  is farthest away from the target surface, and without the extension of the sensor  100  lift-off will be experienced. The extending of the sensor  100  past the distal surface  132  of the housing  114  reduces the amount of lift-off or eliminates lift-off, and may keep the sensitivity of the sensor  100  adequate to provide meaningful NDE data over the entire path of rotation. The sensor  100  extending also allows the deflection angle to be increased in the design of the joint  142 . An increased available deflection angle facilitates applying and using the probe  48 . 
       FIG. 9  shows a high frequency eddy current impedance plane display  150  as may result from application of a probe  48  including an eddy current sensor  100 . This display  150  may aid an operator/inspector in knowing when the probe  48  is coupled to the structure to allow proper inspection. Resistance is plotted on the X-axis and Reactance is plotted on the Y-axis. The eddy current probe is “nulled” in air, which appears on the display  150  at the far left at the label “AIR” where there is no magnetic field measurement, as opposed to the often used technique of nulling the probe  48  while on the part being inspected, and then, as the probe  48  is brought down over the fastener  84 , the eddy current display “dot” comes down to the position where the probe  48  is coupled with the part, which is a stringer in the case shown in  FIG. 2 . 
     Curve A in  FIG. 9  represents decreasing magnetic field readings from right to left, which corresponds to increased lift-off from right to left. Multiple flaw indications are shown in  FIG. 9 . These flaw indications are curves B through F, which are each the result of the sensor  100  detecting the same 0.050 inch deep Electrical Discharge Machining (EDM) notch, but with different distances of lift-off. The curves B through F are also labeled with dimensions that designate the distance of lift-off in inches for each of the respective curves. To obtain a desirable 3:1 signal-to-noise ratio (S/N), in testing with the example discussed above in the discussion of  FIGS. 4-7 , the lift-off of the sensor  100  from the part could not be more than 0.016 inches. Below 0.016 inch lift-off, the probe  48  and structure was considered to be coupled. If the lift-off was greater than this amount, the flaw indication may be detectable, but the S/N was less than desirable and it may become difficult to distinguish a crack in the part from lift-off. 
     In a test with an eddy current sensor mounted to a probe without a spring to extend the sensor out of the housing, and a spindle with a joint allowing an angle of incidence of 10.5 degrees off of a line perpendicular to the target surface, the dot traveled along curve A approximately within range G as the sensor rotated. With a spring that allowed the sensor to extend 0.008 inches out of the housing, the joint angle could be increased to 15 degrees, and the dot traveled approximately only within range H, providing improved ability to accurately detect flaws. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms “a”, “an”, and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     Although specific embodiments have been illustrated and described herein, those of ordinary skill in the art appreciate that any arrangement which is calculated to achieve the same purpose may be substituted for the specific embodiments shown and that the embodiments herein have other applications in other environments. This application is intended to cover any adaptations or variations of the present disclosure. The following claims are in no way intended to limit the scope of the disclosure to the specific embodiments described herein.