Abstract:
A system and method of detecting, quantifying, and characterizing corrosion and degradation of an article, includes receiving signals indicative of a stack of images of a surface of the article; determining depth and nature of features in the stack of images; generating a surface model of the article in response to the determination of the depth and the nature of features; determining features of interest from the surface model; comparing the features of interest with predetermined information on the article; and characterizing the article as corroded or degraded in response to the comparisons of the features of interest.

Description:
BACKGROUND 
       [0001]    The subject matter disclosed herein relates generally to the field of non-destructive inspection and, more particularly, to a handheld apparatus for inspection of a metallic article in the field for detecting, quantifying, and characterizing corrosion and degradation. 
       DESCRIPTION OF RELATED ART 
       [0002]    Pitting corrosion is a surface degradation mechanism in metallic materials. This type of corrosion is insidious in aviation and vehicle structures, as it can significantly reduce the reliability of safety-critical components, such as the dynamic components for drive-train on rotorcraft as well as (non-dynamic) load-bearing structural members. The understanding of the severity of corrosion pits, i.e., the corrosion-pit diameter and depth quantity as well as the nearness of one corrosion pit to the next, is extremely important for structural maintenance of an aviation fleet, spares management, aircraft availability, and safety. 
         [0003]    Rotorcraft are routinely inspected to detect the presence of corrosion of critical components. Current non-destructive methods for corrosion detection on rotorcraft do not lend themselves to automated, in-field use, which can produce subjective results and lead to poor maintenance decisions. These approaches either depend on the subjective evaluation of pitting corrosion observed by the maintenance crew or rely on intense post processing using other detection methods (surface impressions, surface images, ultrasound, acoustic emission, eddy current-electromagnetic testing, infra-red thermography, laser optics, etc.). These approaches are not field friendly, and often require complex setup and training. Field technicians often have to supplement their inspection with online microscopic analysis of the surfaces. Standard field micro-analysis devices provide a two-dimensional image of the three-dimensional surface under magnification, but such images do not provide pit depth information, which is often key to effective corrosion detection. Also, current testing approaches do not possess the resolution necessary to effectively detect and characterize surface pitting and identify trend progressions; all information needed for an effective rotorcraft—or other vehicle—maintenance program. 
         [0004]    Once corrosion is detected, a repair or replacement decision needs to be made. Currently, this decision is qualitative and can result in high cost of ownership due to potentially unnecessary hardware replacements. Further, such maintenance action reduces the availability of the rotorcraft while repairs are made. A hand-held apparatus for in-field inspection and detection of corrosion that has a quantitative and robust methodology would be well received in the art. 
       BRIEF SUMMARY 
       [0005]    According to one aspect of the invention, a system to detect, quantify, and characterize corrosion and degradation having a graphical user interface (GUI); an article; an inspection device configured to receive a stack of images from a surface of the article; memory having one or more instructions; and a processor that is configured to execute the one or more instruction and cause the system to: determine a depth and nature of features in the stack of images; generate a surface model of the article in response to the determining of the depth and the nature of features; determine features of interest from the surface model; compare the features of interest with predetermined information; and characterize the article as corroded or degraded in response to the comparison of the features of interest. 
         [0006]    According to another aspect of the invention, a computer-implemented method of detecting, quantifying, and characterizing corrosion and degradation of an article, includes an inspection device with a graphical user interface having a computing device: receiving, with a processor, signals indicative of a stack of images of a surface of the article; determining, with the processor, depth and nature of features in the stack of images; generating, with the processor, a surface model of the article in response to the determination of the depth and the nature of features; determining, with the processor, features of interest from the surface model; comparing, with the processor, the features of interest with predetermined information on the article; and characterizing, with the processor, the article as corroded or degraded in response to the comparisons of the features of interest. 
         [0007]    According to another aspect of the invention, a graphical user interface having a processor and memory with instructions that when executed by the processor cause the graphical user interface to: receive signals indicative of a stack of images of a surface of an article; determine depth and nature of features in the stack of images; generate a surface model of the article in response to the determination of the depth and the nature of features; determine features of interest from the surface model; compare the features of interest with predetermined information on the article; and characterize the article as corroded or degraded in response to the comparisons of the features of interest. 
         [0008]    In addition to one or more of the features described above, or as an alternative, further embodiments could include a processor that is configured to compare the features of interest with defined features from corroded and degraded samples in coupon test data. 
         [0009]    In addition to one or more of the features described above, or as an alternative, further embodiments could include a processor that is configured to compare the features of interest with a defined parameter from standards. 
         [0010]    In addition to one or more of the features described above, or as an alternative, further embodiments could include a processor that is configured to receive the stack of images as multiple images from a micro lens array. 
         [0011]    In addition to one or more of the features described above, or as an alternative, further embodiments could include a processor that is configured to perform a spatial frequency domain analysis on the stack of images. 
         [0012]    In addition to one or more of the features described above, or as an alternative, further embodiments could include a processor that is configured to determine relative depth information in the stack of images. 
         [0013]    In addition to one or more of the features described above, or as an alternative, further embodiments could include a processor that is configured to multiply the relative depth information with a measured focal length to provide absolute values of depth. 
         [0014]    In addition to one or more of the features described above, or as an alternative, further embodiments could include an inspection device that has interchangeable objective lenses with one or more of a differing magnification, differing focal lengths, differing apertures, differing field of view, and adjustable optical parameters. 
         [0015]    In addition to one or more of the features described above, or as an alternative, further embodiments could include an inspection device that has a lens that changes the image viewing angle for use in in-accessible areas. 
         [0016]    In addition to one or more of the features described above, or as an alternative, further embodiments could include an inspection device that has an internal self-contained variable light source that is configured to illuminate the article. 
         [0017]    In addition to one or more of the features described above, or as an alternative, further embodiments could include a processor that is configured to define a virtual feducial for measurement repeatability. 
         [0018]    Technical effects of the embodiments described above are quantitative and robust methodology for detecting, quantifying, and characterizing corrosion and degradation of safety critical articles in field applications. Additionally, embodiments described above can eliminate the subjective nature of current inspection processes and can bring consistency to the inspection process, thereby increasing the accuracy of corrosion and degradation inspections and potentially reducing the number of unnecessary component replacements and associated costs. 
         [0019]    Other aspects, features, and techniques of the invention will become more apparent from the following description taken in conjunction with the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0020]    The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which like elements are numbered alike in the several FIGURES: 
           [0021]      FIG. 1  is a perspective view of an exemplary aircraft for use with embodiments of the invention; 
           [0022]      FIG. 2  is block diagram of an exemplary architecture of a monitoring system for use with embodiments of the invention; 
           [0023]      FIG. 3  is an exploded view of an inspection device in accordance with an embodiment of the invention; 
           [0024]      FIG. 4  is an exemplary flow diagram for inspecting, detecting, and quantifying corrosion in accordance with an embodiment of the invention; and 
           [0025]      FIG. 5  illustrates an exemplary graphical user interface (GUI) in accordance with an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0026]    Referring to the drawings,  FIG. 1  illustrates a rotary-wing aircraft  10  or helicopter with a hand-held corrosion inspection system  18  (hereinafter “inspection system  18 ”) that is used for non-destructive inspection of a surface of a metal component of aircraft  10  for detecting, quantifying, and characterizing corrosion and degradation in accordance with an embodiment of the invention. As shown, rotary-wing aircraft  10  includes a main rotor assembly  12  that is driven about an axis of rotation R by one or more engines  14 . The main rotor assembly includes a multiple of rotor blades  16  mounted to rotor assembly  12  and are driven for rotation about axis R through a main gearbox (not shown for clarity). Also illustrated, inspection system  18  is provided as a hand-held apparatus that can be used for inspection of a surface  20  of aircraft  10  by an operator or technician in the field. In an embodiment, inspection system  18  includes a field array camera with hardware and software for detecting and quantifying, in an embodiment, pitting corrosion damage or other degradation on surface  20  of a metal article  22  of aircraft  10 , as will be described further in embodiments herein. In exemplary embodiments, inspection system  18  can include one or more light field array cameras in a low-profile hand-held apparatus having magnification optics and algorithms to identify pitting corrosion and other degradation, for example, uniform corrosion, crevice corrosion, galvanic attack, erosion, fretting, exfoliation, de-alloying, stress corrosion cracking, and corrosion fatigue, to determine a diameter and depth of pitting, stress fractures, or other wear, and to identify a number of pits on surface  20 . The inspection system  18  may be a hand held, portable unit, having the components of  FIG. 2 . While inspection system  18  is shown and described being used with a rotary-wing aircraft  10 , inspection system  18  may also be used to detect corrosion or degradation on static and dynamic component surfaces of metal and non-metal articles and structures. For example, inspection system  18  can be used to determine degradation of corrosion protection coatings such as, for example, paint or primer coatings, to determine types of corrosion including uniform corrosion, crevice corrosion, galvanic attack, erosion, fretting, exfoliation, de-alloying, stress corrosion cracking, and corrosion fatigue, to determine particles in oil including estimating the number, shape, size of particles, and to determine particles in water including estimating the number (turbidity), shape, size of particles. 
         [0027]      FIG. 2  is block diagram of an exemplary architecture  100  used in inspection system  18  for the non-destructive detection, quantification, and characterization of corrosion and degradation on article  22  such as those found in aircraft  10  ( FIG. 1 ). Architecture  100  includes hardware  108 , which may be implemented using known processing devices, such as a microprocessor (e.g., a digital signal processor (DSP)) or a field programmable grid array (FPGA)). Hardware  108  interfaces with an inspection device  110 . Inspection device  110  is a light field array camera and includes optical assembly  114 , a light source, a detector (e.g., a charge-coupled device (CCD)) and other components as described in further detail herein. Hardware  108 , software  106 , algorithms  104 , and data visualization  102  are collectively represented by processing unit  122 . 
         [0028]    Hardware  108  can include a main memory such as random access memory (RAM), and may also include a secondary memory. The secondary memory may include, for example, one or more databases, a hard disk storage unit and one or more removable storage units representing a floppy disk drive, a magnetic tape drive, an optical disk drive, a removable memory chip (such as an erasable programmable read only memory (EPROM), or programmable read only memory (PROM)) and associated socket, and the like which allow software and data to be transferred from a removable storage unit to inspection system  18 . The removable storage unit reads from and writes to a hard disk storage unit in a well-known manner. As will be appreciated, the removable storage unit includes a computer usable storage medium having stored therein software and data. 
         [0029]    Software  106  has algorithms for analyzing images from optical assembly  114  and rendering a graphical user interface (GUI)  120  for displaying the analysis results. For a Digital Signal Processing (DSP) solution, the software  106  would include a minimalistic operating system for supporting the multimedia libraries and drivers for the display and optics interfaces. 
         [0030]    Inspection device  110  houses a detector, lenses, and a light source for illuminating the article to be inspected. A single camera with interchangeable objective lenses can be used. Photoreceptors such as, e.g., a complementary metal-oxide semiconductor (CMOS), charge-coupled device (CCD), or film can be used to store sub-images captured through the micro lens array of optical assembly  114 . Image processing algorithms  104  are used to process the acquired sub-images from optical assembly  114 . 
         [0031]    The image processing algorithms  104  can select a series of sub-images across several fields of depth for two-dimensional (2D) analysis and generate a depth map for three-dimensional (3D) analysis, as described in further detail herein. Image filtering, alignment, enhancement, etc., may be performed by image processing algorithms  104  on the sub-image data. Image processing can include applying a Fast Fourier Transform (FFT) on the sub-image data. 
         [0032]    Analysis and data visualization module  102  uses the information from image processing algorithms  104  to detect, quantify, and characterize corrosion and degradation such as, for example, to determine pitting corrosion, to determine a diameter and depth of pitting, and to identify a number of pits on surface of article  22 . The analysis and data visualization module  102  measures features from the 2D image and a 3D depth map, and compares these features to standards  118  or coupon data  116 . Standards  118  and coupon data  116  may be loaded into inspection system  18  remotely (e.g., via software update) so that the inspection system  18  is configurable for inspection of a myriad of articles. In the example, standards  118  may represent acceptable standards of materials for Department of Defense (DOD) aircraft, e.g., surface roughness of metal surfaces in military applications. Also, coupon data  116  may include coupon test data that includes identified corrosion having defined features in corroded samples, which are substantially similar to a surface of article  22 . 
         [0033]      FIG. 3  is an exploded view of an exemplary inspection device  110  in inspection system  18  ( FIG. 2 ) in accordance with an embodiment of the invention. Inspection device  110  is a portable hand-held device that includes a housing body made from housing portions  200 ,  202 ,  204 , and  206 . Housing portions  202 - 206  are coupled together to enclose stationary camera  208  and objective lens or lenses  210  (collectively referred to as “objective  210 ”). Objective  210  can include a single lens or multiple lenses working together, for example, through a lens system to provide differing or varying magnification. Objective  210  may have a fixed or adjustable focal length, aperture, field of view, and magnification. Inspection device  110  may contain a mirror or prism  220  that allows camera  208  to image surfaces that are inaccessible at a straight-in angle. In an embodiment, a technician may use interchangeable objective lenses of varying focal lengths for objective  210 . Light source  218  within objective  210  illuminates article  22  to be inspected. Stationary camera  208  has a micro lens array  216 , which is a 2D matrix of square, microscopic lenses. Micro lens array  216  is mounted between objective  210  and a photoreceptor array  212 , behind aperture  214 , with a separation distance of no more than the focal length of one of the micro lenses between the two arrays. Photoreceptor array  212  can be a CCD, a CMOS device, or film. Objective  210  focuses incident light from article  22  onto micro lens array  216 . Micro lens array  216  performs optical sectioning to produce images at various focal lengths of the surface of article  22 . The sub-images corresponding with each micro lens contain information to reconstruct versions of an image of article  22  with various virtual focal depths and depths of field. The sum of this information is called a light field. Information on the relative depths of field from the sub-images is processed through image process algorithm  104  ( FIG. 2 ) to generate a depth map that is orthogonal to surface of article  22 . Further, the depth map is calibrated against coupon data  116  ( FIG. 2 ) and standards  118  ( FIG. 2 ) to quantify absence or presence of corrosion on article  22 . 
         [0034]      FIG. 4  is an exemplary process  300  for detecting and quantifying corrosion in an article that is performed by inspection system  18  ( FIG. 1 ) in accordance with an embodiment of the invention. As such,  FIG. 2  is also being referenced in the description of the exemplary process  300  of  FIG. 4 . 
         [0035]    As shown, the exemplary process  300  is initiated in block  302  where light field data is acquired by inspection device  110  for an article  22  being inspected. For example, a technician presses a button on inspection device  110  to launch device  110  after placing inspection device  110  on the surface of article  22 . Inspection system  18  activates light source  218  ( FIG. 3 ) to illuminate article  22  ( FIG. 3 ). Objective  210  focuses incident light, from article  22 , through a micro lens array  216 , onto a photoreceptor  212  ( FIG. 3 ). Images are received from each micro lens by photoreceptor  212  and stored as 2D images in memory onboard inspection system  18 . These 2D images from each micro lens in micro lens array (2D sub-images) represent light field image data at different angle of incidences. 
         [0036]    In block  304 , the 2D light field data is analyzed to calculate depth and nature of features. Information from each sub-image is processed in order to determine a depth profile of features in the image data. A depth map is generated from the stack of images using transforms. 
         [0037]    In block  306 , a 3D surface model of article  22  is built from the processed data. For example, an inverse spatial frequency transform (e.g., Inverse Fourier Transform) is performed on the combined coefficients to form a fused image in an image space. Initially, images produces by each micro lens encodes parallax with respect to all other micro lenses. Extracted depth information from the images in the image space provide relative depth information, i.e., an object is in front of another object, and twice as far in front of another object, etc. A 3D model is then created by multiplying the relative depths by a known focal length used in calibration of objective  210  ( FIG. 3 ) to provide an absolute value of depth. The 3D model provides a depth profile of objects of interest relative to the surface of the article  22  being inspected. Depth of features, and nature of features, for example, color and quantity are passed to data visualization  102  for classification in  308 . In an embodiment, a 3D model of article  22  may be displayed to the technician on user interface  120 . 
         [0038]    In block  308 , feature detection is performed on the 3D model in order to detect corrosion. The 3D model is analyzed to detect pitting corrosion by comparing a depth profile of a feature of interest in article  22  to corroded or degraded samples in coupon test data  116 . In addition to the using coupon test data  116 , or as an alternative, another embodiment could include comparing a depth profile of the feature of interest with defined parameters from standards  118 . Features of interest are located, counted, and measured by comparison to coupon test data  116  or standards  118 . In an embodiment, a virtual feducial for measurement repeatability can be defined from the features. A pattern is created by using vectors of minimum distance to a center point between all key features identified in a plane of view. This pattern of vectors represents a unique pattern that is stored in memory for future pattern recognition to locate inspection device  110 . Thus a measurement or test can be repeated when this vector pattern is identified. This process of using a virtual feducial can be utilized for manual as well as automated movement of inspection device  110 . If a feature of interest fails to meet the requirements of coupon test data  116  or standards  118 , then the object of interest is pitting corrosion or other degradation and information on its location and size is stored in processing unit  122 . Additionally, processing unit  122  can store a count of pits detected and determine “PASS” or “FAIL” of the article based on a comparison to coupon test data  116  or standards  118 . In block  310 , the results are classified and results are displayed to a technician. For example, features of interest that fail coupon test data  116  or standards  118  are identified on an image of the surface of article  22  by their location and size and “PASS” or “FAIL” labels are displayed to a technician on user interface  120 . In an embodiment, a 3D model may also be displayed on user interface  120  in addition to or in lieu of the image of the surface of article  22 . In an embodiment, pass and fail semantics may be communicated through text, indicator light, sound, etc. 
         [0039]    The inspection results are displayed to the user in a simple and intuitive manner through a GUI.  FIG. 5  is an exemplary GUI  120 . GUI  120  may include an LCD screen attached to inspection device  110  ( FIG. 3 ). This LCD screen may display images  401  captured from inspection device  110 . On this screen, the user may also have the option to select a test coupon using input  402  or a standard to compare against using input  403 . The user may also have the option to initiate process  300  ( FIG. 4 ) for detecting and quantifying corrosion in an article using input  404  culminating in the display of inspection results  406 . The user may also have the option to view an in-depth report using input  405 . Inputs  402 ,  403 ,  404 , and  405  may be text, mouse, touch, or any combination of these. This LCD screen may also serve as a means to control inspection device  110  ( FIG. 3 ). The GUI  120  may be used to enter information about the article to be inspected, if specific parameters are needed to maximize the success rate of the inspection process, as well as control inspection device  110  ( FIG. 3 ) as needed. 
         [0040]    Embodiments of the hand-held inspection system provide many benefits to the technician or operator. Inspection standards and coupon test data are controlled through software; the technician does not have to be burdened by the nuances of acceptance criteria and can focus on the field application of detecting, quantifying, and characterizing corrosion and degradation on articles. The inspection system can eliminate the subjective nature of current inspection processes and can bring consistency to the inspection process thereby potentially reducing the number of unnecessary component replacements and associated costs. 
         [0041]    The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. While the description of the present invention has been presented for purposes of illustration and description, it is not intended to be exhaustive or limited to the invention in the form disclosed. For instance, aspects of the invention are not limited to rotorcraft, and can be used in any structures and articles. Many modifications, variations, alterations, substitutions or equivalent arrangements not hereto described will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. Additionally, while the various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.