Patent Document

BACKGROUND OF THE INVENTION 
   This application relates generally to inspecting objects, and more specifically to methods and apparatus for inspecting objects using a light measurement system. 
   Objects are sometimes inspected, for example, to determine a size and/or shape of all or a portion of the object and/or to detect defects in the object. For example, some gas turbine engine components, such as turbine or compressor blades, are inspected to detect fatigue cracks that may be caused by vibratory, mechanical, and/or thermal stresses induced to the engine. Moreover, and for example, some gas turbine engine blades are inspected for deformations such as platform orientation, contour cross-section, bow and twist along a stacking axis, thickness, and/or chord length at given cross-sections. Over time, continued operation of the object with one or more defects may reduce performance of the object and/or lead to object failures, for example, as cracks propagate through the object. Accordingly, detecting defects of the object as early as possible may facilitate increasing the performance of the object and/or reducing object failures. 
   To facilitate inspecting objects, at least some objects are inspected using a light measurement system that projects a structured light pattern onto a surface of the object. The light measurement system images the structured light pattern reflected from the surface of the object and then analyzes the deformation of the reflected light pattern to calculate the surface features of the object. However, different areas of the object may have different manufacturing tolerances. Accordingly, some areas of the object may require a greater resolution of light projected onto the object than others to obtain enough data to inspect their tolerances. Some known light measurement systems inspect the object at the greatest resolution desired to inspect the object, or in other words, the resolution desired to inspect an area of the object that has the tightest tolerances. However, for areas with looser tolerances, excess data may be obtained from the greater resolution. Such excess date may be filtered or processed down to the resolution desired for the area with looser tolerances, thereby possibly increasing a time and effort of inspecting the object. Other known light measurement systems may inspect object areas of different tolerances with different inspection tools that have different resolutions. However, inspecting different areas of the object with different inspection tools may increase a time of setting up the system and/or object for inspection. Moreover, to merge inspection data for the entire portion of the object inspected, data from multiple sensors may be registered together, which may be time consuming and/or difficult. 
   BRIEF DESCRIPTION OF THE INVENTION 
   In one aspect, a method is provided for inspecting an object includes emitting light from a light source, projecting the light emitted from the light source onto a surface of the object, splitting light reflected from the object surface into a first image and a second image, receiving the first image and the second image with an imaging sensor, and analyzing the first and second images received by the imaging sensor to facilitate inspecting at least a portion of the object. 
   In another aspect, a structured light measurement system for inspecting an object includes a structured light source configured to project structured light onto a surface of the object, an imaging sensor configured to receive structured light reflected from the object surface, and a light-splitting device positioned to split light reflected from the object into a first image and a second image. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a block diagram of an exemplary embodiment of a structured light measurement system. 
       FIG. 2  is a block diagram of another embodiment of the structured light measurement system shown in  FIG. 1 . 
       FIG. 3  is a block diagram of another embodiment of the structured light measurement system shown in  FIG. 1 . 
       FIG. 4  is a block diagram of another embodiment of the structured light measurement system shown in  FIG. 1 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  is a block diagram of an exemplary embodiment of a structured light measurement system  10  that is used to measure a plurality of surface features of an object  12 . For example, system  10  may be used to inspect and determine surfaces of object  12 , wherein the surfaces may include features such as tilts, bends, twists, and/or warps when compared to a model representative of object  12 . 
   In the exemplary embodiment, object  12  is a rotor blade, such as, but not limited to, a compressor or turbine blade utilized in a turbine engine. Accordingly, and in the exemplary embodiment, object  12  includes an airfoil  14  extending outwardly from a platform  16 . While the following description is directed to inspecting gas turbine engine blades, one skilled in the art will appreciate that system  10  may be utilized to improve structured light imaging for any object. 
   System  10  includes a structured light source  22 , such as, but not limited to, a liquid crystal display (LCD) projector, a liquid crystal on silicon (LCOS) projector, a digital micromirror device (DMD) projector, a laser, a white light lamp, and/or a light emitting diode (LED). System  10  also includes an imaging sensor  24  that receives structured light reflected from object  12 . In the exemplary embodiment, imaging sensor  24  is a camera that receives and creates images using structured light reflected from object  12 , although system  10  may utilize other imaging sensors  24 . One or more computers  26  process images received from sensors  24 , and a monitor  28  may be utilized to display information to an operator. In one embodiment, computer(s)  26  include a device  30 , for example, a floppy disk drive, CD-ROM drive, DVD drive, magnetic optical disk (MOD) device, and/or any other digital device including a network connecting device such as an Ethernet device for reading instructions and/or data from a computer-readable medium  32 , such as a floppy disk, a CD-ROM, a DVD, and/or another digital source such as a network or the Internet, as well as yet to be developed digital means. In another embodiment, computer(s)  26  execute instructions stored in firmware (not shown). Computer(s)  26  are programmed to perform functions described herein, and as used herein, the term computer is not limited to just those integrated circuits referred to in the art as computers, but broadly refers to computers, processors, microcontrollers, microcomputers, programmable logic controllers, application specific integrated circuits, and other programmable circuits, and these terms are used interchangeably herein. 
   System  10  also includes a light-splitting device  34 , a patterning device  36 , and a patterning device  38 . Although other light-splitting devices  34  may be used, in some embodiments light-splitting device  34  includes a prism, a lens, a holographic element, and/or a beamsplitter. Light-splitting device  34  is positioned to receive light reflected from object  12  and, in the exemplary embodiment, split the received light into light  40  of a first image and light  42  of a second image. Light  40  of the first image is directed from light-splitting device  34  to patterning device  36 , and light  42  of the second image is directed from device  34  to patterning device  38 . Although light-splitting device  34  is illustrated and described herein as splitting light reflected from object  12  into first and second images, in some embodiments light-splitting device  34  splits light reflected from object  12  into more than two images. 
   Patterning device  36  is positioned to disperse light  40  into a predetermined pattern (not shown). The predetermined pattern facilitates providing a predetermined resolution of the first image, as viewed by imaging sensor  24 . Although two patterning devices  36  and  38  are illustrated and described herein, system  10  may include any number of patterning devices for dispersing light of any number of images into any number of predetermined patterns. Although other patterns may be used, in some embodiments patterning device  36  disperses light  40  of the first image into a diffraction pattern and/or an interference pattern. Although other patterning devices  36  may be used, in some embodiments patterning device  36  includes a diffraction grating, a phase grating, an LCD device, a DMD device, a light valve, a reference pattern, and/or an LCOS device. 
   For example, in some embodiments patterning device  36  is a diffraction grating that disperses light  40  into a diffraction pattern. In some embodiments, the diffraction grating includes a pattern of periodic lines and spaces, such as, for example, a ronchi ruling. However, the diffraction grating need not include a pattern of lines and spaces, much less periodic lines and spaces. Rather, the diffraction grating may include any pattern on and/or embedded within the substrate. For example, in some embodiments the pattern includes a pattern of lines and spaces, wherein the spacing between lines changes by a predetermined amount to, for example, increase in pitch from one side of an image of light dispersed from patterning device  36  to the other side to compensate for magnification changes across the image field. The pattern may be formed on the substrate using any suitable method and/or structure. For example, in some embodiments the pattern is formed from a plurality of strands of material, such as, but not limited to metal strands (e.g., chrome strands), attached to and/or embedded within the substrate. In other embodiments, the pattern is etched into the substrate, and the etched portions may be filled with a suitable material, such as, but not limited to, metal (e.g., chrome). Although the substrate may be fabricated from other materials, in some embodiments the substrate of grating  36  is fabricated from glass and/or quartz. 
   In some embodiments, and for example, patterning device  36  includes a reference pattern having a shape corresponding to a shape of a reference model representative of object  12 . More specifically, in such embodiments patterning device  36  disperses light into a pattern of a series of lines and spaces as they would appear as projected onto the reference model. As such, the reference pattern can be compared to the pattern projected onto object  12  to highlight a difference in shape between the object  12  and the reference model. 
   In some embodiments, and for example, patterning device  36  includes a pattern (not shown) that disperses light channeled therethrough into an interference pattern, such as, but not limited to, a phase grating. Although other phase gratings may be used, in some embodiments the phase grating includes a bleached photographic plate having a grating pattern thereon and/or a holographic recording on a bleached photographic plate. 
     FIG. 2  is a block diagram of an exemplary embodiment of system  10  wherein patterning device  36  includes a DMD. Light  40  of the first image split by light-splitting device  34  is reflected off a mirror  44  and directed to the DMD of patterning device  36 . Although other mirrors  44  may be used, in some embodiments mirror  44  is a half-silver mirror. Light  40  reflected off the DMD of patterning device  36  is dispersed by the DMD in the predetermined pattern and is channeled through mirror  44  for reception by imaging sensor  24 . Of course, the embodiment of system  10  shown in  FIG. 2  and described herein is exemplary only. Other configurations and/or arrangements may be used when patterning device  36  includes a DMD. 
   Patterning device  38  is positioned to disperse light  42  of the second image split by device  34  into a predetermined pattern (not shown). The predetermined pattern facilitates providing a predetermined resolution of the second image, as viewed by imaging sensor  24 . Although other patterns may be used, in some embodiments patterning device  38  disperses light of the first image into a diffraction pattern and/or an interference pattern. Although other patterning devices  38  may be used, in some embodiments patterning device  38  includes a diffraction grating, a phase grating, an LCD device, a DMD device, a light value, a reference pattern, and/or an LCOS device. 
   For example, in some embodiments patterning device  38  is a diffraction grating that disperses light into a diffraction pattern. In some embodiments, the diffraction grating includes a pattern of periodic lines and spaces, such as, for example, a ronchi ruling. However, the diffraction grating need not include a pattern of lines and spaces, much less periodic lines and spaces. Rather, the diffraction grating may include any pattern on and/or embedded within the substrate. The pattern may be formed on the substrate using any suitable method and/or structure. For example, in some embodiments the pattern is formed from a plurality of strands of material, such as, but not limited to metal strands (e.g., chrome strands), attached to and/or embedded within the substrate. In other embodiments, the pattern is etched into the substrate, and the etched portions may be filled with a suitable material, such as, but not limited to, metal (e.g., chrome). Although the substrate may be fabricated from other materials, in some embodiments the substrate of grating  36  is fabricated from glass and/or quartz. 
   In other embodiments, and for example, patterning device  38  includes a pattern (not shown) that disperses light channeled therethrough into an interference pattern, such as, but not limited to, a phase grating. 
     FIG. 3  is a block diagram of an exemplary embodiment of system  10  wherein patterning device  38  includes a DMD. Light  42  of the second image split by light-splitting device  34  is reflected off a mirror  46  and directed to the DMD of patterning device  38 . Although other mirrors  46  may be used, in some embodiments mirror  46  is a half-silver mirror. Light reflected off the DMD of patterning device  38  is dispersed by the DMD in the predetermined pattern and is channeled through mirror  46  for reception by imaging sensor  24 . Of course, the embodiment of system  10  shown in  FIG. 3  and described herein is exemplary only. Other configurations and/or arrangements may be used when patterning device  38  includes a DMD. 
   The patterned light  40  dispersed from patterning device  36  and the patterned light  42  dispersed from patterning device  38  are each received by imaging sensor  24 . More specifically, the first and second images formed by light  40  and  42 , respectively, are received by imaging sensor  24 . In the embodiment of  FIGS. 1-3 , the first and second images are both received by a single imaging sensor  24 . Alternatively, the first and second images may each be received by a different imaging sensor  24 .  FIG. 4  is a block diagram of system  10  illustrating different imaging sensors  24  for receiving the first and second images. Once received by imaging sensor(s)  24 , the first and second images can then be analyzed, for example using computer(s)  26 , to, for example, determine features of object  12 , such as, but not limited to, surface texture, surface orientation, and/or a material used in fabricating object  12 . For example, although other methods may be used, in some embodiments computer(s)  26  use a phase-step analysis to determine features of object  12  from the first and second images. Moreover, and for example, in some embodiments to determine features of object  12 , computers(s)  26  determine the center of lines projected onto object  12  and use the center positions to determine the distance to an object surface using known triangulation methods. Furthermore, and for example, in some embodiments to determine features of object  12 , computer(s)  26  calculate the Fourier transform of a projected pattern and use local pattern frequency information to calculate a slope of an object surface as a means to follow a contour of object  12 . In some embodiments, the first and second images are optically and/or electronically (for example using computer(s)  26 ) combined to form a common image for analysis thereof. By combining the first and second images into a common image for analysis, system  10  may simplify registration of other data (for example images of object  12  other than the first and second images) with the first and second images. 
   As described above, the predetermined pattern of the first image generated by patterning device  36  facilitates providing a predetermined resolution of the first image, as viewed by imaging sensor  24 . More specifically, patterning device  36  changes a resolution of light  40  of the first image after being split by light-splitting device  34  and before being received by imaging sensor  24 . Similarly, the predetermined pattern of the second image generated by patterning device  38  facilitates providing a predetermined resolution of the second image, as viewed by imaging sensor  24 . More specifically, patterning device  38  changes a resolution of light  42  of the second image after being split by light-splitting device  34  and before being received by imaging sensor  24 . The resolutions of the first and second images can each be selected to be, or approximate, a desired resolution for inspecting a particular area of object  12 . Accordingly, images of different resolutions of object  12  can be taken simultaneously, thereby allowing system  10  to simultaneously inspect different areas of object  12  that have different desired inspection resolutions, possibly reducing an inspection time of object  12 . Moreover, the first and second images, or a common combined image, can be combined with images taken from different angles of view than the first and second images to generate a coarser inspection of object  12 . A technical effect of the systems and methods described herein includes simultaneously inspecting different areas of an object that have different desired inspection resolutions, possibly reducing an inspection time. 
   Although the systems and methods described and/or illustrated herein are described and/or illustrated with respect to gas turbine engine components, and more specifically an engine blade for a gas turbine engine, practice of the systems and methods described and/or illustrated herein is not limited to gas turbine engine blades, nor gas turbine engine components generally. Rather, the systems and methods described and/or illustrated herein are applicable to any object. 
   Exemplary embodiments of systems and methods are described and/or illustrated herein in detail. The systems and methods are not limited to the specific embodiments described herein, but rather, components of each system, as well as steps of each method, may be utilized independently and separately from other components and steps described herein. Each component, and each method step, can also be used in combination with other components and/or method steps. 
   When introducing elements/components/etc. of the assemblies and methods described and/or illustrated herein, the articles “a”, “an”, “the” and “said” are intended to mean that there are one or more of the element(s)/component(s)/etc. The terms “comprising”, “including” and “having” are intended to be inclusive and mean that there may be additional element(s)/component(s)/etc. other than the listed element(s)/component(s)/etc. 
   While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.

Technology Category: 3