Abstract:
A fiber optic impact sensing system includes a light source, an optical detector, and a sensing optical fiber optically coupled with the light source and the optical detector, the sensing optical fiber being operably associated with an outer surface of a structure. An apparatus includes a structure having an outer surface and a fiber optic impact sensing system operably associated with the outer surface of the structure. The fiber optic impact sensing system includes a light source, an optical detector, and a sensing optical fiber optically coupled with the light source and the optical detector. A method includes operably associating a sensing optical fiber with an outer surface of a structure, monitoring an optical output of the sensing optical fiber, and determining whether an amplitude of the optical output is above or below a predetermined threshold value.

Description:
BACKGROUND  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a system and method for sensing an impact. In particular, the present invention relates to a fiber optic impact sensing system and a method for using the sensing system.  
         [0003]     2. Description of Related Art  
         [0004]     As those of ordinary skill in the art appreciate, it is important to avoid mechanically damaging pressure vessels and other structural members. It is, however, inevitable that some damage will occur to such members during use. Sometimes it is not known that damage has occurred to a structural member. In such situations, the structure may fail upon use without warning. At other times, it may be known that damage has occurred but it is not known whether the damage is extensive enough to compromise the structural integrity of the member. Often, sophisticated testing isrequired to determine whether the member is structurally sound for its intended purpose. Accordingly, it is often desirable to monitor the structural “health” of such members so that the likelihood of a catastrophic failure can be minimized.  
         [0005]     The structural integrity of composite members, such as those made from materials comprising strands or filaments of structural fibers disposed in a polymeric matrix, may be particularly compromised if such a member is mechanically damaged. Optical sensor arrays have been developed that can be embedded at discrete locations within a composite member to measure the internal strain of the member during use. Such sensors, however, provide no information as to the structural health of the member prior to use, because an unacceptable strain level may only be encountered during use. Moreover, these sensors fail to provide any information concerning external, impact-induced damage because they are disposed within the member.  
         [0006]     While there are many such sensors well known in the art, considerable room for improvement remains.  
       SUMMARY OF THE INVENTION  
       [0007]     In one aspect of the present invention, a fiber optic impact sensing system is provided. The system includes a light source, an optical detector, and a sensing optical fiber optically coupled with the light source and the optical detector, the sensing optical fiber being operably associated with an outer surface of a structure.  
         [0008]     In another aspect of the present invention, an apparatus is provided. The apparatus includes a structure having an outer surface and a fiber optic impact sensing system operably associated with the outer surface of the structure. The fiber optic impact sensing system includes a light source, an optical detector, and a sensing optical fiber optically coupled with the light source and the optical detector.  
         [0009]     In yet another aspect of the present invention, a method of sensing an impact is provided. The method includes operably associating a sensing optical fiber with an outer surface of a structure, monitoring an optical output of the sensing optical fiber, and determining whether an amplitude of the optical output is above or below a predetermined threshold value.  
         [0010]     The present invention provides significant advantages, including: (1) the ability to determine the structural health of a member prior to its use; and (2) the ability to sense an external impact to the member that may induce damage to the member.  
         [0011]     Additional objectives, features and advantages will be apparent in the written description which follows.  
     
    
     DESCRIPTION OF THE DRAWINGS  
       [0012]     The novel features believed characteristic of the invention are set forth in the appended claims. However, the invention itself, as well as, a preferred mode of use, and further objectives and advantages thereof, will best be understood by reference to the following detailed description when read in conjunction with the accompanying drawings, in which the leftmost significant digit(s) in the reference numerals denote(s) the first figure in which the respective reference numerals appear, wherein:  
         [0013]      FIG. 1  is a stylized, schematic representation of a first illustrative embodiment of a fiber optic impact sensing system according to the present invention, as applied to a pressure vessel;  
         [0014]      FIGS. 2A-2C  are graphical representations of the light amplitude detected by a detector of the present fiber optic impact sensing system over a period of time in which an impact occurs for various scenarios;  
         [0015]      FIG. 3  is a cross-sectional view, taken along the line  3 - 3  of  FIG. 1 , of a portion of the pressure vessel and an illustrative embodiment of a sensing optical fiber of the fiber optic impact sensing system of  FIG. 1 , illustrating one particular placement configuration of the sensing optical fiber according to the present invention;  
         [0016]      FIGS. 4A-4C  are cross-sectional views, corresponding to the view of  FIG. 3 , illustrating alternative placement configurations of the sensing optical fiber according to the present invention;  
         [0017]      FIG. 5  is a stylized, schematic representation of a second illustrative embodiment of a fiber optic impact sensing system according to the present invention, as applied to a pressure vessel;  
         [0018]      FIG. 6  is a stylized, schematic representation of a third illustrative embodiment of a fiber optic impact sensing system according to the present invention, as applied to a pressure vessel; and  
         [0019]      FIG. 7  is a stylized, top, plan view of the sensing optical fiber of the present invention applied to an alternative structure. 
     
    
       [0020]     While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.  
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0021]     Illustrative embodiments of the invention are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developer&#39;s specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.  
         [0022]     The present invention represents a system for optically sensing an impact to a member. The system includes one or more sensing optical fibers disposed proximate an outer surface of the member. Light is propagated through the one or more sensing optical fibers. If the member suffers an impact, the sensing optical fibers are compromised to an extent corresponding to the intensity of the impact, resulting in a corresponding decrease in the amplitude of light propagated through the sensing optical fibers. The level of propagated light is monitored to determine if an impact has occurred and the magnitude of the impact.  
         [0023]      FIG. 1  depicts a first illustrative embodiment of a fiber optic impact sensing system  101  according to the present invention, as applied to an exemplary pressure vessel  103 . Note that while the present invention is described herein as be applied to a pressure vessel, the present invention is not so limited. Rather, the scope of the present invention encompasses the application of the present invention to any structure, member, device, or apparatus. In its most basic form, the sensing system  101  includes a light source  105 , a detector  107 , and a sensing optical fiber  109  extending from light source  105  to detector  107 . Sensing optical fiber  109  is disposed proximate an outer surface  111  of pressure vessel  103 . Light from light source  105  propagates through sensing optical fiber  109  to detector  107 , as indicated by arrows  113 ,  115 . Note that light emitted from light source  105  may exhibit wavelengths within the human visual spectrum or may exhibit wavelengths outside the human visible spectrum.  
         [0024]     Generally, if pressure vessel  103  sustains an impact, sensing optical fiber  109  will be damaged to some degree corresponding to the intensity of the impact. The amount of damage to sensing optical fiber  109  is, in general, inversely proportional to the amplitude of light propagated through sensing optical fiber  109 .  FIGS. 2A-2C  illustrate three particular exemplary scenarios that might be encountered during the operation of sensing system  101 . Each of  FIGS. 2A-2C  provides a graphical representation of the light amplitude detected by detector  107  over a period of time in which an impact occurs. Also, shown in each of  FIGS. 2A-2C  is a graphical representation of a predetermined threshold value  201 . Light amplitudes detected by detector  107  that are greater than threshold value  201  are interpreted as resulting from impacts that will not structurally compromise pressure vessel  103  and are, thus, acceptable. It should be noted that light amplitudes detected by detector  107  may be considered acceptable if they are greater than the threshold  201  within a certain tolerance band, or, in other words, greater than about the threshold  201 . Light amplitudes detected by detector  107  that are less than threshold  201  are considered unacceptable, as the light amplitudes correspond to impacts that may structurally compromise pressure vessel  103 . Note that light amplitudes detected by detector  107  may be considered unacceptable if they are less than the threshold  201  within a certain tolerance band, or, in other words, less than about the threshold  201 .  
         [0025]      FIG. 2A  illustrates a scenario wherein pressure vessel  103  sustains an impact of sufficient magnitude to severely damage sensing optical fiber  109 . In this example, sensing optical fiber  109  is damaged at about time T 1  to a degree that little light is propagated therethrough and detected by detector  107 . The light amplitude detected by detector  107  after time T 1  falls well below threshold value  201 . Accordingly, the structural integrity of pressure vessel  103  has been sufficiently compromised due to the impact that pressure vessel  103  must be replaced or repaired. Detector  107  is operable to provide an indication that a significant impact has occurred.  
         [0026]      FIG. 2B  illustrates a situation wherein pressure vessel  103  sustains an impact of sufficient magnitude to damage sensing optical fiber  109  to a lesser degree than shown in  FIG. 2A . In this example, sensing optical fiber  109  is damaged at about time T 2  such that the light amplitude detected by detector  107  falls just below threshold value  201 . Even though sensing optical fiber  109  is not as severely damaged as in the example of  FIG. 2A , the light amplitude detected by detector  107  indicates that the structural integrity of pressure vessel  103  has been sufficiently compromised to warrant replacement or repair. Detector  107  is operable to provide an indication that a significant impact has occurred.  
         [0027]      FIG. 2C  illustrates a scenario wherein pressure vessel  103  sustains an impact of sufficient magnitude to damage sensing optical fiber  109  but to a lesser degree than shown in  FIG. 2B . In this example, sensing optical fiber  109  is damaged at about time T 3  such that the light amplitude detected by detector  107  falls above threshold value  201 . Even though sensing optical fiber  109  is somewhat damaged, the light amplitude detected by detector  107  indicates that the structural integrity of pressure vessel  103  has not been sufficiently compromised to warrant replacement or repair. Detector  107  is operable to provide an indication that an insignificant impact has occurred.  
         [0028]      FIG. 3  depicts one particular arrangement of sensing optical fiber  109  on outer surface  111  of pressure vessel  103 . In the illustrated configuration, sensing optical fiber  109  is generally helically wrapped around outer surface  111  of pressure vessel  103 . Adjacent portions of sensing optical fiber  109  are spaced apart by a predetermined distance D. In one embodiment, distance D is determined by evaluating the possible sources of impact to pressure vessel  103 . In this embodiment, distance D is smaller than the smallest object deemed likely to impact and damage pressure vessel  103 .  
         [0029]     In the embodiment of  FIG. 3 , sensing optical fiber  109  is bonded to outer surface  111  of pressure vessel  103  by a resin or adhesive  301 . Many composite pressure vessels such as pressure vessel  103  are fabricated using a filament winding process. In one embodiment, sensing optical fiber  109  is applied to outer surface  111  of pressure vessel  103  during the filament winding process, such that resin is applied to sensing optical fiber  109  prior to being applied to outer surface  111 . When assembled pressure vessel  103  is cured, sensing optical fiber  109  is bonded to outer surface  111 . In the embodiment illustrated in  FIG. 3 , a thin, protective covering or layer  303  is disposed over sensing optical fiber  109  to protect sensing optical fiber  109  from incidental damage. Protective layer  303  may comprise, for example, a paint or a syntactic foam.  
         [0030]      FIG. 4A  provides an illustrative embodiment alternative to that of  FIG. 3 . In the illustrated embodiment, sensing optical fiber  109  is generally helically wound about pressure vessel  103  such that adjacent portions of sensing optical fiber  109  are substantially adjacent to one another. This configuration provides optimum coverage of pressure vessel  103  for monitoring an impact thereto. Protective layer  401  is disposed over sensing optical fiber  109  to protect sensing optical fiber  109  from incidental damage. In various embodiments, protective layer  401  may comprise the materials discussed above concerning protective layer  303 . In other respects, the embodiment of  FIG. 4  generally corresponds to that of  FIG. 3 .  
         [0031]     As shown in  FIG. 4B , sensing optical fiber  109  may partially extend into pressure vessel  103 , especially if co-applied using a filament winding process. In such embodiments, protective layer  401  may be disposed over sensing optical fiber  109 , as discussed above. It should be noted that adjacent portions of sensing optical fiber  109  may be substantially adjacent, as shown in  FIG. 4B , or may be spaced apart, corresponding to the configuration shown in  FIG. 3 .  
         [0032]     As shown in  FIG. 4C , sensing optical fiber  109  may be fully embedded in pressure vessel  103  but proximate outer surface  111  of pressure vessel  103 . In this embodiment, protective layer  401  is not necessary, as sensing optical fiber  109  is disposed below outer surface  111  of pressure vessel  103 . It should be noted that adjacent portions of sensing optical fiber  109  may be substantially adjacent, as shown in  FIG. 4C , or may be spaced apart, corresponding to the configuration shown in  FIG. 3 . Thus, as depicted in  FIGS. 4B and 4C , sensing optical fiber  109  may be integral with a structure, e.g., pressure vessel  103 .  
         [0033]      FIG. 5  depicts a second, illustrative embodiment of a fiber optic impact sensing system  501  according to the present invention. In this embodiment, light source  105  is optically coupled by an optical fiber  503  to a fiber coupler  505 . Detector  107  is optically coupled by an optical fiber  507  to fiber coupler  505 . Fiber coupler  505  optically combines optical fibers  503 ,  507  into a single, sensing optical fiber  509 . Sensing optical fiber  509  is a “duplex” or “bidirectional” optical fiber, allowing light to independently propagate in two directions, as indicated by arrow  511 . Fiber coupler  505  is optically coupled with sensing optical fiber  509 .  
         [0034]     Light is emitted from light source  105  and propagates (as indicated by arrow  513 ) through optical fiber  503  to fiber coupler  505 . The light is then propagated through sensing optical fiber  509  to a distal end  515  of sensing optical fiber  509 , where it is reflected. The reflected light then propagates through sensing optical fiber  509  to fiber coupler  505 , where the reflected light is directed into optical fiber  507 . The reflected light propagates through optical fiber  507  (as indicated by arrow  517 ) to detector  107 , where the amplitude of the reflected light is detected.  
         [0035]      FIG. 6  depicts a third illustrative embodiment of a fiber optic impact sensing system  601  according to the present invention. Sensing system  601  is substantially identical to sensing system  501  of  FIG. 5  except a second sensing optical fiber  603  (shown as a broken line in  FIG. 6 ) is included to provide a redundant sensing capability. Light from light source  105  propagates bidirectionally through both sensing optical fibers  509 ,  603 , as indicated by arrows  511 ,  605 . Detector  107  detects the reflected light amplitude from both sensing optical fibers  509 ,  603 . Note that adjacent portions of sensing optical fibers  509 ,  603  may be spaced apart, as in the embodiment of  FIG. 3 , or substantially adjacent, as in the embodiment of  FIG. 4 .  
         [0036]     As discussed above, the fiber optic impact sensing system of the present invention may be used with any desired structure. For example, as depicted in  FIG. 7 , a sensing optical fiber  701  may be applied to an outer surface of a structure  703  in any suitable manner. Light source  105  and detector  107  (not shown in  FIG. 7 ) may be attached to ends  705 ,  707  of sensing optical fiber  701  and operated as described relative to  FIG. 1 . Alternatively, sensing optical fiber  701  may be optically coupled with fiber coupler  505  of  FIGS. 5 and 6  and operated as described above. In such an embodiment, sensing optical fiber  701  comprises a duplex or bidirectional sensing optical fiber. Note that structure  703  may comprise any structural polymeric, metallic, or composite material.  
         [0037]     In various embodiments, sensing optical fiber  109 ,  509 ,  603 ,  701  may extend over all, substantially all, or only a portion or portions of a structure, e.g., pressure vessel  103 , structure  703 , or the like. For example, if it is desirable to monitor impacts to only a portion of a structure, sensing optical fiber  109 ,  509 ,  603 ,  701  only need be applied to that portion of the structure.  
         [0038]     Note that a plurality of sensing optical fibers  701  may be applied to a structure (e.g., pressure vessel  103 , structure  703 , or the like) in a “patchwork” fashion or in some other geometric configuration so that impacts to all, substantially all, or certain portions of the structure may be detected. In such embodiments, ends  705 ,  707  of sensing optical fiber  701  may be optically coupled with other respective ends  705 ,  707  of sensing optical fibers  701  such that a single light source  105  and a single detector  107  are employed. Alternatively, separate light sources  105  and separate detectors  107  may be optically coupled with ends  705 ,  707 .  
         [0039]     The particular embodiments disclosed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the invention. Accordingly, the protection sought herein is as set forth in the claims below. It is apparent that an invention with significant advantages has been described and illustrated. Although the present invention is shown in a limited number of forms, it is not limited to just these forms, but is amenable to various changes and modifications without departing from the spirit thereof.