Patent Publication Number: US-2023142511-A1

Title: Assembly comprising a set of strands and a diagnostic device for diagnosing the state of the set of strands

Description:
TECHNICAL FIELD OF THE INVENTION 
     The present invention relates to the field of detecting degradations in a set of strands. 
     The invention has a privileged application in the field of submerged cables such as mooring cables and makes it possible to detect a ruptured cable or degradation of the mechanical performances thereof. 
     However, the invention is not limited to such a field of application and typically relates to materials comprising a set of strands, the strands extending mainly in a so-called direction of tension in which the set of strands is intended to experience tensile stresses. Thus, the invention can be applied to ropes, fabric bands, straps or composite materials. 
     The invention relates more particularly to an assembly comprising a set of strands and a diagnostic device for diagnosing the state of the set of strands. 
     TECHNICAL BACKGROUND 
     The mooring or anchor cables are submerged structures, the mechanical state of which cannot be checked with the naked eye when they are in use. 
     It is known to insert a silica optical fiber into a cable and to connect this cable to a diagnostic device. The diagnostic device comprises a light source arranged to send a light beam propagating through the fiber and an optical sensor capable of delivering a signal representative of the light intensity of the beam at the exit of the optical fiber. Thus, the diagnostic device makes it possible to detect a ruptured optical fiber when the light intensity measured is zero. 
     However, silica is a material which has low mechanical tensile strength. The strands of a mooring cable are made from a material having a mechanical tensile strength well above that of the silica. Thus, the state of a silica optical fiber integrated into a mooring cable is not representative of the state of the structural strands of the cable. This results in a lack of reliability and performance of the devices for diagnosing the state of a cable of the prior art. 
     SUMMARY OF THE INVENTION 
     The invention proposes an assembly comprising a set of strands according to which:
         the strands mainly extend in a so-called direction of tension in which the set of strands is intended to experience tensile stresses   all the strands that form the set are made from the same material with the same mechanical tensile strength, the strands are able to conduct light at least for certain wavelengths of light,   at least one strand of the set constitutes a diagnostic fiber so that the diagnostic fiber is able to conduct light, the light propagating through the diagnostic fiber between an entrance end and an exit end.       

     The assembly comprises a diagnostic device comprising:
         a light source arranged to send a light beam into the diagnostic fiber via the entrance end,   a first optical sensor capable of delivering a signal representative of the light intensity at the exit end of the diagnostic fiber, the light intensity at the exit end of the diagnostic fiber being correlated to the mechanical state of the diagnostic fiber.       

     According to other features of the invention:
         the set of strands is a mooring and/or anchor cable,   the set of strands is a fabric band or even a strap,   the diagnostic fiber is made of polymer and preferably nylon,   the entrance end and the exit end are one and the same end of the diagnostic fiber and the diagnostic fiber comprises a distal end opposite the entrance end and reflecting the light inside the diagnostic fiber,   the diagnostic fiber is folded in two so that the entrance end and the exit end are juxtaposed,   the diagnostic device further comprises a second optical sensor, and a beam splitter arranged to split a light beam from the light source into a first beam sent into the diagnostic fiber and a second beam sent into the second optical sensor   the set of strands comprises several diagnostic fibers, and the first optical sensor is a camera generating images of the exit ends of the diagnostic fibers,   the assembly comprises a communication module programmed to transmit the signal from the optical sensor or sensors to a remote control unit.       

    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       Further features and advantages of the invention will become apparent from the following detailed description, which may be understood with reference to the attached drawings in which: 
         FIG.  1    is a perspective view of a coiled mooring cable; 
         FIG.  2    is a perspective view of one end of the mooring cable of  FIG.  1    once it is attached to a floating barge; 
         FIG.  3    is a functional diagram of an assembly according to one embodiment of the invention; 
         FIG.  4    is a schematic perspective view of a cross-section of a set of strands according to one embodiment of the invention; 
         FIG.  5    is a schematic perspective view of a set of strands according to a first embodiment of the invention; 
         FIG.  6    is a schematic perspective view of a set of strands according to a second embodiment of the invention; 
         FIG.  7    is an image of one end of a set of strands provided by a camera of a diagnostic device according to one embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the following description, identical, similar or analogous elements will be referred to by the same reference numbers. 
     The invention is more particularly disclosed in the framework of its application to a mooring cable such as that shown in  FIGS.  1  and  2   . 
     The mooring cable constitutes a set  1  of strands. In  FIG.  1   , the cable is shown coiled about a support  6 . It is thus not in service. In  FIG.  2   , the cable is put in service and deployed on a platform  5 . The cable comprises one end forming a loop  12  engaged on a pulley  4  attached to the platform  5 . In service, the cable comprises a portion that is practically submerged over its entire length. 
     However, as mentioned above, the invention is not limited to such an application and can apply to ropes, fabric bands, straps or composite materials. 
     Reference is now made to  FIGS.  3  and  4    to disclose an assembly E according to one embodiment of the invention. The assembly E comprises a set  1  of strands and a diagnostic device  2 . 
     The set  1  comprises strands  11  made from the same material. The strands  11  mainly extend in a direction D of tension in which the set  1  of strands  11  is intended to experience tensile stresses. 
     The strands  11  can be held together in different ways. The strands can be:
         twice-laid and/or braided together,   woven together,   tied together, for example by a sheath,   bonded together, for example by a thermosetting or thermoplastic polymer.       

     According to one particular feature of the invention, the set  1  of strands comprises diagnostic fibers  13 . 
     Each diagnostic fiber  13  is able to conduct light. In other words, each fiber is transparent at least for certain wavelengths of light. The light propagates through the diagnostic fiber  13  between an entrance end  15  and an exit end  17 . 
     The diagnostic fiber  13  can be made of polymer. The diagnostic fiber  13  is, for example, made of transparent nylon. As a variant, the diagnostic fiber  13  can be made of polymethyl methacrylate, commonly abbreviated as “PMMA”. 
     The diagnostic fibers  13  extend mainly in the direction D of tension. The diagnostic fibers  13  are integrated into the set  1  in the same way as the strands  11 . The fibers can be:
         twice-laid and/or braided with the strands  11 ,   woven with the strands  11 ,   tied with the strands  11 , for example by a sheath,   bonded with the strands, for example by a thermosetting or thermoplastic polymer.       

     Each diagnostic fiber  13  has a mechanical tensile strength close to that of one of the strands  11 . For example, the diagnostic fiber  13  has a mechanical tensile strength equal to that of one of the strands  11  to within 5%. 
     According to a particular embodiment of the invention, the diagnostic fibers  13  can be strands  11  of the set  1  themselves. This is possible when the strands  11  are able to conduct light at least for certain wavelengths of light, as is the case for example for strands  11  made from transparent nylon. 
     In this case, some of the strands  11  of the set  1  are both designed to experience tensile stresses and both used to diagnose the mechanical state of the strand  11  itself and thus to detect any degradation via light intensity measurements inside the strand  11  that is able to conduct light. 
     According to another particular embodiment of the invention, the diagnostic fibers  13  are optical fibers discrete from the strands  11  of the set  1 . The diagnostic fibers  13  extend along the entire length of the set  1  of strands. 
     The diagnostic device  2  comprises a light source  21 , a first optical sensor  23 , a second optical sensor  25  and a beam splitter  27 . 
     The light source  21  emits a primary light beam  30 . 
     The light source is, for example, a laser. The light beam  31  entering the diagnostic fiber  13  is then spatially and temporally consistent. 
     As a variant, the light source  21  can be a light-emitting diode or lamp, commonly abbreviated as “LED”. 
     The beam splitter  27  and beam splitter cube is arranged to split the primary light beam  30  from the light source  21  into a first beam  31  sent into the diagnostic fiber  13  at the entrance end  15  and a second beam  32  sent into the second optical sensor  25 . 
     The light beam  31  is sent into the diagnostic fiber  13 . Part of the light beam  31  propagates through the diagnostic fiber  13  and comes out in the form of an exit beam  33 . The beam splitter  27  intercepts the exit beam  33 . Part of the exit beam  33  is reflected in the form of a measuring beam  34 . The measuring beam  34  penetrates the first optical sensor  23 . 
     The first optical sensor  23  is capable of delivering a signal representative of the light intensity at the exit end  17  of the diagnostic fiber  13 . The first optical sensor  23  is, for example, a photodetector like a photodiode or a camera coupled to an image processing device. 
     The light intensity at the exit end  17  of the diagnostic fiber  13  is correlated to the mechanical state of the diagnostic fiber  13 . When the diagnostic fiber  13  is in good condition, the light intensity measured at the exit end  17  is maximal, when the diagnostic fiber  13  is broken, the light intensity measured at the exit end  17  is zero and when the diagnostic fiber  13  is damaged, the light intensity measured at the exit end  17  has an intermediate value between the maximum value and the zero value. 
     The second optical sensor  25  is capable of delivering a signal representative of the light intensity of the second beam  32 . The second optical sensor  25  is, for example, a photodetector like a photodiode. 
     The second optical sensor  25  makes it possible to detect a failure of the light source  21 . In particular, the second optical sensor  25  makes it possible to determine the cause of an intensity measurement by the first optical sensor  23  being less than the maximum value. This cause is either a failure of the light source  21 , or a deterioration of the diagnostic fiber  13 . The second optical sensor  25  makes it possible to avoid wrongly detecting a deterioration of the diagnostic fiber  13 . 
     When the set  1  of strands  11  is a partially submerged cable, it is advantageous if the electronic components of the diagnostic device  2  such as the light source  21 , the first optical sensor  23 , and the second optical sensor  25  are positioned at a non-submerged end of the cable in order to limit the deterioration of the electronic components by the water, particularly by seawater. In this case, the entrance end  15  and the exit end  17  of the diagnostic fibers  13  must both be positioned in a non-submerged end of the cable. 
     In the example of  FIGS.  1  and  2   , the entrance end  15  and the exit end  17  of the diagnostic fibers  13  are positioned in the loop  12 . The diagnostic device  2  can also be integrated into the loop  12  shown. 
       FIGS.  5  and  6    respectively illustrate two embodiments of the invention wherein the entrance end  15  and the exit end  17  of the diagnostic fibers  13  are both placed at the same end of the cable. 
     In  FIG.  5   , the entrance end  15  and the exit end  17  are one and the same end of the diagnostic fiber  13 . The diagnostic fiber  13  comprises a distal end  19  opposite the entrance end  15 . The distal end  19  is arranged to reflect the light inside the diagnostic fiber  13 . For example, the distal end  19  has a straight split facilitating a Fresnel reflection of an incident beam  36  as a reflected beam  37 . The light source  21  sends a light beam  31  into the diagnostic fiber  13  via the entrance end  15 , the incident beam  36  corresponds to some of the light beam  31  that penetrated into the diagnostic fiber  13 . Next, the incident beam  36  is reflected as a reflected beam  37 . Part of the reflected beam  37  exits the diagnostic fiber  13  via the exit end  17  in the form of an exit beam  33 . 
     In  FIG.  6   , the diagnostic fiber  13  is folded in two so that the entrance end  15  and the exit end  17  are juxtaposed. More generally, all the strands of the set in  FIG.  7    are folded in two parts and the set comprises a first portion  16  comprising all of the first parts of the strands and a second portion  18  comprising all of the second parts of the strands. The light source  21  sends a light beam  31  into the diagnostic fiber  13  via the entrance end  15 , the incident beam  36  corresponds to some of the light beam  31  that penetrated into the fiber  13 . Next, the incident beam  36  propagates up to the exit end  17 . Part of the incident beam exits the fiber  13  via the exit end  17  in the form of an exit beam  33 . 
     As a variant, the entrance end  15  and the exit end  17  are at two discrete ends of the set of strands. In this case, the first optical sensor  23 , located at the exit end  17 , is separated from the rest of the components of the diagnostic device  2 , located at the entrance end  15 . Data communication can be established between the first optical sensor  23  and certain other components of the diagnostic device  2 . 
     In the example in  FIG.  7   , the first optical sensor  23  is a camera.  FIG.  7    shows an image  10  of one end of a set of strands given by the camera. In this set of strands, the diagnostic fibers are the strands themselves. The image  10  comprises white dots  110  corresponding to intact strands, gray dots  112  corresponding to damaged strands and black dots  114  corresponding to broken strands. The image  10  makes it possible to know the precise mechanical state of a set of strands in a reliable and efficient manner. 
     The data provided by the diagnostic device  2  can make it possible to determine a lifespan for the set of strands, for example by virtue of an analysis of the image  10  based on predefined criteria. These criteria can be the rate of intact strands, the rate of damaged strands and the rate of broken strands. 
     The diagnostic device  2  comprises a power supply. To allow the diagnostic device  2  to be self-contained, the power supply can be a battery. The diagnostic device  2  can comprise a sealed enclosure making it possible to protect the electronic and optical components of the diagnostic device  2 . 
     The assembly E can comprise a communication module programmed to send the signal from the optical sensor or sensors  23 ,  25  to a remote control unit. The data can be sent by means of acoustic waves or electrical cables. This makes it possible to perform a remote diagnosis on a set of strands. The diagnosis can be performed in real time. 
     It will be understood that various modifications and/or improvements obvious to the person skilled in the art may be made to the various embodiments of the invention disclosed or mentioned in the present description without departing from the scope of the invention. In particular, it is possible to combine the various embodiments together.