Abstract:
Disclosed is an inclinometer system capable of detecting the inclination of the ground using a fiber bragg grating sensor to precisely measure the deformation of the ground. The inclinometer system includes at least one measuring unit, and the measuring unit includes a body provided therein with a receiving part, a frame inserted into the body, a weight member inserted in to the frame and having one end hinged to the frame, the weight member rotating in cooperation to inclination of the body, an optical fiber  5  passing through both the body and the frame such that one end of the optical fiber is fixed to the weight member, a fixing member installed into the frame to fix an opposite end of the optical fiber, and a fiber bragg grating (FBG) sensor attached to the optical fiber.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority from Korean Patent Application No. 10-2008-0090912 filed on Sep. 17, 2008, and Korean Patent Application No. 10-2009-0044476 filed on May 21, 2009, the contents of which are herein incorporated by reference in their entirety. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to an inclinometer system. More particularly, the present invention relates to an inclinometer system capable of detecting the inclination of the ground using a fiber bragg grating sensor to precisely measure the deformation of the ground. 
         [0004]    2. Description of the Related Art 
         [0005]    It is necessary to inspect the displacement of civil engineering structures, such as roads, tunnels, bridges, and dams, an inclined plane, an incision cliff, a subway construction site, and underground foundation work for skyscrapers, or the ground subsidence displacement of a reclamation land and a soft ground by detecting the displacement of the structures or the sidewalls according to the design standard for the structures or construction techniques used in the construction sites. 
         [0006]    Generally, there are many measurement devices employing inclinometer sensors used for civil engineering. The measurement devices have various external appearances suitable for various civil engineering construction sites. For instance, the measurement device is buried in the ground or attached to the civil engineering structure by inputting the measurement device including inclinometer sensors, which have a predetermined length and assembled with each other using bolts, into an inclinometer casing. In a civil engineering field, the inclination displacement of the inclinometer sensor is converted into length (mm) to find the tilt degree of the civil engineering structure or the degree of ground subsidence, and such data are utilized to determine the stability of a civil engineering site. 
         [0007]    Hereinafter, description will be made regarding the installation of a conventional representative inclinometer system for a civil engineering structure used in a civil engineering site. 
         [0008]      FIG. 1  is a sectional view showing the conventional inclinometer system buried in the ground. 
         [0009]    As shown in  FIG. 1 , in order to measure the inclination of a ground  10 , after burring a single inclinometer casing  11  in the ground  10 , a plurality of inclinometer sensors  12 A and  12 B are pushed into the inclinometer casing  11  using a plurality of sensor rollers  13 A and  13 B attached thereto while the inclinometer sensors  12 A and  12 B are being connected to each other using a plurality of bolts  14 A and  14 B. The inclinometer casing  11  is formed by connecting unit pipes having a length of about 3 m with each other, and substantially forms a single pipe. 
         [0010]    Accordingly, after the conventional inclinometer system detects lateral underground displacement  16  using inclinometer sensors  12 A and  12 B, the inclinometer system collects measured data through a plurality of cables  15 A and  15 B exposed to the outside of the sensors  12 A and  12 B to determine the underground displacement. 
         [0011]    However, the conventional inclinometer system or a ground subsistence measuring system has a very complicated structure, and is difficult to be installed. In detail, only the single inclinometer casing  11  is used to measure the inclination and the subsidence of the ground  10 . Accordingly, the inclinometer system indirectly measures the inclination degree of the inclinometer casing by allowing the inclinometer sensors  12 A and  12 B to detect the displacement of the inclinometer casing transferred through the sensor rollers  13 A and  13 B in contact with internal grooves of the inclinometer casing. Therefore, the measured inclination degree of the inclinometer casing makes a great difference from an actual displacement of the inclinometer casing. 
       SUMMARY OF THE INVENTION 
       [0012]    Accordingly, the present invention has been made to solve the above-mentioned problems occurring in the related art. 
         [0013]    An object of the present invention is to provide an inclinometer system capable of measuring fine inclination displacement by using a fiber bragg grating sensor, so that precision of the inclinometer system can be improved. 
         [0014]    In order to accomplish the object of the present invention, it is one aspect of the present invention to provide an inclinometer system including at least one measuring unit. The measuring unit includes a body provided therein with a receiving part, a frame inserted into the body, a weight member inserted into the frame and having one end hinged to the frame, the weight member rotating in cooperation to inclination of the body, an optical fiber  5  passing through both the body and the frame such that one end of the optical fiber is fixed to the weight member, a fixing member installed into the frame to fix an opposite end of the optical fiber, and a fiber bragg grating (FBG) sensor attached to the optical fiber. 
         [0015]    As described above, according to the present invention, the inclinometer system can measure fine inclination displacement and temperature variation by using a fiber bragg grating sensor, so that precision of the inclinometer system can be improved. In addition, maintenance and repair work for the inclinometer system can be simplified. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  is a sectional view showing a conventional inclinometer system buried in the ground; 
           [0017]      FIG. 2  is an exploded perspective view showing an inclinometer system according to the present invention; 
           [0018]      FIG. 3  is an enlarged view showing a portion of a measuring unit of the inclinometer system according to the present invention; 
           [0019]      FIG. 4  is a plan view showing the measuring unit of the inclinometer system according to the present invention; 
           [0020]      FIG. 5  is a perspective view showing the measuring unit according to the present invention; 
           [0021]      FIG. 6  is a sectional pine view showing an internal portion of the inclinometer system according to the present invention; 
           [0022]      FIG. 7  is a sectional side view showing the internal portion of the inclinometer system according to the present invention; 
           [0023]      FIGS. 8 and 9  are sectional side views showing the operation of the fixing unit of the inclinometer system according to the present invention; 
           [0024]      FIG. 10  is a sectional side view showing an inclinometer system according to another embodiment of the present invention. 
           [0025]      FIG. 11  is a view showing the installation of the inclinometer system according to the present invention. 
           [0026]      FIG. 12  is a view showing the inclinometer system according to the present invention when underground displacement does not occur; and 
           [0027]      FIG. 13  is a view showing the inclinometer system according to the present invention when the underground displacement occurs. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0028]    Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to accompanying drawings. 
         [0029]      FIG. 2  is an exploded perspective view showing an inclinometer system A. 
         [0030]    As shown in  FIG. 2 , the inclinometer system A according to the present invention includes a guide pipe P buried in the ground, and a measuring unit Q inserted into the guide pipe P. 
         [0031]    The guide pipe P is an ABS pipe provided therein with a passage  92 . The guide pipe P has a plurality of rail grooves  93  formed at an inner peripheral surface thereof in a longitudinal direction. 
         [0032]    Each rail groove  93  has a triangle or rectangular sectional surface. 
         [0033]      FIG. 3  is an enlarged view showing the measuring unit Q of the inclinometer system A according to the present invention, and  FIG. 4  is a plan view showing the measuring unit Q of the inclinometer system A according to the embodiment.  FIG. 5  is a view showing a frame  6  provided in the measuring unit Q according to the present invention. 
         [0034]    As shown in  FIGS. 3 to 5 , the measuring unit Q includes a body  2 , which is provided therein with a receiving part, the frame  6 , which is inserted into the body  2 , a weight member  7 , which is inserted into the frame  6  such that one end of the weight member  7  is hinged to the frame  6  and rotates as the body  2  is inclined, an optical fiber  5 , which passes through both the body  2  and the frame  6  such that one end of the optical fiber  5  is fixed to the weight member  7 , a fixing member  75 , which is installed in the frame  6  to fix the other end of the optical fiber  5 , and a fiber bragg grating (FBG) sensor  52  attached to the optical fiber  5 . 
         [0035]    Elastic support members  4  are mounted on at both ends of the body  2 , so that the body  2  can be inserted into the guide pipe P while being elastically supported to the inner circumferential surface of the guide pipe P. 
         [0036]    Screws  29  are coupled with one side of the body  2  to adjust the position of the weight member  7  (see  FIG. 2 ). 
         [0037]    In other words, when each screw  29  is fastened such that a front end of each screw  29  is pushed, the tension state of the optical fiber  5  is changed to adjust sensitivity. Details thereof will be made later. 
         [0038]    As shown in  FIG. 3 , each elastic support member  4  includes first and second support rods  41  and  42  which protrude from both ends of the body  2 . The first support rod  41  is provided at a front end thereof with a roller R. The second support rod  42  faces the first support rod  41  and is provided at a front end thereof with the roller R. 
         [0039]    The roller R has a disc shape. Preferably, the roller R has the shape of a bead on an abacus thickness of which is thinned toward ends from the center thereof. The roller R is coupled with the rail groove  93  of the guide pipe P and rolled so that the body  2  is inserted into the guide pipe P. 
         [0040]    The second support rod  42  includes an upper leg  422  having the same length as that of the first support rod  41  and a middle leg  424  hinged to an end of the upper leg  422 . One end of the middle leg  424  is coupled with the body  2  by using a spring  426 . The roller R is installed on the other end of the middle leg  424 . 
         [0041]    One end of the spring  426  is coupled with a bracket  21  installed at the body  2 , and the other end of the spring  426  is coupled with the middle leg  424 , so that the one end of the middle leg  424  is always hauled to the body  2 . Accordingly, the other end of the middle leg  424  and the roller R are biased outward. 
         [0042]    Therefore, the roller R can closely make contact with the rail groove  93  of the guide pipe P. 
         [0043]    Accordingly, the roller R is supported in the rail groove  93  of the guide pipe P, so that the spring  426  is lengthened. As a result, the roller R can stably move because the roller R securely makes contact with the rail groove  93 . 
         [0044]    As shown in  FIG. 5 , the frame  6  includes side plates  62  provided at both sides of the frame  6  and top and bottom plates  63  and  64  covering both ends of the side plates  62  so that the frame  6  has a rectangular hollow body having a space therein with open front and rear surfaces. 
         [0045]    Hinge holes  620  are formed at the side plates  62  provided at both sides of the frame  6 . The hinge holes  620  are coupled with a shaft pin  622 . 
         [0046]    The bottom plate  64  is provided therein with a through hole  643  into which the weight member  7  is inserted. 
         [0047]    The side plates  62  and the top and bottom plates  63  and  64  are made of materials having different thermal expansion coefficients. 
         [0048]    In detail, the side plates  62  of the frame  6  is made of iron, and the top and bottom plates  63  and  64  of the frame  6  are made of aluminum. 
         [0049]    As the temperature increases, the top and bottom plates  63  and  64  are expanded. At this timer since outer peripheral portions of the top and bottom plates  63  and  64  are fixed to the side plates  62 , middle portions of the top and bottom plates  63  and  64  are recessed inward. 
         [0050]    In this case, the FBG sensor  52  is vertically pressed so that the FBG sensor  52  is contracted. This is because both ends of the optical fiber  5  are fixed to the top and bottom plates  63  and  4 . 
         [0051]    In addition, as a temperature is increased, the side plates  62  are expanded in upper and lower directions. 
         [0052]    The expansion force of the top and bottom plates  63  and  64  is compensated by the expansion force of the side plates  62 , so that the optical fiber  5  is not deformed. Accordingly, the FBG sensor  52  maintains the shape thereof without being contracted. 
         [0053]    As shown in  FIG. 5 , a through hole  630  is formed in the top plate  63  such that the optical fiber  5  passes through the through hole  630 , and an upper end of the fixing member  75  is fixed to an inner surface of the top plate  63 . 
         [0054]    The fixing member  75  is made of aluminum and has the shape of a rod having a predetermined length. 
         [0055]    The fixing member  75  is provided at an outer surface thereof with an adhesive injecting groove  701  and provided at a lower end thereof with a protrusion  752 . 
         [0056]    The protrusion  752  is provided at an outer surface thereof with a linear-type guide groove  754  provided in a line with the adhesive injecting groove  701 . 
         [0057]    Accordingly, the optical fiber  5  is inserted into both the adhesive injecting groove  701  and the guide groove  754  such that the optical fiber  5  can be linearly provided. 
         [0058]    As shown in  FIG. 5 , the weight member  7  is made of metal material, provided at an upper end thereof with a hinge part  72  having an insertion hole  72 A communicating with the hinge holes  620  of the side plates  62 , and provided at a lower portion thereof with an inclined surface  7 A. 
         [0059]    The hinge part  72  is provided at an outer surface thereof with a slit  722  formed in a linear line with the guide groove  754  such that the optical fiber  5  passes through the slit  722 . 
         [0060]    The weight member  7  is provided at the upper portion thereof with an adhesive injecting hole  702  to adhesively fix a lower end of the optical fiber  5 . 
         [0061]    The hinge part  72  of the weight member  7  is made of aluminum, and the remaining portion of the weight member  7  is made of alloy of brass. 
         [0062]    The protrusion  752  of the fixing member  75 , and the hinge part  72  of the weight member  7  have rounded surfaces. Accordingly, when the weight member  7  rotates so that the optical fiber  5  is bent, the optical fiber  5  is not damaged. 
         [0063]      FIG. 6  is a sectional plan view showing an internal portion of the inclinometer system according to the present invention, and  FIG. 7  is a sectional side view showing the internal portion of the inclinometer system according to the present invention. 
         [0064]    As shown in FIGS,  4 ,  6 , and  7 , the inclinometer system further includes a fixing unit S to prevent the weight member  7  from being moved. 
         [0065]    In other words, the fixing unit S presses the inclined surface  7 A of the weight member  7  such that an opposite surface  7 B of the inclined surface  7 A closely makes contact with an inner wall of the body  2 , thereby maintaining the fixing state of the weight member  7 . Accordingly, the optical fiber  5  and the FBG sensor  52  are not damaged by shake or shock when the inclinometer system is carried. 
         [0066]    The fixing unit S has a structure in which a support member S 2  presses the weight member  7  by fastening a screw S 1 , so that the support member S 2  fixes the weight member  7  in the close contact with the weight member  7 . 
         [0067]    As shown in  FIG. 6 , the fixing unit S includes the screw S 1  screwed with a hole  220  of a lower end surface  22  of the body  2 , the support member S 2  screwed with a front portion of the screw S 1  and making contact with an outer surface of the weight member  7 , inner and outer packings S 4  and S 5  screwed with the screw S 1  while closely making contact with upper and lower portions of the hole  220 , and a nut S 6  screwed with the screw S 1  and interposed between the inner packing S 4  and the support member S 2 . 
         [0068]    A packing hole  221  having a greater diameter than that of the hole  220  is formed at a lower part of the hole  220  such that the outer packing S 5  can be inserted into the packing hole  221 . 
         [0069]      FIGS. 8 and 9  are sectional side views showing the operation of the fixing unit S of the inclinometer system according to the present invention. 
         [0070]    As shown in  FIG. 8 , when the screw S 1  rotates clockwise, the support member S 2  moves up to closely make contact with the inclined surface  7 A of the weight member  7 . Accordingly, the weight member  7  closely makes contact with the inner wall of the body  2 , so that the weight member  7  is fixed. 
         [0071]    The outer packing S 5  of the screw S 1  is inserted into the packing hole  221  such that the outer packing S 5  closely makes contact with the packing hole  221 . According, water proof is achieved in the packing hole  221 . 
         [0072]    Thus, since the weight member  7  is fixed, the optical fiber  5  is not moved due to shock when the inclinometer system is carried. Accordingly, the optical fiber  5  is not damaged nor deformed. 
         [0073]    Thereafter, as shown in  FIG. 9 , when the screw S 1  rotates counterclockwise, the support member S 2  moves down so that the support member S 2  is separated from the weight member  7 . Accordingly, the weight member  7  is released. 
         [0074]    The inner packing S 4  of the screw S 1  closely makes contact with the upper portion of the hole  220 , so that a water proof state is maintained. 
         [0075]    According to another embodiment of the present invention, a temperature-compensating FBG sensor T is additionally provided on the optical fiber  5  with the FBG sensor  52 . 
         [0076]    The optical fiber  5  can be deformed according to the variation of external conditions such as strength or temperature. The temperature-compensating FBG sensor T measures the actual strain rate of the ground under various thermal conditions. 
         [0077]    When the inclinometer system further includes both the FBG sensor  52  and the temperature-compensating FBG sensor T, the optical fiber  5  is divided into several strands. 
         [0078]      FIG. 10  is a sectional side view showing the inclinometer system according to another embodiment of the present invention. 
         [0079]    As shown in  FIG. 10 , after the optical fiber  5  is inserted into the through hole  630  of the top plate  63 , the optical fiber  5  passes through the fixing member  75 , and then passes around the hinge part  72 . Next, after the optical fiber  5  is moved upward and bent, the optical fiber  5  is moved downward and withdrawn through the bottom plate  64 . Accordingly, the optical fiber  5  has three straight portions. 
         [0080]    In this case, the optical fiber  5  is bent upward at an outer portion of the fixing member  75 . 
         [0081]    In addition, a first FBG sensor  521  is attached to a first strand  5 A of the optical fiber  5 , in which the first strand  5 A extends beyond the fixing member  75  through the top plate  63 . A second FBG sensor  522  is attached to a second strand  5 B of the optical fiber  5  extending upward after passing around the hinge part  72   
         [0082]    The temperature-compensating FBG sensor T is attached to a third strand  5 C of the optical fiber  5  that moves downward after being bended at the upper portion of the fixing member  75 . 
         [0083]    A portion of the third strand  5 C, which is located after the temperature-compensating FBG sensor T, adheres to an internal surface of the side plate  62  of the frame  6 . In order to facilitate the adhesion between the third strand  5 C and the internal surface of the body  2 , a protrusion  69  protrudes from the internal surface of the body  2 . 
         [0084]    Meanwhile, as shown in  FIG. 12 , a single strand of the optical fiber  5  can be prepared, such that the lower end of the optical fiber  5  is fixed to the hinge part  72 . In this case, one FBG sensor  52  is attached to the optical fiber  5 . 
         [0085]    Hereinafter, the assembly and the operational of the inclinometer system according to the present invention will be described in detail. 
         [0086]    The following description is about a single strand of the optical fiber  5  and one FBG sensor  52 . Details about several strands (i.e., three strands) of the optical fiber  5  have been made above. 
         [0087]    The frame  6  is formed by the side plates  62  and the upper and lower plates  63  and  64 . Before the bottom plate  64  is assembled, the hinge part  72  of the weight member  7  is inserted into the frame  6  through the opening. Then, after the insertion hole  72 A of the hinge part  72  is coincident with the hinge hole  620  of the side plate  62 , the shaft pin  622  is coupled with the hinge hole  620 , and then the bottom plate  64  is assembled. 
         [0088]    Then, after the optical fiber  5  passes through the through hole  630  of the top plate  63 , the optical fiber  5  is inserted into the guide groove  754  of the fixing member  75 . Thereafter, the lower end of the optical fiber  5  is inserted into the adhesive injecting hole  702  through the slit  722  formed in the hinge part  72  of the weight member  7 , and an adhesive is injected into the adhesive injecting hole  702  so that the lower end of the optical fiber  5  is fixed. 
         [0089]    An adhesive is also injected into the adhesive injecting hole  701  of the fixing member  75  so that the optical fiber  5  is fixed. 
         [0090]    The assembled frame  6  is fitted into the receiving part of the body  2  so that the frame  6  is securely fixed. Preferably, fastening tools, such as screws, are not used for the frame  6  in order to maintain a tensile force of the frame  6  according to the temperature variation. 
         [0091]    Thereafter, the screws  29  of the body  2  are released or fastened such that the front end of the screws  29  pushes the weight member  7  thereby setting a desirable angle. In such a manner, the measuring unit Q according to the present invention is completely assembled. 
         [0092]      FIG. 11  is a view showing the installation of the inclinometer system according to the present invention. 
         [0093]    As shown in  FIG. 11 , after an insertion hole is formed in the ground by boring the ground, the guide pipe P is inserted into the insertion hole. 
         [0094]    Thereafter, a plurality of measuring units Q is inserted into the guide pipe P. 
         [0095]    As shown in  FIGS. 2 and 3 , the roller R of the elastic support member  4  of the body  2  is inserted into the rail groove  93  and then pushed in the guide pipe P. 
         [0096]    If the inner diameter of the guide pipe P is smaller, the second support rod  42  is relatively biased inward. In addition, if the inner diameter of the guide pipe P is greater, the second support rod  42  is relatively biased outward. Accordingly, the second support rod  42  is always supported on the inner wall of the guide pipe P while maintaining desirable elasticity, so that the measuring unit Q is not affected by the shake of the inclinometer system. 
         [0097]      FIG. 12  is a view showing the inclinometer system according to the present invention when underground displacement does not occur, and  FIG. 13  is a view showing the inclinometer system according to the present invention when the underground displacement occurs. As shown in  FIGS. 12 and 13 , a single strand of the optical fiber  5  and one FBG sensor  52  are installed. 
         [0098]    As shown in  FIG. 13 , when the underground displacement occurs, the weight member  7  rotates clockwise or counterclockwise about the hinge part  7 , so that the optical fiber  5  is extended or contracted. The FBG sensor  52  detects the displacement of the optical fiber  5  to transmit the displacement to a measuring part through a transmit cable. 
         [0099]    Accordingly, the displacement can be detected by the measuring part. 
         [0100]    Although the exemplary embodiments of the present invention have been described, it is understood that the present invention should not be limited to these exemplary embodiments but various changes and modifications can be made by one ordinary skilled in the art within the spirit and scope of the present invention as hereinafter claimed.