Background Art [2] Generally, a fiber bragg grating (FBG) sensor is a wavelength selective device created by forming a grating that periodically modulates an index of refraction in a glass core of an optical fiber to selectively reflect a specific wavelength.

[3] Since the FBG sensor for measuring physical quantity has good physical properties, for example, it has an inherent wavelength and is not affected by an elec- tromagnetic wave, the FBG sensor substitutes for a conventional electrical gauge. A field cf application for the FBG sensor is abruptly increased in recent years.

[4] In spite cf a very small diameter of 125 m m, the FBG sensor has a large tension per unit area. Consequently, since the FBG sensor is easily ruptured by an external shock, it is required to exquisitely attach the FBG sensor to buildings or bridges.

[5] In addition, the FBG sensor should be tightly installed to have proper tension, thereby measuring an accurate value. Since there is no proper fixer for the FBG sensor to a civil construction, an experienced engineer should directly set a value cf the FBG sensor in a site, which is limited in space-time.

[6] As such, although the FBG sensor has a good measuring performance, it is not widely used in various industrial fields, due to difficult installation and manipulation of the FBG sensor.

[7] Meanwhile, the FBG sensor is directly attached to an object to be measured by an adhesive or an optional fixing piece. Therefore, the FBG sensor is likely to be exposed to external circumstances such as rain, wind, bugs or animals.

[8] The FBG sensor exposed to the external circumstances may wrongly measure a strain, so that it is difficult to constantly inspect civil construction and maintain a measuring system.

Disclosure [9] Therefore, an object of the present invention is to solve the problems involved in the prior art, and to provide a fixer for a fiber bragg grating (FBG) sensor, by which the FBG can be installed by any person to provide the FBG sensor with an accurate value, irrespective of a place to be installed, and the FBG sensor can be semi- permanently fixed and protected [10] According to one aspect of the present invention, there is provided a fixer for fixing a fiber bragg grating (FBG) sensor to an object to be measured to measure a wavelength variation cf the object, the fixer including a pair of fixing pieces with a bottom surface adhered to the object, in which both ends of the FBG sensor is inserted and adhered by an adhesive, a tube for spacing the pair of fixing pieces at regular intervals, in which the FBG sensor is inserted into a hollow portion of the tube to protect the FBG sensor from the exterior, and means for fixing the fixing pieces and the pipe.

Description Of Drawings [11] The above objects, other features and advantages of the present invention will become more apparent by describing the preferred embodiment thereof with reference to the accompanying drawings, in which: [12] Fig. 1 is a perspective view of a fixer for a fiber bragg grating (FBG) sensor according to one preferred embodiment cf the present invention.

[13] Fig. 2 is an exploded view cf the fixer in Fig. 1.

[14] Fig. 3 is a bottom view of a fixer for a fiber bragg grating sensor according to another preferred embodiment cf the present invention.

[15] Fig. 4 is a cross-sectional view of the fixer in Fig. 1.

Best Mode [16] Reference will now be made in detail to preferred embodiments cf the present invention, examples cf which are illustrated in the accompanying drawings.

[17] A fixer for a fiber bragg grating (FBG) sensor S to measure a strain of an object to be measured, such as building or bridge, according to the present invention, includes a pair cf fixing pieces 3 with a bottom surface adhered to the object, in which both ends of the FBG sensor S is inserted and adhered by an adhesive F, a tube 2 for spacing the pair cf fixing pieces at regular intervals, in which the FBG sensor S is inserted into a hollow portion cf the tube to protect the FBG sensor S from the exterior, and means for fixing the fixing pieces 3 and the pipe 2.

[18] The fixing means includes a tube receiving portion 3a protruded from each side of the fixing pieces 3, a threaded hole 3d formed on an upper portion cf the tube receiving portion, and a fastening bolt 4 threadedly engaged with the threaded hole 3d for selectively compressing and fastening the tube 2.

[19] Both ends of the tube 2 are fitted into the tube receiving portions 3a between the fixing pieces 3. The FBG sensor S is inserted into the tube 2, and preferably has a degree of clearance so that the FBG sensor S is not restricted between the tube receiving portions 3a of the fixing pieces 3.

[20] The fixing piece 3 has a sensor holding groove 3b with a bottom surface opened to receive the FBG sensor S, and a cover 6 for selectively opening/closing the sensor holding groove 3b at a lower portion of the sensor holding groove.

[21] Specifically, the sensor holding groove 3b is formed along a center portion cf the fixing piece 3, through which the FBG sensor S passes. The sensor holding groove 3b is filled with an adhesive F, with the FBG sensor S being inserted therein. Con- sequently, the FBG sensor S is fixed at both ends thereof by the adhesive, with tension being applied to the FBG sensor.

[22] Referring to Fig. 3, the sensor holding groove 3b is formed with at least one anti- slip groove 3c at an inner side thereof. In the case where the adhesive F filled in the sensor holding groove is hardened, it can prevent a clearance form being produced in the sensor holding groove 3b due to a coefficient of linear expansion between the fixing piece 3 and the adhesive F.

[23] For example, an epoxy resin may be used as the adhesive.

[24] As described above, if the FBG sensor S is tightly fixed by the sensor holding grooves 3b cf the fixing pieces 3, the bottom surface cf the fixing piece 3 is firmly adhered to the surface of the object to be measured (not shown) by an adhesive.

[25] The fixing piece 3 is provided at the upper surface thereof with at least one through threaded hole 3e. In the case where it is difficult to adhere the bottom surface of the fixing piece 3 to the object to be measured by the adhesive, a fastening bolt 5 is threadedly engaged with a fixing plate 7 attached to the object to be measured via the threaded hole 3e, which firmly fixes the fixing piece 3 to the object to be measured If necessary, the fixing piece may be reused by unfastening the bolt 5.

[26] After the fixing piece 3 is firmly attached to the surface of the object by use of the fastening bolt 5 and the fixing plate 7 or the adhesive, the engaging state of the FBG sensor S is loosened or released by unfastening the bolt 4 cf the tube receiving portion 3a which is installed to maintain the tension of the FBG sensor S, thereby completing the installation cf the fixer 1 for the FBG sensor to measure the strain of the object to be measured [27] As described above, when the FBG sensor S is completely installed to the surface of the object, the FBG sensor S is safely protected by the tube 2 and the fixing pieces 3 of the fixer 1 from the external circumstances, such as rain, wind or bugs. In addition, there is no variation in the tension with the passage cf time, thereby correctly measuring the strain.

[28] When the FBG sensor S is directly used at the site, a method of employing the fixer of the present invention may be changed depending upon a kind of an object to be measured or measuring period For example, for a short period of up to 1 year, the fixing piece 3 may be directly attached to the object by use of the adhesive. For a long period cf above 1 year, the fixing piece 3 may be firmly attached to the object by use of the fastening bolt 5 and the fixing plate 7.

[29] As described above, after securing the fixing piece 3 to the object to be measured, it is preferable that the fastening bolt 4 engaged to the upper portion of the tube 2 is removed This is to sensitively transfer the strain cf the object to the FBG sensor S. At this time, it is possible to measure a strain of up to about 1 m s, according to a test.

[30] While the present invention has been described and illustrated herein with reference to the preferred embodiments thereof, it will be apparent to those skilled in the art that various modifications and variations can be made therein without departing from the spirit and scope of the invention. Thus, it is intended that the present invention covers the modifications and variations cf this invention that come within the scope of the appended claims and their equivalents.

Industrial Applicability [31] With the above description, according to the present invention, any person can install the FBG with the fixer. In addition, the FBG sensor can be semi-permanently fixed and be protected from the external circumstance.

[32] As such, it can prevent to wrongly measure a strain cf the object due to the external circumstances. Also, it is possible to constantly measure the civil constructions, without producing distortion due to an electromagnetic wave. In addition, it can solve a cumbersome in that a conventional electric strain gauge should be installed whenever a periodical safety inspection is performed [33] Furthermore, the present invention can reduce time and cost required to install the FBG sensor. Also, it can measure a variation of an inherent wavelength of the FBG sensor, thereby correctly measuring a ratio strain of the object to an initial value and thus exactly measuring a degree of fatigue of the civil construction relative to a con- ventional measuring system.