JP2017146171A - Accelerometer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an accelerometer which can deal with measurement of a wide range of frequency regions.SOLUTION: An accelerometer 1 includes: a vibrator 5 which has an arm member 3 rockable around a supporting shaft 2 and a plumb bob 4 disposed at the end of the arm member 3; an optical fiber sensor 6 disposed in the arm member 3 extending to the direction in which the vibrator 5 rocks (z direction); and an elastic member 7 disposed in the arm member 3 parallel to the optical fiber sensor 6. The accelerometer is designed to measure an acceleration based on a strain amount output from the fiber sensor 6.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an accelerometer, and more particularly to an accelerometer that measures acceleration based on an amount of strain of an optical fiber sensor.

  For example, in order to monitor the deterioration and damage of structures such as bridges, a measurement device that measures acceleration is installed in the structure, and the natural frequency, attenuation (structural attenuation), and deflection of the structure are measured from the measured acceleration. The amount is calculated. As such a measuring device, for example, an electric measuring device using a strain gauge is generally used.

  However, since a measurement device using a strain gauge electrically acquires measurement data, for example, in the case of a structure placed in a harsh environment, there is a possibility that a malfunction due to a disconnection or a short circuit may occur. Moreover, if the strain gauge peels from the structure, the measurement itself becomes impossible.

  Accordingly, various types of devices configured to acquire measurement data using an optical signal have been developed as measurement devices that can avoid the above-described problems (see, for example, Patent Document 1 and Patent Document 2).

  In the accelerometer described in Patent Document 1, a weight member is connected to a structure via an optical fiber and a spring member, and the acceleration of the structure is applied to the strain of the optical fiber arranged parallel to the displacement direction of the weight member. It is comprised so that it may measure based.

  The accelerometer described in Patent Document 2 is a light that connects a weight member to a structure via an optical fiber and a spring member, and deforms the acceleration of the structure in a direction orthogonal to the displacement direction of the weight member. The measurement is based on the deformation amount of the fiber.

JP 2000-230935 A JP 2005-156435 A

  However, in the accelerometer described in Patent Document 1, since the weight member is directly connected to the optical fiber, there is a problem that the measurable frequency range is limited to a range in which the optical fiber can be elastically deformed. . Further, in the accelerometer described in Patent Document 2, since the optical fiber is disposed along the spring member, the amount of strain is calculated based on the bending of the optical fiber. Therefore, there is a problem that the amount of bending of the optical fiber is small with respect to the amount of oscillation of the weight, it is difficult to measure vibration with small amplitude and vibration in the low frequency region, and the measurable frequency region is narrow.

  The present invention has been devised in view of such problems, and an object thereof is to provide an accelerometer that can support measurement in a wide frequency range.

  According to the present invention, an oscillator including an arm member that is swingable about a support shaft, a weight that is disposed at an end of the arm member, and the swing direction of the oscillator And an optical fiber sensor disposed on the arm member so as to extend in the direction, and an acceleration is measured based on an amount of strain output by the optical fiber sensor.

  The accelerometer may include an elastic member disposed on the arm member in parallel with the optical fiber sensor.

  The optical fiber sensor and the elastic member may be arranged on both sides of the arm member.

  The optical fiber sensor and the elastic member may be disposed on the opposite side of the weight with the support shaft interposed therebetween.

  The arm member may include a long hole formed along the longitudinal direction through which the support shaft is inserted.

  According to the accelerometer according to the present invention described above, the optical fiber sensor expands and contracts when the vibrator swings, and the acceleration can be measured based on the amount of distortion. Further, according to the present invention, the position of the support shaft of the arm member can be changed according to the vibration characteristics generated in the measurement object, and measurement in a wide frequency range can be supported.

It is a figure which shows the structure of the accelerometer which concerns on 1st embodiment of this invention, (a) is a longitudinal cross-sectional view, (b) is a BB arrow directional cross-sectional view in Fig.1 (a). It is a schematic block diagram at the time of applying the accelerometer shown in FIG. 1 to the vibration measurement of a bridge. It is a longitudinal cross-sectional view which shows the accelerometer which concerns on 2nd embodiment of this invention. It is a longitudinal cross-sectional view which shows the accelerometer which concerns on other embodiment of this invention, (a) is 3rd embodiment, (b) is 4th embodiment, (c) has shown 5th embodiment. .

  Embodiments of the present invention will be described below with reference to FIGS. 1 (a) to 4 (c). Here, FIG. 1 is a figure which shows the structure of the accelerometer which concerns on 1st embodiment of this invention, (a) is a longitudinal cross-sectional view, (b) is a BB arrow directional cross section in FIG. 1 (a). Figure. FIG. 2 is a schematic configuration diagram when the accelerometer shown in FIG. 1 is applied to bridge acceleration measurement. Note that the XYZ axes shown in FIGS. 1A and 1B indicate a triaxial orthogonal coordinate system in which the Z axis is the vertical direction.

  The accelerometer 1 according to the first embodiment of the present invention includes, for example, as shown in FIG. 1, an arm member 3 that is swingable about a support shaft 2 and an end portion of the arm member 3. A vibrator 5 provided with a weight 4, an optical fiber sensor 6 disposed on the arm member 3 so as to extend in a swinging direction (Z-axis direction) of the vibrator 5, and an optical fiber sensor 6 An elastic member 7 disposed in parallel on the arm member 3 and a housing 8 that houses the vibrator 5 and the like are provided, and configured to measure acceleration based on the amount of strain output by the optical fiber sensor 6. ing.

  Components constituting the accelerometer 1 (the vibrator 5, the optical fiber sensor 6, and the elastic member 7) are accommodated in a substantially rectangular parallelepiped casing 8 and unitized. The housing | casing 8 may have the flange part 8a which forms the attachment part to the structure S which is a measurement object. The housing 8 is a container that protects each component of the accelerometer 1 from the external environment, and preferably has sufficient rigidity and waterproofness.

  Both ends of the support shaft 2 are fixed to the side surface of the housing 8 as shown in FIG. In the present embodiment, the support shaft 2 is disposed along the horizontal direction (Y-axis direction). Note that the support method of the support shaft 2 is not limited to the illustrated configuration. For example, the support shaft 2 may be supported by a pair of support members arranged on the lower surface of the housing 8.

  As shown in FIG. 1A, the arm member 3 is pivotally supported by the support shaft 2 so as to be able to swing in a vertical plane (XZ plane). In the present embodiment, the support shaft 2 is inserted through the intermediate portion of the arm member 3.

  A weight 4 is disposed at one end of the arm member 3. In the present embodiment, the weight 4 is fixed to the end of the arm member 3, but the weight 4 may be configured so that the position of the weight 4 can be changed along the longitudinal direction of the arm member 3. For example, a configuration may be employed in which a screw is cut at one end of the arm member 3 and the weight 4 is screwed into the screw. Moreover, the structure which forms the opening part which penetrates the arm member 3 in the weight 4 and connects the arm member 3 and the weight 4 with a pin from the side surface may be sufficient. Moreover, the weight 4 may be replaceable with a weight having a different weight depending on the application.

  The arm member 3 and the weight 4 constitute a vibrator 5. In this embodiment, the support shaft 2 is fixed to the housing 8 and the arm member 3 is swingable with respect to the support shaft 2. However, the support shaft 2 is connected to the housing 8 so as to be rotatable. The arm member 3 may be fixed to the support shaft 2 so that the support shaft 2 and the arm member 3 can swing.

  The optical fiber sensor 6 is, for example, a sensor in which a Bragg grating 61 whose refractive index changes periodically is formed inside the optical fiber. The Bragg grating 61 reflects only light of a specific wavelength according to the interval when the optical fiber expands and contracts and the lattice interval changes. Therefore, by introducing light having a broadband spectrum into the optical fiber sensor 6 and measuring the wavelength of the reflected light, it is possible to detect distortion generated in the optical fiber.

  Further, since the optical fiber sensor 6 is capable of multipoint measurement with a single optical fiber, the optical fiber sensor 6 is configured with a single optical fiber as shown in FIG. The optical fiber sensor 6 may be disposed on both sides of the arm member 3. Specifically, the optical fiber sensor 6 includes one end fixed to the lower surface of the housing 8, the other end fixed to the upper surface of the housing 8, and an intermediate portion fixed while penetrating the arm member 3. It is equipped with.

  Therefore, the optical fiber sensor 6 is disposed so as to extend in the swing direction (Z-axis direction) of the arm member 3. Further, the other end of the optical fiber sensor 6 may be fixed to the housing 8 via the optical connector 12 as illustrated. An optical cable 11 that transmits light is connected to the optical connector 12.

  The configuration of the optical fiber sensor 6 is not limited to the illustrated configuration, and may be a configuration using a plurality of optical fiber sensors 6, for example. For example, in FIG. 1A, the optical fiber sensor 6 disposed above the arm member 3 and the optical fiber sensor 6 disposed below the arm member 3 may be configured by different optical fiber sensors 6. Good. In this case, each optical fiber sensor 6 is connected to an optical connector and an optical cable that individually transmit light.

  Although not shown, the optical fiber sensor 6 may be arranged only on one side of the arm member 3. For example, in FIG. 1A, the optical fiber sensor 6 may be disposed only above the arm member 3, or the optical fiber sensor 6 may be disposed only below the arm member 3.

  The elastic member 7 is a pair of coil springs arranged on both sides of the arm member 3, for example, as shown in FIG. The elastic member 7 disposed above the arm member 3 includes one end fixed to the upper surface of the housing 8 and the other end fixed to the arm member 3. The elastic member 7 disposed below the arm member 3 includes one end fixed to the lower surface of the housing 8 and the other end fixed to the arm member 3.

  The elastic member 7 is disposed in parallel with the optical fiber sensor 6 and holds the arm member 3 in a substantially horizontal state in a stationary state where no acceleration in the vertical direction is applied to the accelerometer 1. In addition, the elastic member 7 is capable of defining the swing range (upper limit and lower limit) of the arm member 3 by arbitrarily selecting and using a member having a predetermined elastic coefficient, and a measurable acceleration frequency. The area can be adjusted.

  The elastic member 7 is not limited to the illustrated configuration, and rubber, an air damper, or the like may be used as long as the arm member 3 can be elastically supported. Although not shown, the elastic member 7 may be disposed only on one side of the arm member 3. For example, in FIG. 1A, the elastic member 7 may be disposed only above the arm member 3, or the elastic member 7 may be disposed only below the arm member 3.

  In the present embodiment, the optical fiber sensor 6 and the elastic member 7 are disposed on the opposite side of the weight 4 with the support shaft 2 interposed therebetween. By disposing the elastic member 7 at the end opposite to the weight 4, the moment acting on the arm member 3 by the weight 4 can be effectively suppressed, and the swing range (amplitude) of the arm member 3 can be reduced. ) Can be reduced. Therefore, the accelerometer 1 according to the present embodiment can be applied to a place where vibration with a large amplitude occurs.

  The optical fiber sensor 6 may be fixed at any position on the arm member 3 as long as it is between the weight 4 and the elastic member 7, but if it is too close to the support shaft 2, In some cases, the amount of expansion and contraction becomes small, and it becomes difficult to measure the amount of distortion. Therefore, it is preferable that the optical fiber sensor 6 is disposed at an intermediate portion between the weight 4 and the support shaft 2 or an intermediate portion between the elastic member 7 and the support shaft 2. Since the optical fiber sensor 6 also has a certain elastic force, as shown in the figure, it is effective to arrange it at the intermediate portion between the elastic member 7 and the support shaft 2.

  Here, with reference to FIG. 2, processing when applied to vibration measurement of the bridge 13 using the accelerometer 1 described above will be described. The bridge 13 is comprised by a pair of abutment 13a and the upper structure 13b supported by the abutment 13a via a support, for example. A plurality of accelerometers 1 are arranged at predetermined locations of the upper structure 13b. These accelerometers 1 are connected to an analysis device 14 via an optical cable 11.

  The analysis device 14 includes, for example, a light source 14a that supplies light having a broadband spectrum, a coupler 14b that connects the light source 14a and the optical cable 11, and an optical sensor 14c that measures the wavelength of light returned from the accelerometer 1. An acceleration calculation unit 14d that measures acceleration based on the measured wavelength, and an analysis unit 14e that analyzes the state of the bridge 13 based on the measured acceleration.

  The light supplied from the light source 14 a to the optical cable 11 is transmitted to the optical fiber sensor 6 of each accelerometer 1. The light reflected by the Bragg grating 61 of each optical fiber sensor 6 is transmitted to the coupler 14b via the optical cable 11, and is transmitted from the coupler 14b to the optical sensor 14c. The optical sensor 14c measures the frequency of the transmitted light and calculates the wavelength.

  Data of the wavelength calculated by the optical sensor 14c is supplied to the acceleration calculation unit 14d. The acceleration calculation unit 14d compares the reference wavelength data measured when the bridge 13 is in a healthy state with the wavelength data measured at the time of monitoring, and the amount of distortion of the optical fiber sensor 6 is determined from the change in wavelength. Is calculated. Then, the acceleration calculation unit 14d calculates acceleration based on the calculated distortion amount.

  The acceleration data calculated by the acceleration calculation unit 14d is supplied to the analysis unit 14e. The analysis unit 14 e analyzes the state of the bridge 13 based on the acceleration measured by the accelerometer 1. For example, the analysis unit 14e analyzes the state of the bridge 13 by calculating analysis data such as the natural frequency, attenuation (structural attenuation), and deflection amount of the bridge 13. The analysis unit 14e determines the state of the bridge 13 (for example, the degree of deterioration or damage) by comparing the calculated analysis data with the theoretical value calculated by the structural analysis of the bridge 13. You may do it.

  In FIG. 2, the bridge 13 is illustrated as an example of the structure S that is a measurement target of the accelerometer 1, but the structure S is not limited to the bridge 13. For example, the structure S may be other structures such as a sluice, a building steel frame, a factory building, a plant structure, and an offshore structure.

  According to the accelerometer 1 according to the present embodiment described above, the optical fiber sensor 6 is disposed so as to extend in the swing direction (Z-axis direction) of the arm member 3 constituting the vibrator 5, thereby providing the vibrator 5. The optical fiber sensor 6 expands and contracts when the oscillates, and acceleration can be measured based on the amount of distortion.

  By the way, in the accelerometer 1 described above, when vibration in the vertical direction (Z-axis direction) occurs in the structure S, the arm member 3 swings around the support shaft 2 in the Z-axis direction by the inertial force of the weight 4. To do. The natural frequency of the swinging arm member 3 generally depends on the distance between the support shaft 2 and the weight 4. For example, if the distance between the support shaft 2 and the weight 4 is set to be large, the natural frequency can be reduced, and if the distance between the support shaft 2 and the weight 4 is set to be small, the natural vibration is set. The number can be increased. Therefore, the acceleration can be measured in a wide frequency range by adjusting the position of the support shaft 2.

  For example, when designing the optimum accelerometer 1 for a specific structure S, the position of the support shaft 2 may be designed according to the vibration characteristics of the structure S to be applied. At this time, each component of the accelerometer 1 is designed in consideration of the weight of the weight 4 and the elastic coefficient of the elastic member 7. When the arm member 3 of the accelerometer 1 is configured to be replaceable, a plurality of arm members 3 having different positions for fixing the support shaft 2 are prepared, and the arm member 3 is selected according to the application. You just have to do it.

  Thus, according to the accelerometer 1 according to the present embodiment, the position of the support shaft 2 of the arm member 3 can be changed according to the vibration characteristics generated in the structure S that is a measurement object, and a wide range of frequencies can be obtained. It can cope with the measurement of the area. Therefore, it can be applied not only to vibration measurement of a large structure having a low-order vibration mode characteristic such as a bridge but also to vibration measurement of a structure S having a high-order vibration mode characteristic.

  Next, an accelerometer 1 according to another embodiment of the present invention will be described with reference to FIGS. 3 and 4. Here, FIG. 3 is a longitudinal sectional view showing an accelerometer according to the second embodiment of the present invention. FIG. 4 is a longitudinal sectional view showing an accelerometer according to another embodiment of the present invention, in which (a) is a third embodiment, (b) is a fourth embodiment, (c) is a fifth embodiment, Is shown. In addition, in each figure, about the component same as the accelerometer 1 which concerns on 1st embodiment mentioned above, the same code | symbol is attached | subjected and the overlapping description is abbreviate | omitted.

  The accelerometer 1 according to the second embodiment shown in FIG. 3 has an arm member 3 configured so that the distance between the weight 4 and the support shaft 2 can be adjusted. Specifically, the arm member 3 includes a long hole 31 that is formed along the longitudinal direction and through which the support shaft 2 is inserted. With this configuration, the support shaft 2 can be moved along the longitudinal direction of the long hole 31, and the distance between the weight 4 and the support shaft 2 can be adjusted.

  Various methods of positioning the support shaft 2 are conceivable. For example, the support shaft 2 may be positioned by a bolt / nut 32 penetrating the support shaft 2 inserted through the long hole 31 and the arm member 3. In this case, since the support shaft 2 and the arm member 3 are fixed, the support shaft 2 is rotatably supported by the housing 8 via a bearing. Although not shown, a bearing may be arranged between the support shaft 2 and the arm member 3 so that the bearing can be relatively moved along the long hole 31 and can be fixed at a predetermined position.

  The accelerometer 1 according to the third embodiment shown in FIG. 4A is obtained by omitting the elastic member 7 from the accelerometer 1 according to the first embodiment shown in FIG. In the third embodiment, the optical fiber sensor 6 has a function of elastically supporting the arm member 3 in addition to the sensor function. In the third embodiment, in order to detect the distortion amount with high accuracy, the deformation of the optical fiber sensor 6 needs to be within the range of elastic deformation. Accordingly, the accelerometer 1 is suitable for measuring vibrations with a small amplitude and acceleration in a low frequency region.

  The accelerometer 1 according to the fourth embodiment shown in FIG. 4B has an optical fiber sensor 6 and an elastic member 7 disposed between a weight 4 and a support shaft 2. Even the accelerometer 1 having such a configuration has the same effect as the accelerometer 1 according to the first embodiment described above. Moreover, as shown in the figure, the stress applied to the optical fiber sensor 6 can be reduced by arranging the optical fiber sensor 6 on the support shaft 2 side and arranging the elastic member 7 on the weight 4 side. Of course, the positions of the optical fiber sensor 6 and the elastic member 7 may be interchanged.

  The accelerometer 1 according to the fifth embodiment shown in FIG. 4C has a structure in which the orientation of the accelerometer 1 according to the first embodiment shown in FIG. 1 is deflected by 90 ° in the vertical plane (XZ plane). The acceleration of the object S in the horizontal direction (X-axis direction) is measured. For example, as shown, the support shaft 2 is disposed along the Y-axis direction, the optical fiber sensor 6 and the elastic member 7 are disposed along the X-axis direction, and the arm member 3 is stationary along the Z-axis direction. Are arranged.

  As described above, the accelerometer 1 can arbitrarily change the orientation of the components housed in the housing 8 according to the place where the accelerometer 1 is arranged in the structure S. Further, by using both the accelerometer 1 according to the first embodiment and the accelerometer 1 according to the fifth embodiment, the acceleration in the vertical direction and the horizontal direction can be simultaneously measured.

  The present invention is not limited to the above-described embodiment, and it is needless to say that various modifications can be made without departing from the spirit of the present invention.

DESCRIPTION OF SYMBOLS 1 Accelerometer 2 Support axis 3 Arm member 4 Weight 5 Vibrator 6 Optical fiber sensor 7 Elastic member 8 Housing | casing 11 Cable 12 Connector 13 Bridge 13a Abutment 13b Upper structure 14 Analyzing device 14a Light source 14b Coupler 14c Optical sensor 14d Acceleration calculation Part 14e Analysis part 31 Long hole 32 Bolt / Nut 61 Bragg grating

Claims (5)

An oscillator comprising: an arm member arranged to be swingable about a support shaft; and a weight arranged at an end of the arm member;
An optical fiber sensor disposed on the arm member so as to extend in the swinging direction of the vibrator,
Measure acceleration based on the amount of strain output by the optical fiber sensor,
Accelerometer characterized by that.   The accelerometer according to claim 1, further comprising an elastic member disposed on the arm member in parallel with the optical fiber sensor.   The accelerometer according to claim 2, wherein the optical fiber sensor and the elastic member are disposed on both sides of the arm member.   The accelerometer according to claim 3, wherein the optical fiber sensor and the elastic member are arranged on the opposite side of the weight with the support shaft interposed therebetween. The accelerometer according to any one of claims 1 to 4, wherein the arm member includes a long hole formed along the longitudinal direction and through which the support shaft is inserted.