JP2000186956A - Optical fiber vibration mode sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To extract only the specified arbitrary vibration mode signal components from among vibration signals of a beam structure in which many vibration modes are superposed to vibrate complicatedly, in order to constitute a simple and sure vibration control system. SOLUTION: Monochromatic light emitted from a laser beam source 4 is coupled to a single mode fiber 6 by a condenser lens 5 to be transmitted to a two-mode optical fiber sensor 2 attached to a beam structure 1 via splice tool 7. A dual-mode optical fiber bonded to a surface and a reverse face of a beam alternately in order to correspond to positive and negative codes of a twice differentiated value related to the position of a vibration mode intended to be extracted in the beam structure 1. A light intensity signal provided from an emitting end of the dual-mode optical fiber is converted into an electric signal of monovibration mode required for control by a photodetector 8, a by-pass filter 9 and a signal amplifier 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of actively controlling vibration and sound emitted from a structure, in order to perform the control simply and effectively, by specifying a complex vibration waveform of the structure. The present invention relates to a vibration sensor having a filter function for extracting only the vibration mode vibration signal.

[0002]

2. Description of the Related Art An active vibration / sound control system has a sensor function, a processor function, and an actuator function in the system, and a processor calculates a sensor signal related to vibration and sound based on a certain control algorithm. By adding a signal to the actuator, control is performed to reduce the sensor signal.

[0003] Since a structure vibrates in a form in which vibration modes inherent to the structure are superimposed, a vibration waveform is generally complicated. If this vibration is detected by a normal sensor and control is attempted, the control will be performed due to problems such as lack of vibration data due to the sensor arrangement and complicated vibration data processing / computation performed by the processor in real time. Was inadequate.

Therefore, the current active vibration control method is as follows.
In order to perform quick and reliable control, multiple vibration mode components that compose the vibration of a structure are extracted for each vibration mode, and control by mode, which attempts to control each vibration mode, has attracted attention. A sensor capable of extracting a vibration mode has been developed.

With respect to the above, in a conventional point sensor represented by an acceleration pickup, in order to extract only an arbitrary vibration mode component of a structure, the number of sensors corresponding to the number of excited vibration modes is required. In addition, since it is necessary to weight sensor signals, a circuit and an arithmetic unit for multiplying and adding signals obtained from individual sensors are required. As a result, an expensive and complicated sensor unit is formed.

In an optical fiber representing a distributed constant sensor, the diameter and refractive index of the core / cladding are changed by changing the core drawing speed during the production of the optical fiber or by doping with a different material. There is an attempt to perform the above calculation in an analog manner by spatially changing the sensor sensitivity to match the target function, but it is very difficult to finely adjust the sensor sensitivity.
In addition, huge costs are required for manufacturing the sensor.

Therefore, if a desired vibration mode signal can be easily extracted from a sensor unit with a commercially available optical fiber on the market, a simple, practical and inexpensive vibration mode filter can be constructed, which is very effective in industry. .

[0008]

SUMMARY OF THE INVENTION According to the present invention, when a beam structure vibrates in a form in which a plurality of vibration modes are superimposed, a signal of a specific vibration mode is selected from among vibration signals having a plurality of frequency components. Extraction of only components can be realized by a simple installation method using one commercially available optical fiber, and as a result, it is easy to construct a simple vibration control system.

[0009]

The above object of the present invention can be effectively solved by using a commercially available two-mode optical fiber and attaching it only to specific positions on the front surface (front surface and back surface) of a beam structure. .

[0010] Here, the two-mode optical fiber means an optical fiber in which the form of a light wave propagating in the core of the optical fiber is limited to only two modes, that is, LP01 mode and LP11 mode.

That is, the present invention focuses on a mode function relating to a vibration mode to be extracted, and in a section in which a function obtained by second-order differentiating this mode function with respect to position has a positive value,
By mounting alternately on the front side of the beam structure and on the back side in the section where the value has a negative value, it is possible to extract almost only the vibration signal of the target vibration mode with one two-mode optical fiber. This is a characteristic vibration mode sensor, and is particularly effective for extracting a third or higher-order vibration mode vibration signal component.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an optical fiber vibration mode sensor according to the present invention will be described in more detail with reference to embodiments shown in the drawings. FIG. 1 is a perspective view showing an outline of an embodiment of an optical fiber vibration mode sensor according to the present invention, and shows an example of a cantilever beam which is the most typical beam. FIG. 2 is a top view of a cantilever beam 1, a two-mode optical fiber 2, and a fixing part 3, which are the most important parts of the present invention.

The apparatus is roughly divided into a light source unit for introducing monochromatic light into an optical fiber, a single mode fiber unit for guiding monochromatic light to a two-mode optical fiber which can be a vibration sensor, and a unit for detecting vibration. It comprises a mode optical fiber section and a signal processing section.

[0014] Monochromatic light having a wavelength of 633 nm generated by the He-Ne laser light source 4 is condensed by the convex lens 5 and introduced into the core of the single mode fiber 6.
The monochromatic light propagates through the single-mode fiber 6 and propagates to the two-mode optical fiber 2 via a splice device (connecting portion) 7.

Here, the single mode fiber means an optical fiber in which the form of light propagating in the core is only the LP01 mode.

The cantilever beam structure 1 is clamped from both sides by a fixing portion 3. The fixing portion 3 of the cantilever beam structure portion 1 is fixed to the fixing portion 3 so that the two-mode optical fiber 2 can pass therethrough. A trench is dug in 3. The light intensity of the light passing through the two-mode optical fiber 2 attached to the cantilever beam structure 1 is converted and amplified into a voltage signal by a photodetector 8, a DC component of the signal is removed by a high-pass filter 9, and an amplifier 10 The signal is amplified, and as a result, a change in the light intensity signal is output.

In the present invention, the method of attaching the two-mode optical fiber 2 to the cantilever structure 1 is not particularly limited.
Use a double-sided tape with a high adhesive strength and a thickness of several microns, or use a two-mode optical fiber
It is desirable to dig a shallow groove having a diameter of an optical fiber into which the optical fiber can be inserted, and to incorporate the two-mode optical fiber 2 therein.

At the place where the attachment of the two-mode optical fiber 2 is changed from the front surface to the back surface or from the back surface to the front surface, a loop is formed to the extent that the optical fiber is not damaged, and care is taken not to join this portion to the structure. Since the loop portion does not receive the distortion of the cantilever structure 1, the size of the loop may be appropriate, but it is desirable that the loop portion be as small as possible in order to suppress the required amount of the two-mode optical fiber 2 as a sensor material.

Further, in the portion where the two-mode optical fiber 2 is not attached to the cantilever structure 1, that is, the optical fiber introduction portion up to the structure, the detector for measuring the light intensity from the structure and the above-mentioned loop portion. It is also possible and effective to connect the single mode fiber 6 with little influence of distortion to the two mode optical fiber 2.

In addition, although the thickness (diameter) of the two-mode optical fiber 2 is not limited, if the diameter is large and the rigidity per unit length is large, when the two-mode optical fiber 2 is attached to a structure, the vibration mode of the structure The smaller the diameter, the better. With a commercially available optical fiber having a core diameter of 3 μm, a cladding diameter of 125 μm, and a coating diameter of about 250 μm, there is no problem with a cantilever made of a metal having a thickness of 0.1 mm or more or a material having the same rigidity. Absent.

Next, a method of installing the two-mode optical fiber 2 on the cantilever structure 1 which is particularly important in the present invention will be described.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In order to clarify the installation method, the longitudinal direction of the cantilever 1 is defined as the Z-axis, the position of the joint between the cantilever 1 and the fixed part 3 is zero, and the free end of the cantilever 1 is determined. The position where the optical fiber should be attached is described by normalizing to 1.0.

Embodiment 1: The second derivative with respect to the position of the third vibration mode takes a value of zero because the position is 0.132,
0.496 and 1.000. In the present invention, if the position is from 0.000 to 0.132 on the front surface of the cantilever, from 0.132 to 0.496 on the back surface, and from 0.496 to 1.000 on the front surface again, The signal component of the tertiary vibration mode can be detected very large compared to other mode components by simply pasting it in parallel to the longitudinal direction of the cantilever, but the mounting position is changed as follows Then, still more effective extraction of the third vibration mode is possible. That is, the position is from 0.000 to 0.
The extraction efficiency of the tertiary vibration mode can be particularly improved by pasting on the front surface up to 132, on the back surface from 0.151 to 0.457, and again on the front surface from 0.523 to 0.935.

The effect of extracting the third-order vibration mode vibration signal in the above method was measured. Here, as the cantilever structure 1, an aluminum plate having a thickness of 3 mm, a width of 40 mm, and a length of 500 mm is used, and 100 mm of the length of 500 mm is gripped by the fixing part 3 having a vice structure. It was made to carry. A frequency transfer function of an optical fiber output signal with respect to a vibrating force when a point 15 mm away from the fixed portion 3 of the cantilever beam structure 1 was shocked by an impulse hammer was measured. For comparison, a non-contact type gap sensor was installed near the free end of the cantilever 1 at a distance of about 1 mm, and the frequency transfer function of the gap sensor output signal with respect to the exciting force during the impulse excitation was also measured.

Here, the analysis frequency range is 1000 Hz
Up to. There are five eigenvalues of the cantilever beam structure 1 included in this frequency range. Therefore, the magnitude of another vibration mode signal component with respect to the magnitude of the third vibration mode component for the purpose of extraction was evaluated.

Table 1 shows that, when the vibration amplitude relating to the tertiary vibration mode to be extracted is 0 dB, the vibration amplitude relating to the other vibration modes is compared with the tertiary vibration mode component.
It is a table showing how much it will be. 0 dB is a vibration amplitude equal to the third vibration mode component, and
-20 dB indicates that the vibration amplitude is 1/10 as compared with the third-order vibration mode component.

In order to compare with a signal from a normal sensor, in the table, the vibration amplitude relating to the third vibration mode is set to 0 in the frequency transfer function measured using the non-contact sensor.
The ratio of the magnitudes of the vibration amplitudes of the other vibration modes in the case of dB is expressed in dB in the same manner as above.

According to Table 1, in the frequency transfer function of the non-contact type sensor, the vibration amplitude of the first-order vibration mode component is the largest, followed by the second and third order. However, according to the method of the present invention, the vibration amplitude of the tertiary vibration mode is detected to be the largest, and 1,2, and
The vibration amplitude in the fourth and fifth vibration modes is 20 dB or less.

This indicates that the optical fiber mode sensor according to the present invention substantially extracts only the vibration component related to the third vibration mode. Since a very large value is detected as compared with the vibration in the other mode, the component in the other mode is buried in the signal of the third vibration mode, and the obtained time vibration waveform is almost a sine wave. It is very effective as a control signal.

Further, in order to show that the method according to the invention is also effective for other vibration mode vibration components, a second embodiment is shown.
An effective method of extracting the fourth-order vibration mode vibration component and the result thereof will be described below.

Embodiment 2: The second derivative with respect to the position of the fourth-order vibration mode takes a value of zero because the position is 0.094,
0.356, 0.642, and 1.000. In the present invention, the position from 0.000 to 0.094 is applied to the surface of the cantilever structure 1 from 0.094 to 0.356.
On the back side, from 0.356 to 0.642 on the front side, from 0.642 to 1.000 on the back side, all sections are simply pasted in parallel to the longitudinal direction of the cantilever in a straight line However, the signal component of the fourth vibration mode can be detected much larger than the other mode components. However, if the attachment position is changed as follows, it is possible to extract the fourth vibration mode more effectively. That is, when the position is from 0.000 to 0.094, the surface is
If it is attached to the back surface until 0.369 to 0.620, and to the back surface from 0.656 to 1.000, the extraction efficiency of the fourth vibration mode is particularly improved.

The fourth-order vibration mode extraction effect in the above method was measured. Here, the cantilever structure 1 has the same size and the same size as described above, and the method of measuring the effect is the same as in the example of the third vibration mode extraction.

Table 2 shows the results of the fourth-order vibration mode extraction intended for the extraction. As in the case of Example 1, the result of the frequency transfer function by the non-contact gap sensor is also shown.

According to Table 2, the magnitude of the vibration amplitude for the fourth vibration mode is significantly larger than the vibration amplitude value for the other vibration mode components, and a difference of 20 dB or more compared to the other vibration mode components also exists. Is recognized. This is nothing but the fact that the optical fiber mode sensor of the present invention substantially extracts only the vibration component related to the fourth vibration mode.

Therefore, the signal output from the two-mode fiber mode sensor is substantially only a fourth-order vibration mode component, and as a result, the signal time waveform becomes a sine wave having a frequency corresponding to the natural frequency of the fourth-order vibration mode. It can be fully used as a control signal.

When the two-mode optical fiber is attached to the cantilever structure in the above-described manner, only the intended vibration mode vibration component can be largely extracted. If the order of the mode becomes higher, a value at which the second order differential value of the mode function becomes zero may be used as the sticking position.

This method is not limited to a cantilever beam, but is also effective for a fixed beam at both ends and a simple support beam at both ends which are one-dimensional structures.

For example, in the case of the beam structure 1 having fixed ends at both ends as shown in FIG. 3, when the positions of the fixed ends at both ends are normalized to 0 and 1.0, the second order differential value relating to the position of the vibration mode becomes 0. Are 0, 0.0 in the case of the third vibration mode.
94, 0.356, 0.644, 0.906, and 1, respectively.

Therefore, according to the above-described method, the positions 0 to 0.094 on the front surface, 0.094 to 0.356 on the back surface, 0.356 to 0.644 on the front surface, 0.644
If a two-mode optical fiber is stuck on the front and back alternately along the longitudinal direction so that the back side is from 0.906 to the back side and the back side is from 0.906 to 1.0, the signal related to the target tertiary vibration mode is obtained. Only the components can be extracted.

Further, also in the fourth vibration mode, the position where the second derivative of the mode function becomes 0, that is,
0, 0.073, 0.277, 0.500, 0.72
By attaching the two-mode optical fiber 2 to the sections 3, 0.927, and 1.0 in the order of front and back, it is possible to extract a signal component related to the fourth-order vibration mode.

In the simple-supported beam structure 1 at both ends as shown in FIG. 4, when the positions of the support portions at both ends are normalized to 0 and 1.0, the second-order differential value with respect to the position of the tertiary vibration mode becomes 0. Are 0, 0.333, 0.666, and 1.0. By alternately attaching 0 to 0.333 to the front surface, 0.333 to 0.666 to the back surface, and 0.666 to 1 to the front surface, it is possible to extract a signal relating to the third vibration mode.

Further, in the simple support beam at both ends, 4
The values of the second-order differential with respect to the position of the next vibration mode become 0 at 0, 0.25, 0.50, 0.75, and 1.0. If they are stuck alternately on the back side, it is possible to extract a signal in the fourth vibration mode.

Further, according to this method, since it is only necessary to apply a straight line only to a specific location, it can be easily applied to a two-dimensional structure such as a simple flat plate at both ends or a fixed plate at both ends having a linear nodal line. It has advantages that can be applied.

[0044]

According to the method of the present invention, an arbitrary vibration mode vibration component of a beam structure vibrating in a complicated manner can be extracted. As a result, since the signal waveform output from the optical fiber vibration mode sensor is represented by a simple sine wave, a simple operation that does not require an arithmetic circuit such as a feedback control system, which was impossible only by using a conventional sensor, is not required. A vibration control system can be constructed, and vibration control can be reliably performed.

[Brief description of the drawings]

FIG. 1 is a perspective view of a cantilever structure showing one embodiment of the present invention.

FIG. 2 is a top view of the cantilever structure shown in FIG.

FIG. 3 is a perspective view of a fixed-end beam structure showing one embodiment of the present invention.

FIG. 4 is a perspective view relating to a beam structure supporting both ends simply showing one embodiment of the present invention.

[Description of Signs] 1 Beam (structure) 2 2-mode optical fiber 3 Fixed portion 4 He-Ne laser light source 5 Convex lens 6 Single mode fiber 7 Splice device (connecting device) 8 Photodetector 9 High-pass filter 10 Amplifier 11 Support portion

[Table 1]

[Table 2]

Claims (2)

[Claims] In a beam structure, an optical fiber is attached in a straight line parallel to the longitudinal direction of the beam to extract only a vibration mode vibration signal of a target structure with one optical fiber. Optical fiber vibration mode sensor. 2. In the beam structure, the second derivative of the position of the vibration mode function for the optical fiber takes a positive value on the surface of the beam, and in the case of a negative value, the second derivative value. The optical fiber vibration mode sensor according to claim 1, wherein the optical fiber vibration mode sensor is attached to the back surface.