JP2002538426A - Bragg grating device for measuring mechanical forces, use of the Bragg grating device, and method of driving the Bragg grating device - Google Patents

Abstract

(57) [Summary] A Bragg grating device for measuring mechanical force (K, K ') is composed of an optical fiber (1), an optical Bragg grating (11) formed in the fiber, and a force transmitting device (2). It is provided and converts the force to be measured into the elongation force of the fiber (1) and / or the contraction force (K1, K1 ') of the fiber. A high measurement sensitivity is obtained by the force transmission device (2), and a high-sensitivity measurement sensor for measuring other physical quantities, such as voltage, temperature, acceleration, and vibration, is achieved.

Description

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a Bragg grating device for measuring mechanical forces, a method for driving a Bragg grating device, and a method for using the Bragg grating device.

A Bragg grating device for measuring mechanical forces is described in German Patent Application No. 1964.
It is known from the specification of GB 8403. The device comprises: a) at least one optical fiber for guiding the light beam in the direction of propagation; b) a unique Bragg wavelength for each grating that varies in the direction of propagation depending on the elongation and / or contraction of the fiber. An optical Bragg grating integrated in the fiber, and c) attached to the fiber at two fixed points spaced apart from each other in the direction of propagation and including the grating and extending in the direction of propagation. And an extended body.

[0003] Such devices have been used to detect pressure and / or pulling forces oriented in the direction of propagation that coincides with the longitudinal direction of the fiber, where the extension is the pressure and / or pulling to be measured. It does not function as an "amplifier" for force.

[0004] Fibers containing Bragg gratings are biased in the direction of propagation by, for example, elastic springs.

[0005] An embodiment of such an apparatus is a temperature compensated embodiment, further comprising an unloaded reference fiber with an integrated reference Bragg grating. As a result, a temperature effect that causes a shift in the Bragg wavelength can be detected, and can be removed by appropriate evaluation.

[0006] US Pat. No. 5,682,445 discloses: a) at least one optical fiber for guiding a light beam in the direction of propagation; b) changes in the direction of propagation depending on the state of extension and / or contraction of the fiber. An optical Bragg grating with a unique Bragg wavelength for each grating to be integrated into the fiber, and c) attached to the fiber at two fixed points spaced apart from each other in the direction of propagation including the grating. A Bragg grating device having a leverless transmission without a rotating shaft is described.

[0007] Leverless transmissions without a rotating shaft are used to bias the fibers and gratings between fixed points in the direction of propagation.

[0008] A leverless transmission without an axis of rotation has at least two sections that extend in the direction of propagation, each of which has an end face, which are interconnected. . Each of the two sections has an opposite end face at one end. The other end face of the section is fixedly connected to the fiber at one fixing point and the other end of the other section is fixedly connected to the fiber at another fixing point.

[0009] Stress in the fiber acting in the propagation direction is caused by the two section lengths measured between the end faces in the propagation direction varying relative to each other.

It is an object of the present invention to provide a Bragg grating device for measuring mechanical forces, which has broader applications than conventional Bragg grating devices of this kind.

This problem is solved by the features of claim 1.

According to a solution of the invention, a Bragg grating device for measuring mechanical forces according to the invention comprises: a) at least one light guide which is made of an elastic material and guides a light beam in the direction of propagation; At least one optical Bragg grating having a Bragg wavelength that varies in the direction of propagation of the beam depending on the state of extension and / or contraction of the beam; and c) determining the force to be measured in the direction of propagation of the conductor. A force transmitting device that converts the stretching force and / or the contracting force into the force to be measured (or converts the stretching force and / or the contracting force in the propagation direction of the conductor into the force to be measured).

A wide field of application is obtained, in particular, because the conversion ratio between the force to be measured and the converted force of the force transmitting device is different from 1.

Various transmissions, for example, a gear mechanism are basically suitable as the force transmission device. In an advantageous embodiment of the device according to the invention, the force transmitting device has at least one lever which is rotatable about an axis of rotation substantially fixed with respect to the conductor and which is fixed to the conductor. And is subject to the forces to be measured. This embodiment is particularly simple to implement structurally.

The conversion ratio of the force transmitting device is, in this case, the distance from the point of application of the force to be measured to the lever to the axis of rotation of the lever and the distance from the axis of rotation to the point of attachment of the lever to the conductor. It is adjusted by selecting and. That is, the conversion ratio is determined by the ratio between the former distance and the latter distance.

The force transmitting device has a lever, and the distance from the fixed rotation axis to the attachment point where the lever is attached to the conductor is greater than the distance from the rotation axis to the point of application of the force to be measured to the lever. Is also large, in particular, the displacement caused by the force to be measured increases.
When the force transmitting device has a lever, and the distance from the rotation axis to the mounting point where the lever is attached to the conductor is smaller than the distance from the rotation axis to the point of application of the force to be measured to the lever, Amplification of the force takes place.

In this embodiment, the case in which the rotation axis is located between the conductor and the point of application of the force to be measured on the lever, and / or the point of application of the force to be measured on the lever is between the conductor and the rotation axis. Lever is used in cases where the conductor is located between the axis of rotation and / or where the conductor to be measured is applied to the lever.

In an advantageous embodiment of the invention, the conductor is fixed at a substantially fixed point with respect to the axis of rotation of the lever, which is a distance from the lever-fixed point of the conductor containing the grating in the direction of beam propagation. It is arranged in.

In this embodiment, a support is preferably provided, on which a lever is rotatably locked about an axis of rotation, and the conductor is mounted at a fixed point. The support is preferably of unitary construction, for example, consisting of only one material. As a result, this embodiment can advantageously be manufactured structurally simply and at low cost and avoid complex and expensive support structures with a large number of components.

Preferably, the conductor is stressed in the direction of propagation. This allows the Bragg grating to expand and / or contract in the region defined by the stress.

As the light guide, a transparent elastic material for guiding the light beam in the propagation direction is basically used. Preferably, the conductor comprises an optical fiber in which the Bragg grating is formed.

In a further advantageous embodiment of the device according to the invention, a force generating device is provided which generates a mechanical force which is converted for the measurement by means of a force transmitting device, which device is preferably provided at that location. The force to be measured is generated, for example, randomly or in a controlled manner.

In an advantageous configuration of this embodiment, the force-forming device has a transducer device for converting a physical quantity different from the mechanical force into the force to be measured. Physical quantities are, for example, temperature, electric and / or magnetic field strength, acceleration, vibration, etc., depending on the transducer device.

If the physical quantity is, for example, electric field strength or voltage, the transducer device has a body made of piezoelectric material, which expands and / or contracts depending on the electric field strength or voltage. Here, this property is used to form the force to be measured.

If the physical quantity is, for example, acceleration and / or deceleration, in particular vibrational acceleration, the transducer device has a movable mass with acceleration and / or deceleration. Here, the inertial properties of the mass are used to generate the force to be measured.

Another embodiment of the device according to the invention has the advantage of being able to measure mechanical forces that depend on physical quantities different from, for example, mechanical forces, as well as other sensor devices that measure the physical quantities themselves, such as temperature sensors , Voltage sensor, acceleration sensor or vibration sensor.

The device according to the invention is generally such that a light beam is guided in a conductor to a Bragg grating formed in the conductor, whereby the Bragg wavelength generated on the basis of the light beam guidance is a measure of the force to be measured. It is measured as a quantity.

To compensate for effects due to temperature, a reference light guide without stretching and contracting forces can be provided. This reference conductor has a reference Bragg grating,
Through this reference Bragg grating, temperature effects that cause a shift in the Bragg wavelength are detected and, after appropriate evaluation, are eliminated. The reference conductor and the conductor used for measuring the force are advantageously homogeneous. The same is true for the reference Bragg grating and the Bragg grating used for measuring the force.

The present invention will be described in detail below with reference to the illustrated embodiments. FIG. 1 shows an embodiment of the displacement increasing device according to the present invention. FIG. 2 shows an embodiment of the embodiment of FIG. FIG. 3 shows an embodiment of the force amplifying device of the present invention. FIG. 4 shows an implementation of the embodiment of FIG.

The figures are schematic and not to scale.

In the illustrated embodiment, reference numeral 1 denotes a light guide (eg, a glass fiber light guide), for example, consisting of an optical fiber. The fiber 1 guides the incoming coupled light beam P in the direction of propagation. This propagation direction coincides with the longitudinal direction 10 of the fiber 1 parallel to the drawing plane.

An optical Bragg grating 11 having a Bragg wavelength λ 1 unique to the grating is formed in the fiber 1. The Bragg wavelength depends on the elongation state in the propagation direction of the fiber 1 and / or
Or it changes depending on the contracted state.

The general force transmission device, designated by the reference numeral 2, converts the force to be measured into a force acting on the fiber 1 in the longitudinal direction 10. This force causes the fiber 1 to move in the longitudinal direction 1
It is elongated and / or contracted at zero.

The force transmitting device 2 has a lever 20, which is rotatable on the one hand about a rotation axis 21 which is substantially fixed with respect to the fiber 1, and which is attached to the fiber 1 on the other hand. A force to be measured acts on the lever.

In the drawing, the rotation axis 21 is oriented in a direction perpendicular to the drawing plane, and the lever 20 is rotated in a direction horizontal to the drawing plane.

The lever 20 is attached to the fiber 1 at an attachment point 22. The fiber 1 itself is fixed at a fixed point 32 with respect to the rotation axis 21 of the lever 20, which is at a distance a measured in the longitudinal direction 10 from the mounting point 22 of the lever 20.
Attached to. The distance a includes the grid 11.

When the force K to be measured at the point of action 23 coincident with the rotation axis 21 is applied to the lever 20, a force K 1 is generated at the attachment point 22 from the fixed point 32 to the attachment point 22, and this force is applied to the fiber 1 and The grid 11 is elastically extended in the longitudinal direction 10.

When the force K ′ is attenuated, the elongation of the fiber 1 and the grating 11 decreases, and with a sufficiently small force K, the fiber 1 and the grating 11 reach the original unstretched state again.

In order to be able to measure the force K ′ caused by the rotation of the lever 20 in the clockwise direction c about the rotation axis 21, the fiber 1 is attached to the fiber 1 from the fixed point 32 in the longitudinal direction 10 to the attachment point 22. A predetermined stress B is biased, which counteracts the force K1 'generated at the mounting point 22 by the force K'. Such a force K '
Can be measured when K1 ′ ≦ B.

The point of action 23 of the force to be measured does not limit the generality, but for simplicity in all figures, the point of attachment 22 where the lever 20 is attached to the fiber 1
It is assumed that they are arranged on a lever axis 200 connecting the and the rotation shaft 21 to each other.
The lever axis extends horizontally with respect to the drawing plane and crosses the rotation axis 21 vertically.

In the embodiment of FIG. 1, the distance d 1 from the rotating shaft 21 to the attachment point 22 where the lever 20 is attached to the fiber 11 is determined by the force K, K ′ to be measured from the fixed rotating shaft 11 to the lever 20. It is larger than the distance d2 to the action point 23.

This embodiment is suitable for the case where the expansion and / or contraction transmitted from the fiber 1 on the grating 11 is small, and the shift occurring in the Bragg wavelength λ 1 inherent to the grating is measured.

Extension and / or contraction is obtained at the attachment point 22 via the lever 20. This extension and / or contraction is greater than the extension and / or contraction without the lever 20 by a factor k = d1 / d2> 1.

FIG. 2 shows a special implementation of the embodiment of FIG. In this implementation, a support 3 is provided, at which point a lever 20 is rotatably locked about a fixed rotation axis 21, and the fiber 1 is fixed at a fixed point 32. I have.

The fiber 1 is fixed to the support 3 at another fixing point 34, and the mounting point 22 of the lever 20 and the grating 11 are arranged between the fixing point 32 and the other fixing point 34.

A stress B is applied to the fiber 1 between two fixed points 32 and 34.

The support 3 is integrally formed, for example, of quartz glass or other glass. This support preferably has a hollow space 30.

The hollow space 30 is, for example, a notch formed in a surface member of the support 3. FIG. 2 shows such a surface element in plan view and is designated by the reference numeral 31. The hollow space 30 is the surface member 3 defined by the inner edge 301 of the surface member 31.
1 are formed, and extend from the surface member 31 in the depth direction perpendicular to the plane of FIG.

The fiber 1 is laid over the opening 310 of the hollow space 30. The fiber is fixed at fixing points 32 and 34 on both sides of the opening 310.

For example, the lever 20 is accommodated in the hollow space 30. The lever 20 mainly extends horizontally with respect to the drawing plane of FIG. 2 and holds the fiber 1. The lever is attached to fiber 1 at attachment point 22.

The lever axis 200 advantageously extends mainly perpendicular to the longitudinal axis 10 of FIG. 1, as shown in FIG. 2, but is arranged obliquely with respect to the longitudinal direction. Is also good.

The rotation shaft 21 of the lever 20 is a rotation joint 320 for locking the lever 20 to the support 3.
The lever 20 may be a rotating shaft 2 fixed relatively to the support 3.
1 can be rotated.

For example, the lever 20 is locked to the support 3 via the rotary joint 320,
This rotary joint is arranged between the support 3 and the lever 20 and interconnects the two.

A rotary joint 320 of this kind is realized, for example, by a deformable connecting member between the lever 20 and the support 3.

In the embodiment of FIG. 2, such a deformable connecting member 320 is arranged between the edge of the opening 310 and the end 201 of the lever 20 opposite the edge 301. . The connecting member 320 has, for example, a flexible connecting member 321 which is rigid in a direction perpendicular to the drawing plane of FIG. Flexible in the vertical direction.

The connecting member 320 defines the rotation shaft 21, which is not completely fixed to the support 3 and thus the fiber 1, but is supported within a predetermined tolerance. . This means that the rotating shaft 21 is almost fixed.

In FIG. 2, the point of action 23 of the forces K, K ′ to be measured is the rotation axis 21 and the attachment point 22.
This is different from FIG. 1 in which the rotation shaft 21 is disposed between the action point 23 and the attachment point 22.

The forces K, K ′ to be measured are formed in the implementation of FIG. 2 by, for example, a piezoelectric actuator 4 or a body made of another piezoelectric material. This actuator is fixedly connected to the support 3 and the lever 20 and expands and / or contracts along the actuator axis 400 depending on the applied voltage U. This actuator axis 400 is horizontal with respect to the drawing plane of FIG.
Intersect vertically or diagonally. As a result, the piezoelectric actuator 4 that expands and / or contracts exerts forces K and K ′ to be measured on the lever 20. This force is directed to the point of action 23 and is considered to be acting thereon.

The piezoelectric actuator 4, which is fixedly connected to the support 3 and the lever 20, forms a force-forming device, which is converted by the force transmitting device 2 into the mechanical forces K, K to be measured. 'Fire. The piezoelectric actuator 4 itself forms a transducer device, which converts a physical quantity different from the mechanical force K, K 'into the force K, K' to be measured. In this case, the voltage U is converted into forces K, K '.

The forces generated by the piezoelectric actuator 4 or other bodies made of piezoelectric material are extremely high, but the degree of extension and / or contraction of such bodies is very small. The embodiments of FIGS. 1 and 2 are very well suited for amplifying the expansion and / or contraction for this ratio, in which case the resolution of the Bragg wavelength λ1 and thus the measuring sensitivity can be greatly increased. . This corresponds to the case where this embodiment is used as a voltage sensor.

If, instead of a piezoelectric actuator, a body made of a material that expands and / or contracts depending on, for example, temperature or magnetic field strength is used to generate the force to be measured, the implementation of FIGS. By way of example, a temperature sensor or a magnetic sensor with a respectively high measuring sensitivity can be realized.

In the embodiment shown in FIG. 3, unlike the embodiment shown in FIGS. 1 and 2, the distance d 1 from the rotation shaft 21 to the attachment point 22 where the lever 20 is attached to the conductor 1 is different from the rotation shaft 21. Is smaller than the distance d2 from the point of force K, K 'to the lever 20 to the point of action 23 to be measured.

In this embodiment, the stretching and / or contraction transmitted from the fiber 1 to the grating 11 is small due to the very small forces K 1, K 1 ′ that cause the stretching and / or contraction, and therefore the grating-specific Bragg This corresponds to the case where the shift occurring in the wavelength λ1 cannot be measured.

In this embodiment, forces K 1 and K 1 ′ are obtained at the mounting point 22 via the lever 20. This force is 1 / k less than the forces K and K 'to be measured at the lever action point 23.
= D2 / d1> 1.

FIG. 4 shows a special implementation of the embodiment of FIG. This embodiment differs from the embodiment of FIG. 2 only in the second lever ratio and in the way in which the forces K and K 'to be measured are formed. Otherwise, the implementation of FIG. 4 is identical to that of the embodiment of FIG. 2, and the corresponding parts have the same reference numbers.

In the embodiment of FIG. 4, for example, unlike the embodiment of FIGS. 1 and 2 or the embodiment of FIG. 3, the mounting point 22 of the lever 20 is connected to the rotation axis 21 of the lever 20 and the force K to be measured. K
'And the action point 23 of the'.

The forces K, K ′ to be measured are in this case, for example, inertial forces, which represent the inertial mass M acting on the lever 20 when the lever 20 accelerates. The point of action 23 of the forces K, K 'corresponds in this case to the center of gravity of the mass M.

In this case, the lever 20 and its mass M that are rotatably locked to the support 3 about the rotation axis 21 are the mechanical forces K and K ′ to be measured, which are converted by the force transmitting device 2. Is formed as a force forming device. The rotary shaft 21 and the lever 20 itself having the mass M apply a physical quantity different from the mechanical forces K and K ′ to the force K to be measured.
, K ′.

When the acceleration is small, even if the mass M is large, only a very small inertial force is generated, and the Bragg grating 11 does not extend at all in the longitudinal direction 10 or only slightly. However, according to the implementation of FIG. 4, such small inertial forces K, K ′ are
1 can be converted into the forces K1 and K1 'that are large enough to utilize the force K1. This is because a sufficient displacement can be obtained here.

According to the embodiments shown in FIGS. 3 and 4, it is possible to realize an acceleration sensor and / or a vibration sensor each having a large measurement sensitivity.

The devices shown are generally such that the light beam P is coupled into the fiber 1 and guided in the fiber 1 to the Bragg grating 11, and the Bragg wavelength λ 1 reflected by the Bragg grating 11 is measured. Is driven. The measured wavelength λ1 or the wavelength shift is a measure of the force or physical quantity to be measured.

FIG. 2 shows a reference fiber 5, which has a reference Bragg grating 51 for compensating for temperature-induced effects. The reference fiber 5 is arranged in parallel with the fiber 1 and bridges the hollow space 30 and the lever 20 without applying stress. The reference fiber is fixed to the support 3 at points 52 and 54 on the surface member 31 so that mechanical stress that can be measured by elongation of the support 3 due to temperature is not generated in the reference fiber 5. Reference fiber 5 and fiber 1 may be considered the same fiber. Similarly, the reference Bragg grating 51 is the Bragg grating 11
Is configured to be equal to

[Brief description of the drawings]

FIG. 1 is a view showing an embodiment of a displacement increasing device of the present invention.

FIG. 2 is a diagram showing an embodiment of the embodiment of FIG. 1;

FIG. 3 is a diagram showing an embodiment of the force amplifying device of the present invention.

FIG. 4 is a diagram showing an embodiment of the embodiment of FIG. 3;

Claims (15)

[Claims] At least one light guide (1), made of an elastic material, for guiding a light beam (P) in a propagation direction (10), and formed in said light guide (1), said conductor (1) An optical Bragg grating (11) having a Bragg wavelength (λ1) that varies in the propagation direction depending on the extension and / or contraction of
And a force transmitting device (2) for converting the force (K, K ') to be measured into an extension force and / or a contraction force (K1, K1') in the propagation direction (10) of the light guide (1). A Bragg grating device for measuring mechanical force (K, K ′), comprising: 2. The force transmitting device (2) has at least one lever (20) which is rotatable about an axis of rotation (21) substantially fixed with respect to the conductor (1). And the force (K, K ′) to be measured is fixed to the conductor (1) and applied to the lever.
3. The device according to claim 1 or 2, wherein 3. The force transmitting device (2) has a lever (20) and has a rotating shaft (2).
The distance (d1) from 1) to the attachment point (22) where the lever (20) is attached to the conductor (1) is determined by the force (K, K ′) to be measured from the rotation axis (21).
3.) The device as claimed in claim 2, wherein the distance (d2) to the point of action (23) is greater than the distance (d2). 4. The force transmitting device (2) has a lever (20) and has a rotating shaft (2).
The distance (d1) from 1) to the attachment point (22) where the lever (20) is attached to the conductor (1) is determined by the force (K, K ′) to be measured from the rotation axis (21).
4.) The device according to claim 2, wherein the distance (d2) to the point of action (23) is smaller than the distance (d2). 5. The conductor (1) is fixed at a substantially fixed point (32) with respect to the axis of rotation (21) of the lever (20), said point being in the direction of propagation (10).
5 is arranged at a predetermined distance (a) from an attachment point attached to the lever, and includes a grid (11) within the distance.
Item. 6. A support (3), on which a lever (20) is rotatably locked about a rotation axis (21), on which the conductor (1) is fixed. (
Apparatus according to claim 5, fixed at 32). 7. The device according to claim 6, wherein the support is formed in one piece. 8. Apparatus according to claim 1, wherein the conductor has a stress in the direction of propagation. 9. Apparatus according to claim 1, wherein the conductor comprises an optical fiber. 10. A force generating device (3, 20, 4; 3, 20, 21, M) for generating a mechanical force that is converted for measurement by a force transmitting device (2).
Apparatus according to any one of claims 1 to 9. 11. The force forming device (3, 20, 4; 3, 20, 21, M) includes a force (K, K ′) for measuring a physical quantity (U) different from a mechanical force (K, K ′). 11. The device according to claim 10, comprising a converter device (4; 20, 21, M) for converting to (1). 12. The device according to claim 11, wherein the transducer device has a body made of piezoelectric material. 13. The device according to claim 11, wherein the converter device (20, 21, M) has a movable mass (M). 14. Use of a Bragg grating device according to claim 10 for measuring a physical quantity (U). 15. Guideing a light beam (P) in a conductor (1) to a Bragg grating (11) formed in said conductor (1); Measuring the Bragg wavelength (λ1) generated on the basis of the guidance as a measure of the force to be measured (K, K ′). A method for driving a Bragg grating device according to claim 1.