KR20010108257A - Bragg grating device for measuring a mechanical force, utilization of said device and method for operating the same - Google Patents

Abstract

The present invention relates to a Bragg grating device for measuring mechanical forces (K, K '), which includes an optical fiber (1) and an optical Bragg grating (11) formed in the optical fiber (1), the measured force And a force transmission device 2 for converting the fiber bar 1 into forces K1 and K1 'for stretching and / or contracting the fiber 1. The device provides high measurement sensitivity and provides sensors for measuring different physical parameters such as electrical tension, temperature, acceleration, vibration, and the like.

Description

BRAGG GRATING DEVICE FOR MEASURING A MECHANICAL FORCE, UTILIZATION OF SAID DEVICE AND METHOD FOR OPERATING THE SAME}

Bragg grating apparatus for measuring mechanical forces is disclosed in German Publication 196 48 403. The apparatus comprises one or more optical fibers for directing optical radiation in a propagation direction and grating-specific Bragg wavelengths integrated into the fibers and varying as a function of the stretching and contraction of the fibers in the direction of propagation. optical Bragg grating having a specific Bragg wavelength, and an elongated body fixed to the fiber at two anchor points, arranged at a distance from each other in the direction of propagation, each including a grating and extensible in the direction of propagation It includes.

These devices are oriented in the direction of propagation and are used to record the compressive and / or tensile forces that match the longitudinal direction of the fiber, and the elongated body does not act as an "amplifier" for the compression or tension to be measured.

Fibers comprising Bragg gratings may be prestressed in tension in the direction of propagation, for example by elastic springs.

One embodiment of the device is a temperature-compensating variant, which has an additional unloaded reference fiber with integrated reference brag grating, thereby at a Bragg wavelength The temperature effect causing the shift can be recorded and eliminated by appropriate assessment.

U. S. Patent No. 5,682, 445 shows a Bragg grating device, which includes one or more optical fibers for directing optical radiation in the direction of propagation, and grating-specific, integrated within the fiber and changing as a function of the stretching and contraction of the fibers in the direction of propagation. Optical Bragg grating with Bragg wavelength and a lever transmission without rotation axis and fixed to the fiber at two fixed points, arranged at a distance from each other in the direction of propagation, each of which includes a grating It includes.

The axis-free lever transmission is used for the purpose of transferring the stress in the direction of propagation to the grating between the fiber and the anchor point.

For this purpose, the axisless lever has two or more parts extending in the direction of propagation and each having one end, which ends are firmly connected to each other. Each of these two parts has the other end opposite the one end of the part. The other end of one part is firmly connected to the fiber at one of the two anchor points, and the other end of the other part is firmly connected to the fiber at the other anchor points.

The stress acting in the propagation direction on the fiber can be generated by the change in length and can be measured relative to each other between the ends in the propagation direction of the two parts.

The present invention relates to a bragg grating device for measuring mechanical force, and to the use and method of operation of the device.

1 shows amplified deflections in an exemplary embodiment of the device according to the invention,

2 illustrates an implementation of the embodiment of FIG. 1,

3 shows amplified forces in an exemplary embodiment of the device according to the invention,

4 illustrates an implementation of the embodiment of FIG. 3.

The present invention is based on the object of providing a Bragg grating device for measuring mechanical force, and makes it possible to have a wide range of applications in comparison with known Bragg grating devices of this type.

This object is achieved by the features of claim 1.

According to this solution, the Bragg grating device for measuring the mechanical force according to the present invention comprises at least one optical conductor made of an elastic material for guiding optical radiation in the direction of propagation, One or more optical Bragg gratings with varying Bragg wavelengths as a function of the elongation and / or contraction of the conductor in the direction of propagation, and a force that converts the measured force into a force that causes the conductor to elongate and / or contract in the direction of propagation And a delivery device.

In particular, a wide range of applications can be obtained by a force transmission device having one and another transmission ratio between the measured force and the converted force.

In principle, any type of mechanism, for example a gear mechanism, is suitable as the force transmission device. A preferred and characteristic improvement of the device according to the invention is a force transmission having one or more levers which can be rotated about a rotation axis substantially fixed relative to the conductor and which act on the conductor and which is to be measured thereon. It is configured in the same way as the device. Such an improved device can be implemented particularly simply during construction.

In this case, the transmission ratio of the force transmission device is set by selecting a given distance between the operating point of the force to be measured on the lever and the rotational axis of the lever, and selecting the given distance between the rotational axis and the fixed point of the lever on the conductor. And may be given by the ratio of the second mentioned distance to the first mentioned distance.

In particular, if the force transmission device has a lever in which the distance between the fixed axis of rotation and the point of attachment of the lever on the conductor is greater than the distance between the axis of rotation and the point of action of the force to be measured on the lever, the force is measured An increase in deflection is provided, and the increase in force is achieved when the force transmission device has a lever whose distance between the rotation axis and the point of attachment of the lever on the conductor is smaller than the distance between the rotation axis and the point of action of the force being measured on the lever. Is provided.

The improved device may have a lever whose axis of rotation is located between the conductor and the point of action of the force being measured on the lever and / or a lever at which the point of action of the force being measured on the lever is located between the conductor and the axis of rotation, and And / or the conductor may have a lever positioned between the axis of rotation and the point of action of the force being measured on the lever.

In a preferred embodiment of the improved device, the conductor is fixed at a point substantially fixed relative to the axis of rotation of the lever and aligned at a distance from the point of attachment of the lever on the conductor including the grating, in the direction of radiation transmission. .

This embodiment preferably has a carrier body to which the lever is attached so that the lever can rotate about an axis of rotation, and the conductor is fixed at a fixed point. The carrier body may preferably be formed in one piece, in particular composed of a single material. As a result, the embodiment can preferably be produced simply at an efficient unit cost within the construction period and can be produced avoiding a complicated and expensive carrier structure made of a large number of parts.

The conductor is preferably prestressed in the direction of propagation. This allows for both stretching and contraction of Bragg grating within the range determined by prestress.

The optical conductor used can in principle be any body made of a transparent elastic material which guides optical radiation in the direction of propagation. The conductor preferably has an optical fiber, and Bragg grating is formed therein.

A preferred refinement of the device according to the invention has a force generating device for generating a mechanical force that is measured and converted by a force transmission device, in particular in such a way that the force to be measured is generated at a certain position, for example It can be designed in such a way as to be controlled according to the bar.

In a preferred and characteristic improved device of this refinement, the force generating device has a converter device for converting a physical variable into a mechanical force which is different from the mechanical force to be measured, preferably the physical variable may be different from the mechanical force. Depending on the converter device, it may be, for example, temperature, electric field strength and / or magnetic field strength, acceleration, vibration, and the like.

If the physical variable is, for example, electric field strength or voltage, the converter device may have a body made of piezoelectric material, which stretches and / or contracts as a function of the electric field strength or voltage, This behavior is used to generate the force to be measured.

If the physical variable is, for example, acceleration and / or deceleration, in particular if it is a vibration, the converter device may have a moveable mass, the acceleration and / or deceleration acting there, and the mass The inertial behavior of is used to generate the force to be measured.

The refinement of the device according to the invention not only has the advantage of measuring the mechanical force, which depends in particular on the physical variables other than the mechanical force, but also itself to measure the physical parameters such as, for example, temperature, electrical voltage, acceleration or vibration sensors. Has the additional advantage of being able to be used as a sensor device.

The apparatus according to the invention is generally operated in a manner in which optical radiation is guided to Bragg grating formed in the conductor, and the Bragg wavelength generated by Bragg grating due to the supplied optical radiation is the magnitude of the force to be measured. It is measured as

To compensate for temperature-induced effects, there may be an optical regference conductor without stretching and contracting forces, in which a reference bragg grating is formed, thereby forming a Bragg wavelength. The temperature effect causing the change can be recorded and eliminated by appropriate evaluation. The reference conductor and the conductor used for the measurement of the force are preferably of the same type. The same is true for the base Bragg grating and the Bragg grating used to measure the force.

The present invention will be explained in more detail through the following illustrative embodiments with reference to the drawings.

The drawings are schematically depicted and are not to scale.

In the embodiment shown in the figures, the optical conductor, indicated by reference numeral 1, consists of an optical fiber, for example a glass fiber optical waveguide, for example. The fiber 1 directs the combined optical radiation P in the direction of propagation coinciding with the longitudinal direction 10 of the fiber parallel to the plane of the drawing.

Within the fiber bar 1 optical Bragg grating 11 having a grating-specific Bragg wavelength λ 1 which varies as a function of the stretching and / or contraction of the fiber 1 in its longitudinal direction 10 in the longitudinal direction 10. ) Is formed.

The force transmission device indicated by reference numeral 2 converts the force to be measured into a force acting in the longitudinal direction 10 of the fiber bar 1, and stretches and / or contracts the fiber bar 1 in the longitudinal direction 10.

The force transmission device 2 has a lever 20, which, firstly, can be rotated around an axis of rotation 21 substantially fixed relative to the fiberbar 1, and secondly, secured to the fiberbar 1 and The force to be measured acts on it.

In the figure, since the axis of rotation 21 is aligned in a direction perpendicular to the plane of the figure, the lever 20 rotates in a direction parallel to the plane of the figure.

The lever 20 is fixed to the fiber 1 at the fixation point 22. The fiber 1 itself is fixed at a point 32 fixed relative to the axis of rotation 21 of the lever 20, which point 32 is a fixed point of the lever 20 on the fiber 1. 22 is located at a distance a, measured in the longitudinal direction 10. The grating 11 is included in said constant distance a.

If the force K to be measured presses the lever 20 at the operating point 23 which does not coincide with the rotational axis 21, and also pushes the lever 20 in the counterclockwise direction C with respect to the rotational axis 21. As a result of the rotation, a force K1 that is directed from the fixed vertex 32 to the attachment point 22 is generated at the attachment point 22 to extend the fiber 1 and grating 11 in the longitudinal direction 10. Elastically stretches.

When the force K is reduced, the extension of the fiber bar 1 and the grating 11 is reduced, until the fiber bar 1 and the grating 11 are originally stretched until they finally have a sufficiently small force K. Is reached again.

In order to be able to measure the force K 'which results in rotating the lever 20 clockwise C around the axis of rotation 21, the fiber bar 1 is attached from the fixed point 32 to the attachment point. It is prestressed in the longitudinal direction 10 by a specific prestressing force B towards (22), which cancels the force K1 'generated at the attachment point 22 by this force K'. . This force K 'can be measured while K1≤B.

In all figures, in order not to limit the simplicity and generality, the operating point 23 of the force to be measured is a lever connecting the attachment point 22 of the lever 20 on the fiber 1 and the rotational axis 21 to each other. It is considered to be aligned on axis 200 and lies parallel to the plane of each figure and intersects at right angles with axis of rotation 21.

In the embodiment of FIG. 1, the operating point of the force K or K 'measured at the lever 20 and the rotation axis 21 at which the distance d1 between the rotation axis 21 and the attachment point 22 is fixed. 23) is greater than the distance d2 between.

This embodiment is suitable when the stretching and / or contraction transmitted by the fiber 1 to the grating 11 is too small to measure the change affected as a result of the grating-specific Bragg wavelength λ 1.

By lever 20, elongation and / or deflation is obtained at attachment point 22 larger than elongation and / or deflation without lever 20 by a factor of k = d1 / d2 >

FIG. 2 illustrates a particular implementation of the embodiment of FIG. 1. In this implementation a carrier body 3 is provided, with a lever 20 which is rotatable about the axis of rotation 21 attached, and the fiber bar 1 is fixed at a fixed point 32.

The fiber 1 is also fixed at the other fixing point 34 on the carrier body 3, so that the attachment point 22 and the grating 11 of the lever 20 have one fixing point 32 and another fixing point 34. ).

The fiber 1 is prestressed with a prestress B between two anchor points 32, 34.

The carrier body 34 is formed integrally and consists of, for example, quartz glass or other glass. Desirably, it has a cavity 30.

The cavity 30 is, for example, a recess formed in the surface portion of the carrier body 3. In FIG. 2, this surface portion appears to be planar and is indicated at 31. The cavity 30 forms an opening 310 in the surface portion 31, bounded by an inner rim 301 of the surface portion 31, and downward from the surface portion 31 with respect to the drawing plane of FIG. 2. Extend vertically

The opening 310 of the cavity 30 is covered by a fiber 1 which is fixed to, for example, a flat surface 31 at fixed points 32, 34 on both sides of the opening 310.

The lever 20 is received in the cavity 30. The lever 20 extends substantially parallel to the drawing plane of FIG. 2 and extends below the fiber bar 1 and is secured to the fiber bar 1 at the attachment point 22.

The lever axis 200 preferably extends substantially perpendicular to the longitudinal axis 10 of the fiber 1, as shown in FIG. 2, but may be aligned at an angle with respect to the longitudinal axis.

The rotation axis 21 of the lever 20 may be the rotation axis of the rotary joint 320, the rotary joint 30 having the lever 20 to the carrier body 3, and the lever 20 to the rotation axis ( 21) so as to be able to rotate relative to the carrier body 3 around.

For example, the lever 20 is attached to the carrier body 3 by the rotary joint 320, the rotary joint 320 is aligned between the carrier body 3 and the lever 20 to connect the two together. .

A rotary joint 320 of this type can be implemented, for example, by a deformable connection between the lever 20 and the carrier body 3.

In the embodiment of FIG. 2, this deformable connection 320 is aligned between the rim 301 of the opening 310 and the end 201 of the lever 30 facing this rim 301. The connection part 320 is embodied by a flexible connecting tab 321, for example rigid in a direction perpendicular to the drawing plane of FIG. 2 and flexible in a direction parallel to the plane of the drawing perpendicular to the lever axis 200. do.

The axis of rotation 21 thus formed by the connection part 320 is not exactly fixed with respect to the carrier body 3 and the fiber 1, but is displaced within some acceptable limits. Displaced within some acceptable limits means that the axis of rotation 21 is substantially fixed.

In FIG. 2, the force being measured is different from FIG. 1 in which the operating point 23 of the force K or K 'to be measured is aligned with the rotation axis 21 between the operating point 23 and the attachment point 22. An operating point 23 of K or K 'is positioned between the rotational axis 21 and the attachment point 22.

In the implementation of FIG. 2, the force K or K ′ to be measured is firmly connected to the carrier body 3 and the lever 20, for example, and parallel to the plane of FIG. 2 along the actuator axis 400. Generated in accordance with the electrical voltage U applied by the piezoelectric actuator 4, which is stretched and / or retracted, and other elements made of piezoelectric material, perpendicular to the lever axis 200 or at an angle at the operating point 23 To cross. As a result, the piezoelectric actuator 4 which is stretched and / or retracted may act as a function point 23 by acting the force K or K 'to be measured as the operating point 23.

The piezoelectric actuator 4 which is firmly fixed to the carrier 3 and the lever 20 forms a force generating device which generates the mechanical force K or K 'to be measured and is converted by the force transmission device. The piezoelectric actuator 4 is a converter device for converting a physical variable other than the mechanical force K or K 'from which it is measured, here converting an electrical voltage U into a force K or K'. To form.

The force generated by the piezoelectric actuator 4 or an element made of piezoelectric material is very large, while the elongation and / or contraction of such an element is very small. 1 and 2 are well suited to enlarge and explain the relationship between extension and / or contraction, and at the same time lead to a significant increase in the analysis of Bragg wavelength [lambda] 1 and the sensitivity measured thereby. The measured sensitivity also applies for use in this example as an electrical voltage sensor.

If, instead of a piezoelectric actuator for generating a force to be measured, an element made of a material which stretches and / or contracts as a function, for example, temperature or magnetic field strength, this means that the temperature or magnetic field sensor By using the embodiment of Fig. 2 it is possible to achieve high sensitivity in each case.

In the embodiment of FIG. 3, unlike FIG. 1 and FIG. 2, the distance d 1 between the rotation axis 21 and the attachment point 22 of the lever 20 on the conductor 1 is equal to the rotation axis 21 and the lever ( 20 is smaller than the distance d2 between the operating points 23 of the force K or K 'to be accumulated on.

This embodiment is suitable when the stretching and / or contraction transmitted by the fiber 1 to the grating 11 is too small to measure the change affected by the grating-specific Bragg wavelength λ 1, which is the stretching and This is because the force (K or K ') that causes contraction is very small.

In the case of this embodiment, in the lever 20, the forces K1 and K1 'at the attachment point 22 are the forces K or K' measured by the coefficient 1 / k = d2 / d1> 1. It is obtained more at the operating point 23 on the lever.

4 illustrates a particular implementation of the embodiment of FIG. 3. Apart from the different lever relationships, this implementation only differs in generating the force K or K 'to be measured in the implementation of the embodiment of FIG. Otherwise, the implementation of FIG. 4 is constructed in the same manner as the implementation of the embodiment of FIG. 2, with parts corresponding to each other being designated by the same reference numerals.

In the implementation of FIG. 4, according to an embodiment different from the embodiment of FIGS. 1 and 2 and 3, the attachment point 22 of the lever 20 is measured with the axis of rotation 21 of the lever 20. It is aligned between the operating points 23 of the forces K or K '.

In this case, for example, the force K or K 'measured by the inertial mass M inherent in the lever 20 during the acceleration movement of the lever 20 acts on the lever 20. It is inertial force. The operating point 23 of the force K or K 'coincides with the center of gravity of the mass M in this case.

In the case of this result, the lever 20 attached to the carrier body 3 can be rotated around the axis of rotation 21 and the mass M and measured mechanically converted by the force transmission device 2. It is possible to form a force generating device for generating a force K or K '. The lever 20 with the axis of rotation 21 and the mass M is itself used to convert the acceleration (K or K) here to convert a physical variable different from the mechanical force K or K 'on which it is measured. A converter device for converting to ') is formed.

Under a small acceleration, the mass M only generates small inertial forces, although large, it is not possible to extend Bragg grating 11 or only small in the longitudinal direction 10. By virtue of the implementation of FIG. 4, this type of small inertial force K or K 'can be converted into a large force K1 or K1' sufficient to extend to the grating 11, which is sufficient to obtain sufficient deformation. To be able.

3 and 4, acceleration and / or vibration sensors can be implemented with high measurement sensitivity in each case.

Each of the devices shown in the figures is operated in the usual way of connecting optical radiation P to fiber 1, in which fiber is guided to Bragg grating 11 and reflected by grating 11. The Bragg wavelength lambda 1 to be measured is measured. The measured wavelength [lambda] 1 or its change is the physical variable to which the force is measured or measured.

2 shows a reference fiber 5 with a reference Bragg grating 51 to compensate for the temperature-induced effect. The reference fiber 5 is aligned parallel to the fiber 1 and mediates the cavity 30 and the lever 20 without stress, and one point 52, 54 indicates that the extension of the temperature-induced carrier body 3 It is attached to the surface portion 31 on the carrier body 3 in a manner that does not generate any measurable mechanical stress in the reference fiber 5.

The reference fiber 5 and the fiber 1 are obtained from the same fiber. Similarly, the reference Bragg grating 51 and Bragg grating 11 are formed in the same way.

Claims (15)

Bragg grating device for measuring mechanical force (K, K '), One or more optical conductors 1 of elastic material, for guiding optical radiation P in the direction of propagation 10, One or more optical Bragg gratings 11 formed in the conductor 1 and having a Bragg wavelength λ 1 that varies as a function of the elongation and / or contraction of the conductor 1 in the propagation direction 10, and Apparatus comprising a force transmission device (2) for converting the forces (K, K ') to be measured into forces (K1, K1') which cause the conductor (1) to stretch and / or contract in the direction of propagation (10). . The force transmission device (2) according to claim 1 or 2, having at least one lever (20), The lever 20 can be rotated around a rotation axis 21 which is substantially fixed relative to the conductor 1, The lever 20 is attached to the conductor 1, and The force (K, K ') to be measured on the lever (20). 3. The force transmission device (2) according to claim 2, wherein the force transmission device (2) has a distance d1 between the rotation axis (21) and the attachment point (22) of the lever (20) on the conductor (1). 21) and a lever (20) greater than the distance (d2) between the operating points (23) of the forces (K, K ') being measured on the lever (20). 4. The force transmission device (2) according to claim 2 or 3, wherein the force transmission device (2) has a distance d1 between the rotational axis (21) and the attachment point (22) of the lever (20) on the conductor (1). And a lever (20) smaller than the distance (d2) between the axis of rotation (21) and the operating point (23) of the force (K, K ') being measured on the lever (20). The conductor (1) according to claim 2, wherein the conductor (1) is fixed at a point (23) substantially fixed relative to the axis of rotation (22) of the lever (20), and the grating (11) Arrangement at a distance (a) in the direction of propagation of radiation (10) from the point of attachment of the lever (20) on the conductor (1) comprising a. 6. The device according to claim 5, wherein the device has a carrier body (3) to which the lever (20) is attached so that the lever (20) can rotate around the axis of rotation (21), and the conductor (1) Device fixed at a fixed point (23). Device according to claim 6, wherein the carrier body (3) is formed in one piece. 8. Device according to one of the preceding claims, wherein the conductor (1) has a prestress (B) in the direction of propagation (10). Device according to one of the preceding claims, wherein the conductor (1) has an optical fiber. 10. The force generating device (3, 20) according to any one of claims 1 to 9, wherein the device is measured to generate mechanical forces (K, K ') which are measured and converted by the force transmission device (2). 4; 3,2,21, M). 11. The force generating device (3) according to claim 10, wherein the force generating devices (3,20,4; 3,2,21, M) have a physical variable (U) different from the mechanical force (K, K ') being measured. A device having a converter device (4; 20, 21, M) for converting to (K, K '). 12. The device according to claim 11, wherein the converter device (4) has a body made of piezoelectric material. 13. Device according to claim 11 or 12, wherein the converter device (20, 21, M) has a movable mass (M). Use of the device according to any one of claims 10 to 13 for measuring physical parameters. A method of operating an apparatus according to any one of claims 1 to 14, Directing optical radiation (P) in the conductor (1) to Bragg grating (11) formed in the conductor (1), and Measuring the Bragg wavelength (λ1) generated by the Bragg grating (11) due to the optical radiation (P) applied as an amount of force (K, K ') to be measured.