DD283219A5 - ARRANGEMENT FOR A MAGNETOSTRICTIVE-OPTICAL ACCELERATION GAUGE - Google Patents

Abstract

The invention relates to an accelerometer, which is using an interferometer able to measure very accurately accelerations and thus z. B. in the Traegheitsnavigation and in gradiometers can be used. The essential features of the accelerometer are the use of a vibratory spring-mass system which, due to its motion caused by an acceleration, alters the magnetic field of an electromagnet in which an element of magnetostrictive material is located. This is wrapped with an optical fiber that is part of an interferometer. As a result of the magnetic field change, the magnetostrictive material experiences strains which lead to an extension or shortening of the optical fiber. This results in a change in the light path, which leads to a phase shift of the light compared to a reference arrangement of the interferometer. This phase difference is proportional to the acting acceleration. FIG {accelerometer; magnetostrictive; optical; mechanical suspension; vibratory spring-mass system; interferometer; active optical measuring fiber; Reference fiber; Electromagnet}

Description

For this 7 pages drawings

field of use

The invention relates to a magnetostrictive accelerometer which is capable of very accurately measuring both vertical and horizontal accelerations with the aid of an interferometer. It is therefore suitable for all technical applications where accurate acceleration measurements are to be performed, such as: As in the inertial navigation or in the gradiometry.

Characteristic of the known state of the art

Many solutions for accelerometers are known in the patent literature, all of which operate with electromagnetic or capacitive measured value recording (eg DE 2833915, DE 2164321, DE 2759499, DE 2759500, DE 2840652, DE 2840698, DE 2840700, US 3438265, US 4141765, US 3438266, US Pat. US 4145929, SU 670896). Since the device according to the invention uses an optical measured value recording, there is thus no functional similarity with these known technical solutions. The technical literature (W.B.Spillman Jr., Appl. Optics, 21/1982, 2653-4, A.Schwaiger, rtp, 1983, H. 2) describes optical accelerometers using optical fibers or fiber optic sensors. Above all, the photoelastic effect of some transparent materials (Spillman) as well as other properties of the optical fibers are exploited. Likewise, proposals are known in which micromechanical spring-mass systems are applied to the optical fibers, which then model the light in the fibers accordingly (Schwaiger). All of these known solutions are based on principles of action which deviate from the present invention, so that there is no functional similarity. In addition, high resolutions are not achievable with the known principles.

The device according to the invention is able to measure very accurately accelerations with the aid of a magnetostrictive element and an interferometer.

Object of the invention

The object of the invention is to propose an accelerometer which is suitable for the very accurate measurement of vertical and horizontal accelerations and thus applicable to many metrological problems (eg in inertial navigation).

Explanation of the essence of the invention The invention is based on the object, a magnetostrictive-optical accelerometer for the measurement of

to propose vertical and horizontal accelerations.

The accelerometer according to the invention (Fig. 1) consists of a vibratory Foder-mass system, ds

from a test mass 1, the spring 2 and the diaphragm spring guide 3; 4 composed. The mass 1 is preferably made of ferromagnetic material. In its equilibrium position, it dips slightly into the electromagnet 5.

In the opposite end of the electromagnet 5 is a cylinder 6, which consists of magnetostrictive material. This carries the windings of an optical fiber 7, which is part of an interferometer. The interferometer is next to the active measuring fiber 7 of the reference fiber 8, the light source 9, the couplers 10; 11 and the

Detector 12.

The reference fiber 8 lies with as many windings as the active measuring fiber 7 to an identical magnetostrictive cylinder

13. This is also in exactly the same way and catfish inside an electromagnet 14. This

Reference arrangement is separated from the measuring arrangement by a magnetic shield 15. The electromagnets 5; 14

are at the same DC voltage source (not shown).

In the function of the accelerometer is by the active measuring fiber 7 and the reference fiber 8 by means of the coupler 10; 11

directed monochromatic light of the light source 9 to the detector 12. Furthermore, located on both electromagnets 5; 14

DC voltage, whereby two constant magnetic fields form. These lead to constant deformations of the

magnetostrictive cylinder 6; 13 and constant strains of the active measuring fiber 7 and the reference fiber 8. The magnetic field of the electromagnet 5 deviates from that of the electromagnet 14 and thus the deformation of the magnetostrictive Zylinderβ of that of the cylinder 13 because of the presence of the test mass 1 in the measuring arrangement. The resulting

Phase shift of the light between the active fiber 7 and the reference fiber 8 is at the detector 12 of the interferometer

detectable. This phase shift is constant when the test ground 1 is at rest, irrespective of any dc source interference.

Acts on the accelerometer acceleration in the direction of the diaphragm spring guide 3; 4

spanned sensitive axis 16, the test mass 1 is displaced within the electromagnet 5. This results

a magnetic field change of the electromagnet 5, which leads to a change in the transverse strain of the magnetostrictive cylinder 6 and thus to an extension or shortening of the active measuring fiber 7. This change in length has a change of

Light path result, as an additional phase shift of the light between the active measuring fiber 7 and the reference fiber

8 is detectable on the detector 12. The additional phase shift is proportional to the acting acceleration.

embodiment

The structure and function of the accelerometer will be explained in more detail with reference to several embodiments and figures.

Fig. 1: Basic structure of the Beschleunigungsmessero 2: side view of the accelerometer of the embodiment 1 (section) Fig.3: Diaphragm spring variants 4: side view of the accelerometer of the embodiment 2 (section) 5: side view of the accelerometer of the embodiment 3 (section) 6: side view of the accelerometer of the embodiment 4 (section) Fig. 7: side view of the accelerometer of the embodiment 5 (section). Exemplary embodiment 1 The accelerometer (FIGS. 1 and 2) consists of a multipart housing 17, in which the test mass 1, the Electromagnet 5 and the coil spring 2 are located. The test mass 1 is a ferromagnetic cylinder with a mass of

10g. By the electromagnet 5 and the coil spring 2, the test mass 1 is held in an equilibrium position in which this is opposite to the electromagnet 5 so that it just dips into this. The test mass 1 is by means of two circular, planar, open-ended membrane springs 3; 4 (FIG. 3) in the housing 17. The mem- brane springs 3; 4 consist of 0.1 mm thick brass foil with an outer diameter of 50mm. They ensure a low-friction axial movement of the test mass 1 with high radial rigidity.

In the opposite end of the electromagnet 5 is a cylinder 6 made of magnetostrictive material (eg nickel).

is made. It has a diameter of 8 mm and a length of 15 mm. On this cylinder 6 are 10 windings of an optical fiber 7 which is part of an interferometer.

The interferometer consists of the light source 9, which is designed as a semiconductor single-mode laser, from the optocouplers 10;

11, the active measuring fiber 7, the reference fiber 8, both of which are designed as monomode fibers, and the detector 12.

The reference fiber 8 is also 10 windings to a magnetostrictive cylinder 13, which also consists of nickel

and the same dimensions as the cylinder 6 has. The cylinder 13 is identical to the cylinder 6 in one

Electromagnets 14.

Ie reference arrangement is magnetically shielded 15 of the measuring arrangement, so that no mutual interference occurs. The electromagnets 5; 14 are connected to the same DC voltage source.

Both electromagnets 6; 14 influence the light in the two optical fibers 7 by their constant magnetic field; 8. This influence is due to the transverse strain of the magnetostrictive cylinders 6; 13 due to the magnetic fields and the resulting lengthening or shortening of the optical fibers 7; 8. Due to the presence of the test mass 1 in the measuring arrangement, the light in both fibers 7; 8 different degrees of influence, so that the detector 12 of the interferometer, a constant phase shift between the light beams of the fibers 7; 8 is detectable.

When acting on the accelerometer acceleration, the test mass 1 is displaced within the electromagnet 5, so that changes the magnetic field. This magnetic field change causes a change in the transverse strain of the magnetostrictive cylinder 6 and thus an additional extension or shortening of the active measuring fiber 7. This change in length results in a modified light path, which is detectable as an additional phase shift of the light at the detector 12. The additional phase difference between the active measuring fiber 7 and the reference fiber 8 is proportional to the acting acceleration.

Embodiment 2 The accelerometer also consists in the second embodiment of a multi-part housing 17, in which

the test mass 1 and the electromagnet 5 are located (FIG. 4). The test mass itself is designed as a ferromagnetic central part of a circular, flat, open-ended diaphragm spring 18, the mass of which is 0.1 g. The diaphragm spring 18 is made of 0.01 mm thick brass foil with an outer diameter of 50 mm.

The electromagnet 5 is designed as a flat coil. At its opposite end is the magnetostrictive Nickel cylinder 6 with the 10 windings of optical fiber 7. The nickel cylinder has the same dimensions as in Embodiment 1. The structure of the interferometer corresponds to the embodiment 1. Dabe ¹ is the reference fiber 8, also 10th Windings around the identical magnetostrictive cylinder 13, which is identical to the measuring arrangement in the electromagnet 14

which is also designed as a flat coil.

Dia measuring and the reference arrangement are magnetically shielded from each other 15. The designed as a flat coil Electromagnet 5; 14 are at the same DC voltage source. The operation of the device of the second embodiment corresponds to that of the first. Embodiment 3 In the third embodiment (FIG. 5), the test mass 1 consists of a permanent magnet with a mass of 10 g. This is by the coil spring 2 and the circular, flat, open-end diaphragm spring 4 in an equilibrium position Held within the housing 17. Below the test mass 1 is the magnetostrictive nickel cylinder 6 with the 10th Windings of the active measuring fiber 7. The nickel cylinder 6 has the same dimensions as in the embodiment 1. The active measuring fiber 7 is part of an interferometer whose structure corresponds to that in the first embodiment and its Reference fiber 8 is also designed with 10 windings to the identical magnetostrictive cylinder 13. Di'3 measuring and reference arrangement are separated by a magnetic shield 15. The operation of the device corresponds in principle to that of the first embodiment, except that a constant Initial phase shift between the light beams of the active measuring fiber 7 and the Roferenzfaser 8 only by the Presence of the test ground 1 and its permanent magnetic field in the vicinity of the magnetostrictive cylinder 6 caused If the test mass 1 is moved by an acting acceleration relative to the magnetostrictive cylinder 6, then changes for

this the magnetic field. The resulting transverse expansion of the cylinder 6 leads to an extension or shortening of the active measuring fiber 7, which results in an additional phase shift of the light. This additional phase shift is proportional to the acting acceleration.

Embodiment 4 The test mass 1 (Fig.6) also consists of a permanent magnet with a mass of 10g, by the leaf spring 21st

is held in an equilibrium position. Below the test mass 1 is the magnetostrictive nickel cylinder 6 with the 10 windings of the active measuring fiber 7. It has the same dimensions as in the first embodiment.

The active measuring fiber 7 is part of an interferometer whose structure corresponds to that in the first embodiment and its Referenzfaser8 also with 10 windings to the identical magnetostrictive cylinder 13 is executed. The measuring and reference arrangement are separated by a magnetic shield 15. The operation of the device corresponds to that of the fourth embodiment. EXECUTIVE BELGIUM 5 In the fifth embodiment, each of the mechanical structure of the embodiments 1 ... 4 is maintained. However, the active measuring fiber 7 and the reference fiber 8 of the interferometer are not around the magnetostrictive cylinder 6;

13 wound. Instead of these cylinders 6; 13, thin magnetostrictive films 19; 20 is preferably made of nickel, which at the same time the sheath or the cladding of the two optical fibers 7; 8 (FIG. 7).

In the case of an acting acceleration, as a result of the magnetic field change, an additional longitudinal expansion of the

magnetostrictive film 19 and thus the active measuring fiber 7.

This results in the reference fiber 8, a phase difference of the light, which is received by the detector 12 and the

acting acceleration is proportional.

Claims (4)

An arrangement for a magnetostrictive optical accelerometer, comprising a measuring arrangement with a vibratory spring-mass system (1, 2, 3, 4) and a compensation arrangement, each of which generates a magnetic-field-generating (5, 14) and a magnetic-field-sensitive (6; 13) element and an interferometer formed from two optical fibers (7, 8), characterized in that the spring-mass system (1 ... 4) of the measuring arrangement is arranged in the immediate vicinity of the corresponding magnetic field-generating element (5) , μ η d that both in the measuring and in the compensation arrangement, the magnetic field sensitive element (6; 13) in the immediate vicinity of the magnetic field generating element (5; 14) is arranged, and in that the magnetic field sensitive elements (6; optical fiber (7; 8) of the interferometer are firmly connected. 2. arrangement flat claim 1, characterized in that the spring-mass system (1 ... 4) of the measuring arrangement of a ferromagnetic test mass (1), a coil spring (2) and a diaphragm spring guide (3, 4), and that below the spring-mass system (1 ... 4) as a magnetic field generating element, an electromagnet (5) is arranged so that the test mass (1) of the spring-mass system (1 ... 4) in their equilibrium position) is slightly immersed in the electromagnet (5), and that in the lower end of the electromagnet (5) has a magnetostrictive element (6) is fixedly connected to an optical fiber (7), and that the compensation arrangement in their spatial arrangement of the electromagnet 3n (14), the magnetostriction element (13) and the associated optical fiber (8) <Jer measuring device is identical and both electromagnets (5; 14) are supplied by the same DC voltage source. 3. Arrangement according to claim 1, characterized in that the test mass (1) of the spring-mass system (1 ... 4) of the measuring arrangement consists of a permanent magnet, which also represents the magnetic field generating element, and that below the spring mass -System (1 ... 4) a magnetostrictive element (6) is arranged, which is fixedly connected to an optical fiber (7), and in that the compensation arrangement in their spatial arrangement of a fixed identical permanent magnet and the magnetostrictive element (13) the associated optical fiber (8) of the measuring arrangement is identical. 4. Arrangement according to claim 1 ... 3, characterized in that the magnetostrictive elements both identical cylinders (6; 13) represent, around which the optical fibers (7; 8) are wound with the same number of turns, as well as identical thin magnetostrictive films (19, 20) simultaneously embodying the cladding of the optical fibers (7, 8).