WO2015132123A1

WO2015132123A1 - Method for detecting the direction of mechanical tensions in a ferromagnetic work piece and sensor arrangement

Info

Publication number: WO2015132123A1
Application number: PCT/EP2015/054032
Authority: WO
Inventors: Carl Udo Maier; Jochen Ostermaier
Original assignee: Siemens Aktiengesellschaft
Priority date: 2014-03-07
Filing date: 2015-02-26
Publication date: 2015-09-11
Also published as: DE102014204268A1

Abstract

The invention relates to a method for detecting the direction of mechanical tensions in a ferromagnetic work piece (4) by means of at least four magnetoelastic sensors (7), wherein a magnetic field is introduced into a ferromagnetic work piece by each of the at least four magnetoelastic sensors (7), and the direction of mechanical tensions in a ferromagnetic work piece (4) is determined or calculated by measurement of the magnetic flux through each of the at least four magnetoelastic sensors (7) on the surface of a ferromagnetic work piece (4).

Description

description

Method for detecting the direction of mechanical stresses in a ferromagnetic workpiece and sensor arrangement

The invention relates to a method for operating a sensor arrangement with sensors according to the magnetoelastic principle and to a sensor arrangement for measuring mechanical stresses on ferromagnetic workpieces.

A magnetoelastic sensor is based on the inverse

magnetostrictive effect, ie the effect that ferromagnetic materials experience a change in magnetic permeability when mechanical stresses occur. Since mechanical stresses are induced by tensile and compressive forces as well as by torsion, the inverse magnetostrictive effect can be used for force and torque measurement and is therefore very versatile. Sensors for measuring the inverse magnetostrictive effect comprise a transmitting or exciting coil with which a magnetic field is induced in a ferromagnetic region of a workpiece. In this case, a response signal is generated in the region or in a layer whose magnetic flux density depends on the permeability of the material. This in turn is determined by the mechanical stresses prevailing in the region or in the layer. The magnetic flux density of the response signal determines the current strength of the current induced in a receiving coil due to the magnetic flux density passing through it. From the current intensity, the mechanical stresses in the ferromagnetic region or in the ferromagnetic layer can then be calculated.

During the machining and loading of steel or other ferromagnetic workpieces, such as during a forming or a heat treatment, undesired mechanical stresses arise in the workpiece. These mechanical stresses can adversely affect the service life of workpieces. influence. The detection of these mechanical stresses should therefore be considered early, so that under some circumstances process parameters or design features can be adapted. Furthermore, the life of older components can be determined variably, so that they are replaced only when needed.

So far, there has been a need to roughly orient a sensor initially according to these mechanical stresses.

Due to manufacturing tolerances, the receiving coils have a limited reproducibility in the production and a limited accuracy in the measurement.

It is therefore an object of the present invention to provide a method and an arrangement for one or more magnetoelastic sensors for accurately measuring the direction of mechanical stresses on a ferromagnetic workpiece, wherein the reproducibility of sensors or of measurements is optimized ,

The task is solved by the respective feature combination of independently formulated claims. The dependent claims each contain advantageous embodiments of the invention.

If sensors for detecting mechanical stresses work according to the magnetoelastic effect, a magnetic field is introduced through a coil into a ferromagnetic layer or a ferromagnetic workpiece. For the detection of mechanical stresses, sensor coils are arranged around an exciter coil. With a predetermined orientation of the outer sensor coils relative to the exciter coil, the alignment of the mechanical stresses in the ferromagnetic material is detected. Ideally, according to FIG. 4, eight receiver coils are evenly distributed on a circle around an exciter coil. However, it is also a different number of coils and a modified arrangement thereof conceivable. An increase in the number of coils has the advantage that an increased resolution of the data is possible.

An arrangement according to the invention for at least four magnetoelastic sensors comprises at least one ferrite core, to which at least one exciter coil generating a magnetic field, equivalent to a transmitter coil, is applied, and at least four receiver coils, so that at least four magneto-elastic sensors are formed. According to one aspect of the invention, four or more magnetoelastic sensors are provided and arranged in a measurement surface. This arrangement of magnetoelastic sensors has described characteristics and advantages. Further features, characteristics and advantages of the present invention will become apparent from the following description of exemplary embodiments with reference to the enclosed, non-limiting figures.

FIG. 1 shows an arrangement of magnetoelastic sensors with a central exciter coil 1 and four receiver coils 2,

FIG. 2 shows an arrangement of magnetoelastic sensors with a central exciter coil 1 and four generally rotatable receiver coils 2,

FIG. 3A shows an arrangement of magnetoelastic sensors with a central exciter coil 1 and four receiver coils 2 in a starting position, FIG. 3B shows an arrangement of magnetoelastic sensors with a central exciter coil 1 and four receiver coils 2 as in FIG. 1, but rotated by 45 °,

FIG. 4 shows an arrangement of magnetoelastic sensors with a central exciter coil 1 and eight receiver coils 2,

FIG. 5 shows a magnetic circuit with field lines B, corresponding to one with exciting coil 1 and receiving coil 2 in side view,

Figure 6 shows a ferrite core 3 having a central excitation coil 1 and mutual receiving coils 2 corresponding to two magnetoelastic sensors 7. In order to detect the direction of a mechanical stress, an array of excitation coil 1 and receiving coils 2 is rotated during a measurement taking data at each setting become. With a quadruple arrangement with only four magnetic field sensors, a quarter turn corresponding to 45 ° with respect to a starting position corresponding to FIG. 1 suffices. If an object needs to be scanned, the rotary motion of the magnetoelastic sensors comprising exciter coil 1 and receiver coils 2 comes to the actual scanning movements or the measuring surfaces added; see FIG. 2.

Another way to reliably determine the direction of the mechanical stresses is to use two arrays of magnetoelastic sensors positioned adjacent to each other and rotated 45 ° from each other, as shown in Figure 3A, and for example to test an object both Sensor arrangements guided over the surface of a workpiece. With suitable evaluation Tealgorithmen one receives the direction of the mechanical tension.

If additional magnetic field sensors 7 are arranged in the arrangement, in particular on a measuring surface 5, then the directions of the mechanical stresses can be detected by a single arrangement and without additional rotational movement, as shown in FIG. 4 with eight magnetoelastic sensors 7.

Other geometries for the arrangement of magnetoelastic sensors 7 are conceivable. Examples of geometric locations for positioning the outer receiving coils 2 around the excitation coil 1 are, for example, a circle, square, double ring, triple ring or the like.

It is essential that the directions of the mechanical stresses are detected. It is according to the invention not necessary to know beforehand the approximate direction of the voltages to make an initial alignment of the arrangement of magnetoelastic sensors. Overall, a system for measuring mechanical stresses with an array of sensors according to the magnetoelastic principle is substantially optimized.

According to FIG. 1, the number of magnetoelastic sensors 7 can be set to four.

Another possibility for increasing the measured value security is the rotation 6 of a measuring surface 5, in which the

Exciting coil 1 and the receiving coils 2 and their active surface are arranged.

In order to avoid a rotation of the arrangement, a double execution can be used, so that the arrangement is made double, is positioned next to each other and rotated by 45 ° to each other. According to FIG. 4, an eightfold embodiment of the receiver coils 2 or in combination with an exciter coil 1, the magnetoelastic sensors 7 are arranged, so that no rotation 6 and no duplicate design are necessary.

It is measured on a ferromagnetic layer or a ferromagnetic workpiece 4, wherein voltages are measured in magnitude and direction. In this case, a magnetic circuit is formed when a magnetoelastic sensor 7 is positioned on a ferromagnetic surface. The layer can be applied to the object to be measured. Alternatively, the object to be measured itself may consist of a ferromagnetic material. In this case, a magnetic field flows through the magnetoelastic sensor 7. A ferromagnetic layer disposed on an object or a ferromagnetic workpiece 4 closes the magnetic

Circle.

For the measurement process with corresponding sensors, a magnetic field is generated by means of the excitation coil 1, the magnetic flux density of which is represented by the field lines B in FIG. The field lines B pass through the ferromagnetic layer and are closed via the ferrite core 3. By means of the receiving coil 2, for example a Hall sensor, the magnetic flux density of the magnetic field can be measured. The measured value depends on the magnetic permeability in the ferromagnetic layer, which in turn is influenced by the stresses prevailing in the ferromagnetic layer. Therefore, the voltages prevailing in the ferromagnetic layer can be measured or calculated from the measurement result for the magnetic flux density obtained with the respective receiver coil 2. Since the ferromagnetic layer either represents the object itself or is connected to the object, those in the ferromagnetic represent

Layer prevailing voltages and the prevailing in the test object voltages. An exemplary embodiment of an arrangement according to the invention and a magnetoelastic sensor 7 are shown in FIG. The exciter coil 1 according to FIG. 6 is arranged on the middle limb of the ferrite core 3. On the two outer legs of the ferrite core 3 are the receiving coils 2, which may be formed as Hall sensors. The magnetic flux density of the magnetic field generated by the excitation coil 1 is measured in this embodiment at two points which lie opposite one another with respect to the exciter coil 1 mirror-symmetrically.

The arrangement of a further embodiment comprises a ferrite core 3 with a central leg and four surrounding the middle leg outer legs.

According to FIGS. 3A and 3B, the exciter coil 1 is arranged on the middle leg of a ferrite core 3, and the receiver coils 2 can be designed as GMR sensors or AMR sensors in the present exemplary embodiment. The arrangement of the pairs of legs on the measuring surface 5 has an orientation or angle rotated by 45 ° relative to each other and there is a point symmetry in the arrangement of the outer legs with respect to the middle leg. This embodiment enables a two-dimensional detection of forces, as is advantageous, for example, for measuring torsions in a shaft or for measuring torques of a shaft. The shaft can either consist of a ferromagnetic material or be coated with such a ferromagnetic material.

In a torsion, a tensile force prevails in one direction and a compressive force in the direction perpendicular thereto. This means that the magnetic permeability of the ferromagnetic material of the shaft becomes larger in one direction and smaller in the other direction. In certain arrangements of magnetoelastic sensors, the Permeabilities in both directions can be detected separately, so that the torsion of the wave can be determined from the recorded permeabilities and the calculated tensile or compressive stresses.

A ferrite core 3 may have a central leg and at least two outer legs surrounding and connected to the middle leg, with the ends of the ferrite core being on the legs. The excitation coil 1 is arranged in this embodiment on the middle leg of the ferrite core, the magnetic field sensors / receiving coils 2 on the outer legs of the ferrite core. It is particularly advantageous if the outer legs surround the middle leg in each case the same distance, which means the same distance between the excitation coil 1 and magnetic field sensor 2. In this case, the signals received by the receiving coils 2 can not be influenced by different distances of the respective legs of the exciting coil. In the case of two outer legs of the ferrite core may in particular have an E-shape. As a result, the distance can be increased by the ferromagnetic material to be measured compared to the U-shape, resulting in an improved sensitivity of the arrangement results. In this configuration, the receiving coils 2 are in relation to each other

Excitation coil 1 preferably mirror-symmetrically opposite to influences on the measurement, which are based exclusively on the different distances to the excitation coil 1 exclude.

If the ferrite core 3 has more than two outer legs, the receiving coils 2 can be arranged in particular point-symmetrically or rotationally symmetrically around the ferrite core 3 around. In particular, in the presence of four outer legs can thus be well detected voltages that extend in mutually perpendicular directions in the ferromagnetic layer. Such an arrangement can be particularly advantageous. liable to be used for measuring torsion and torques, for example on shafts.

Claims

claims

1. A method for detecting the direction of mechanical stresses in a ferromagnetic workpiece (4) by means of at least four magnetoelastic sensors (7),

in which

- A magnetic field is introduced through each of the at least four magnetoelastic sensors (7) in a ferromagnetic workpiece (4), and

the direction of mechanical stresses in a ferromagnetic workpiece (4) is determined or calculated by measuring the magnetic flux through each of the at least four magnetoelastic sensors (7) on the surface of a ferromagnetic workpiece (4).

2. The method of claim 1, wherein

the ferromagnetic workpiece (4) is scanned on the surface by at least four magnetoelastic sensors (7) which are each connected to one of the at least four receiving coils (2) at the periphery of the at least one exciter coil (1) by a combination of at least one central exciter coil (1). wherein receiving coils (2) are uniformly distributed relative to the circumference of the at least one exciting coil (1) and have a distance therefrom.

3. The method according to any one of claims 1 or 2, wherein

for determining the direction of mechanical stresses in a ferromagnetic workpiece (4) whose surface is scanned by means of at least four magnetoelastic sensors arranged on a measuring surface (5), the measuring surface (5) being rotatably mounted for measuring in different angular positions, and adjusted during a measurement.

4. The method according to any one of claims 1 to 3, wherein

for determining the direction of mechanical stresses in a ferromagnetic workpiece (4) at least two measuring surfaces (5) each having at least four magnetoelastic sensors (7) are positioned adjacent and moved together for superficial scanning.

5. The method according to any one of claims 1 to 4, wherein

at least eight receiving coils (2) corresponding to eight magnetoelastic sensors (7) are used to detect the direction of mechanical stresses in the ferromagnetic workpiece (4), which are evenly distributed relative to the circumference of the at least one exciter coil (1) and to this Distance to be positioned.

6. The method according to any one of claims 1 to 5, wherein

for determining the direction of mechanical stresses in a ferromagnetic workpiece (4) whose surface is scanned scanning.

7. Arrangement of magnetoelastic sensors for detecting the direction of mechanical stresses in a ferromagnetic workpiece (4), comprising:

at least one central exciter coil (1) for generating a magnetic field,

- At least four receiving coils (2) which are magnetically coupled to the at least one exciter coil (1) via a ferrite core (3) and each represent a magnetoelastic sensor (7), wherein

the at least one central excitation coil (1) is centrally positioned in the arrangement and the at least four receiving coils (2) are uniformly distributed on the circumference of the at least one excitation coil (1) and have a spacing therefrom.

8. Arrangement according to claim 7, wherein

for detecting the direction of mechanical stresses in the ferromagnetic workpiece (4), the at least four magnetoelastic sensors (7) are rotatable about an axis of the at least one exciter coil (1) oriented approximately perpendicular to the workpiece surface.

9. Arrangement according to one of claims 7 or 8, wherein

for detecting the direction of mechanical stresses in the ferromagnetic workpiece (4) at least two measuring surfaces (5) are positioned next to each other with magnetoelastic sensors and are rotated by 45 ° from each other.

10. Arrangement according to one of claims 7 to 9, which for detecting the direction of mechanical stresses in the ferromagnetic workpiece (4) at least eight receiving coils (2), which are distributed uniformly on the circumference of the at least one exciting coil (1).