Measurement of positions, mechanical displacements and rotations and stresses of bodies

Abstract

The invention concerns a device and a method for measuring the relative position and angles between two bodies to be measured (7, 77). The invention is characterized in that it comprises one or more permanent magnets (6) and in that the position to be measured is determined indirectly via a magnetic field. The magnetic field is detected by one or more magnetic field sensors (3) read by a microchip. A mathematical minimization method is used to calculate back to the position and angles of the permanent magnet system (6) in relation to the magnetic field sensors (3). The energy required to read out the sensors can be obtained from the excitation field of a readout device. The sensor can perform without energy supply and can be read out by means of standard readout devices, such as an NFC-capable mobile telephone.

Claims

1. Method for measuring the distance between two bodies (7, 77), characterized in that at least two magnetic field sensor (3) are mounted on one body (77) and at least one permanent magnet (6) is mounted on another body (7), and at least one component of the magnetic field of at least two sensors (3) are measured (H.sub.measurement) and a magnetic field H.sub.theory is calculated, which is generated by the permanent magnet system (6) for a given alignment y.sub.magnet that is comprised that the difference d between the theoretical field H.sub.theory and the measured field H.sub.measurement is determined d(y.sub.magnet)=H.sub.theory(y.sub.magnet)H.sub.measurement and the alignment y.sub.magnet of the permanent magnet system (6) is determined in such a way that the mathematical norm of the vector d is minimized and thus the alignment y.sub.magnet of the magnetic system (6) relative to the field sensors (3) is determined.

2. Method for measuring the alignment y.sub.magnet between two bodies (7, 77), characterized in that at least two magnetic field sensors (3) are mounted on one body (77) and a magnet system consisting of at least one permanent magnet (6) is mounted on another body (7) and the permanent magnets at the positions of the sensors generating a magnetic field H.sub.measurement and at least one component of the magnetic field of at least two sensors (3) is measured, characterized in that the orientation of the magnet system y.sub.magnet is determined by first training a machine learning method where for a plurality of alignments y.sub.magnet of the permanent magnet system (6) the expected magnetic field H.sub.theory(y.sub.magnet) is determined at the locations of the sensors and used as training data for the machine learning method and hence the machine learning method can predict for a certain measured field H.sub.measurement an approximation of y.sub.magnet.

3. Method according to claim 1, wherein the starting value of the alignment of the magnet system y.sub.magnet,0 is determined from the method according to claim 2.

4. Method according to claim 1, wherein the alignment of the magnet system y.sub.Magnet only includes the local displacements in space, thus y.sub.magnet=x.sub.magnet.

5. Method according to claim 1, wherein the distance between two bodies (7, 77) is determined from the orientation of the magnet system y.sub.magnet.

6. Method according to claim 1, wherein a soft magnetic shield is mounted between the permanent magnets (6) and the body (7).

7. Method according to claim 2, wherein a soft magnetic shield is mounted between the permanent magnets (6) and the body (7).

8. Method according to claim 1, wherein the theoretical field is scaled with a factor , and this factor is determined in minimizing the distance d.

9. Method according to claim 1, wherein at least one permanent magnet has a non-parallel magnetization with respect to one of the other permanent magnets.

10. Method according to claim 1 wherein the magnetization of a permanent magnet consists of a pseudo-random code.

11. Method according to claim 2 wherein the magnetization of a permanent magnet consists of a pseudo-random code.

12. Method according to claim 2, wherein at least one of the methods is used such as neural networks, gradient boost or regression.

13. Method according to claim 2, wherein for a plurality of alignments y.sub.magnet, the machine learning method is training with expected magnetic fields H.sub.theory(y.sub.magnet) that are determined by physically changing the orientation of the magnetic field system (6) relative to the sensor array (3) and for the known vector y.sub.magnet the values H.sub.theory(y.sub.magnet) are determined by reading out the magnetic field sensors (3).

14. Method according to claim 1, wherein the expected magnetic fields H.sub.theory(y.sub.magnet) at the locations of the sensors are determined by an analytical or numerical calculation of the magnetic field.

15. Method according to claim 2, wherein values from methods of claim 13 are also used in the training of the machine learning method.

16. Device for measuring the distance between two bodies (7, 77), characterized in that at least two magnetic field sensors (3) are mounted on one body (77) and at least two permanent magnets (6) are mounted on another body (7), and this permanent magnet system thus generates a magnetic field which has no rotational symmetry, at least two components of the magnetic field are measured by the magnetic field sensors (3), and based on the measured magnetic field the alignment of body (7) relative to body (77) is determined.

17. Device according to claim 16, wherein the energy used for reading the magnetic field sensors (3) is obtained from the electromagnetic field of a readout device.

18. Device according to claim 16, wherein the magnetization direction of the permanent magnets describes a pseudo random code.

19. Device according to claim 16, wherein at least one permanent magnet (6) has a non-collinear magnetization with respect to one of the other permanent magnets.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0036] The invention is explained in more detail below on the basis of the drawing. Thereby shows, or rather show, quite schematically:

[0037] FIG. 1 a device according to the invention for measuring displacements with four magnets

[0038] FIG. 2 example of the Euler angles (,,) of the sensor system (3) and exemplary magnetic field distribution of the permanent magnets (6)

[0039] FIG. 3 a device for measuring displacements with a magnet

[0040] FIG. 4 a variant for measuring displacements between two bodies with a different arrangement of the magnets

[0041] FIG. 5 a variant for measuring displacements between two bodies with an anti-parallel alignment of the magnetization of the magnets

[0042] FIG. 6 a variant for measuring displacements between two bodies with a Halbach magnetization of the magnets

[0043] FIG. 7 a variant of the permanent magnets using a pseudo random code.

[0044] FIG. 8 a variant of the magnetization of the permanent magnets, where at each position p.sub.1 a unique bit pattern exists in y-direction.

[0045] FIG. 9 a variant of the magnetization of the permanent magnets, where at each position p.sub.1 a unique bit pattern exists in the x,y plane.

[0046] FIG. 10 a variant for measuring displacements between two bodies where the magnets are placed closer to the body (77) than the sensors and an optional soft magnetic element (66) (soft magnetic shield or soft magnetic ribbon) is placed under the magnets

[0047] FIG. 11 a variant for measuring the mechanical pressure on the body (7)

[0048] FIG. 12 a variant for determining the position and attitude of a joystick

[0049] FIG. 13 a variant for determining the deviation of a mounted shaft

[0050] FIG. 14 a variant for measuring displacements between three bodies

[0051] FIG. 15 a variant for measuring the strains of a body

[0052] FIG. 16 possible components of a microchip

[0053] FIG. 17 shows the comparison between the measured position of the permanent magnet and the specified linear behaviour

[0054] FIG. 18 shows the arrangement of magnets and sensors of another concrete example

[0055] FIG. 19 shows the standard deviation of the x-position of the displacement

[0056] FIG. 20 shows the standard deviation of the angle

DETAILED DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0057] FIG. 1 shows the sensor device (1) consisting of several magnetic field sensors (3), a mico chip (4), which has an RFID transponder with an antenna (9) or a cable connection (8) and the permanent magnet (6). The permanent magnets have a fixed alignment to each other and are attached to a second body (7), whereby the relative position is determined from body (7) to body (1). The magnetic field sensors (3) measure the current magnetic field H.sub.measure,i of the permanent magnet system (6) at the location of the i-th sensor x.sub.i. This field is compared by the microchip (4) with the simulated or previously measured magnetic field of the permanent magnet system H.sub.theory,i. From this a distance norm d is determined in order to be able to determine the position of the permanent magnet system (6) by minimizing the unknowns, i.e. the position and orientation in space (Euler angle). This means that the position and rotation of the permanent magnet system (6) relative to the magnetic field sensors (3) can be calculated without mechanical connection.

[0058] One or more permanent magnets (6) are mounted in a holder (11) on the body (7) to be measured. The magnetic field sensors (3) and the microchip (4) are placed together in a housing (12) and are mounted on the same body (7), or on a mechanically separated body (77).

[0059] The permanent magnets can be glued or screwed directly to a housing or integrated directly into the body to be measured.

[0060] Due to the use of several magnetic field sensors (3), external disturbing influences such as the earth's magnetic field or temperatures can be compensated. To further compensate the influence of temperature on the sensor signal, a micro-chip (4) with an internal or external temperature sensor can be used. By knowing the current temperature, the temperature-dependent measured resistance value of the magnetic field sensor can be compensated.

[0061] FIG. 3 shows a manifestation of the invention where only one permanent magnet is used to determine the position between the magnets (6) and the sensor array (3). A possible rotation of the magnet (6) around its axis of symmetry cannot be detected because the magnetic field is rotationally symmetric around this axis.

[0062] FIG. 4 represents a version of the sensor described in FIG. 1 for measuring the distance and angular displacement between the reference body (77) and the body (7) to be measured. The permanent magnets (6) have a magnetization that is not parallel to each other. The permanent magnets (6) are placed above the magnetic field sensors (3) by means of a holder (11), which can assume a wide variety of geometric shapes and sizes. The magnetic field sensors (3), the micro-chip (4), the antenna (9) and optionally a battery (10) in a housing (12) or a protective cover (12) is shown. Displacements and rotations between the reference body (77) and the body to be measured (7) can be carried out via solving the inverse problem as described for FIG. 1.

[0063] FIG. 5 shows a characteristic of the sensor described in FIG. 1. for measuring the distance and angular rotation between the reference body (77) and the body (7) to be measured, the permanent magnets having an antiparallel magnetization. Furthermore, arrangements are possible where the magnetisation of the permanent magnets is generally not colinear.

[0064] FIG. 6 shows a characteristic of the sensor described in FIG. 1. for measuring the distance and angular rotation between the reference body (77) and the body (7) to be measured, the permanent magnets having a magnetization which are magnetized according to a Halbach arrangement. This arrangement results in a maximum magnetic field on the side near the body (77) and a minimum field on the opposite side. Due to the large magnetic field, interference fields and magnetic noise of the sensors are minimized.

[0065] Other magnetic configurations of permanent magnets can consist of a pseudo random code (PRC) of the permanent magnet. A pseudo random code arranged along one track overlaps so that the first (N1) bits of the current code are identical to the last (N1) bits of the previous code. Any N bit long code, i.e. positions, can be determined by scanning the pseudo random code using a window containing N bits.

[0066] For example, the permanent magnets are arranged with the north pole up (z direction) or down (z direction) according to a PRC, as shown in FIG. 7. Therefore, N bits, defined by the orientation of the permanent magnet, encode in an absolute way the position of this sequence of N bits. When the sequence is measured by the sensor array (3), the absolute position can be decoded.

[0067] Thus the coding is unique at each position p.sub.i. If the magnetic field resulting from this encoding is read out with the magnetic field sensors (3), it is possible to deduce the position p.sub.i, as well as through the previously described algorithms within the positions p.sub.i with even higher accuracy relative to the permanent magnets (6). In other words, in a first step the rough position can be determined on the basis of the unique bit pattern of the pseudo random code and in a second step a subbinary resolution can be achieved with the algorithm described above.

[0068] FIG. 8 shows a code where more than one track of permanent magnets is used. Here a unique bit pattern can be realized at each position pi.

[0069] FIG. 9 shows a Pseudo Random Code which is not unwound along an axis but along a curve (62) in the x-y plane.

[0070] FIG. 10 shows a characteristic of the sensor described in FIG. 1. for measuring the distance and the angular rotation between the reference body (77) and the body (7) to be measured, whereby, compared with FIG. 1, the positions of permanent magnets (6) and magnetic field sensors (3) are interchanged. The magnetic field sensors are near the reference body (77) and the magnetic field sensors (3) are at a further distance and fixed to the body (7). This arrangement is of particular advantage if the reference body (77) itself is a magnetic material, such as iron or steel. In the application this is an important case, if for example joints and connections of bridges made of steel or iron are to be measured. Due to the fixed position of the magnets (6) and the reference body (77), the magnetic field is not changed if the position of the body to be measured (7) changes. This is not the case with the arrangement as shown in FIG. 1. The influence of interfering magnetic fields of a magnetic reference body (77) can be reduced if a soft magnetic element (66) is placed between the permanent magnets. This magnetic shield can be made of iron, Mumetal or any other soft magnetic material. The intrinsic magnetic susceptibility can be greater than 100.

[0071] FIG. 11 shows a characteristic of the sensor described in FIG. 1. In this case the body to be measured is not a rigid object but a body which changes its mechanical form as a function of external influences such as temperature or pressure. An example is that the body (7) itself has a membrane which changes its shape as a function of pressure and thus leads to a change in the position of the magnet (6). This change in position can be determined by the magnetic sensors (3) based on the change in the magnetic field.

[0072] FIG. 12 shows a system for measuring the distance and angular displacement between the reference body (77) and the body to be measured (7). This characteristic represents the body (7) to be measured as an elongated cylinder which penetrates a plane (78). An example is the detection of positions of a switch or the continuous detection of the movement of a lever.

[0073] FIG. 13 shows a system for measuring the distance, angular displacement and rotational speed between the reference body (77) and the body to be measured (7). The body (7) to be measured rotates along an axis.

[0074] FIG. 14 shows a system for measuring the distance and angular displacement between the reference body (77) and several bodies (7) to be measured. Each body (7) to be measured is equipped with a permanent magnet (6).

[0075] FIG. 15 shows a system where the permanent system and the sensors (3) are mounted on the same body. Thus a change in length of the body (7) to be measured can be detected.

[0076] These changes describe elongation of the material of which the body is made, which is caused by stress, temperature or aging.

[0077] Instead of a permanent magnet (2), for example, electromagnets can also be used.

[0078] The respective actual arrangement of the various magnetic field sensors (3) and permanent magnet system (6) may differ from those shown. For example, the permanent magnet system (6), magnetic field sensor (3), microchip (4) and antenna (9) can be interchanged. The casing (11, 12) in which the permanent magnet (6) or other components (3, 4, 6, 9, 10) are embedded can be made of a wide variety of materials. Plastics such as thermoplastics, duroplastics, elastomers are particularly preferred. For high temperature applications, refractory ceramics such as compounds of silicate raw materials, compounds based on magnesite, SiOxides-, aluminium oxide, silicon carbide, boron nitride, zirconium oxide, silicon nitride, aluminium nitride, tungsten carbide and aluminium titanate can-be used.

[0079] As magnetic field sensors Hall sensors, AMR, sensors, GMR sensors and TMR sensors, magnetoimpetance sensors or squid sensors can be used. For TMR and GMR sensors, sensors that show a vortex state in the free magnetic layer are particularly suitable (US20150185297A1).

[0080] Magnetic materials for the permanent magnets can be sintered magnets, polymer-bound magnets or magnets produced by additive manufacturing (Huber, C., et al. Applied Physics Letters 109.16 (2016): 162401). Examples of hard magnetic materials are rare earth magnets (NdFeB,SmFeB), magnetic ferrites (SrFe,BaFe), Alnico magnets.

[0081] FIG. 16 shows the typical components of the microchip including wired communication and wireless communication. This includes optional memory, such as EEPROM (electrically erasable programmable read-only memory), optional battery, antenna, electronic product code (EPC), optional temperature sensor, multiplexer and optional real time clock (RTC). The transmission frequency for wireless communication can be ISM (2.4 Ghz), UHF (0.3 to 3 GHz), HF (3 to 30 MHz), or any other common operating frequency. Preferred RF carrier frequencies are between 12 MHz-14 MHz (NFC) and 860-970 MHz (UHF).

[0082] FIG. 17 shows a graph showing the dependence of the measured position of the sensor. In this case the body to be measured was moved along a straight line.

[0083] FIG. 18 shows a possible geometrical arrangement of the sensors. Here the distance of the outermost sensors is 30 mm. The sensor array (3) consists of (33 sensors) Two magnets with opposite magnetisation are used. The magnets have a dimension of radius=4 mm, height=10 mm and the saturation polarization is Js=1 T. The lateral distance of the magnets (edge to edge) is 5 mm. The distance of the surface of the magnets to the surface of the sensors is 3 mm. The sensor noise B.sub.noise (rms) is B.sub.noise=1 mT.

[0084] In FIG. 19 the standard deviation of the determined x-position is determined for different positions of the body to be measured (7). The body to be measured was placed in a range of 20 mm in x-direction and y-direction. The maximum inaccuracy is about 0.6% of the measuring range.

[0085] Possible geometries and arrangements of the magnets and sensors are for example those where the smallest lateral extension of at least one permanent magnet is greater than 0.2 times the average distance of the sensors (3) and the distance between the centres of the magnets is greater than 0.2 times the average distance of the sensors. Due to the high field gradients, such arrangements lead to an accurate determination of the alignment in space.

[0086] In FIG. 20 the standard deviation of the rotation angle around the z-axis is determined for different positions of the body to be measured (7). The body to be measured was placed in a range of 20 mm in x-direction and y-direction. The maximum inaccuracy of the rotation angle is 0.018 rad, which corresponds to approx. 1.

[0087] Different combinations of the elements shown and described are also possible and, of course, in the future new materials with the above-mentioned properties can be used, even if their names do not correspond to those currently used. The reason for this explicit statement is that especially the material sciences are in rapid development and no restriction of protection should be derived from this.