Load measurement method, load measurement device and load measurement setup

Abstract

Load measurement method for measuring a mechanical load on a test object (14), comprising the steps: a) Generating and applying a magnetic field to the test object (14) using a magnetic field generation device (18), b) Detecting a magnetic field altered by the test object (14) as a result of a mechanical load on the test object (14) using a first magnetic field detection device (20) in order to generate a first measurement signal (U1, UAB), c) Detecting a magnetic field changed by the test object (14) as a result of the mechanical load on the test object (14) using a second magnetic field detection device (22) in order to generate a second measurement signal (U2, UAT), d) Computational determination of a third measurement signal (UBT) from the first measurement signal (U1, UAB) and the second measurement signal (U2, UAT), and e) Determining an output signal from the third measurement signal and at least one of the first and second measurement signals (u1, U2) and f) Determining the mechanical stress applied to the test object (14) based on the output signal; 1.1 where step e) includes: forming the difference between one (U2, UAT) of the first and second measurement signals and the computationally determined third measurement signal (UBT) to generate the output signal, and / or 1.2 where step b) includes: Detecting the changed magnetic field by means of several magnetic field sensors connected in series (26-1, 26-2; A1, A2, B1, B2) and tapping off a sum or difference signal (UAB, U1) from these magnetic field sensors (26-1, 26-2; A1, A2, B1, B2), and wherein step c) comprises: Detecting the changed magnetic field by means of one (A1) or a subgroup (26-1, A1, A2) of these magnetic field sensors (26-1, 26-2; A1, A2, B1, B2) in order to tap a partial signal (U2, UAT) from this one or the subgroup of magnetic field sensors (26-1, 26-2; A1, A2, B1, B2).

Description

[0001] The invention relates to a method, a device, and an arrangement for measuring mechanical loads on a test object. Loads are understood to be forces, torques, or mechanical stresses on the test object.

[0002] It is known, for example, from EP 2 615 439 A1, EP 1 772 716 A1, EP 0 168 692 A2, DE 699 36 138 T2, DE 600 07 641 T2, and DE 30 31 997 A1 that the physical quantities torque, force, and position on ferromagnetic objects can be determined using magnetic measuring methods. Magnetoelastic (or inverse magnetostrictive) sensors or eddy current or eddy current sensors are typically used. The ferromagnetic materials used change their permeability under the influence of tensile or compressive stresses (also known as the Vilari effect). Differentiating between the individual effects is usually difficult in practice; only the eddy current sensor is easier to distinguish from the other effects due to its frequency dependence.In addition, the state of the object's magnetization is often unknown or is permanently influenced by processing and handling, making widespread industrial use difficult. Furthermore, predicting the service life of the magnetized objects is often impossible under the often quite harsh environmental conditions in which the technology is used (for example, but not exclusively, heavy industry, transmissions, hydraulic systems in construction machinery or agricultural equipment, and much more).

[0003] EP 3 051 265 A1 discloses compensating for this disadvantage by actively magnetizing the coils using an alternating magnetic field in the kHz range. For this purpose, generator and detector coils, namely two first magnetic field detection coils A1, A2 and two second magnetic field detection coils B1, B2, and a central generator coil Lg, are used in a cross arrangement (X-arrangement). The difference between the coil pair AB = (A1+A2) - (B1+B2) is determined in an analog signal processing scheme. Another comparable method using analog evaluation is known from DE 35 11 442 A1.

[0004] Based on this state of the art, the invention has set itself the task of creating a load measuring method, a load measuring device and a load measuring arrangement with improved signal quality

[0005] To achieve this object, the invention provides the method, the device and the arrangement according to the independent claims.

[0006] Advantageous embodiments are the subject of the subclaims.

[0007] Advantageous embodiments are preferably intended to provide an improved signal-to-noise ratio, in particular with an improved possibility of determining a load direction.

[0008] Particularly preferred embodiments relate to a torque sensor circuit for an optimal signal-to-noise ratio without phase effects or a method that can be carried out therewith.

[0009] According to a first aspect, the invention provides a load measuring method for measuring a mechanical load on a test object, comprising: a) generating and applying a magnetic field to the test object by means of a magnetic field generating device, b) detecting a magnetic field changed by the test object as a result of a mechanical load on the test object by means of a first magnetic field detection device in order to generate a first measurement signal, c) detecting a magnetic field changed by the test object as a result of the mechanical load on the test object by means of a second magnetic field detection device in order to generate a second measurement signal, and d) Calculating a third measurement signal from the first measurement signal and the second measurement signal and e) determining an output signal from the third measurement signal and at least one of the first and second measurement signals, and f) Determine the mechanical load applied to the test object based on the output signal.

[0010] According to a first alternative of the stress measurement method according to the invention, step e) comprises the step: Forming the difference between one of the first and second measurement signals and the computationally determined third measurement signal to generate the output signal.

[0011] According to a second alternative of the stress measurement method according to the invention, step b) comprises: Detecting the changed magnetic field by means of several magnetic field sensors connected in series and tapping a sum or difference signal from these magnetic field sensors and that step c) includes: Detecting the changed magnetic field by means of one or a subgroup of these magnetic field sensors in order to tap a partial signal from this one or the subgroup of magnetic field sensors.

[0012] In some embodiments of the stress measurement method, both the first and the second alternative are provided.

[0013] It is preferred that step b) comprises detecting the changed magnetic field by means of at least one first magnetic field sensor and at least one second magnetic field sensor and analog tapping of a difference signal from the at least one first and the at least one second magnetic field sensor in order to generate the first measurement signal.

[0014] It is preferred that step c) comprises detecting the changed magnetic field by means of the at least one first magnetic field sensor in order to generate the second measurement signal.

[0015] It is preferred that step d) comprises computationally determining the measurement signal of the second magnetic field sensor from the difference signal and the measurement signal of the first magnetic field sensor.

[0016] It is preferred that step b) comprises detecting the changed magnetic field by means of at least two first magnetic field sensors and at least two second magnetic field sensors, and that step b) comprises using a connection of the magnetic field sensors such that the signals of a pair of a first and a second magnetic field sensor are added in analog form and the signals of the pairs are subtracted in analog form and output as an analog difference signal.

[0017] It is preferred that the sum signals of the at least one first magnetic field sensor and the at least one second magnetic field sensor are further tapped and evaluated in particular to detect a distance to the test object

[0018] It is preferred that an amplitude of the signal of the at least one second magnetic field sensor is determined as the third measurement signal in order to determine a difference between the amplitudes of the signals from the at least one first magnetic field sensor and the at least one second magnetic field sensor as the resulting signal.

[0019] It is preferred that a coil or a solid-state magnetic field sensor is used as the magnetic field sensor.

[0020] It is preferred that the interconnection of the plurality of magnetic field sensors is varied in order to tap different sum or difference signals from the plurality of magnetic field sensors.

[0021] It is preferred that at least one sensor head is used which has magnetic field sensors of the first and second magnetic field detection devices and a generator coil of the magnetic field generation device.

[0022] It is preferred that a plurality of sensor heads, each comprising magnetic field sensors of the first and second magnetic field detection devices and a generator coil of the magnetic field generation device, are arranged distributed around the test object and used for joint measurement signal generation.

[0023] It is preferred that at least one sensor head is used which has planar coils as magnetic field sensors of the first and second magnetic field detection devices and as a generator coil of the magnetic field generation device, which are arranged in or on a circuit board element.

[0024] It is preferred that step a) comprises the imposition of an alternating magnetic field, in particular with frequencies of 1 kHz to 1000 kHz.

[0025] It is preferred that steps b) and c) comprise averaging the measurement signals over several wave trains, wherein preferably an averaging is carried out over between 10 and 10,000 wave trains.

[0026] It is preferred that steps b) and c) comprise an averaged common mode for amplitude measurement.

[0027] It is preferred that at least one X-arrangement or V-arrangement of magnetic field sensors of the first and second magnetic field detection device and the magnetic field generation device with a common ferromagnetic reinforcement core is used.

[0028] It is preferred that multiple X or V arrangements are used distributed around the test object.

[0029] According to a further aspect, the invention provides a load measuring device for measuring a mechanical load on a test object comprising: a magnetic field generating device for applying a magnetic field to the test object, a first magnetic field detection device for detecting a magnetic field changed by the test object as a result of a mechanical load on the test object and for delivering a first measurement signal, a second magnetic field detection device for detecting a magnetic field changed by the test object as a result of the mechanical load on the test object and for delivering a second measurement signal, and a computing device for calculating a third measurement signal from the first measurement signal and the second measurement signal, and an evaluation device configured to generate an output signal indicating the load on the test object from the third measurement signal and at least one of the first and second measurement signals.

[0030] According to a first alternative of the load measuring device according to the invention, the evaluation device is designed to form a difference between one of the first and second measurement signals and the computationally determined third measurement signal in order to generate an output signal on the basis of which the mechanical load applied to the test object can be determined.

[0031] It is preferred that the first magnetic field detection device comprises at least one first magnetic field sensor and at least one second magnetic field sensor and is designed to tap a difference in amplitudes of signals of the first and second magnetic field sensors from the at least one first and at least one second magnetic field sensor, this difference forming the first measurement signal.

[0032] According to a second alternative, which can be provided alternatively or cumulatively to the first alternative, it is provided that the first magnetic field detection device has a plurality of magnetic field sensors which are connected in series in order to tap a common signal from the plurality of magnetic field sensors.

[0033] In the second alternative, it is further provided that the second magnetic field detection device has one or a subgroup of these magnetic field sensors belonging to the first magnetic field detection device in order to tap a signal only from a part of the magnetic field sensors of the first magnetic field detection device.

[0034] It is preferred that the second magnetic field detection device comprises the at least one first magnetic field sensor and is designed to output an amplitude from the first magnetic field sensor as a second measurement signal.

[0035] It is preferred that the computing device is designed to computationally determine the amplitude of the second magnetic field sensor from the difference signal and the measurement signal of the first magnetic field sensor and to output it as a third measurement signal.

[0036] It is preferred that the first magnetic field detection device comprises at least two first magnetic field sensors and at least two second magnetic field sensors and such a connection or connection option (e.g. by means of a connection path and / or a switching device) of the magnetic field sensors that the signals of a pair of a first and a second magnetic field sensor are added in analog form and the signals of the pairs are subtracted in analog form and output as an analog difference signal.

[0037] It is preferred that a sum signal tapping device is further provided for tapping sum signals of the at least one first magnetic field sensor and the at least one second magnetic field sensor, wherein in particular the evaluation device is designed to detect a distance to the test object by evaluating the sum signals.

[0038] It is preferred that the computing device is designed to determine an amplitude of the signal from the at least one second magnetic field sensor as a third measurement signal, and that the evaluation device is designed to determine a difference between the amplitudes of the signals from the at least one first magnetic field sensor and the at least one second magnetic field sensor as a resulting output signal.

[0039] It is preferred that coils or solid-state magnetic field sensors serve as magnetic field sensors.

[0040] It is preferred that the magnetic field generating device is designed to impose an alternating magnetic field, in particular with frequencies of 1 kHz to 1000 kHz, on the test object.

[0041] It is preferred that the evaluation device is designed to average the measurement signals over several wave trains, wherein preferably an averaging is carried out over between 10 and 10,000 wave trains.

[0042] It is preferred that a common-mode device is provided for the averaged common mode of the magnetic field sensors for amplitude measurement.

[0043] It is preferred that magnetic field sensors of the first and second magnetic field detecting means and the magnetic field generating means form an X-arrangement or a V-arrangement with a common ferromagnetic reinforcement core.

[0044] Furthermore, the invention relates to a load measuring arrangement comprising a load measuring device according to one of the preceding embodiments and a test object whose load is to be measured.

[0045] The different designs of the load measuring device are suitable for carrying out designs of the load measuring method.

[0046] The different configurations of the load measurement method can be carried out by means of configurations of the load measurement device or the load measurement arrangement.

[0047] Embodiments of the invention are explained in more detail below with reference to the accompanying drawings, in which: Fig. 1 shows a first preferred embodiment of a sensor head of a load measuring device for measuring a mechanical load, such as in particular force, tension or torque on a test object; Fig. 2 shows a second preferred embodiment of the sensor head; Fig. 3 a side view of the sensor head of Fig. 1 together with the test object; Fig. 4 a view comparable Fig. 3 of a further embodiment of the sensor head; Fig. 5 a view comparable Fig. 3 yet another embodiment of the sensor head; Fig. 6 is a block diagram of a prior art load measuring device; Fig. 7 is a graph showing the voltage versus time for coil pairs of the strain gauge according to the prior art of Fig. 6 in case shows that a positive torque is applied to the test object; Fig. 8 the graph of Fig. 7 in case no torque is applied to the test object; Fig. 9 the graph of Fig. 7 in case a negative torque is applied to the test object; Fig. 10 is a block diagram showing a structure of a strain measuring device according to an embodiment of the invention; and Fig. 11 is a circuit diagram of a strain measuring device according to an embodiment of the invention.

[0048] In the Fig. 1 to 5 show various embodiments of sensor heads 10 for a load-measuring device 12. The load-measuring device 12 serves to measure mechanical loads, such as, in particular, torques, forces, or stresses, in an at least partially magnetizable test object 14, such as a shaft, a power transmission device, a gear part, a bolt, a membrane (e.g., a pressure sensor), or the like, which is formed in particular from or with ferromagnetic materials. The test object 14 and the load-measuring device 12 together form a load-measuring arrangement 16.

[0049] The load measuring device 12 has a magnetic field generating device 18 and several magnetic field detecting devices 20, 22.

[0050] The magnetic field generating device 18 has a generator coil Lg and a driver circuit 24 (see Fig. 6, Fig. 11 and Fig. 12) to drive the generator coil Lg.

[0051] The magnetic field detection devices 20, 22 comprise magnetic field sensors 26 in the form of detector coils A1, A2, B1, B2 or solid-state magnetic field sensors 27 and an evaluation device 25 (see Fig. 6, Fig. 11 and Fig. 12) for evaluating the signals of the magnetic field sensors 26.

[0052] The Fig. 1 with a view to the front side directed towards the test object 14, the embodiment of the sensor head 10 is shown in Fig. 3 from the side. This embodiment has two first magnetic field sensors 26-1 designed as first detector coils A1, A2, and two second magnetic field sensors 26-2 designed as second detector coils B1, B2. The detector coils A1, A2, B1, B2 are arranged in a cross-shaped arrangement or X-arrangement 28 on a common flux concentrator 30 made of ferromagnetic material. The generator coil Lg is arranged centrally—here also on a corresponding projection of the flux concentrator 30—with the first detector coils A1 and A2 facing each other, and the second detector coils B1 and B2 facing each other.

[0053] Fig. 2 shows a further embodiment of the sensor head 10 with a V-arrangement 32, where only a first magnetic field sensor 26-1 - e.g. the first detector coil A1 - and only a second magnetic field sensor 26-1 are arranged at an angle to each other with the generator coil Lg at the apex of the angular shape.

[0054] How Fig. 4 shows, instead of detector coils, solid-state magnetic field sensors 27 can also be provided as first and second magnetic field sensors 26-1, 26-2.

[0055] Fig. 5 shows an embodiment of the sensor head 10 in which the coils - detector coils A1, A2, B1, B2 and generator coil Lg - are provided as planar coils 34 in a printed circuit board element 36 - e.g. designed as PCB boards.

[0056] The strain measuring device 12 according to embodiments of the present invention implements a new signal processing concept for tapping and processing the signals of the magnetic field sensors 26-1, 26-2.

[0057] The signal processing concept described here can be applied to any sensor system that has several magnetic field sensors 26-1, 26-2, such as four detector coils (A1, A2, B1, and B2 form an X variant) or only two detector coils (A1 and B1 form a V variant).

[0058] In the embodiments shown, the magnetic field is generated via the flux concentrator 30 with the excitation coil or generator coil Lg.

[0059] Other structures and designs can also be used for the described signal processing, for example, a variety of different magnetic field sensors 27 (Hall sensors, MR or GMR sensors = Giant Magneto Resistance, German, "Giant Magneto Resistance Effect") or the most diverse magnetic flux concentrators 30 available on the market (English flux concentrator) can be used.

[0060] Fig. 6 shows a known load measuring device 112 in which such sensor heads 10 are used so far and which picks up the signals of the detector coils A1, A2, B1, B2 in analog form in order to carry out an analog differential measurement. Fig. Figure 6 shows the basic setup of the purely analog, active magnetization (state of the art - marketed by Torque and More under the name TAM A3 technology). For example, the generator coil Lg is operated between 1 and 20 kHz, while the detector coils Ai or Bi (with i=1 or 2) are operated between 1 kHz and 100 kHz.

[0061] How to connect the coils on the left side of Fig. 6, the pair of first detector coils A1, A2 are connected in series and the pair of second detector coils B1, B2 are also connected in series, the pairs being connected in series in opposite directions to each other.

[0062] This results in the output signal UAB: UAB=UAT−UBT=(U(A1)+U(A2))−(U(B1)+U(B2), where UAT is the voltage of the pair A of first detector coils A1, A2, UBT the voltage of the pair B of second detector coils B1, B2, U(A1) is the voltage of the first detector coil A1, U(A2) is the voltage of the other first detector coil A2, U(B1) is the voltage of the second detector coil B1, and U(B2) is the voltage of the other second detector coil B2.

[0063] The measured signal is the amplitude of UAB. The phase of UAB is not measured. As a result, the sign information is lost.

[0064] Fig. 7 shows the voltages UAB, UAT and UBT in case of a positive torque on the test object 14, Fig. 8 shows the voltages UAB, UAT and UBT when no torque acts on the test object 14, and Fig. Figure 8 shows the voltages UAB, UAT and UBT in case of a negative torque on the test object 14.

[0065] For signal processing using the analog principle, it is recommended to use the difference signal AB as a direct analog measurement variable – in the form of the amplitude of the voltage UAB explained above – in order to achieve an optimal S / N ratio. Typically achievable noise values ​​are approximately 8µV relative to a signal level of a few mV (0.1%...0.5% relative to the entire measuring range = FS). A further problem is that the signal UAB (corresponds to AB) contains both amplitude information and phase information. The phase information leads to a non-linearity in the measurement signal, which, in the case of large signal changes, can cause the characteristic curve to bend significantly; a clear torque direction cannot be determined. By deliberately introducing an asymmetry (e.g.Although the operating point can be shifted by using coils with different numbers of turns, uncertainties remain regarding the non-linear behavior at the minimum, the unknown or changing operating point (before a complete measuring range has been traversed during calibration) and possible disadvantages regarding temperature and distance sensitivity.

[0066] The Fig. The known differential, single-channel approach shown in Figure 6 also leads (in any case, regardless of the number of coils) to a phase offset between the detected signals of the two sensor coils (or the two pairs of sensor coils), which must be compensated for in order to obtain a correct result, i.e. a suitable difference. Due to the phase offset, the signal values ​​of the two sensor coils (or the two pairs of sensor coils) must not be used at the same time; instead, the phase offset must be taken into account, and those signal values ​​which are relative to one another by the determined phase offset must be used to calculate the difference. To determine this phase offset, the zero crossings of the signals of the two sensor coils are used.

[0067] One method to circumvent these disadvantages is to discretely sample the alternating magnetic field, thus performing a discrete-time measurement instead of a continuous-time measurement. Directly measuring the amplitudes of A=(A1+A2) and B=(B1+B2) results in a somewhat poorer S / N ratio (noise power of approximately 50µV relative to a useful signal of 10...20mV), but a clear determination of the torque direction and a separation of phase and amplitude are possible.

[0068] Particularly preferred embodiments of the method and the device for measuring loads on test objects by means of active magnetization use a temporal sampling of the difference between the amplitudes of (AB) and one of the two coil pairs A or B and from this the mathematical determination of B (amplitude and phase) or for the second case A (amplitude and phase).

[0069] Preferably, the sampling takes place at very high frequencies (several 100 kHz) so that several thousand wave trains of the alternating magnetic field (samples) can be evaluated.

[0070] After averaging, between 100 and 1000 samples per second can be output as an output signal, so the temporal resolution of the output signal is in the range of one to a few milliseconds.

[0071] The resulting signal-to-noise (S / N) value ranges between 8,000 and 12,500, depending on the safety factor used (corresponding to a mechanical load of 60 and 150 MPa). This corresponds to a noise level of approximately 2 µV or 0.013%FS to 0.008%FS based on a measurement range of 16 to 25 mV of the useful signal.

[0072] In contrast to the purely analog measurement of UAT-UBT, both channels are preferably measured separately and thus amplitude and phase are determined separately.

[0073] Advantageously, no wound coils are used, but planar coils 34 integrated in a printed circuit board 36, as they have been known for some time, in order to achieve a high reproducibility of the manufacturing processes at the same time low costs (see Fig. 5).

[0074] In Fig. 10 shows a preferred embodiment of the stress measurement method in a time block sequence, while in Fig. 11 shows a schematic block diagram of a preferred embodiment of the load measuring device 12.

[0075] In this embodiment, a first magnetic field detection device 20, which supplies a first measurement signal U1 on a first channel, comprises the first magnetic field sensors 26-1, A1, A2 and the second magnetic field sensors 26-2, B1 and B2, wherein the magnetic field sensors 26-1, 26-2, A1, A2, B1, B2, as previously described with reference to the prior art—if present in pairs—are connected in series (A1+A2) and (B1+B2) in pairs and in series in the opposite direction to each other. Thus, the first magnetic field detection device 20 corresponds to the analog structure and the analog channel of the single-channel known circuit from Fig. 6. The differential signal UAB is supplied as the measuring signal.

[0076] Additionally, a second magnetic field detection device 22 is provided for supplying a second measurement signal U2, UAT, which comprises only the at least one first magnetic field sensor 26-1 (e.g., only the one first magnetic field sensor 26-1 in the V-arrangement or only the pair of first magnetic field sensors A1+A2 in the X-arrangement) and supplies the measurement signal of only the at least one first magnetic field sensor 26-1. UAT is thus supplied as the measurement signal U2.

[0077] In addition, a computing device 40 is provided which computationally determines the measurement signal of the at least one second magnetic field sensor 26-2 from these measurement signals UAB and UAT.

[0078] In Fig. 10 is the magnetic field generation S1 by means of an H-bridge as driver circuit 24 (see Fig. 11) with subsequent edge attenuation S2. The magnetic field thus generated is applied to the test object 14 by means of the sensor head 10 and in particular the generator coil Lg. In step S3 - magnetic field detection - the coil arrangement of the sensor head 10 taps the signal AB (in the form of U1=UAB) and also the signal of the first magnetic field sensor(s) U2=UAT - corresponding to A - is tapped. In step S4, the tapped measurement signals U1, U2 undergo vibration damping by RC circuits R2-C2-R4 and R3-C3-R5, respectively, and amplification in a respective amplifier 42. They are then digitized in an AD converter and processed in the evaluation device 25.

[0079] Fig. 10 shows the digital signal evaluation path (from left to right), the last arrow represents the digital output, the signal processing enables compensation of temperature, hysteresis and the distance between sensor and test object.

[0080] Fig. Figure 11 shows a basic circuit for two-channel measurement data processing. The driver circuit 24, in the form of an H-bridge (four-quadrant controller, a typical motor driver = electronic H-bridge circuit consisting of four semiconductor switches (transistors) that convert a DC voltage (supply) into an AC voltage of variable frequency and pulse width (Out_1, Out_2)), drives the generator coil Lg (Gen). R1 ​​and C1 are used to generate sinusoidal signals from the square-wave signals. For example, magnetic fields with frequencies in the range of 1 kHz to 20 kHz are generated.

[0081] Sampling is preferably carried out at frequencies in the range from 1 kHz to several 100 kHz, with further preferably a common mode (e.g. implemented as software in a microprocessor) for improved amplitude measurement and an averaging over several wave trains (10 to 1000 wave trains) being carried out.

[0082] A further advantage of the described signal processing is the freedom of choice of ferromagnetic materials for the flux concentrator 30, which can be used in the present method in the respective coil-ferromagnetic material combinations. Current sensor heads 10 use not only iron cores milled from raw material, but also 3D-printed cores or transformer laminations that require expensive assembly. There is now the prospect of omitting the core itself entirely, in addition to commercially available, inexpensive ferrite cores, and covering the rear cover with a metallic foil.

[0083] In further embodiments not shown in detail here, the outputs of the individual magnetic field sensors 26-1, 26-2, A1, A2, B1, B2 can be tapped and evaluated individually or in different combinations, as a differential signal or a sum signal. Different measurement signals can thus be tapped and further measurement signals can be calculated from them. The first and second magnetic field measuring devices 20, 22 can thus be constructed from different magnetic field sensors 26-1, 26-2, A1, A2, B1, B2.

[0084] The four detector coils (A1, A2, B1, B2) can be interconnected in different ways depending on the application in order to obtain a usable measurement signal via an amplifier 42.

[0085] The interconnection of the coils or, more generally, the magnetic field sensors 26-1, 26-2 can be implemented as hardware - e.g., via a suitably designed circuit board element 36 - or in a switching electronics - e.g., controlled by software.

[0086] For this purpose, the outputs of detector coils A1, A2, B1, and B2 can be individually connected to sensor electronics, which either connects the outputs together or evaluates them individually, depending on the application. In particular, subgroups of detector coils can be tapped in the same direction to generate a sum signal or with different polarity to obtain a differential signal.

[0087] An advantage of such a preferred embodiment of the signal conditioning described here is the alternating wiring of the coil pairs, so the wiring (A1-B1) - (A2-B2) allows local defects (e.g. cracks in the shaft) to be detected (this is not possible today with the A3 integral sensor designed as X).

[0088] This option of alternating (e.g. reciprocal) wiring has another advantage: in the context of safety-relevant applications (e.g. SIL classification according to the IEC 61508 series of standards "Functional Safety of Safety-Related Electrical / Electronic / Programmable Electronic Systems"), various methods for controlling or eliminating faults can be supported. This enables monitoring during operation to detect random faults, as well as the safe control of detected faults and the transition to a safely defined state. For this purpose, two signal paths can be used, with evaluations carried out in the first channel (A1-B1) and the second channel (A2-B2). If these two originally identical values ​​deviate by, for example, more than twice their specification, the two pieces of information can be offset against each other and, if necessary, checked for plausibility.

[0089] If the coils are connected according to (A1+B1) - (A2+B2), it is advantageous to find out whether stress gradients or transverse forces occur - this constellation is, however, not exclusively used in applications in which varying axle loads and different traction ratios are to be determined.

[0090] If the coils A1, A2, B1 and B2 are sampled directly and combined with each other in a second process step, additional information on the temporal signal invariance can be obtained.

[0091] In the area of ​​large diameters > 100 mm of the test object 14 (e.g., a shaft), the methodology can be advantageously used to arrange several individual sensors around a rotating shaft (as described and shown in DE 10 2017 107 111.3) and then calculate their measurements. In this case, the signal to be analyzed is based on the multiple circuit n[(A1+A2)-(B1+B2)], which then allows averaged data processing in a second step. For example, n = the number of measuring points assumes values ​​between four and sixteen.

[0092] All described interconnections and constellations can generally be used either in an “X” mode (X arrangement 28, Fig. 1) or in a “V” mode (V arrangement 32, Fig.2) are used. In the first case, four detector coils are provided in addition to the generator coil Lg; in the second case, two detector coils are provided in a special arrangement (angles between 70 and 110°). In the case of two coils (V-arrangement 32), A1-B1 is selected. This has the advantage that a simple integral sensor consisting of two to, for example, sixteen elements, as described in DE 10 2017 107 111.3 for four measuring elements, allows for significantly higher resolution around the shaft and thus the signal non-uniformity can be further improved in the case of poor concentricity (from 1% FS to 0.2% FS).

[0093] Finally, from the alternating fields at Lg and at Ai, Bi (with i= 1 or the relative phase relationship between signal A and B, the phase between A or B relative to the generator as well as the sampled signal (AB) relative to the generator can be derived and usefully calculated.

[0094] In this context, the reverse-connected (see alignment of the coil with the beginning of the windings) and the synchronized configuration of all described variants are also considered to fall under the invention.

[0095] A preferred embodiment of the method for measuring a force or voltage applied to a test object 14 comprises the following steps: generating a magnetic field; Applying the generated magnetic field to the test object 14; Applying a force to the test object 14; Detecting the magnetic field changed by the test object 14 as a result of the applied force with a first magnetic field detection device 20 and providing a first measurement signal U1, UAB with the first magnetic field detection device 20 (“AB”); Detecting the magnetic field changed by the test object 14 as a result of the applied force with a second magnetic field detection device 22 and providing a second measurement signal U2, UAT with the second magnetic field detection device 22 (“A” or “B”); Calculation of the third measurement signal UBT (“B” or “A”) from the first measurement signal (“AB”) and the second measurement signal (“A” or “B”); Determining the resulting signal “output signal A*-B*” as the difference between the second measurement signal and the third, mathematically determined measurement signal = amplitude (A) - amplitude (B); Determine the force or voltage applied to the test object based on the resulting signal.

[0096] Preferably, the sum signals of coils A1+A2+B1+B2 can be tapped and evaluated, thus advantageously allowing a distance measurement to the test object 14 to be realized. Thus, in addition to the force or voltage, the distance between the sensor head 10 and the test object 14 can also be measured.

[0097] Furthermore, an averaged common mode is preferred to achieve a simplified amplitude measurement.

[0098] Preferably, additionally or alternatively, a measurement signal from a circuit (A1+B1) - (A2+B2) can be tapped.

[0099] As mentioned, two or four solid-state magnetic field sensors 27 can also be used instead of the detector coils A1, A2, B1, B2. Especially when such magnetic field sensors 27 are used, the concept presented here also works with direct current and / or a non-changing magnetic field. List of reference symbols: 10 Sensor head 12 Load measuring device 14 test object 16 Load measuring arrangement 18 Magnetic field generating device 20 first magnetic field detection device 22 second magnetic field detection device 24 driver circuit 25 Evaluation device 26 Magnetic field sensor 26-1 first magnetic field sensor 26-2 second magnetic field sensor 27 Solid-state magnetic field sensor 28 X-arrangement 30 Flow concentrator 32 V arrangement 34 Planar coil 36 PCB element 40 computing device 42 amplifiers 44 A / D converters 112 Load measuring device (state of the art) A1 first detector coil A2 first detector coil B1 second detector coil B2 second detector coil LG generator coil S1 Magnetic field generation S2 edge weakening S3 Magnetic field detection S4 Vibration damping, amplification S5 A / D conversion, signal processing

Claims

[1] Load measuring method for measuring a mechanical load on a test object (14), comprising the steps: a) generating and applying a magnetic field to the test object (14) by means of a magnetic field generating device (18), b) detecting a magnetic field changed by the test object (14) as a result of a mechanical load on the test object (14) by means of a first magnetic field detection device (20) in order to generate a first measurement signal (U1, UAB), c) detecting a magnetic field changed by the test object (14) as a result of the mechanical load on the test object (14) by means of a second magnetic field detection device (22) in order to generate a second measurement signal (U2, UAT), d) Calculating a third measurement signal (UBT) from the first measurement signal (U1, UAB) and the second measurement signal (U2, UAT), and e) determining an output signal from the third measurement signal and at least one of the first and second measurement signals (u1, U2) and f) determining the mechanical load applied to the test object (14) based on the output signal; 1.1 wherein step e) comprises: forming the difference between one (U2, UAT) of the first and second measurement signals and the computationally determined third measurement signal (UBT) to generate the output signal, and / or 1.2 where step b) comprises: Detecting the changed magnetic field by means of several magnetic field sensors (26-1, 26-2; A1, A2, B1, B2) connected in series and tapping a sum or difference signal (UAB, U1) from these magnetic field sensors (26-1, 26-2; A1, A2, B1, B2), and wherein step c) comprises: Detecting the changed magnetic field by means of one (A1) or a subgroup (26-1, A1, A2) of these magnetic field sensors (26-1, 26-2; A1, A2, B1, B2) in order to tap a partial signal (U2, UAT) from this one or the subgroup of magnetic field sensors (26-1, 26-2; A1, A2, B1, B2). [2] Load measuring method according to claim 1, characterized by , that step b) comprises detecting the changed magnetic field by means of at least one first magnetic field sensor (26-1) and at least one second magnetic field sensor (26-2) and tapping a difference signal from the at least one first (26-1) and the at least one second (26-2) magnetic field sensor in order to generate the first measurement signal and that step c) comprises detecting the changed magnetic field by means of the at least one first magnetic field sensor (26-1) in order to generate the second measurement signal and that step d) comprises computationally determining the measurement signal of the second magnetic field sensor (26-2) from the difference signal and the measurement signal of the first magnetic field sensor (26-1). [3] Load measuring method according to one of the preceding claims, characterized by , 3.1 that step b) comprises detecting the changed magnetic field by means of at least two first magnetic field sensors (26-1, A1, A2) and at least two second magnetic field sensors (26-2, B1, B2) and that step b) comprises using such a connection of the magnetic field sensors (26-1, 26-2) that the signals of a pair of a first (A1, A2) and a second (B1, B2) magnetic field sensor are added analogously and the signals of the pairs (A1, A2; B1, B2) are subtracted analogously and output as an analog difference signal (U1, UAB), and / or 3.2 that furthermore the sum signals of the at least one first magnetic field sensor (26-1) and the at least one second magnetic field sensor (26-2) are tapped and evaluated in particular for detecting a distance to the test object (14) and / or 3.3 that an amplitude of the signal of the at least one second magnetic field sensor (26-2) is determined as the third measurement signal in order to determine a difference between the amplitudes of the signals from the at least one first magnetic field sensor (26-1) and the at least one second magnetic field sensor (26-2) as the resulting output signal and / or 3.4 that a coil (A1, A2, B1, B2) or a solid-state magnetic field sensor (27) is used as the magnetic field sensor (26-1, 26-2) and / or 3.5 that the interconnection of the plurality of magnetic field sensors (26-1, 26-2; A1, A2, B1, B2) is varied in order to tap different sum or difference signals from the plurality of magnetic field sensors. [4] Load measuring method according to one of the preceding claims, characterized by , 4.1 that step a) comprises the imposition of an alternating magnetic field, in particular with frequencies of 1 kHz to 1000 kHz, and that steps b) and c) comprise averaging the measurement signals over several wave trains, preferably averaging over between 10 and 10,000 wave trains and / or 4.2 that at least one sensor head (10) is used, which has magnetic field sensors (26-1, 26-2; A1, A2, B1, B2) of the first and second magnetic field detection devices (20, 22) and a generator coil (Lg) of the magnetic field generation device (18), and / or 4.3 that a plurality of sensor heads (10), each having magnetic field sensors (26-1, 26-2; A1, A2, B1, B2) of the first and second magnetic field detection devices (20, 22) and a generator coil (Lg) of the magnetic field generation device (18), are arranged distributed around the test object (14) and are used for joint measurement signal generation, 4.4 that at least one sensor head (10) is used which has planar coils (34) as magnetic field sensors (26-1, 26-2; A1, A2, B1, B2) of the first and second magnetic field detection devices (20, 22) and as a generator coil (Lg) of the magnetic field generation device (18), which are arranged in or on a circuit board element (36). [5] Load measuring method according to one of the preceding claims, characterized by that steps b) and c) comprise an averaged common mode for amplitude measurement. [6] Load measuring method according to one of the preceding claims, characterized bythat at least one X-arrangement (28) or V-arrangement (32) of magnetic field sensors (26-1, 26-2) of the first and second magnetic field detection device (20, 22) and the magnetic field generating device (18) with a common ferromagnetic reinforcement core (30) is used. [7] Load measuring method according to claim 6, characterized by that several X or V arrangements (28, 32) are used distributed around the test object (14). [8] Load measuring device (12) for measuring a mechanical load on a test object (14) comprising: a magnetic field generating device (18) for applying a magnetic field to the test object (14), a first magnetic field detection device (20) for detecting a magnetic field changed by the test object (14) as a result of a mechanical load on the test object (14) and for supplying a first measurement signal (U1, UAB), a second magnetic field detection device (22) for detecting a magnetic field changed by the test object (14) as a result of the mechanical load on the test object (14) and for supplying a second measurement signal (U2, UAT), and a computing device (40) for calculating a third measurement signal (UBT) from the first measurement signal (U1, UAB) and the second measurement signal (U2, UAT), and an evaluation device (25) which is designed to generate an output signal indicating the mechanical load from the third measurement signal (UBT) and at least one of the first (UAB) and the second measurement signal (UAT), characterized by , 8.1 that the evaluation device (25) is designed to form a difference between one (UAT) of the first and second measurement signals and the computationally determined third measurement signal (UBT) in order to generate an output signal on the basis of which the mechanical load applied to the test object (14) can be determined, and / or 8.2 that the first magnetic field detection device (20) has a plurality of magnetic field sensors (26-1, 26-2; A1, A2, B1, B2) connected in series to tap a common signal (UAB, U1) from the plurality of magnetic field sensors (26-1, 26-2; A1, A2, B1, B2), and that the second magnetic field detection device (22) has one (A1) or a subgroup (26-1, A1, A2) of these magnetic field sensors (26-1, 26-2; A1, A2, B1, B2) belonging to the first magnetic field detection device (20) in order to tap a signal only from a part of the magnetic field sensors (26-1, 26-2; A1, A2, B1, B2) of the first magnetic field detection device (20). [9] Load measuring device (12) according to claim 8, characterized by , that the first magnetic field detection device (20) has at least one first magnetic field sensor (26-1) and at least one second magnetic field sensor (26-2) and is designed to tap a difference in amplitudes of signals of the first and the second magnetic field sensor (26-1, 26-2) from the at least one first (26-1) and the at least one second magnetic field sensor (26-2), this difference forming the first measurement signal (U1, UAB), and that the second magnetic field detection device (22) comprises the at least one first magnetic field sensor (26-1) and is designed to output an amplitude from the first magnetic field sensor (26-1) as a second measurement signal, and that the computing device (40) is designed to computationally determine the amplitude of the second magnetic field sensor (26-2) from the difference signal (UAB) and the measurement signal of the first magnetic field sensor (26-1) and to output it as a third measurement signal. [10] Load measuring device according to claim 8 or 9, characterized by , 10.1 that the first magnetic field detection device (20) comprises at least two first magnetic field sensors (26-1, A1, A2) and at least two second magnetic field sensors (26-2, B1, B2) and such an interconnection of the magnetic field sensors (26-1, 26-2, A1, A2, B1, B2) that the signals (UAT, UBT) of a pair (A1, A2; B1, B2) of a first (26-1) and a second (26-2) magnetic field sensor are added analogously and the signals of the pairs are subtracted analogously and output as an analog difference signal (U1, UAB), and / or 10.2 that a sum signal tapping device is further provided for tapping sum signals of the at least one first magnetic field sensor (26-1) and the at least one second magnetic field sensor (26-2), wherein in particular the evaluation device (25) is designed to detect a distance to the test object (14) by evaluating the sum signals and / or 10.3 that the computing device (40) is designed to determine an amplitude of the signal of the at least one second magnetic field sensor (26-2) as a third measurement signal, and that the evaluation device (25) is designed to determine a difference between the amplitudes of the signals from the at least one first magnetic field sensor (26-1) and the at least one second magnetic field sensor (26-2) as a resulting output signal, and / or 10.4 that coils (A1, A2, B1, B2) or solid-state magnetic field sensors (27) serve as magnetic field sensors (26-1, 26-2) and / or 10.5 that a device is provided for variably interconnecting the magnetic field sensors (26-1, 26-2, A1, A2, B1, B2), in particular for reversing or rectifying the polarity of one or a subgroup (26-1, A1, A2) of the magnetic field sensors relative to the remaining magnetic field sensors (26-2, B1, B2). [11] Load measuring device (12) according to one of claims 8 to 10, characterized by , that the magnetic field generating device (18) is designed to impose an alternating magnetic field, in particular with frequencies of 1 kHz to 1000 kHz, on the test object, and that the evaluation device (25) is designed to average the measurement signals over several wave trains, wherein preferably an averaging is carried out over between 10 and 10,000 wave trains. [12] Load measuring device (12) according to one of claims 8 to 11, characterized by , 12.1 that a common mode device is provided for the averaged common mode of the magnetic field sensors for amplitude measurement and / or 12.2 that magnetic field sensors (26, 26-1, 26-2) of the first and second magnetic field detection device (20, 22) and the magnetic field generating device (18) form an X-arrangement (28) or a V-arrangement (32), preferably with a common ferromagnetic reinforcement core (30), and / or 12.3 that at least one sensor head (10) is provided, which has magnetic field sensors (26-1, 26-2; A1, A2, B1, B2) of the first and second magnetic field detection devices (20, 22) and a generator coil (Lg) of the magnetic field generation device (18), and / or 12.4 that a plurality of sensor heads (10), each having magnetic field sensors (26-1, 26-2; A1, A2, B1, B2) of the first and second magnetic field detection devices (20, 22) and a generator coil (Lg) of the magnetic field generation device (18), are arranged distributed around the test object (14) and are designed for common signal generation, 12.5 that at least one sensor head (10) is provided which has planar coils (34) as magnetic field sensors (26-1, 26-2; A1, A2, B1, B2) of the first and second magnetic field detection devices (20, 22) and as a generator coil (Lg) of the magnetic field generation device (18), which are arranged in or on a circuit board element (36). [13] Load measuring arrangement (16) comprising a load measuring device (12) according to one of claims 8 to 12 and a test object (14) whose load is to be measured.

Images