Apparatus and method for measuring impedance of tribological contacts

Abstract

An apparatus for measuring an impedance (Z) along a current path (P) through a first machine component (10) and a second machine component (20) is disclosed. The first machine component (10) and the second machine component (20) are mounted for movement relative to one another, and the apparatus can be connected to a voltage source (50). The apparatus comprises: a first coil (T1), a second coil (T2), an ammeter (300) and an evaluation device (400). The first coil (T1) comprises a first coil core (112) around which a first coil winding (114) is wound, the first coil core (112) extending at least partially around the first machine component (10) and the first coil winding (114) being able to be excited by an alternating voltage signal (UB) from the voltage source (50) in order to inductively generate an alternating current (I) along the current path (P). The second coil (T2) comprises a second coil core (212) around which a second coil winding (214) is wound, the second coil core (212) extending at least partially around the first machine component (10) in order to generate a measurement current (Ib) in the second coil (T2) as a result of the induced alternating current (I) along the current path (P). The ammeter (300) is designed to measure the measurement current (Ib) generated in the second coil winding (214). The evaluation device (400) is designed to determine the impedance (Z) along the current path (P) on the basis of the alternating voltage signal (Ub) and the measurement current (Ib).

Description

[0001] DEVICE AND METHOD FOR IMPEDANCE MEASUREMENT OF TRIBOLOGICAL CONTACTS

[0002] The present invention relates to a device and a method for measuring impedances for currents through mounted machine components and in particular to a wear-free inductive impedance spectroscopy of rolling bearings.

[0003] BACKGROUND

[0004] Until now, sliding contacts have primarily been used to measure bearing impedances during operation, creating a current between two machine components that move relative to each other. By measuring this current, a resistance or capacitance value, and thus the impedance along the current path between the machine components, can be determined.

[0005] However, such an approach is subject to wear, as the sliding contacts must be replaced regularly. Furthermore, the sliding contacts do not provide reliable, consistent contact with the corresponding moving components, resulting in considerable noise in the recorded measurement signal. Eventually, the sliding contacts used become dirty, and at high speeds, contact is no longer reliable. All of this leads to a contact impedance that can no longer be ignored and is difficult to measure or compensate for.

[0006] Therefore, there is a need for devices and methods for measuring bearing impedances that can be reliably measured over long periods without resorting to sliding contacts. BRIEF DESCRIPTION OF THE INVENTION

[0007] At least some of the above-mentioned disadvantages are overcome by a device according to claim 1, a machine holder according to claim 9 and a method according to claim 12 or 14.

[0008] Embodiments relate to a device for measuring an impedance of at least one tribological contact along a current path between a first machine component and a second machine component. The first machine component and the second machine component are mounted so as to be movable relative to one another, and the device is connectable to a voltage source. The device comprises a first coil, a second coil, an ammeter, and an evaluation device.

[0009] The first coil comprises a first coil core around which a first coil winding is wound, the first coil core extending at least partially around the first machine component. The first coil winding can be excited by an alternating voltage signal from the voltage source to inductively generate an alternating current along the current path.

[0010] The second coil comprises a second coil core around which a second coil winding is wound. The second coil core extends at least partially around the first machine component to generate a measuring current in the second coil through the induced alternating current along the current path.

[0011] The ammeter is configured to measure the measuring current generated in the second coil winding. The evaluation device is configured to determine the impedance along the current path based on the AC voltage signal and the measuring current.

[0012] In the simplest case, the at least one tribological contact is a bearing that holds the machine components. However, the at least one tribological contact can also be or include a seal (e.g., a mechanical seal), a chain, a toothed element (e.g., gears), or a cam-and-tappet contact. In a mechanical seal, one part can be fixed to one machine component (e.g., a shaft) and the other fixed to the other machine component (e.g., a housing).

[0013] In this disclosure, the term "bearing" should be understood to include all elements or components suitable for maintaining two relatively movable machine elements in a well-defined state relative to each other. Bearings include, for example, rolling bearings or plain bearings to ensure rotary movements (e.g., of shafts or wheels) or linear movements (e.g., of rails).

[0014] The current path can be galvanically closed or open. It is understood that this definition depends on the frequency. A galvanically open current path for a direct current can represent a closed current path for an alternating current.

[0015] The first coil can thus represent an excitation coil, while the second coil can be a measuring coil that measures the current generated by the excitation of the first coil. The alternating voltage signal can be applied to the first coil by the voltage source through appropriate contacts. The voltage source can apply a predetermined alternating voltage signal as the alternating voltage signal. For example, the signal can have a specific frequency, but it can also have a predetermined frequency curve or a specific frequency range to enable frequency dependence in the determination of the impedance.

[0016] The evaluation device is, for example, connected to the voltage source and can control it. The evaluation device can also be connected to the ammeter in order to obtain the corresponding results of the current measurement. It is understood that the first machine component and the second machine component only need to be movable relative to one another. For example, one of the two machine components can represent a housing or holder that allows movement of the other machine component. The movement can be, for example, a rotation. However, embodiments are not restricted to rotation. It is also possible for a relative linear movement to take place between the two machine components.Accordingly, corresponding bearings, such as rolling bearings, ball bearings, plain bearings, are formed between the first machine component and the second machine component, which enable the corresponding movement between the machine components.

[0017] Optionally, the first coil comprises a further coil winding, which is also wound around the first coil core and is electrically insulated from the first coil winding, and / or a voltmeter. The technical effect of the further coil winding is that it largely eliminates the influence of the first coil or the first coil winding on the measurement, since the further coil winding measures the voltage induced by the first coil, so that, for example, the efficiency of generating the induced alternating current is irrelevant. This offers the advantage that the induced voltage can be measured independently of the magnetizing current.

[0018] The ammeters can, for example, include a shunt resistor to convert the current into a voltage signal, which can then be easily measured with a voltmeter. Knowing the resistance value of the shunt resistor allows a clear conclusion to be drawn about the current. The current can be determined, for example, in the evaluation device. For this purpose, the evaluation device receives the corresponding measurement results from the ammeter or voltmeter and determines the current value based on them.

[0019] Optionally, the first coil core is arranged in a ring shape around its entire circumference, around part of the first machine component. The first coil winding and the further coil winding can be formed singly (once) or multiple times in different angular sections of the annular coil core. The first coil core can thus be a ring that has been slipped onto the first machine component or a part thereof (e.g., part of a shaft or another elongated section, such as a rail). Along this annular coil core, the first coil winding can be formed in one angular section (e.g., between a first angle and a second angle), while the further coil winding is formed in another angular section (e.g., between a third angle and a fourth angle).According to embodiments, it is also possible for the first coil winding and the second coil winding to alternate, so that a plurality of first windings and a plurality of further coil windings are formed along the annular coil core. It would also be possible for the first coil winding and the further coil winding to be wound one inside the other, since they are electrically insulating, so that no short circuit can occur.

[0020] Optionally, the evaluation device is configured to control the voltage source and optionally apply the AC voltage signal to the first coil winding or to apply no voltage. If no voltage is applied to the first coil winding, the evaluation device can determine the impedance and / or the measuring current during the relative movement of the first machine component and the second machine component.

[0021] The evaluation device according to this exemplary embodiment is thus capable of switching off the voltage source and detecting the current flowing in the first machine component independently of the voltage source. This current can be caused, for example, by an inverter-driven electric motor, e.g., as rotor-ground current, circular current, EDM current, or capacitive bearing current. The bearing currents can also arise from electrostatic charging or from induction due to rapid switching operations in inverters. The evaluation device can compensate for existing currents by deliberately applying an alternating voltage signal, so that no current subsequently flows during the movement of the first machine component and the second machine component.This compensating alternating current offers the advantage of significantly reducing wear and aging on the bearings between the first and second machine components. Induced bearing currents are a source of increased wear.

[0022] Therefore, the evaluation device is optionally configured to apply the alternating voltage signal to the first coil winding based on a previously measured measuring current such that the second coil winding is current-free. In further embodiments, the deliberately generated countercurrent can be dynamically adjusted to continuously keep the bearing current-free (also taking aging processes into account).

[0023] Optionally, the evaluation device is configured to generate the AC voltage signal based on one of the following modulation methods:

[0024] - Amplitude modulation,

[0025] - phase modulation,

[0026] - Frequency spreading,

[0027] Orthogonal frequency division multiplexing, OFDM, with randomly selected phases for subcarriers.

[0028] Spread spectrum is a process in which a narrowband signal, which only covers a small frequency range, is converted into a signal with a wider bandwidth, whereby the energy previously concentrated in the narrow frequency range is distributed over the wider frequency range. Frequency spread is used in signal transmission to reduce interference from neighbouring electrical devices, thus achieving greater robustness against narrowband interference. In mechanical components, very specific frequencies are often subject to interference which, for example, are correlated with certain speeds of the rotating objects. Another important source is the electrical circuits used. The frequency range of the mechanical vibrations correlated with the speed is often many orders of magnitude below the relevant measurement frequency.Vibrations of the machine element can be the desired measurement variable.

[0029] OFDM frequency division multiplexing is an orthogonal frequency division multiplexing technique that uses perpendicular frequency bands for signal transmission. Multiple orthogonal carriers are used for data transmission, whereby the orthogonal carriers cannot, in principle or ideally, interfere with each other because they transmit orthogonal signals.

[0030] The AC voltage signal according to this embodiment is not applied at just one specific frequency. Rather, a variety of frequencies are used. This allows the frequency dependence of the impedance to be accurately captured.

[0031] Optionally, the evaluation device is configured to store calibration data, wherein the calibration data defines a correction for a measured voltage value and / or a measured current value or their Fourier transform. For example, the calibration data in the evaluation device is so-called de-embedding calibration data, which takes into account the embedding of the device in a specific environment or can compensate for corresponding influences that have nothing to do with the bearing impedance. In this calibration, for example, predetermined bearings are used between the first and second machine components, the electrical conductivity or impedance of which is known. Thus, in subsequent measurements, the bearing impedance can be determined as a deviation from the predetermined bearings. Therefore, only the bearing impedance or its change is determined, but not the impedance of the environment (embedding of the bearings).The calibration can be created as a curve or a table containing the correction values ​​for the measured complex quantities. Embodiments also relate to a machine mount having a first machine component and a second machine component, a first tribological contact and a second tribological contact, wherein the first tribological contact and the second tribological contact are formed between the first machine component and the second machine component. The machine mount also comprises at least one device as previously described, wherein the first coil and the second coil of the device are arranged between the first tribological contact and the second tribological contact in order to determine an impedance of the first tribological contact and the second tribological contact.

[0032] Optionally, the machine mount comprises a plurality of tribological contacts and a plurality of devices as previously described. The first tribological contact and the second tribological contact are then two adjacent tribological contacts from the plurality of tribological contacts, and one device from the plurality of devices is arranged between further adjacent tribological contacts along the first machine component or another machine component.

[0033] Optionally, the machine mount comprises one or more of the following features: the first machine component is a shaft, the second machine component comprises a mount for the first machine component, the second machine component comprises a housing for the first machine component, the first machine component and the second machine component are electrically conductively connected,

[0034] - the first tribological contact is a rolling bearing or a plain bearing or a toothed element or a chain or a cam-follower contact, the second tribological contact is a rolling bearing or a plain bearing or a toothed element or a chain or a cam-follower contact.

[0035] For example, the two inner and outer rings of the (rolling) bearings sit in their bearing seats without any additional insulation, with the bearing seats being electrically connected to each other by metal parts (e.g., the shaft or housing). It does not matter whether the shaft or the housing, for example, or both parts, rotate. The device arrangement described above can be mounted between the two bearings, which fulfills at least two functions:

[0036] 1. A first coil wound around a sample ferrite core applies a differential voltage (a monofrequency or multifrequency AC signal) between the left and right parts of the wave. This is possible even though the wave is a single piece of metal. The two "halves" of the wave therefore have different electrical potentials.

[0037] 2. Another coil wound around a ferrite core measures the current resulting from the differential voltage flowing through the two bearing impedances.

[0038] The impedance of the series circuit can be calculated from the measured current and voltage.

[0039] Embodiments also relate to a method for determining an impedance along a closed current path through a first machine component and a second machine component, wherein the first machine component and the second machine component are mounted so as to be movable relative to one another. The method comprises:

[0040] Inductively generating an alternating current along the closed current path by a first coil which is excited by an alternating voltage signal and which extends at least partially around the first machine component;

[0041] Generating a measuring current in a second coil by the induced alternating current along the closed current path, wherein the second coil extends at least partially around the first machine component;

[0042] Measuring the measuring current; and

[0043] - based on the AC voltage signal and the measuring current, determining the impedance along a closed current path.

[0044] Optionally, the procedure further includes the following:

[0045] Performing a calibration by using a single frequency or a plurality of frequencies of a frequency band for the AC signal and using a predetermined bearing with predetermined electrical properties (electrical characteristics) between the first and the second machine component.

[0046] Embodiments also relate to a method for measuring a bearing impedance of one or more bearings between a first machine component and a second machine component. The method comprises:

[0047] - forming an alternating voltage signal with a frequency spread along a current path between the first machine component and the second machine component;

[0048] Detecting a measuring current generated by the modulated AC voltage signal;

[0049] - Conduct impedance spectroscopy for the bearing(s) based on the modulated AC voltage signal and the measured current. One of the modulation methods mentioned above can be used for this purpose.

[0050] These methods, or at least parts thereof, can also be implemented or stored in the form of instructions in software or on a computer program product, wherein stored instructions are capable of carrying out at least some steps of the method when the method is run on a processor. Therefore, the present invention also relates to a computer program product or a computer-readable storage medium having software code (software instructions) stored thereon, which is designed to carry out one of the previously described methods or parts thereof when the software code is executed by a processing unit. The processing unit can be any form of computer or control unit (e.g., the evaluation device having a corresponding microprocessor capable of executing software code). The processing unit can also be an FPGA configuration or an ASIC.For example, the stored software may be configured to perform the step of determining according to the method when the software is installed on the evaluation device.

[0051] Compared to conventional methods, practical examples offer the following advantages:

[0052] - Through contactless inductive couplings, both a voltage and a current can be impressed and measured in exemplary double roller bearings without having to use parts subject to wear.

[0053] - The properties of the inductive coupling can be compensated by a broadband calibration procedure, so that the measurement results provide clear conclusions about the bearings and the condition of the bearings, while the influences of the used (inductive) coupling can be compensated.

[0054] - The broadband nature of impedance spectroscopy also helps to avoid interference caused by emissions and couplings of electric or magnetic fields, which often occur in metallic machine components that are movable relative to one another and generally wherever power electronics (or similar) are used.

[0055] - This also means that maintenance work can be reduced, as wear-free monitoring of rolling bearings becomes possible.

[0056] - Finally, the overall reliability of the rolling bearings is increased and early detection of damage is possible.

[0057] BRIEF DESCRIPTION OF THE CHARACTERS

[0058] The embodiments of the present invention will be better understood from the following detailed description and the accompanying drawings of the various embodiments, which, however, should not be construed as limiting the disclosure to the specific embodiments, but are for explanation and understanding only.

[0059] Fig. i shows a sectional view through an embodiment of a device for measuring bearing impedances.

[0060] Fig. 2 shows a spatial view of the embodiment from Fig. i.

[0061] Fig. 3A, 3B show equivalent circuit diagrams for measuring devices as implemented by embodiments.

[0062] Fig. 4A B show an embodiment of a complex machine mount with a plurality of tribological contacts, the impedances of which can be determined using a plurality of devices.

[0063] Fig. 5 shows a schematic flow diagram for a method for measuring a bearing impedance of at least one bearing. DETAILED DESCRIPTION

[0064] Fig. i shows a sectional view through an embodiment of a device for measuring bearing impedances for a movably mounted first machine component 10 relative to a second machine component 20. In the present case, it is a rolling bearing, wherein the first machine component 10 can be, for example, a shaft 10 and the second machine component 20 can be a holder for the shaft 10 or a housing which holds the shaft 10 during the rotational movement about an axial axis R.

[0065] It is understood that embodiments are not intended to be limited to rolling bearings or rotary movements, but are also applicable to linear movements or other movements that are possible between two machine components that are movable relative to one another. In particular, the impedance measurement can relate to any type of tribological contact (e.g., gears, mechanical seals, cam-tappet contact). For the sake of simplicity, various aspects of embodiments are described below for rotary movements of a shaft that is supported or held by two rolling bearings.

[0066] By way of example, the exemplary embodiment from Fig. 1 comprises a first bearing 30 and a second bearing 40 (e.g. rolling bearings), which are arranged between the first machine component 10 and the second machine component 20. The exemplary rotational movement is made possible by rolling elements 35, 45. A first coil Ti and a second coil T2 are arranged at least (at least) partially around the first machine component 10. The first coil Ti and / or the second coil T2 can be formed with their coil bodies 112, 212 in a ring shape around the first machine component 10. The first machine component 10 can be a cylindrical shaft, wherein the exemplary rotational movement plays no role for the sensing.

[0067] It is important that a closed current path P is present between the first machine component 10 and the second machine component 20. Ideally, no insulating layer is formed along the current path P. For example, the first rolling bearing 30 and the second rolling bearing 40 are in direct metallic contact with the first machine component 10 and the second machine component 20 (i.e., there is no insulating layer between the rolling bearings 30, 40 and the machine components 10, 20). However, there may be corresponding gaps (e.g., lubrication gaps) between the machine components 10, 20 or in the rolling bearings 30, 40, which may lead to a capacitive effect being present there. However, this may also be an indication of wear, so that embodiments can detect such a gap in a change in the electrical characteristic.

[0068] The concrete arrangement of the elements can be as follows, for example. The first coil Ti comprises a first coil core 112, around which a first coil winding 114 is wound at least in section. It is understood that the drawing is only a schematic representation, i.e. the coil core 112 and the coil windings 114 are only shown very schematically. The coil core 112, in turn, can be annular and extends around at least part of the first machine component 10. The second coil T2 can be formed in the same way. That is, the second coil T2 can comprise a second coil core 212, around which a second coil winding 214 is wound. The second coil core 212 can likewise extend at least partially as a ring around the first machine component 10.The first coil Ti and the second coil T2 are arranged between the first bearing 30 and the second bearing 40, such that an electric current I induced by the first coil Ti flows along the current path P through the openings of the ring-shaped first coil core 112 and through the ring-shaped second coil core 212. The induced alternating current I thus encloses both a part of the first coil Ti and a part of the second coil T2. The corresponding current paths are thus interlaced. As a result of this arrangement, upon excitation of the first coil Ti, the closed alternating current I is induced and can simultaneously be detected by the second coil T2, since the alternating current I induces a measuring current Ib there. For this effect, it is therefore sufficient that the closed current path P runs through both coils Ti, T2 in a central region.In other words, the closed current path P runs along the shaft parallel to the magnetic field lines generated by the coils Ti and T2, or the first coil Ti and the second coil T2 cannot be separated from each other without crossing the closed current path.

[0069] The exemplary embodiment of the device further comprises an ammeter 300 and an evaluation device 400. The ammeter 300 is designed to measure the measuring current Ib from the second coil T2. A voltage source 50 is coupled to the device and is designed to apply the corresponding alternating voltage signal Ub to the first coil Ti via corresponding supply lines. A connection between the voltage source 50 and the evaluation device 400 can be used, for example, to control the voltage source 50, to apply a specific alternating voltage signal Ub to the first coil Ti, or to transmit the information about the applied alternating voltage Ub to the evaluation device 400.

[0070] The evaluation device 400 can detect the impedance Z based on the measured measuring current Ib and the applied alternating voltage signal Ub at the first coil Ti, wherein the total impedance Z is the sum of individual impedances Za, Zb (e.g. of the first bearing 30 and the second bearing 40) along the current path P. In particular, a spectral detection can be carried out by the evaluation device 400, i.e. the functional dependence on the frequency can be determined. For this purpose, the frequency of the impressed alternating voltage signal Ub can be changed so that the impedance can be determined not only for one frequency, but for a plurality of frequencies or a frequency band. Fig. 2 shows a spatial view of the embodiment from Fig. 1, wherein the first machine component 10 is, by way of example, the shaft which is rotatably mounted in a holding device 20 by the first rolling bearing 30 and the second rolling bearing 40.The first rolling bearing 30 and the second rolling bearing 40 are spaced apart from each other along an axial direction (rotational axis) of the shaft. The first coil Ti and the second coil T2 are arranged laterally adjacent to each other between the spaced-apart rolling bearings 30, 40. The second machine component 20 is shown as a sleeve, for example. However, it can also be a housing, with the shaft 10 being guided out of the interior of the housing 20, for example.

[0071] Fig. 2 also shows the closed current path P, along which the electric current I is induced by the first coil Ti. The current path P runs laterally along the axial direction of the shaft 10, passes the first rolling bearing 30 and runs in the opposite direction back to the second rolling bearing 40. After passing the second rolling bearing 40, the electric current again enters the shaft 10 and thus forms the closed current path P. Along this closed current path P, the alternating current I is induced by the first coil Ti, wherein the frequency is given by the alternating voltage signal Ub, which is applied in the first coil Ti by the voltage source 50 (not shown in Fig. 2).

[0072] For example, the first rolling bearing 30 forms a first impedance Za and the second rolling bearing 40 a second impedance Zb, which represent a complex-valued resistance for the alternating electrical current I, which is composed of an ohmic resistance, a capacitive resistance and an inductive resistance. As long as there is direct galvanic contact between the metallic bodies, the magnitude of the impedance is primarily determined by the ohmic resistance. However, due to the lubrication of the rolling elements, a capacitive component is generally always present and the specific electrical characteristic (e.g. the complex phase) can be used to permanently monitor the condition of the rolling bearing. The measured impedance corresponds to the sum of the two partial impedances Z_a and Z_b, which occur between the outer ring and inner ring of rolling bearings 30, 40 mounted on the shaft and are conductively connected by the machine housing 20.

[0073] According to further embodiments, more than two impedances (e.g., rolling bearings, but also, for example, coupling capacitors or sliding contacts or other machine elements such as mechanical seals and gear contacts) can be present on the shaft 10 relative to the machine housing 20, in which case the above arrangement can be installed in the space between the impedances. In this case, an alternating electrical voltage is applied at several positions (each between two bearings), and the resulting currents are measured at all measuring points. This allows any number of impedances to be measured individually by solving the system of equations resulting from the circuit and the measured currents and voltages for the impedances.

[0074] Fig. 3A and Fig. 3B show corresponding equivalent circuit diagrams as they can be implemented by embodiments.

[0075] Fig. 3A shows an equivalent circuit diagram for the embodiment, as shown, for example, in Figs. 1 and 2. This circuit includes the voltage source 50, which is connected to a ground 52 and optionally also has an amplifier 55. The voltage source 50 couples to the first coil Ti to apply an alternating voltage Ub in the first winding 114. The first coil Ti comprises a coil core 112, which, for example, extends annularly around at least part of the first machine component 10 (see Figs. 1, 2).

[0076] In the embodiment shown, the first coil Ti comprises a further

[0077] Coil winding 116 to generate a voltage signal through the magnetic flux caused by the first coil winding 114, which voltage signal can be measured by a voltmeter 118. The first coil winding 114 comprises, for example, Ni windings, while the further coil winding 116 comprises N2 windings. The voltage sensing element 118 comprises, for example, a shunt resistor Zo or input resistor, which is connected in series with the further coil winding 116, so that the voltage induced there can be measured without reflections.

[0078] The first coil Ti is also coupled to a secondary winding with a number of turns of "1", which represents the closed current path P that runs through the first machine component 10 and the second machine component 20. The second machine component 20 can, for example, form the ground 52. The second winding 214 of the second coil T2 is arranged laterally spaced from the winding 114 of the first coil Ti (see, for example, Fig. 2). The impedances Za and Zb are also shown, which represent the impedance values ​​of the first rolling bearing 30 and the second rolling bearing 40 by way of example. Both impedances are connected to one another via the ground connection 52 (the second machine component 20). The second coil T2, in turn, comprises a second coil core 212, which can extend annularly around a part of the first machine component 10 and comprises a second winding 214, which has, for example, N3 windings.

[0079] The alternating current I along the closed current path P induces the measuring current Ib in the second winding 214 of the second coil T2. This measuring current Ib leads to a voltage drop across a shunt resistor Zo, which is, for example, part of the current sensor 300. Thus, the measuring current Ib and the voltage signal Ub can be transmitted to the evaluation device 400, where the first impedance Za and the second impedance Zb, or their sum, are determined based on them. The impedance Zo can also be the input impedance (500 Ω) of the (voltage) measuring device.

[0080] The operation of the arrangement shown can also be described as follows. A test signal U_test from voltage source 50 is optionally amplified using amplifier 55 and applied to the primary winding (first coil winding 114) of the first coil Ti (transformer; single-phase transformer). The resulting magnetic flux change generates a differential voltage U_diff (AC voltage signal Ub) across shaft 10. This can be measured via an auxiliary winding N_2 (further coil winding 116) or estimated from the amplifier output voltage. The differential voltage is divided across both partial impedances Z_a and Z_b according to their complex ratio and causes a current to flow through shaft 10.The current flow through the shaft 10 is measured by the second coil T2 (transformer; single-phase transformer) used as a current transformer by causing a proportional voltage drop / at the input impedance Z_o of the measuring transformer (ammeter 300).

[0081] The impedance can finally be calculated from the measured voltage signal U_diff and current signal: Z = U / I.

[0082] Optionally, the influence of the specific measurement setup can be removed from the measured values ​​by using previously determined calibration data. According to exemplary embodiments, all known de-embedding methods are suitable for this purpose: e.g., an open calibration, a short calibration, an open / short calibration, or an open / short / load calibration. These calibration methods eliminate, for example, influences from supply lines, adapters, the measurement setup, the geometries of the machine components 10, 20, and other parameters of the embedding of the device in a specific system. Specifically, a test gate can be switched in different ways: open (open), short (short), or a load (load) can be applied.

[0083] An OSLT (Open, Short, Load, Through) calibration is particularly suitable. With this method, the calibration data represents the inverse system of the test setup in the form of multi-port parameters. The calibration data is determined by measuring the system behavior at defined excitation voltages U_test or AC voltage signals Ub using test adapters. These test adapters can be implemented, for example, in the form of dummy bearings. These are components that are installed in place of the bearings and have defined electrical properties. For through-measurement, an additional measurement signal is fed out of the setup for each test adapter.

[0084] As described above, according to exemplary embodiments, an auxiliary winding N_2 (an additional coil winding 116) is used to determine the differential voltage U_diff, which can be wound around the same ferrite core (first coil core 112). The voltage U dropped across this winding is measured. It is proportional to the differential voltage U_diff. This minimizes the influence of the highly variable main inductance of the first coil Ti on the measurement result, since the magnetization current-dependent voltage dropped across the leakage inductance is not included in the measurement result.

[0085] The calibration data thus form correction values ​​for the specific setup and remain valid under different operating conditions, e.g. at different temperatures.

[0086] Fig. 3B shows an equivalent circuit diagram for an embodiment of the evaluation device 400, in which the alternating voltage signal Ub not only has a single frequency, but is a modulated signal, which is formed, for example, via a frequency spread. The signal evaluation is carried out as follows.

[0087] First, the AC voltage signal Ub and the measured current signal Ib are acquired by the evaluation device 400. In the evaluation device 400, both variables are transformed into the frequency domain using a fast Fourier transformation unit 410, 420. Accordingly, a voltage signal in the frequency domain Uf and a current signal in the frequency domain If are provided and converted into the corrected voltage signal Uf and the corrected current signal If using the (inverse) calibration data in a computing unit 430. A quotient device 440 then forms the ratio of the two variables, which ultimately provides the desired impedance Z. This replacement of a monofrequency signal U_test with a spread spectrum signal (frequency spread) initially offers the technical effect of reducing interference sensitivity and interference emission.In this case, it is also possible to perform impedance spectroscopy of the impedances Z to be measured. In a preferred embodiment, for example, an OFDM-based method with random subcarrier phases (OFDM; orthogonal frequency division multiplex) can be used. The measured values ​​are thus obtained by applying the Fourier transform 410, 420 to the measured values ​​U and / or subsequent application of the calibration data S-1 (in unit 430) and quotient formation in unit 440 (see Fig. 3B). The magnitude and phase of the connected impedance Z cause the phase and amplitude modulation of the individual subcarriers in these signals. This allows the impedance values ​​to be determined across the entire bandwidth of the input signal.

[0088] Fig. 4A shows an exemplary embodiment of a machine mount with a plurality of machine components 10, 20 that are movable relative to one another and a plurality of bearings 31, 32, ... and further exemplary gears 36 that couple the machine components 10, 20 to one another. Fig. 4B shows an equivalent circuit diagram for the current flows resulting from the various bearings 31, 32 and the gears 36, respectively. It is understood that only two machine components are shown as examples and that the machine mount can be as complex as desired and can have any desired tribological contacts.

[0089] Specifically, Fig. 4A shows, by way of example, a machine mount having a first bearing 31 and a second bearing 32, both of which rotatably support a first shaft 10, for example. The machine mount also comprises a third bearing 33 and a fourth bearing 34, which rotatably support a second shaft 20, for example. Furthermore, a first gear 36 is formed on the first shaft 10, and a second gear 37 is formed on the second shaft 20, which rotatably mesh with one another in order to transmit a rotary movement from the first shaft 10 to the second shaft 20, or vice versa. According to the exemplary embodiment shown, a first device 100a is formed on the first shaft 10 between the first gear 36 and the first bearing 31, and a second device 100b is formed between the first gear 36 and the second bearing 32.Similarly, a third device 100c is formed on the second shaft 20 between the second gear 37 and the third bearing 33, and a fourth device 100d is formed between the second gear 37 and the fourth bearing 34. The devices 100a, 100b, 100c, 100d can be formed in the same way as the devices previously described in Figures 1 to 3B. The first bearing 31, the second bearing 32, the third bearing 33, and the fourth bearing 34 can in turn be rolling bearings, ball bearings, or even plain bearings. However, they can also be seals (e.g., mechanical seals) or other tribological contacts. It is also possible for the first shaft 10 and the second shaft 20 to be arranged so as to be axially displaceable along their respective longitudinal directions, for example to enable switching between different gears. Fig. 4A shows only two gears 36, 37 as an example.It can also be a complex gearshift with multiple shafts.

[0090] Fig. 4B shows the corresponding equivalent circuit diagram for the current paths. The first bearing 31 comprises a first impedance Zi, the second bearing 32 is characterized by the second impedance Z2, the third bearing 33 by the third impedance Z3, and the fourth bearing 34 by the fourth impedance Z4. Likewise, the first gear 36 and the second gear 37, which mesh with each other, are characterized by a fifth impedance Z5. The first device 100a, the second device 100b, the third device 100c, and the fourth device 100d are also schematically illustrated and designed to measure the respective currents / voltages as previously described. Thus, a total of four current or voltage measurements can be performed independently of one another to detect the respective impedances. This can be performed by the evaluation device 400 shown. The machine mount shown is merely an example.According to further embodiments, additional gears, mechanical seals, rolling bearings, plain bearings, or even general contacts (e.g., cam-tappet contacts) can be provided, all of which allow the passage of alternating current. It is understood that an alternating current can also pass through a mechanical seal, even if two metallic objects are not necessarily in direct contact, but rather a small gap or insulating material is present. Nevertheless, alternating current propagation across a gap is possible, as is also the case in a capacitor. Depending on the specific mounting, the alternating current signal will have to be adapted accordingly in order to specifically select certain current paths.For example, depending on the selected frequency, a specific current path with a correspondingly low capacitive resistance can be selected, while other current paths with a higher capacitive resistance can be measured at other frequencies.

[0091] Therefore, exemplary embodiments do not refer solely to one fixed and one rotating part; the arrangement can also be more complex. For example, multiple bearings or general coupling impedances can be located on a shaft. These include, for example, the gears 36, 37 shown, which behave electrically very similarly to a bearing and for which the impedances can be determined according to exemplary embodiments. Depending on the number of devices 100 present, a system of equations results for determining the impedances of all tribological contacts (bearings, gears, etc.).

[0092] Further embodiments utilize this signal processing not only in conjunction with the inductive measuring device described above, but also for other bearing impedance measurements. Therefore, embodiments also relate to a method for measuring a bearing impedance of at least one bearing between a first machine component 10 and a second machine component 20, the method comprising the following: - forming an alternating voltage signal Ub with a frequency spread along a current path between the first machine component 10 and the second machine component 20;

[0093] - detecting a measuring current Ib generated by the modulated alternating voltage signal Ub; and

[0094] - Carrying out an impedance spectroscopy for the at least one bearing based on the modulated alternating voltage signal Ub and the measured measuring current Ib.

[0095] This process can, but need not, be performed using the device described above. According to this process, current coupling can also be achieved using other methods (e.g., capacitive or sliding contacts).

[0096] Fig. 5 shows a schematic flowchart for an (inductive) method for determining an impedance Z along a closed current path P through a first machine component 10 and a second machine component 20, wherein the first machine component 10 and the second machine component 20 are mounted so as to be movable relative to one another. The method comprises:

[0097] - Inductive generation S110 of an alternating current I along the closed current path P by a first coil Ti which is excited by an alternating voltage signal Ub and the first coil Ti extends at least partially around the first machine component 10;

[0098] - generating S120 a measuring current Ib in a second coil T2 by the induced alternating current I along the closed current path P, wherein the second coil T2 extends at least partially around the first machine component 10;

[0099] - Measuring S130 of the measuring current Ib; and

[0100] - based on the alternating voltage signal Ub and the measuring current Ib, determining S140 the impedance Z along the closed current path P.

[0101] The methods may also be, at least partially, computer-implemented, i.e., they may be implemented by instructions stored on a storage medium capable of carrying out the steps of the method when run on a processor. The instructions typically comprise one or more instructions, which may be stored in various ways on different media in or peripheral to a control unit (having a processor), which, when read and executed by the control unit, cause the control unit to perform functions, functionalities, and operations necessary to carry out a method according to the present invention.Therefore, embodiments also include a computer program product or a computer-readable storage medium having software stored thereon, which is configured to carry out at least the step of determining S140 according to the method described above when the software is installed on the evaluation device described above.

[0102] Further embodiments use (only) the transformer T2 (second coil) to measure the current Ib in the shaft 10 to solve a different problem: In many mechanical engineering applications, electrical currents occur between the inner and outer rings of bearings, which damage the rolling bearings. There is a need to know these currents in order to measure the actual current load on the bearings and, for example, to draw conclusions for development or to predict bearing damage. In these embodiments, a first coil Ti does not need to be present or can be deactivated.

[0103] Alternatively or additionally, according to further embodiments, active compensation of bearing voltages or bearing currents can be performed. For example, a voltage can be specifically applied to the first coil Ti to eliminate converter-induced bearing currents, i.e., the electrical currents generated by the rolling bearing (see above) are compensated by the induced alternating current I. As a result, the rolling bearing is current-free, and damage can be avoided. This can also occur dynamically (e.g., depending on the load or the rotational speed). Accordingly, the second coil T2 and the ammeter 300 do not need to be formed or can at least be deactivated.

[0104] To do this, the flowing current could first be measured as described above (e.g. through the second coil T2) and a voltage could be applied to the first coil Ti that is just high enough to eliminate the bearing currents.

[0105] The features of the invention disclosed in the description, the claims and the figures may be essential for the realization of the invention both individually and in any combination.

[0106] LIST OF REFERENCE SYMBOLS

[0107] IO first machine component

[0108] 20 second machine component

[0109] 30 first rolling bearing

[0110] 35 rolling elements of the first rolling bearing

[0111] 40 second rolling bearing

[0112] 45 rolling elements of the second rolling bearing

[0113] 50 voltage source

[0114] 52 Mass

[0115] 55 amplifiers

[0116] 112 first coil core

[0117] 114 first coil winding

[0118] 116 additional coil windings

[0119] 118 voltage eaters

[0120] 212 second coil core

[0121] 214 second coil winding

[0122] 300 ammeters

[0123] 400 Evaluation device

[0124] 410,420 FFT facilities

[0125] 430 computing device

[0126] 440 Quotient facility

[0127] Ti first coil (transformer)

[0128] T2 second coil (transformer)

[0129] Z, Za, Zb impedances (e.g. of the bearings)

[0130] P (closed) current path

[0131] Ub AC voltage signal

[0132] Ib measuring current

[0133] I alternating current

[0134] R axial axis (e.g. axis of rotation for rotary movements)

Claims

CLAIMS 1. A device for measuring an impedance (Z) of at least one tribological contact along a current path (P) between a first machine component (10) and a second machine component (20), wherein the first machine component (10) and the second machine component (20) are mounted so as to be movable relative to one another and the device is connectable to a voltage source (50), the device comprising: a first coil (Ti) with a first coil core (112) around which a first coil winding (114) is wound, wherein the first coil core (112) extends at least partially around the first machine component (10) and the first coil winding (114) is excitable by an alternating voltage signal (Ub) from the voltage source (50) in order to inductively generate an alternating current (I) along the current path (P);a second coil (T2) with a second coil core (212) around which a second coil winding (214) is wound, wherein the second coil core (212) extends at least partially around the first machine component (10) in order to generate a measuring current (Ib) in the second coil (T2) by means of the induced alternating current (I) along the current path (P); an ammeter (300) which is configured to measure the measuring current (Ib) generated in the second coil winding (214); and an evaluation device (400) which is configured to determine the impedance (Z) along the current path (P) based on the alternating voltage signal (Ub) and the measuring current (Ib); 2. Device according to claim i, wherein the first coil (Ti) further comprises comprising: a further coil winding (116) which is also wound around the first coil core (112) and is electrically insulated from the first coil winding (114), a voltmeter (118) which is arranged to measure a voltage at the further coil winding (116).

3. Device according to claim 2, wherein the first coil core (112) extends annularly all the way around a part of the first machine component (10), and wherein the first coil winding (114) and the further coil winding (116) are formed singly or multiple times in different angular sections of the annular coil core (112).

4. Device according to one of the preceding claims, wherein the evaluation device (400) is designed: to control the voltage source (50) and optionally to apply the alternating voltage signal (Ub) to the first coil winding (114) or to apply no voltage; and if no voltage is applied to the first coil winding (114), to determine the impedance (Z) and / or the measuring current (Ib) during the relative movement of the first machine component (10) and the second machine component (20).

5. Device according to claim 4, wherein the evaluation device (400) is designed to apply the alternating voltage signal (Ub) to the first coil winding (114) based on a previously measured measuring current (Ib) such that the second coil winding (214) is current-free.

6. Device according to claim 4 or claim 5, wherein the evaluation device (400) is arranged to generate the alternating voltage signal (Ub) based on at least one of the following modulation methods: - Amplitude modulation, - phase modulation, - Frequency spreading, Orthogonal frequency division multiplexing, OFDM, with randomly selected phases for subcarriers.

7. Device according to one of the preceding claims, wherein the evaluation device (400) is arranged to store calibration data, wherein the calibration data define a correction for a measured voltage value and / or a measured current value or their Fourier transform.

8. The device according to claim 7, wherein the calibration data in the evaluation device (400) are de-embedding calibration data that take into account an embedding of the device in an environment.

9. A machine mount comprising: a first machine component (10) and a second machine component (20) which are mounted so as to be movable relative to one another; a first tribological contact (30) and a second tribological contact (40), wherein the first tribological contact (30) and the second tribological contact (40) are formed between the first machine component (10) and the second machine component (20); and a device according to one of claims 1 to 8, wherein the first coil (Ti) and the second coil (T2) are arranged between the first tribological contact (30) and the second tribological contact (40) in order to determine an impedance (Z) of the first tribological contact (30) and the second tribological contact (40).

10. The machine mount according to claim 9, comprising a plurality of tribological contacts (30, 40) and a plurality of devices according to one of claims 1 to 8, wherein the first tribological contact (30) and the second tribological contact (40) are two adjacent tribological contacts from the plurality of tribological contacts (30, 40) and one device from the plurality of devices is arranged between further adjacent tribological contacts along the first machine component (10).

11. The machine mount according to claim 9 or claim 10, which has at least one of the following features: the first machine component (10) is a shaft, the second machine component (20) comprises a mount for the first machine component (10), the second machine component (20) comprises a housing for the first machine component (10), the first machine component (10) and the second machine component (20) are electrically conductively connected, - the first tribological contact (30) is a rolling bearing or a plain bearing or a toothed element or a chain or a cam-tappet contact, - the second tribological contact (40) is a rolling bearing or a plain bearing or a toothed element or a chain or a cam- Tappet contact.

12. A method for determining an impedance (Z) along a current path (P) through a first machine component (10) and a second machine component (20), wherein the first machine component (10) and the second machine component (20) are mounted so as to be movable relative to one another, the method comprising: Inductively generating (S110) an alternating current (I) along the current path (P) by a first coil (Ti) which is excited by an alternating voltage signal (Ub) and which extends at least partially around the first machine component (10); Generating (S120) a measuring current (Ib) in a second coil (T2) by the induced alternating current (I) along the current path (P), wherein the second coil (T2) extends at least partially around the first machine component (10); Measuring (S130) the measuring current (Ib); and based on the alternating voltage signal (Ub) and the measuring current (Ib), determining (S140) the impedance (Z) along the current path (P).

13. The method of claim 12, further comprising: Carrying out a calibration by using a plurality of frequencies of a frequency band for the alternating voltage signal (Ub) and using a predetermined bearing with predetermined electrical properties between the first and the second machine component (10, 20). 14- Method for measuring a bearing impedance of at least one bearing between a first machine component (10) and a second machine component (20), the method comprising: forming a modulated alternating voltage signal (Ub) with a Frequency spreading along a current path (P) between the first machine component (10) and the second machine component (20); detecting a measuring current (Ib) generated by the modulated AC voltage signal (Ub); Carrying out an impedance spectroscopy for the at least one bearing based on the modulated alternating voltage signal (Ub) and the detected measuring current (Ib).

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