Arrangement and method for monitoring the state of a rolling bearing cage, and cage structure

Abstract

The invention relates to an arrangement and a method for monitoring the state of a rolling bearing cage, and to a cage structure. The arrangement (10) for monitoring the state of a rolling bearing cage comprises: - at least one cage structure (12) for a rolling bearing, wherein the cage structure (12) comprises at least one conductor which is an electrical or optical conductor (16), - at least one measuring device (18) which is designed to generate a measurement signal which can be changed in accordance with a structural change of the conductor (16).

Description

[0001] Fraunhofer Society...eV

[0002] P150792PC00

[0003] Arrangement and method for condition monitoring of a rolling bearing cage and cage structure

[0004] The invention relates to an arrangement and a method for monitoring the condition of a rolling bearing cage as well as a cage structure.

[0005] In large rolling bearings, such as those used in wind turbines, the rolling elements are kept at a distance by cages to ensure smooth rolling and defined guidance of the rolling elements on the bearing raceways. Incorrect design or mechanical overload of the cages can lead to structural damage or even failure. Such damage can occur as primary damage due to material failure or as secondary damage due to other bearing defects. In both cases, cage damage impairs the functionality of the entire bearing and significantly reduces its remaining service life.

[0006] Particularly in roller slewing bearings, cage failure has serious consequences: The rolling elements are no longer reliably guided on the intended raceway. An unguided roller is forced into a circular path by the constraints of the bearing design, resulting in uneven loading and ultimately roller failure. Consequently, metal particles enter the raceway system, which can lead to total bearing failure.

[0007] To date, measures to prevent cage failure have focused on preventive design considerations to limit the risk of the described failure scenarios. Nevertheless, a residual risk remains for early and undetected failures, which can lead to unexpected failure of the bearing and the entire system in which the bearing is installed.

[0008] One object of the invention is therefore to improve the operational reliability of rolling bearings, in particular large rolling bearings such as those used for wind turbines.

[0009] This problem is solved by the subject matter of the independent claims. Advantageous embodiments are specified in this description, in the figure, and in the dependent claims.

[0010] According to the invention, it was recognized that the aforementioned problem can be solved by providing a means of detecting cage damage, particularly during operation, for which, however, no satisfactory solutions currently exist. To enable such detection, the invention specifically proposes an arrangement for monitoring the condition of a rolling bearing cage, the arrangement comprising:

[0011] • at least one cage structure for a rolling bearing, wherein the cage structure comprises at least one conductor which is an electrical or optical conductor, at least one measuring device which is configured to generate a measuring signal which is variable according to a structural change of the conductor.

[0012] This enables timely fault detection and thus predictive maintenance planning, thereby reducing both downtime and repair costs. Furthermore, the arrangement can be added to existing bearing structures without fundamental modifications, for example, by simply replacing the cage structure and, if necessary, adding a separate measuring device.

[0013] Within the scope of the present invention, a cage structure can be understood as a component that serves to guide and position rolling elements in a rolling bearing. The cage structure can be fully circumferential, for example in a ring-shaped configuration, positioning and guiding a plurality of rolling elements, in particular rollers, along a circular raceway. Alternatively, the cage structure can also be configured as a cage segment extending only along a portion of the circumference or a section of the raceway. Such a cage segment can, for example, be configured as a ring segment. Depending on the configuration, a cage segment can accommodate at least one, two, three, or even more rolling elements.The arrangement can comprise several such cage segments, each with a conductor, the absence of damage of which can be monitored, for example, by one or more measuring devices (f) of the arrangement. The multiple measuring devices of the arrangement can, if present, be distributed circumferentially around an axis of rotation of the rolling bearing, so that the at least one cage structure can be moved past them for detection. The cage structure, and in particular a base body thereof as described below, can comprise metal, plastic, or a composite material, independent of the conductor, and / or be constructed in one piece or in multiple parts. The cage structure, and in particular its base body, can be manufactured, for example, by casting, machining, injection molding, or additive manufacturing. The rolling bearing in which the cage structure is used can, in particular, be a large-diameter bearing.Such a bearing is typically intended for applications requiring large diameters, for example in wind turbines, construction machinery, rotary drives, or similar large installations. A large slewing bearing can, for instance, have an outer diameter of over 3000 mm, particularly over 5000 mm, and up to and including 6000 mm or more.

[0014] The conductor can be embedded in the cage structure material, for example, during a casting process or other primary forming manufacturing method. It is also possible to subsequently attach the conductor to or onto an already manufactured cage structure, and in particular to a base body thereof, for example, by gluing, overmolding, or mechanical fixing. A base body can be understood as the component of the cage structure that is different from the conductor and / or that is designed to accommodate at least one rolling element.

[0015] The measuring device can be configured to acquire a measured quantity and generate a measurement signal based on it, whereby the measured quantity, and thus the measurement signal, is influenced by the conductor, for example, due to deformation or other structural changes. The measuring device can generate the measurement signal analogously or digitally. It can evaluate the measurement signal, for example, by checking for threshold exceedance or falling below a certain value, or by analyzing other predefined signal characteristics that indicate a potential failure. Thus, the measuring device can also be configured for failure detection. The measuring device can be permanently located outside the cage, for example, on a stationary component of the bearing or the bearing environment. Alternatively, the measuring device can be integrated into and / or attached to the cage structure.In this case, it can be configured to wirelessly transmit the measurement signal or a derived control signal—in particular, a signal indicating the presence or absence of damage—to a higher-level monitoring system or a control unit of the overall system in which the bearing is integrated. Based on such a signal, for example, a warning message can be generated for an operator and / or the operation of the overall system can be automatically adjusted, restricted, or stopped. Exemplary faults, or in other words, damage events that can be detected by the arrangement according to the invention, include, among other things, the occurrence of deformation or cracking of the conductor and / or cage structure, in each case particularly above permissible limits, as well as the detection of a cage breakage.

[0016] The conductor can generally extend circumferentially and / or transversely to it, in the latter case particularly along an axis of rotation around which the bearing or the rolling elements it contains move together during operation. Experience has shown that fractures, cracks, or other structural changes occur particularly frequently in these directions. Additionally or alternatively, according to one embodiment, the conductor can also extend radially, that is, along a direction perpendicular to the aforementioned axis of rotation. In other words, the radial direction refers in particular to an orientation that points outwards from the center of the bearing's axis of rotation, or vice versa, i.e., orthogonal to the circumferential direction. The circumferential direction, on the other hand, revolves around the axis of rotation, in particular in a circular fashion.

[0017] Similarly, according to one embodiment, the conductor can run in and along different radial planes, for example with sections at different radial distances relative to the axis of rotation of the rolling bearing.

[0018] According to one embodiment, it is also possible to provide several conductors in different radial planes or at radial distances from the axis of rotation. In particular, a stacked or staggered arrangement of several conductors is possible in the radial direction, each extending in at least one radial plane.

[0019] According to a further development, the conductor is elongated, for example, wire-shaped or fiber-shaped, in particular glass fiber-shaped. The fiber shape can also be formed by a bundle of individual fibers. In particular, the conductor can have a length of at least 5 cm, at least 10 cm, or at least 20 cm.

[0020] According to further training, a conductor forms a closed loop, at least when assuming a fault-free or undamaged initial structure. In an electrically designed conductor, such a loop can, for example, form a coil in which a current can be generated by induction. Such an induced current can be detected by a suitable measuring device and evaluated for characteristic changes.

[0021] In an optically designed conductor, such as a fiber optic cable, an optical signal can be transmitted from one end of the conductor to the other. The signal path can be affected by structural changes in the conductor—for example, due to deformation, bending, cracking, or material breakage. The affected signal can be detected by the measuring device and interpreted as a measurement signal, whereby the absence of a measurement signal can indicate a break. In the optical case, a closed conductor loop can be achieved, in particular, by connecting both ends of an elongated fiber optic cable to the measuring device, thus enabling a continuous signal flow and allowing changes in transmission characteristics to be detected.

[0022] According to further training, the conductor is an electrical conductor, and the measuring device is designed to generate an alternating magnetic field that induces a current in the closed conductor loop. This enables reliable and robust detection of structural changes in the conductor, as changes in the induced current or impedance, for example, allow conclusions to be drawn about breaks, cracks, or deformations of the conductor loop as potential defects. A further advantage is that the measuring device can be positioned outside the cage structure, i.e., in a fixed location, for example, on a housing component of the bearing and / or in the vicinity of its rotating components. This eliminates the need to integrate sensors into the moving cage and to provide solutions for power supply and signal exchange with such sensors.This reduces system complexity and increases maintainability. In principle, and not limited to a specific further development, several measuring devices can be arranged circumferentially, so that multiple positions are available for signal acquisition along a revolution of the rolling bearing and its cage structure. During a revolution of the cage structure—especially during rotation around the aforementioned axis of rotation—the measurement signal can be acquired at least whenever the conductor is near a measuring device and / or moves directly past it. If several cage segments are provided, each equipped with a conductor of the type disclosed herein, a single stationary measuring device can monitor several of these cage segments, for example, at least whenever they move past the measuring device.

[0023] According to further training, the measuring device includes an excitation coil for generating the alternating magnetic field and is designed to detect a change in the excitation coil's impedance based on the measurement signal and / or as the measurement signal itself. The excitation coil's impedance is a frequency-dependent AC resistance composed of an ohmic component and an inductive (and possibly capacitive) component. When the coil is operated with an alternating current, it generates an alternating magnetic field that can induce a current flow in an adjacent, closed conductor loop—for example, the electrical conductor arranged in or on the cage structure.

[0024] This induced current, in turn, generates a magnetic field that interacts with the original alternating field of the coil. The strength and phase of this interaction depend, among other things, on the geometry and electrical integrity of the conductor loop. If the conductor's structure changes, for example, due to cracking, cross-sectional reduction, or complete breakage, the electromagnetic coupling between the coil and the conductor loop also changes. This results in a measurable change in the impedance of the excitation coil, which allows conclusions to be drawn about any potential damage.

[0025] By analyzing the impedance signal – for example, via amplitude changes, phase shifts, or resonance behavior – the measuring device can draw conclusions about structural changes in the conductor. This enables contactless, reliable, and continuous monitoring of the cage structure's condition during operation.

[0026] One advantage of this design is that the measurement takes place directly within the excitation system, i.e., within the coil itself, without the need for additional sensors. This allows the system to be particularly compact, robust, and simple in design, which increases reliability and facilitates integration into existing environments.

[0027] Alternatively or additionally to impedance measurement, another measurement principle can be used when employing an electrical conductor. For example, the conductor can be designed like a passive RFID tag, which, in combination with an external measuring device, generates a reflection signal. In such a configuration, the conductor, possibly together with other optional electronic components—such as an antenna, a resonator, or a simple circuit—forms a passive element that, when excited by an electromagnetic field, generates a characteristic feedback signal. This feedback signal can be influenced by structural changes in the conductor, particularly by cracks, breaks, or deformations.

[0028] In the event of a line break or a geometric change, the resonant frequency or the signal response of the passive tag may change or disappear entirely. The measuring device can be configured to detect such changes in the reflected signal and thus allow conclusions to be drawn about potential damage to the cage structure. This principle, like impedance measurement, enables contactless, wireless, and energy-efficient condition monitoring, especially for rotating and difficult-to-access cage structures.

[0029] According to further training, the measuring device is designed to generate the measurement signal based on (or according to) a magnetic field induced by the electrical conductor. The magnetic field, which arises in the closed conductor loop as a result of a current induced by the alternating field generated by the excitation coil, can be detected outside the cage structure. The detection of the magnetic field thus takes place outside the excitation system, independent of any impedance measurement within the excitation coil itself.

[0030] For this purpose, the measuring device can include, for example, a Hall sensor, a separate receiver coil, or another suitable magnetic field-sensitive element designed to detect the magnetic field generated by the conductor loop. Structural changes in the conductor, such as cracking or breaks, lead to a change in the current flow in the loop and thus to a change in the generated magnetic field. These changes can be detected and used to identify potential damage.

[0031] One advantage of this magnetic field-based design is that the measurement is decoupled from the excitation system, allowing for an additional, independent evaluation structure even under more complex environmental conditions or for redundancy. Furthermore, the spatial separation of the excitation and receiving units can increase sensitivity and enable flexible arrangements along the bearing circumference.

[0032] According to further training, the measuring device is designed to detect the magnetic field outside the excitation coil.

[0033] According to a further development, the cage structure is designed to be electrically non-conductive, at least in the area in contact with the conductor. This can be achieved, for example, by making the relevant section of the cage structure from an electrically insulating material, such as a plastic or an insulatingly coated metal. Such a design can, in particular, prevent unwanted electrical coupling or short circuits and thus improve the function of the measuring device or even make it possible in the first place.

[0034] According to an alternative or supplementary design, the cage structure can be electrically conductive, at least in certain areas, with the conductor having an insulating sheath or other electrical insulation from the cage structure. Such a design allows the conductor to be integrated into electrically conductive cage materials, such as those commonly used in metallic cages. The electrical insulation can be achieved, for example, by sheathing, embedding in insulating substrate material, or by using insulating intermediate layers.

[0035] Both variants enable reliable electrical decoupling between the conductor and the cage structure, which enhances the functionality of the sensors and, in particular, ensures precise detection of structural changes in the conductor. Furthermore, these designs offer flexibility regarding the choice of material and manufacturing technology for the cage structure.

[0036] According to a further training, the measuring device is designed to couple an optical signal into the optical conductor for modification. This coupling can be achieved, for example, by a light source connected to one end of the optical conductor. The optical signal is guided through the optical conductor and modified by structural changes such as bending, stretching, breaks, or material alterations. The modified signal can then be acquired as a measurement signal or converted into one and evaluated.

[0037] In particular, the conductor can be an elongated optical conductor whose two ends are coupled to the measuring device. This allows it to form a closed conductor loop, with the elongated conductor itself serving as the measuring section along which the aforementioned structural changes occur and can be detected.

[0038] According to a further development, the measuring device is arranged within the cage structure and can be inductively powered. This is particularly relevant for a measuring device of the aforementioned type, which is designed to couple an optical signal into the optical fiber. The inductive power supply enables a wireless design that requires no electrical connection between the rotating cage structure and stationary system components. This allows for a particularly compact, autonomous, and low-maintenance integration of the measuring device into the cage structure itself. Furthermore, the measuring device can also be configured to evaluate the optical signal guided in the optical fiber and influenced by the operating conditions, or to transmit it to an external unit for evaluation, for example, wirelessly via a radio connection.

[0039] The invention also relates to a method for monitoring the condition of a cage structure for a rolling bearing, wherein the cage structure comprises at least one conductor which is an electrical or optical conductor, and wherein the method comprises: generating a measurement signal with a measuring device, wherein the measurement signal is variable according to a structural change of the conductor.

[0040] All explanations and variants of arrangement features can also apply to the identical procedural features and be provided for in these cases.

[0041] According to a further development of the method, the conductor forms a closed conductor loop, at least when assuming a flawless initial structure, and the method further includes:

[0042] Generating an alternating magnetic field using the measuring device, which is designed to induce a current in the closed conductor loop.

[0043] The invention also relates to a cage structure for a rolling bearing, wherein the cage structure comprises at least one conductor, which is an electrical or optical conductor and which has at least one material that differs from at least one remaining material of the cage structure. The cage structure can comprise a base body mentioned above, which in particular defines the geometric shape and function of the cage, for example for guiding and positioning the rolling elements. The conductor can be attached to or embedded in this base body.

[0044] The cage structure can be configured according to any of the embodiments disclosed herein, as described in particular in connection with an arrangement according to the invention. For example, the cage structure can be electrically and / or optically non-conductive, at least in an area contacting the electrical conductor, wherein the material of this area is different from the material of the conductor. For this purpose, the base body can, for example, comprise or consist of an electrically non-conductive plastic and / or a plastic that does not exhibit optical conductivity in the sense of directional light guidance. Alternatively, the cage structure can be wholly or partially electrically conductive, for example, by using a metallic material or a conductive composite material.In this case, the conductor may additionally have an insulating sheath or another form of electrical insulation relative to the cage structure, whereby a material different from that of the cage structure may also be used, such as a sheathing, a coating or an insulating embedding material.

[0045] By combining different materials within the cage structure, reliable integration of the conductor for condition monitoring can be achieved without impairing the mechanical function or structural integrity of the cage. At the same time, functional decoupling is achieved, which improves the metrological evaluation capabilities.

[0046] According to a further development, the conductor can have a length of at least 5 cm, and in particular at least 10 cm, preferably extending circumferentially around the cage structure. Such a length can, in particular, increase the sensitivity to structural changes and improve the evaluability of the measurement signal.

[0047] An exemplary embodiment is explained below with reference to the attached schematic figure 1.

[0048] Figure 1 shows a schematic perspective view of an arrangement 10 according to an embodiment of the invention, comprising a cage structure according to an embodiment of the invention. The arrangement 10 is configured to carry out methods according to embodiments of the invention.

[0049] Figure 1 schematically shows a cage segment 12 of a large slewing bearing (not shown otherwise) as an example of a cage structure according to the invention. The cage segment 12 extends in a circumferential direction U around a geometric center point M, through which an axis of rotation of the bearing runs orthogonal to the plane of the bearing blade. This axis of rotation is jointly circumscribed by the bearing, the rolling elements arranged therein, and the cage segment 12. A radial direction R is also shown to clarify the spatial orientation and runs orthogonal to the circumferential direction U and to the axis of rotation.

[0050] The cage segment 12 has several receiving areas 14, each of which receives a rolling element (not shown). Between the receiving areas are webs 16, which are part of a base body of the cage segment 12. The illustration with three receiving areas 14 is exemplary and not limiting; there may also be more or fewer receiving areas 14.

[0051] In the illustrated embodiment, the base body of the cage segment 12 consists of a plastic material that is electrically and optically non-conductive. Several conductors 16 are embedded in the base body – for example, by means of a casting process – in this example, three electrical conductors. These are each designed as closed conductor loops that extend essentially in a constant radial plane. The conductors 16 run primarily in the circumferential direction U, but also extend transversely to this direction, resulting in a spatially staggered arrangement of conductor loops in the radial direction R. The length of the conductors 16 is several centimeters, in particular more than 10 cm, thus enabling sensitive detection of structural changes.

[0052] The arrangement of multiple conductors 16 in different radial planes as well as along the circumferential direction U offers additional advantages. This enables redundant damage detection. Furthermore, this design increases the probability of early detection of structural changes, such as cracking initiating both radially inwards and radially outwards, and thus improves the operational reliability of the overall system.

[0053] Outside the cage structure 12, a stationary measuring device 18 is provided, past which the cage segment 12 is moved during rotation about the axis of rotation. In the example shown, the measuring device 18 comprises an excitation coil 20, which is configured to generate an alternating magnetic field. This alternating field can induce a current in the closed electrical conductor loops 16. Structural changes in a respective conductor 16, such as cracks or breaks, lead to a change in the coupling between the excitation coil 20 and the conductor loop, which manifests itself in a measurable change in the impedance of the excitation coil 20. The impedance measurement is performed directly in the excitation system, i.e., within the excitation coil 20 itself, without the need for additional sensors.

[0054] Alternatively or additionally, the measuring device 18 in the example shown includes a detection device 22, which is configured to detect a magnetic field generated by a respective conductor loop. This detection takes place outside the excitation system, for example by means of a Hall sensor or a separate receiver coil. Here, too, a conductor break or deformation leads to a change in the magnetic field, which can be detected by the detection device 22 or, more generally, by the measuring device 18.

[0055] The measuring device 18 is designed to monitor the measurement signal generated based on the acquired measurement quantity, such as impedance or a magnetic field-related measurement quantity, with regard to predetermined error criteria. If such an error criterion – for example, exceeding or falling below a threshold – is met, a defined error condition is detected. In the event of a complete break in the cage structure and thus an interruption of an electrical conductor 16 or all conductors 16, the induced magnetic field may fail to appear, and a significant change or a complete drop in impedance may occur.

[0056] As indicated by the data or signal arrow P, the measuring device 18 can transmit a corresponding fault signal to a higher-level control unit 24 or transmit the measurement signal to control unit 24 for evaluation and damage detection. In the event of damage, the control unit 24 can, for example, issue an acoustic, visual, or electronic warning message or adjust the operation of a system encompassing the cage structure, for example, restricting or stopping it, in order to prevent further damage to the bearing. The electronic warning message can, for example, be issued to a monitoring system, such as that of a wind farm, whereby the monitored bearing may be installed in a wind turbine of the wind farm. As an alternative to an electrical conductor, one or more of the conductors 16 can also be designed as optical conductors. In this case, a measuring device 18' can be integrated into the cage structure 12.The measuring device 18' can, for example, be molded in or subsequently attached. A corresponding embodiment for one of the conductors 16 is indicated in Figure 1. The integrated measuring device 18' can be inductively powered, for example by an externally arranged coil, similar to the excitation coil 20.

[0057] The measuring device 18' can be configured to couple an optical signal into the optical fiber and monitor it. Structural changes to the optical fiber—such as bending, cracking, or breakage—lead to a change in light propagation, for example, through attenuation, scattering, or interruption. The modified signal and the feedback signal can be evaluated by the measuring device 18' and / or transmitted wirelessly to an external system. Wireless transmission can be achieved, for example, using radio technology such as Bluetooth Low Energy or other energy-efficient communication protocols.

Claims

godparent 1. Arrangement (10) for condition monitoring of a rolling bearing cage, comprising: • at least one cage structure (12) for a rolling bearing, wherein the cage structure (12) comprises at least one conductor which is an electrical or optical conductor (16), • at least one measuring device (18) which is configured to generate a measurement signal which is variable according to a structural change of the conductor (16).

2. Arrangement (10) according to claim 1, where the structural change includes at least one of the following changes: • a break in the electrical conductor (16), • a crack in the electrical conductor (16), • a deformation of the electrical conductor (16).

3. Arrangement (10) according to claim 1 or 2, wherein the conductor (16) is elongated and in particular has a length of at least 5 cm, at least 10 cm or at least 20 cm.

4. Arrangement (10) according to one of the preceding claims, wherein the conductor (16) forms a closed conductor loop, at least when assuming a fault-free initial structure.

5. Arrangement(10) according to claim 4, wherein the conductor (16) is an electrical conductor and the measuring device (18) is configured to generate an alternating magnetic field which is configured to induce a current in the closed conductor loop, in particular wherein the measuring device (18) comprises an excitation coil (20) for generating the alternating magnetic field and is configured to detect an impedance change of the excitation coil (20) on the basis of the measurement signal.

6. Arrangement (10) according to claim 4, wherein the measuring device (18) is configured to generate the measuring signal on the basis of a magnetic field induced by the electrical conductor (16).

7. Arrangement (10) according to claim 5, wherein the measuring device (18) is configured to detect the magnetic field outside the excitation coil (20).

8. Arrangement (10) according to one of the preceding claims, wherein the cage structure (12) is electrically non-conductive at least in an area touching the conductor (16); or wherein the cage structure (12) is at least partially electrically conductive and the conductor (16) comprises an insulating sheath or other electrical insulation from the cage structure (12).

9. Arrangement (10) according to one of the preceding claims, wherein the conductor (16) is an optical conductor (16) and the measuring device (18) is configured to detect an optical signal influenced by the conductor (16) as a measuring signal.

10. Arrangement according to claims 4 and 9, wherein the conductor (16) is an elongated optical conductor (16) whose two ends are coupled to the measuring device (18).

11. Arrangement (10) according to claim 9 or 10, wherein the measuring device (18) is configured to couple an optical signal into the conductor (16) for influence; and / or wherein the measuring device (18) is arranged in the cage structure (12) and can be inductively supplied with energy.

12. Method for condition monitoring of a cage structure (12) for a rolling bearing, wherein the cage structure (12) comprises at least one conductor (16) which is an electrical or optical conductor (16), and wherein the method comprises: Generating a measurement signal with a measuring device, wherein the measurement signal is variable according to a structural change of the conductor (16).

13. Cage structure (12) for a rolling bearing, comprising at least one conductor (16) which is an electrical or optical conductor, wherein the cage structure (12) comprises at least one material which is different from at least one remaining material of the cage structure (12).

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