WO2012069066A1

WO2012069066A1 - Sensing of the spin of a roller in a bearing in operational use

Info

Publication number: WO2012069066A1
Application number: PCT/EP2010/007151
Authority: WO
Inventors: Frank De Wit; Sebastian Ziegler
Original assignee: Aktiebolaget Skf
Priority date: 2010-11-25
Filing date: 2010-11-25
Publication date: 2012-05-31

Abstract

A rolling element bearing has a plurality of rolling elements retained in a cage. The spinning of one or more specific ones of the rolling elements is determined by means of sensing the relative movement of the specific rolling element relative to the cage in operational use of the rolling element bearing. The specific rolling element accommodates a coil whose core includes a Wiegand wire, and the cage accommodates two magnets next to the specific rolling element. The magnets generate magnetic fields of opposite direction at the path traversed by the Wiegand wire when the specific rolling element is spinning around its axis of symmetry. When the Wiegand wire passes a particular magnet, the magnetization of the Wiegand wire flips polarity as a result of which a voltage is induced in the coil. Monitoring this induced voltage enables to extract information about the spin.

Description

SENSING OF THE SPIN OF A ROLLER IN A BEARING IN OPERATIONAL USE

FIELD OF THE INVENTION

The invention relates to a rolling element bearing, comprising a first ring, a second ring, a cage and a plurality of rolling elements accommodated between the first ring and the second ring and retained in the cage. The invention relates to a component configured for use as a specific one of a plurality of rolling elements accommodated in a cage in a rolling element bearing. The invention relates to another component configured for use as a cage of a rolling element bearing and operative to retain a plurality of rolling elements of the rolling element bearing in operational use. The invention further relates to a method of determining an attribute of a spin of a specific one of a plurality of rolling elements retained in a cage of a rolling element bearing in operational use of the rolling element bearing. The expression "spin" refers to the rotation velocity of a rolling element that is spinning around an imaginary axis fixed to the rolling element in operational use of the rolling element bearing. The expression "attribute of a spin" refers to, e.g., the magnitude of an angular velocity of the rolling element (i.e., the angular speed) around the imaginary axis fixed to the rolling element, and/or to the polarity of the angular velocity (i.e., the direction of spinning). The invention also relates to a method of determining an attribute of a mechanical load on a rolling element bearing in operational use.

BACKGROUND ART

Consider a rolling element bearing that comprises a first ring, a second ring and a plurality of rolling elements accommodated between the first ring and the second ring. The rolling element bearing also comprises a cage between the first ring and the second ring. The cage is operative to retain the rolling elements in fixed positions relative to one another in operational use of the rolling element bearing. The rolling elements enable the first ring and the second ring to rotate coaxially relative to each other. So long as the rolling elements have rolling contact with the first ring and the second ring, the friction generated as a result of the relative motion of the first ring and the second ring is relatively low compared with the friction when one or more of the rolling elements is in sliding contact with the first ring and/or the second ring.

CONFIRMATION COPY Sensing the spin of a rolling element in a rolling element bearing in operational use, would enable to extract information about the current state of the rolling element bearing. For example, accumulating the values of the spin over time and processing the accumulated values on a computer, would enable to determine the expected, currently remaining service life of the rolling element bearing. As another example, consider a rolling element bearing in circumstances wherein the first ring and the second ring are coaxially rotating back and forth relative to one another over an angle that is substantially smaller than 360°. Some or all of the rolling elements are then said to be "rocking". A rocking rolling element tends to push the lubricant away from the region, where the rocking rolling element and a relevant one of the first ring and the second ring come in contact with one another and deform under the mechanical load imposed on the rolling element bearing. Removal of the lubricant is generally undesirable. Accordingly, being able to determine whether or not a rolling element is rocking could be important to condition monitoring of the rolling element bearing. The spin and the rate of change of the spin depend on, e.g., the mechanical load on the rolling element bearing.

Typically, the spin of a particular one of the rolling elements varies during a single complete rotation of the rolling element around a rotation axis of the rolling element bearing. This stems from the fact that during a compete rotation of the particular rolling element around the axis of the rolling element bearing, the particular rolling element experiences a pressure that varies along the path of the compete rotation. To explain this consider, for example, a radial bearing whose outer ring is mounted in a housing, and whose inner ring is fixed to a horizontal shaft. The shaft is enabled to rotate relative to the housing. Assume first that the shaft is not rotating, and is subjected to a mechanical load in the upward vertical direction. The mechanical load on the shaft causes the inner ring of the radial bearing to be pushed upwards against those among the rolling elements that are positioned in the upper half of the radial bearing. The rolling elements in the upper half are pushed, in turn, against the upper half of the outer ring of the radial bearing, as a result of which the outer ring is pushed vertically upwards against the housing. The housing is stationary and exerts a reaction force vertically downwards on the outer ring. The rolling elements in the lower half of the radial bearing will not experience any load, or a reduction in a load if the radial bearing was pre-stressed. The material region in the outer ring that is subjected to the actual stresses as a result of the mechanical load on the shaft and that deforms as a result thereof, is referred to as the "loaded zone" in the outer ring. If the direction of the mechanical load on the shaft does not change, the location of the loaded zone relative to the outer ring of the radial bearing will not change. If the shaft is rotating while subjected to the mechanical load in the upward vertical direction, the location of the loaded zone does not change with respect to the outer ring. Each particular one of the rolling elements will therefore enter and exit the loaded zone once while completing a rotation around the shaft, and experience a change in pressure and, therefore, a change in friction that may give rise to a change in spin.

Japanese patent application publication JP2000065846 discloses a system for measuring a rotation of a roller in a rolling element bearing. The abstract of the publication refers to the drawing accompanying the abstract and reads as follows. The problem to be solved: to determine rotation of a roller as a change of a magnetic field passing through a Hall element by opposedly arranging each of the N poles and each of the S poles in a pair in the radius direction on the roller rolling face. The solution: As to magnetic poles 6 arranged on a rolling face of a roller 4, each of the N poles and each of the S poles are arranged opposedly mutually in the radius direction of the roller 4, and in the circumference direction, the N pole and the S pole are adjacent to each other. In the vicinity of the end face of an inner ring 2, eleven Hall elements 3 are arranged at equal intervals excepting one place along the circumference direction around the axial center of a bearing. When the roller 4 is rotated according to rotation of the bearing (rotation of the inner ring 2), the magnetic poles 6 touching an outer ring 1 and the inner ring 2 are reversed every time when the roller 4 is turned by 60 degrees, and an inverse phase is set, so that the orientation of the magnetic field is reversed. This process is repeated so that wave-form is outputted. In this process, outputs from the respective eleven Hall element 3 are added up by means of an operation amplifier 12 and without respect to a revolution phase of the roller 4, stable output waveform can be provided in compliance with a change of the magnetic field based on a rotating motion of the roller 4

Accordingly, Japanese patent application publication JP2000065846 teaches accommodating magnetic poles on the rolling surface of the roller, and accommodating Hall elements along the circumference of the inner ring. SUMMARY OF THE INVENTION

The inventor proposes to equip the rolling element bearing of the type specified above, with a sensor for sensing a physical quantity that is representative of the current spin of one or more specific ones of the rolling elements of the rolling element bearing. The operation of the sensor is based on the following insight. In operational use of the rolling element bearing, each individual one of the rolling elements remains in a fixed position relative to the cage, but may spin around an imaginary axis fixed to the individual rolling element. That is, each specific rolling element may move relative to the cage while a particular point of the specific rolling element, e.g., the center of mass of the specific rolling element, retains a fixed position relative to the cage. The inventor now proposes to determine the current relative movement of the specific rolling element with respect to the cage.

Accordingly, the invention relates to a rolling element bearing that comprises a first ring, a second ring, a cage and a plurality of rolling elements accommodated between the first ring and the second ring and retained in the cage. The rolling element bearing accommodates a sensor that is operative to sense a spinning of a specific one of the rolling elements around a spin axis of the specific rolling element and with respect to the cage in operational use of the rolling element bearing. That is, the sensor is configured for sensing a relative movement, e.g., spinning, of the specific rolling element with respect to the cage as a reference.

Note that the spinning of the specific rolling element is determined in the invention as a relative movement of the specific rolling element with respect to the cage. In Japanese patent application publication JP2000065846, the spinning of the roller is determined with respect to the inner ring.

In a first embodiment of the rolling element bearing of the invention, the sensor comprises a first coil having a first core with a first Wiegand wire, and also comprises magnetic means for generating a magnetic field. The first coil is accommodated at one of the cage and the specific rolling element, whereas the magnetic means is accommodated at the other one of the cage and the specific rolling element. The magnetic field is configured for flipping a polarity of a magnetization of the first Wiegand wire a pre-determined number of times during a single revolution of the specific rolling element with respect to the cage and around the spin axis. Sensors based on the Wiegand effect as such are known in the art. A Wiegand sensor comprises one or more Wiegand wires made of a specific ferromagnetic alloy (Vicalloy) and subjected to a specific physical treatment. A Wiegand wire has an outer shell with a high coercivity and an inner core with a low coercivity. If a magnet and a Wiegand wire are being brought together, the outer shell first shields the inner core from the magnetic field. However, when a threshold value has been reached of the strength of the magnetic field at the location of the Wiegand wire, the magnetization of both the outer shell and the inner core rapidly switches polarity, e.g., within microseconds. Once the polarity of the magnetization of the Wiegand wire has flipped, the Wiegand wire will retain the acquired magnetization until the magnetization flips again in response to a another magnetic field whose vector points in another direction at the location of the Wiegand wire and whose strength has passed another threshold. The flipping of the polarity is relatively fast. Accordingly, a significant voltage is developed in a coil, whose core is formed by a Wiegand wire when the magnetization switches polarity.

Note that, in the rolling element bearing of the invention the sensor, whose operation is based on the interaction of the Wiegand wire with the coil, is self-sufficient in the sense that the sensor itself does not need a separate power supply such as a battery or a generator. In contrast, the operation of the sensor disclosed in Japanese patent application publication JP2000065846 is based on Hall elements. As known, a Hall element produces a very low signal level and thus requires amplification. Commercially available Hall-effect sensors contain a Hall element and an amplifier, both implemented in an integrated circuit that needs to be powered via a power supply in operational use of the Hall-effect sensor. Also note that in the sensor of the rolling element bearing in the invention the interaction is between the specific rolling element and the cage. In contrast, the sensor in Japanese patent application publication JP2000065846 has the magnets at the rolling surface of the roller interact with Hall elements at the inner ring of the bearing. In the first embodiment above, the spinning of the specific rolling element relative to the cage causes the magnetic field and the first Wiegand wire to move relative to one another. The first Wiegand wire traverses a closed path relative to the magnetic field during each single revolution of the specific rolling element around its spin axis. A direction of the magnetic field, as experienced by the first Wiegand wire, varies along the closed path in such a manner that the magnetic field causes the polarity of the magnetization of the first Wiegand wire to flip a number of times during a single traversal of the path, depending on whether the specific rolling element remains in rolling contact with the raceways of the rolling element bearing or assumes a sliding contact with the raceways over one or more stretches of the closed path. The magnetic means can be implemented in a variety of manners.

In a first implementation example, the magnetic means comprises a first magnet and a second magnet. When the first Wiegand wire is passing the first magnet, the polarity of the magnetization of the first Wiegand wire flips as a result of which a voltage is induced in the coil. The polarity of the induced voltage corresponds with the change in polarity of the magnetization. That is, the polarity of the induced voltage enables to determine which of the first magnet and the second magnet was close by at the moment of flipping, thus conveying information about the orientation of the specific rolling element relative to the cage at the moment of flipping. When the first Wiegand wire is subsequently passing the second magnet, the polarity of the magnetization is flipped back again. What has been specified in functional language above about the flipping induced by the magnetic means, here: the first magnet and the second magnet, boils down to an arrangement of the first magnet and second magnet, wherein a first magnetic field of the first magnet and a second magnetic field of the second magnet have substantially different, e.g., opposite, directions as experienced by the first Wiegand wire when passing the relevant one of the first magnet and the second magnet. After having passed the second magnet, the magnetization has assumed the polarity it initially had when the first Wiegand wire was approaching the first magnet. Using the first magnet and the second magnet therefore enables to flip the polarization of the magnetization of the first Wiegand wire flip two times. As the rolling element is enabled to spin while retained in a fixed position relative to the cage, flipping the polarity of the magnetization two times per full spin of 360°, of the specific rolling element around its spin axis, enables to identify when a full spin has occurred for this specific rolling element in this first implementation example.

In a second implementation example of the magnetic means, the magnetic means comprises a number of 2N discrete magnets, N being an integer larger than unity. This implementation increases the number of flips of the polarity of the magnetization of the first Wiegand wire per complete revolution of the specific rolling element around its spin axis. As a result, the resolution is increased at which the spinning angle and therefore angular speed can be determined. In a third implementation example, the magnetic means comprises a number of M magnets, M being an integer, equal or larger than unity, as well as flux guidance means. The flux guidance means is operative to guide the magnetic flux of the M magnets so as to create, in effect, a number of 2M magnets. The flux guidance means comprises, e.g., for each individual one of the M magnets an individual strip of a ferromagnetic material. Each individual one of the M magnets has a first pole and a second pole. Assume that the first pole is closer to the path traversed by the first Wiegand wire than the second pole. A strip of the ferromagnetic material in the vicinity of the second pole can then be used to effectively relocate the magnetic field of the second pole to a suitable position relative to the path traversed by the first Wiegand wire. Accordingly, using a single magnet and flux guidance means, the effect is created as accomplished with the first magnet and the second magnet in the first implementation example.

In a fourth implementation example of the magnetic means, the magnetic means comprises a Halbach array.

In a fifth implementation example of the magnetic means, the magnetic means comprises a two-pole magnetic ring or a multiple magnetic ring.

The voltage induced in the first coil can be used to generate a radio frequency (RF) signal for receipt by a receiver external to the rolling element bearing. The signal indicates that a flipping of the magnetization has occurred. When using the first implementation example of the magnetic means, comprising the first magnet and the second magnet as discussed above, the polarity of the voltage, represented in the RF signal, indicates the particular one of the first magnet and the second magnet responsible for triggering the flipping, and therefore, the angular position of the rolling element relative to the cage. A time series of RF signals enables to extract a magnitude of the speed at which the specific rolling element is spinning. Alternatively, the voltage induced can be used to power electronic circuitry accommodated at the sensor. The electronic circuitry, powered by energy induced in the coil, can be configured to store data in local memory, representative of, for example, the number of spinning revolutions of the specific rolling element, executed over its service life up to date, information about the range of magnitude of the angular speed experienced by the specific rolling element, etc.

Similar considerations apply in case of using the third implementation example of the magnetic means, wherein M equals unity, thereby effectively emulating the first implementation example.

Similar considerations apply in case of using the second implementation example, the fourth implementation example and the fifth implementation example. However, merely determining the polarity of the induced voltage is usually not enough in the fourth implementation example or the fifth implementation example, in order to determine the angular position of the specific rolling element relative to the cage. For this to work, one needs to count the number of induced voltage pulses that have occurred since the start of the current revolution of the specific rolling element.

As specified above, the first coil with the first Wiegand wire is accommodated at one of the cage and the specific rolling element, whereas the magnetic means is accommodated at the other one of the cage and the specific rolling element. Typically, the cage faces each individual one of the rolling elements from two or more substantially different directions. For example, the cage has a first surface that faces a first side of the specific rolling element, and a second surface that faces a second side of the specific rolling-element. The first side and the second side of the specific rolling element are each oriented substantially perpendicularly to the (current) spin axis of the specific rolling element. The first side faces in a direction substantially opposite to another direction wherein the second side faces. See, e.g., the cross- section diagrams of the radial bearings in "General Catalog", SKF, version 6000 EN, 2005, pages 20-21 "Bearing terminology". Accordingly, the magnetic means or the first coil can be accommodated at the cage near a specific one of the first surface and the second surface. Consider now the scenario wherein the magnetic means is accommodated at the cage and is comprised of multiple discrete devices: for example, a number of 2N discrete magnets, or a number of M discrete magnets with flux guidance means, or multiple Halbach arrays or multiple magnetic rings, or a combination thereof. Then, some of these discrete devices can be accommodated at the first surface and others of the discrete devices can be accommodated at the second surface. The coil and the Wiegand wire, accommodated at the specific rolling element, and the discrete devices accommodated at the cage, are then arranged in such a way, that the discrete devices of the magnetic means at both the first surface of the cage and the second surface of the cage interact with the Wiegand wire to cause intended flips of the polarity of the magnetization when the specific rolling element is spinning relative to the cage. Using the space of both the first surface and the second surface enables to accommodate a larger number of discrete devices of the magnetic means than using only a specific one of the first surface and the second surface, thus facilitating an increase in resolution when determining angular speed of the spinning specific rolling element.

A second embodiment of the rolling element bearing of the invention comprises the first embodiment, discussed above, but the sensor now also comprises at least a further coil having a further core with a further Wiegand wire. The first coil and the further coil are arranged to remain in a fixed position relative to one another in operational use of the rolling element bearing. The first coil and the further coil, on the one hand, and the magnetic means, on the other hand, are positioned so as to enable to determine a direction of the spinning.

The arrangement of the first coil with the first Wiegand wire and of the further coil with the further Wiegand wire is accommodated at one of the specific rolling element and the cage, whereas the magnetic means is accommodated at the other one of the of the specific rolling element and the cage.

In the second embodiment, a first Wiegand wire and at least one further Wiegand wire are present in an arrangement, wherein their positions are fixed relative to one another. This enables to detect a direction of the relative movement of the specific rolling element and the cage. Explanation is as follows.

First consider an embodiment wherein the sensor of a specific rolling element is equipped with a single coil having a core with a Wiegand wire. Also note that a point on the specific rolling element, which is spinning relative to the cage, traverses a cyclic path relative to the cage. When the Wiegand wire is passing the first magnet, a first voltage with a first polarity is induced in the coil, and when the Wiegand wire is passing the second magnet, a second voltage with a second polarity is induced in the coil. The cyclic path can be traversed in a clockwise direction or in a counter-clockwise direction. Each of a traversal in the clockwise direction and another traversal in the counter-clockwise direction produces the same alternating time series of first voltages and second voltages in the coil. A variation in a length of time between the occurrence of a first voltage and the successive second voltage is typically due to a change in angular speed of the specific rolling element during a single spinning revolution.

As an aside, the magnitude of the first voltage and the magnitude of the second voltage may be substantially the same at a constant angular speed of the spinning rolling element, or they may be substantially different at a constant angular speed of the spinning rolling element. At constant angular speed, the magnitude of the first voltage and the magnitude of the second voltage depend on the strength of the magnetic fields generated by the first magnet and by the second magnet as experienced by the Wiegand wire, and on the orientation of the Wiegand wire relative to the magnetic fields. Now consider as an example the second embodiment, wherein the sensor of a specific rolling element is equipped with a first Wiegand wire in a first coil and with a second Wiegand wire in a second coil. When the first Wiegand wire is passing the first magnet, a first voltage with a first polarity is induced in the first coil, and when the first Wiegand wire is passing the second magnet, a second voltage with a second polarity is induced in the first coil. Similarly, when the second Wiegand wire is passing the first magnet, a third voltage with a third polarity is induced in the second coil, and when the second Wiegand wire is passing the second magnet, a fourth voltage with a fourth polarity is induced in the second coil. Accordingly, the spinning of the specific rolling element gives rise to a first alternating time series of first voltages and second voltages in the first coil, and a second alternating time series of third voltages and fourth voltages in the second coil. However, each individual one of the first alternating time series and the second alternating time series does not reliably convey the direction of the angular velocity of the specific rolling element while it is spinning. As indicated above, the angular speed may change abruptly, owing to local damage of the specific rolling element and/or of a raceway of the rolling element bearing, or owing to a change in mechanical load, etc., as a result of which the direction of the spinning cannot be determined with certainty. Now, consider merging the first time series and the second time series into a combined time series. The direction of the angular velocity can be inferred from, e.g., the sequence or order wherein the first voltage, the second voltage, the third voltage and the fourth voltage occur per single revolution of the specific rolling element.

As specified above, the cage faces each individual one of the rolling elements from two or more substantially different directions and provides two or more surfaces near which the magnetic means can be accommodated. Consider now a scenario with multiple (two or more) coils, each with a respective Wiegand wire, accommodated at one of the cage and the specific rolling element. If the coils are all accommodated at the cage and the magnetic means is accommodated at the specific rolling element, the multiple coils can be distributed between the two or more surfaces facing the specific rolling element. The magnetic means is then arranged at the rolling element so as to be able to trigger the polarity flips of the Wiegand wires near the relevant ones of the surfaces of the cage facing the specific rolling element. For example, the magnetic means is implemented using discrete devices distributed between the first side of the rolling element and the opposite second side of the rolling element. Alternatively, if the coils are all accommodated at the specific rolling element and the magnetic means is accommodated at the cage, the multiple coils can be distributed between the first side of the rolling element and the opposite second side of the rolling element, and the magnetic means is distributed among the two or more surfaces of the cage facing the specific rolling element. Alternatively, some of the multiple coils are accommodated at the specific rolling element and other ones of the multiple coils are accommodated at the cage and, likewise, some of the multiple discrete devices forming the magnetic means are accommodated at the specific rolling element and others of the multiple discrete devices ate accommodated at the cage. The availability of multiple surfaces at the cage and multiple sides at the specific rolling element enables to select a suitable spatial distribution of the components forming the sensor depending on the specific design of the rolling element bearing.

In a fourth embodiment, the sensor forms a functional part of a power supply of an electronic circuit accommodated at the rolling element bearing. The voltages induced in the first coil and/or in the further coil are relatively high owing to the fast rate at which the polarity of the magnetization of the relevant Wiegand wire flips. The sensor can therefore be used to generate power for supplying an electronic circuit accommodated at the rolling element bearing. As a result, the electronic circuit can be used as an autonomous entity whose operation does not rely on a battery onboard the rolling element bearing or on a power supply external to the rolling element bearing. The electronic circuit can be configured for, e.g., condition monitoring of the rolling element bearing. The electronic circuit can be equipped with further sensors for sensing environmental parameters such as temperature, humidity, acidity, etc., the further sensors being powered by the Wiegand-wire-based sensor, discussed earlier.

The invention also relates to a first component configured for use as a specific one of a plurality of rolling elements that are accommodated in a cage in a rolling element bearing. The first component comprises a coil with a core that includes a Wiegand wire, wherein the coil with the core that includes the Wiegand wire has a fixed location at the first component. Such a first component can be used as a specific one of a plurality of rolling elements of a rolling element bearing wherein one or more coils with Wiegand wires are accommodated at the specific rolling element, and wherein the magnetic means is accommodated at the cage. In an implementation of the first component, the coil with the core that includes the Wiegand wire is accommodated in a hole or in recess made in the first component. In another implementation, the first component has a single axis of rotational symmetry, and the coil with the core that includes the Wiegand wire is accommodated at a surface of the first component that is substantially perpendicular to the single axis of rotational symmetry.

The invention further relates to a second component configured for use as a specific one of a plurality of rolling elements accommodated in a cage in a rolling element bearing. The second component has a single axis of rotational symmetry. The second component comprises magnetic means for generating a magnetic field. The magnetic means is mounted so as have a fixed location at a surface of the second component that is substantially perpendicular to the single axis of rotational symmetry. The magnetic field has a fixed orientation with respect to the second component. Such a second component can be used as a specific one of a plurality of rolling elements of a rolling element bearing, wherein one or more coils with Wiegand wires are accommodated at the cage, and wherein the magnetic means is accommodated at the specific rolling element.

The invention further relates to a third component configured for use as a cage of a rolling element bearing and operative to retain a plurality of rolling elements of the rolling element bearing in operational use of the rolling element bearing. The third component comprises a coil with a core that includes a Wiegand wire, wherein the coil with the core that includes the Wiegand wire has a fixed location at the third component.

The invention further relates to a method of determining an attribute of a spin, e.g., angular speed or direction, of a specific one of a plurality of rolling elements retained in a cage of a rolling element bearing in operational use of the rolling element bearing. The spin is around an imaginary axis fixed to the specific rolling element. The method comprises sensing a relative movement of the specific rolling element with respect to the cage in operational use of the rolling element bearing. That is, the spinning of the specific rolling element is determined by capturing the movement of the specific rolling element relative to the cage.

The invention further relates to a method of determining an attribute of a mechanical load on a rolling element bearing in operational use of the rolling element bearing. The rolling element bearing comprises a first ring, a second ring, a cage and a plurality of rolling elements accommodated between the first ring and the second ring and retained in the cage. The method comprises monitoring a spinning of at least a specific one of the rolling elements around a spin axis of the specific rolling element and with respect to the cage in operational use of the rolling element bearing; and determining the attribute from the monitored spinning. Consider, for example, a radial bearing whose outer ring is mounted in a housing, and whose inner ring is fixed to a horizontal shaft. The shaft is therefore enabled to rotate freely relative to the housing. Assume first that the shaft is not rotating, and is subjected to a mechanical load in the upward vertical direction. The mechanical load on the shaft causes the inner ring of the radial bearing to be pushed upwards against those among the rolling elements that are positioned in the upper half of the radial bearing. The rolling elements in the upper half are pushed, in turn, against the upper half of the outer ring of the radial bearing, as a result of which the outer ring is pushed vertically upwards against the housing. The housing is stationary and exerts a reaction force vertically downwards on the outer ring. The rolling elements in the lower half of the radial bearing will not experience any load, or a reduction in a load if the radial bearing was pre-stressed. The loaded zone in the outer ring is that material region in the outer ring that is subjected to the actual stresses as a result of the mechanical load on the shaft and that deforms as a result thereof. If the direction of the mechanical load on the shaft does not change, the location of the loaded zone relative to the outer ring of the radial bearing will not change. If the shaft is rotating while subjected to the mechanical load in the upward vertical direction, the location of the loaded zone does not change with respect to the outer ring, but the intensity of the deformation will now vary with the ball-pass frequency of the rolling elements, as each time other ones of the rolling elements pass through the upper half of the radial bearing.

During a single revolution of a specific rolling element around the shaft, the specific rolling element could therefore experience changes in angular speed, e.g., a sudden angular acceleration when entering the loaded zone of the spherical roller bearing, and a sudden angular deceleration when exiting the loaded zone. That is, the specific rolling element could traverse the path of the revolution around the shaft while magnitude or direction of the spin of the specific rolling element around its spin axis changes. By means of determining the magnitude and/or direction of the spin, information could be extracted about the character of the loaded zone, e.g., location and extent, and therefore about the mechanical load.

Within the context of load sensing, reference is made to US patent 5,503,030, issued to Jan- Olof Bankestrom for "Load sensing Bearing", assigned to Aktiebolaget SKF; and incorporated herein by reference. This US patent discloses a device for load measurement in roller bearings whereby the measurement is carried out by means of sensors arranged to measure forces applied on the bearing, and which communicate with means for recording, processing and evaluation of signals emitted from the sensors, which are representative of the bearing load, whereby at least one roller body per roller body row is provided with at least one bore in which is provided at least one sensor, as well as means for amplification and transmission of signals emitted from said sensor to a receiver provided at the non-rotating bearing ring of the bearing, from which receiver said signals are conducted further to external means for signal processing, and so on.

BRIEF DESCRIPTION OF THE DRAWING

The invention is explained in further detail, by way of example and with reference to the accompanying drawing, wherein:

Fig.1 is diagram of a first cylindrical roller bearing, illustrating typical components;

Fig.2 is diagram of a second cylindrical roller bearing according to the invention;

Figs.3, 4, 5, 6, 7 and 8 are diagrams to illustrate operation of a first example of a sensor accommodated at second cylindrical roller bearing according to the invention;

Figs.9, 10 and 1 1 are diagrams to illustrate operation of a first example of a sensor accommodated at the second cylindrical roller bearing according to the invention; and

Fig.12 is a diagram of a side view of a cylindrical roller of the invention retained in a cage and illustrating operation of a second example of a sensor.

Throughout the Figures, similar or corresponding features are indicated by same reference numerals.

DETAILED EMBODIMENTS

A rolling element bearing comprises a first ring, a second ring and a plurality of rolling elements. The rolling elements are accommodated in a cage between the first ring and the second ring. The cage is operative to retain the rolling elements in fixed positions relative to one another.

If all goes well, each of the rolling elements makes rolling contacts with both the first ring and the second ring in operational use of the rolling element bearing, thus enabling the first ring and the second ring to freely rotate relative to one another around a common axis and with low friction. If all rolling elements remain in rolling contact with both the first ring and the second ring, each respective one of the rolling elements spins around a respective imaginary axis, fixed to the respective rolling element, at the same rate as other ones of the rolling elements. However, a specific one of the rolling elements may lose rolling contact with the first ring and/or with the second ring somewhere along a path traversed by the specific rolling element around the axis of the rolling element bearing. The loss of rolling contact may be due to, e.g., the elastic deformation of the rolling element bearing supporting a mechanical load, lack of lubrication, damage to the rolling elements or to the raceways of the rolling element bearing, etc. The specific rolling element may then have hardly any physical contact at all with the first ring and/or with the second ring on a part of the traversed path, or the specific rolling element may have a partly sliding contact on another part of the traversed path. If the spin of the specific rolling element can be determined, while the specific rolling element is traversing its path around the axis of the rolling element bearing, information can be extracted about the current state of the rolling element bearing for the purpose of, e.g., predicting a length of the remaining service life of the rolling element bearing, or for condition monitoring of the rolling element bearing.

In the invention, the rolling element bearing is equipped with a sensor in order to sense a physical quantity that is representative of the current spin of a specific one of the rolling elements of the rolling element bearing. The operation of the sensor is based on the following. In operational use of the rolling element bearing, the specific rolling element remains in a fixed position relative to the cage, but may spin an imaginary axis fixed to the specific rolling element (i.e., a spin axis). That is, the specific rolling element may move relative to the cage while retaining a fixed position relative to the cage. The invention now proposes to determine the current relative movement of the specific rolling element with respect to the cage. Fig. l is a diagram of a rolling element bearing 100, here: a first cylindrical roller bearing, illustrating relevant components. The diagram of Fig.l shows the first cylindrical roller bearing 100 partly broken open in order to render its constituents visible. The first cylindrical roller bearing 100 comprises a first ring 102, a second ring 104, and a plurality of rolling elements accommodated between the first ring 102 and the second ring 104. Only a first one of the rolling elements and a second one of the rolling elements are indicated with reference numerals 106 and 108, respectively, in order to not obscure the drawing. The rolling elements are shaped as cylindrical rollers. The rolling elements enable the first ring 102 and the second ring 104 to rotate relative to one another around a bearing axis 1 10. The rolling elements are retained in a cage 1 12 to ensure an even spacing of the plurality of rolling elements in an angular direction. Fig.2 is a diagram a second cylindrical roller bearing 200, modified according to the invention in the invention. The second cylindrical roller bearing 200 is represented as it appears when viewed from a vantage point on the bearing axis 1 10. The configuration of the second cylindrical roller bearing 200 is similar to the configuration of the first cylindrical roller bearing 100, and corresponding features will be referred to with the same reference numerals as used in the diagram of Fig. l. The second cylindrical roller bearing 200 is equipped with a sensor for sensing, in operational use of the second cylindrical roller bearing 200, a movement of a specific one of the cylindrical rollers, e.g., the specific cylindrical roller 202, with respect to the cage 1 12. In operational use of the second cylindrical roller bearing 200, the specific cylindrical roller 202 spins around an axis 201 of rotational symmetry of the specific cylindrical roller 202.

The specific cylindrical roller 202 comprises a first coil whose first core includes a first Wiegand wire. A first combination of the first coil (not shown separately) and the first core (not shown separately) is indicated with the reference numeral 204. The first combination 204 may be accommodated in a recess made in a surface of the specific cylindrical roller that faces the cage 1 12. Alternatively, the first combination 204 is attached to this surface.

The cage 1 12 comprises a first magnet 206 and a second magnet 208, e.g., embedded in the cage 112 or attached to the cage 112. The magnetic field of the first magnet 206 and the magnetic field of the second magnet 208 have opposite directions as explained earlier. The sensor of the second cylindrical roller bearing 200 comprises the first combination 204 of the first coil, whose first core includes the first Wiegand wire, and the first magnet 206 and the second magnet 208. The operation of the sensor is based on the interaction of the first combination 204 of the first coil, whose first core includes the first Wiegand wire, with the magnetic fields of the first magnet 206 and of the second magnet 208.

In operational use of the second cylindrical roller bearing 200, the location of the specific cylindrical roller 202 is fixed with respect to the cage 1 12. However, the cylindrical roller 202 is free to spin around its spin axis, e.g., the axis 201 of rotational symmetry of the specific roller 202, in order to enable a rotation of the first ring 102 and the second ring 104 relative to one another. When the specific cylindrical roller 202 spins around its spin axis 201, the first combination 204 of the first coil and the first Wiegand wire traverses a circular path around the spin 201 of the specific cylindrical roller 202. This circular path runs past the first magnet 206 and past the second magnet 208. Each time the first Wiegand wire passes the first magnet 206, the polarity of the magnetization of the first Wiegand wire flips from a first direction to a second direction, and each time the first Wiegand wire passes the second magnet 208, the polarity of the magnetization of the first Wiegand wire flips from the second direction back to the first direction. The flipping of the polarity of the magnetization induces a voltage in the first coil .The occurrence of the voltage is therefore representative of the flipping of the polarity of the magnetization and, hence, of the spinning of the specific cylindrical roller 202. As the polarity of the induced voltage depends on the direction of the magnetic field, the polarity of the induced voltage enables to determine the angular position of the specific cylindrical roller 202 relative to the cage 1 12 at an accuracy that is determined by the angular position of the first magnet 206 and the angular position of the second magnet 208 relative to the cage 112..

In an embodiment of the second cylindrical roller bearing 200, a low-power microcontroller (not shown) is accommodated in or at the specific cylindrical roller 202 that is powered by a small battery while in sleep mode. The microcontroller has a clock that remains running in sleep mode. A pulse generated by the first coil in the first combination 204 wakes the microcontroller from sleep mode and let the microcontroller enter an active mode. In the active mode, the microcontroller determines the length of the time lapsed between the moment of receipt of the current pulse and the moment of receipt of the previous pulse. The length of the time lapsed between receipts of two successive pulses is indicative of the average magnitude of the spinning speed of the specific cylindrical roller 202. Note that the angle, over which the specific cylindrical roller 202 has spun in the time interval between the two successive pulses, is pre-determined. The angle is determined by the angular position of the first magnet 206 and the angular position of the second magnet 208 relative to the path traversed by the first combination 204 with respect to the cage 1 12. For example, if the first magnet 206 and the second magnet 208 are positioned 180° apart, the time interval between two successive pulses indicates the period it took the specific cylindrical roller 202 to spin half a revolution. The ratio of the pre-determined angle and the time lapsed gives the average angular speed assumed by the specific cylindrical roller 202 for traversing this angle. Optionally, the microcontroller determines another average of the angular speed at which the specific cylindrical roller 202 is spinning, by means of summing the length of the lapsed times in a longer series of successive pulses, e.g., summing the lengths of the lapsed times for an integer number of complete spinning revolutions of the specific rolling element 202. Using the longer times series has the advantage of reducing the influence of the exact locations of the first magnet 204 and the second magnet 206 and of the first Wiegand wire. Information about the average angular speed thus determined can be sent as data in a radio-frequency signal via a low-power radio link to the outside world.

Consider the case wherein two or more specific ones of the cylindrical rollers in the second cylindrical roller bearing 200 have been individually equipped with a respective coil, a respective Wiegand wire and a respective microcontroller. The respective microcontroller in a respective one of such specific rolling elements may identify itself to the outside world by means of a unique identifier assigned to the microcontroller in advance and included in the signal sent by the individual sensor. Thus, an external agent can keep track of the spinning of multiple cylindrical rollers.

Alternatively, or in addition to the above microcontroller, one or more specific ones of the cylindrical rollers, e.g., the specific cylindrical roller 202, may each be equipped with a dedicated Application Specific Integrated Circuit (ASIC; not shown). The ASIC of the specific cylindrical roller 202 is configured for counting the number of complete spinning revolutions of the specific cylindrical roller 202 and/or the number of oscillations of the specific cylindrical roller 202 in case the specific cylindrical roller 202 is rocking, during the service life of the second cylindrical roller bearing 200. The ASIC stores the number of revolutions and/or the number of oscillations in a local memory of the ASIC, e.g., a nonvolatile memory. If the specific cylindrical roller 202 executes a number of spinning revolutions in the order of 10¹⁰ during the service life of the second cylindrical roller bearing 200, the local memory needs a minimum storage capacity of about 60 bits. As the power consumption of the ASIC is very low by design, energy extracted from the coil with the Wiegand wire will suffice to power the ASIC. If the ASIC has a radio-frequency identification (RFID) transponder section, the data stored in the internal memory of the ASIC can be read out any time by means of powering the ASIC via a magnetic coupling from an external reader device, using a technology known in the art of RFID-tag transponders.

Figs. 3, 4, 5, 6, 7 and 8 are diagrams to illustrate the operation of a first example of the sensor accommodated at the second cylindrical roller bearing 200. As specified above, the sensor comprises the first combination 204 of the first coil, whose first core includes the first Wiegand wire, the first magnet 206 and the second magnet 208. In the example shown, the first combination 204 is attached to, and spins with, the specific cylindrical roller 202, whereas the first magnet 206 and the second magnet 208 are attached to the cage 1 12. Figs. 3, 4, 5, 6 and 7 illustrate the relative position of the first combination 204 with respect to the cage 1 12 at various moments when the specific cylindrical roller 202 is spinning. Fig.8 is a diagram wherein the time runs vertically downwards and wherein the magnitude of the voltage, induced in the first coil of the first combination 204, is represented by horizontally.

Fig.3 is a diagram that illustrates the specific cylindrical roller 202 spinning in the direction indicated by an arrow 210. The position of the first combination 204 relative to the cage 112 is shown at moment t = Ti as having just passed the first magnet 206. There is no voltage induced in the first coil of the first combination 204.

Fig.4 is a diagram of the specific cylindrical roller 202 at a next moment t = Ti + δ. The position of the first combination 204 relative to the cage 1 12 is shown as entering the region, wherein the magnetic field of the second magnet 208 is strong enough at the location of the first combination 204 in order to flip the direction of magnetization of the first Wiegand wire in the first combination 204. As a result of flipping the direction of the magnetization, a voltage is induced in the first coil of the first combination 204. The voltage has a certain polarity. The diagram of Fig.8 shows the induced voltage occurring at the moment t = Ti + δ. Of course, there will be another contribution to the voltage induced in the first coil of the first combination 204 owing to the first coil experiencing a changing magnetic field when the first coil enters, and thereafter exits, the space wherein the strength of the magnetic field of the second magnet 208 is significant. This other contribution, however, will be ignored here as this other contribution is considered negligible in comparison to the voltage induced by the flipping of the direction of magnetization of the first Wiegand wire.

Fig.5 is a diagram of the specific cylindrical roller 202 at a next moment t = Ti + 2δ. The first combination has passed the second magnet 208. There is no voltage induced in the first coil of the first combination 204.

Fig.6 is a diagram of the specific cylindrical roller 202 at a next moment t = Tj + 3δ. The position of the first combination 204 relative to the cage 1 12 is shown as entering the region, wherein the magnetic field of the first magnet 206 is strong enough at the location of the first combination 204 in order to flip the direction of magnetization of the first Wiegand wire in the first combination 204. As a result of flipping the direction of the magnetization, a voltage is induced in the first coil of the first combination 204. The voltage has a polarity opposite to the one of the voltage induced at the moment t = Ti + δ illustrated by Fig.4. The diagram of Fig.8 shows the induced voltage occurring at the moment t = Ti + 3δ.

Fig.7 is a diagram that illustrates the specific cylindrical roller 202 wherein the position of the first combination 204 relative to the cage 1 12 is shown at moment t = Ti + 4δ, as having just passed the first magnet 206 again. There is no voltage induced at the first coil of the first combination 204, and the specific cylindrical roller bearing 202 is back in the same state as it was at the moment t = Tj of Fig.3.

Fig. 9 is a diagram of another example of the sensor accommodated at the cylindrical roller bearing 200. In this other example of the sensor, the specific cylindrical roller 202 has been equipped with a second combination 902 of a second coil (not indicated separately) having a second core (not indicated separately) with a second Wiegand wire (not indicated separately), in addition to the first combination 204 of the first coil having the first core with the first Wiegand wire. When an individual one of the first combination 204 and the second combination 902 passes a respective one of the first magnet 206 and the second magnet 208, the magnetization of the relevant one of the first Wiegand wire and the second Wiegand wire flips polarity. Now, consider that the first coil and the second coil are connected to a low- power microcontroller (not shown) of the kind discussed earlier. That is, the low-power microcontroller is accommodated in or at the specific cylindrical roller 202 and is powered by a small battery while in sleep mode. The microcontroller has a clock that remains running in sleep mode. Each of a voltage pulse in the first coil of the first combination 204 and another voltage pulse in the second coil of the second combination 902 wakes the microcontroller from sleep mode and let the microcontroller enter an active mode. In the active mode, the microcontroller determines the length of the time lapsed between the moment of receipt of the current pulse and the moment of receipt of the previous pulse. The length of the time lapsed between receipts of two successive pulses is indicative of the average magnitude of the spinning speed of the specific cylindrical roller 202. Moreover, the microcontroller is configured for discriminating between a pulse from the first coil and a pulse from the second coil, e.g., based on the identity of the port connected to the relevant one of the first coil and the second coil, or based on a difference between the amplitude of the voltage induced in the first coil and the amplitude of the voltage induced in the second coil. Accordingly, the microcontroller is not only capable of determining an average of the angular speed of spinning, but also of determining a direction of the spinning. To explain this further, consider the diagrams of Fig.10 and Fig.1 1.

Fig.10 is a diagram representing the occurrences of induced voltage peaks in the first coil and in the second coil over a time period of two spinning revolutions of the specific cylindrical roller 202. When the first coil of the first combination 204 passes the first magnet 206, a first voltage peak 1002 of a first polarity is induced in the first coil. When the second coil of the second combination 902 passes the first magnet 206, a second voltage peak 1004 of the first polarity is induced in the second coil. When the first coil of the first combination 204 passes the second magnet 208, a third voltage peak 1006 of a second polarity is induced in the first coil. When the second coil of the second combination 902 passes the second magnet 208, a fourth voltage peak 1010 of the second polarity is induced in the second coil.

The diagram of Fig.10 shows that the second voltage peak 1004 occurs just after the first voltage peak 1002 and long before the third voltage peak 1006, owing to the angular distance between the first combination 204 and the second combination 902 being substantially smaller than 90° as illustrated in the diagram of Fig.9. The conclusion can now be drawn that the specific cylindrical roller 202 is spinning clockwise. The diagram of Fig.1 1 shows that the second voltage peak 1004 occurs just before the first voltage peak 1002 and long before the fourth voltage peak 1008, owing to the angular distance between the first combination 204 and the second combination 902 being substantially smaller than 90° as illustrated in the diagram of Fig.9. The conclusion can now be drawn that the specific cylindrical roller 202 is spinning anti-clockwise.

Fig.12 is a diagram showing a side view of the specific rolling element 202 of the invention, e.g., a cylindrical roller, retained in the cage 1 12. The specific rolling element 202 has the spin axis 201, around which the specific rolling element 202 spins in operational use of the rolling elements bearing. The spin axis 201 is here the single axis of rotational symmetry of the specific rolling element 202. In addition to the first magnet 206 and the second magnet 208, the cage 1 12 now accommodates an even number of further magnets: a third magnet 1202, a fourth magnet 1204, a fifth magnet 1206, a sixth magnet 1208, a seventh magnet 1210 and an eighth magnet 1212. The first magnet 206, the second magnet 208, the third magnet 1202, the fourth magnet 1204, the fifth magnet 1206, the sixth magnet 1208, the seventh magnet 1210 and the eighth magnet 1212 are arranged so as to provide a magnetic field along the circular path of the first combination 204 that alternates direction with the position of the combination. For example, the first magnet 206, the second magnet 208, the third magnet 1202, the fourth magnet 1204, the fifth magnet 1206, the sixth magnet 1208, the seventh magnet 1210 and the eighth magnet 1212 are implemented as a circular Halbach array. In the example illustrated in Fig.12, the magnetic fields of the first magnet 206, the fourth magnet 1204, the fifth magnet 1206 and the eighth magnet 1212 all substantially point in a first direction perpendicular to the diagram at the location of the path of the first combination 204, whereas the magnetic fields of the second magnet 208, the third magnet 1202, the sixth magnet 1208 and the seventh magnet 1210 all substantially point in a second direction, opposite the first direction and perpendicular to the diagram at the location of the path of the first combination 204. The number of pulses induced in the coil of the first combination 204 during a single spinning revolution equals the number of magnets in the spatially alternating sequence along the path of the combination 204. Accordingly, with a higher number of magnets a higher resolution as regards angular location of the specific cylindrical roller 202 and, therefore, as regards angular speed of the specific cylindrical roller 202 can be obtained. For completeness: the combination 204 is shown in the diagram of Fig.12 as not hidden from view by the arrangement of the magnets (the first magnet 206, the second magnet 208, the third magnet 1202, the fourth magnet 1204, the fifth magnet 1206, the sixth magnet 1208, the seventh magnet 1210 and the eighth magnet 1212) in order to explain operation. In practice the positions of the magnets relative to the path, traversed by the combination coil and the Wiegand wire when the specific cylindrical roller 202 is spinning, are preferably such that the Wiegand wire is exposed to magnetic fields, whose strengths have suitably high magnitudes to flip the polarity of the magnetization. This may, under circumstances, imply that the circular path, traversed by the Wiegand wire relative to the cage 1 12 when the specific cylindrical roller 202 is spinning, has substantially a radius that is substantially the same as the radius of the circular arrangement of the magnets in the diagram of Fig.12.

The Figures discussed above show embodiments, wherein the first combination 204 of the first coil and the first Wiegand wire (and the second combination 902 of the second coil and the second Wiegand wire in Fig.9) are accommodated at the specific cylindrical roller 202, and wherein the first magnet 206 and the second magnet 208 (and the further magnets in Fig.12) are accommodated at the cage 1 12. In an alternative configuration, the first combination 204 (and the second combination 902 in Fig.9) is (are) accommodated at the cage 1 12, whereas the first magnet 206 and the second magnet 208 (and the further magnets in Fig.12) are accommodated at the specific cylindrical roller 202.

The alternative combination may have following advantages. Consider the surface of the portion of the cage 1 12 where the cage 1 12 overlaps the disc-shaped flank of the specific cylindrical roller 202 when viewed along the spin axis 201 of the specific cylindrical roller 202. The area of this surface is typically smaller than that area of the disc-shaped flank. Accordingly, it is, under circumstances more attractive to accommodate the first magnet 206, the second magnet 208 and the further magnets of Fig.12 at the disc-shaped flank than at the cage 1 12, as there is more room available. More importantly, if the spinning of two or more specific ones of the cylindrical rollers is individually monitored, each respective one of the specific cylindrical rollers is assigned a respective combination of a respective coil, whose core includes a respective Wiegand wire. If the respective combinations are all accommodated at the cage, a single electronic circuit can be used, accommodated at the cage, to process the signals produced by the voltages induced in the respective coils, thus reducing costs.

The invention has been illustrated above with reference to a cylindrical roller bearing. It is clear that the invention can be used with other types of rolling element bearings, such as taper roller bearings, taper roller bearings, etc.

Claims

A rolling element bearing (200; 1200), comprising:

a first ring(102), a second ring(104), a cage (1 12) and a plurality of rolling elements (106, 108, 202) accommodated between the first ring and the second ring and retained in the cage;

^• a sensor (204, 206, 208, 902, 1202, 1204, 1206, 1208, 1210, 1212), accommodated at the rolling element bearing and operative to sense a spinning of a specific one of the rolling elements around a spin axis (201) of the specific rolling element and with respect to the cage in operational use of the rolling element bearing.

The rolling element bearing of claim 1, wherein:

the sensor comprises:

a first coil (204) having a first core with a first Wiegand wire; and

■ magnetic means (206, 208; 1202, 1204, 1206, 1208, 1210, 1212) for generating a magnetic field;

the first coil is accommodated at one of the cage and the specific rolling element;

the magnetic means is accommodated at the other one of the cage and the specific rolling element; and

the magnetic field is configured for flipping a polarity of a magnetization of the first Wiegand wire a pre-determined number of times during a single revolution of the specific rolling element with respect to the cage and around the spin axis.

The rolling element bearing of claim 2, wherein:

the sensor comprises at least a further coil (902) having a further core with a further Wiegand wire;

the first coil and the further coil are arranged to remain in a fixed position relative to one another in operational use of the rolling element bearing; and

the first coil and the further coil, on the one hand, and the magnetic means, on the other hand, are positioned so as to enable to determine a direction of the spinning.

4. The rolling element bearing of claim 2or 3, wherein the sensor forms a functional part of a power supply of an electronic circuit accommodated at the rolling element bearing.

5. A first component (202) configured for use as a specific one of a plurality of rolling elements accommodated in a cage (112) in a rolling element bearing (200), wherein: the first component comprises a coil (204) with a core that includes a Wiegand wire; and

the coil with the core that includes the Wiegand wire has a fixed location at the first component.

6. A second component (202) configured for use as a specific one of a plurality of rolling elements accommodated in a cage (1 12) in a rolling element bearing (200), wherein: the second component has a single axis (201) of rotational symmetry;

the second component comprises magnetic means for generating a magnetic field; the magnetic means has a fixed location at a surface of the second component that is substantially perpendicular to the single axis of rotational symmetry; and

the magnetic field has a fixed orientation with respect to the second component.

7. A third component (1 12) configured for use as a cage of a rolling element bearing (200) and operative to retain a plurality of rolling elements (106, 108, 202) of the rolling element bearing in operational use of the rolling element bearing, wherein the third component comprises a coil with a core that includes a Wiegand wire, wherein the coil with the core that includes the Wiegand wire has a fixed location at the third component.

8. A method of determining an attribute of a spin of a specific one (202) of a plurality of rolling elements (106, 108, 202) retained in a cage (1 12) of a rolling element bearing (200) in operational use of the rolling element bearing, wherein:

the spin is around an imaginary axis (201) fixed to the specific rolling element;

the method comprises sensing a relative movement of the specific rolling element with respect to the cage in operational use of the rolling element bearing.

9. A method of determining an attribute of a mechanical load on a rolling element bearing

(200) in operational use of the rolling element bearing, wherein:

the rolling element bearing comprises a first ring (102), a second ring (104), a cage

(1 12) and a plurality of rolling elements (106, 108, 202) accommodated between the first ring and the second ring and retained in the cage; and

the method comprises:

monitoring a spinning of at least a specific one (202) of the rolling elements around a spin axis (201) of the specific rolling element and with respect to the cage in operational use of the rolling element bearing; and

determining the attribute of the mechanical load from the monitored spinning.