EP4649296A1

EP4649296A1 - System for evaluation of bearing degradation

Info

Publication number: EP4649296A1
Application number: EP24741785.0A
Authority: EP
Inventors: Kye Yak See; Fei FAN; Zhenyu Zhao; Hong Yee Alvin WONG; Chi Cuong Hoang
Original assignee: Nanyang Technological University
Current assignee: Nanyang Technological University
Priority date: 2023-01-09
Filing date: 2024-01-04
Publication date: 2025-11-19
Also published as: CN120500618A; WO2024151209A1

Abstract

A system and method for evaluation of bearing degradation includes a first support, a shaft, and at least one vibration sensor The first support is configured to hold a bearing. The shaft defines an axial direction along a length of the shaft, and is coupleable to a race of the bearing to apply an axial mechanical loading on the bearing. A first inductive probe and a second inductive probe are inductively coupleable with the shaft at respective probe locations spaced apart along the shaft. The second current probe is configured to measure a circulating current responsive to the first inductive probe inducing a current in the shaft. The at least one vibration sensor is disposed at the first support. The at least one vibration sensor is configured to provide a vibration signal responsive to sensing vibration concurrently with the circulating current being measured.

Description

SYSTEM FOR EVALUATION OF BEARING DEGRADATION

RELATED APPLICATION

[0001] This application claims the benefit of priority to the Singapore application no. 10202300062Y filed January 9, 2023, the contents of which are hereby incorporated by reference in their entirety for all purposes.

TECHNICAL FIELD

[0002] The present disclosure relates to the testing of bearings, and more particularly to a system and method for testing bearing degradation.

BACKGROUND

[0003] Bearings play an important role in almost all machines with moving parts. In some applications, bearing failure can lead to expensive equipment downtime and repairs. In other applications, bearing failure can lead to safety issues. As part of predictive maintenance, it would be useful if the lifespan of any set of bearings (when the bearings are unlikely to fail) can be predicted so that the bearings can be replaced before catastrophic failure occurs. Unfortunately, with the advancement of power electronics and the electrification of motor drive systems, bearings are often subject to an electrical load on top of a mechanical load. Compared to mechanical loading, the impact of electrical loading is much more difficult to determine. Some bearings fail after a few years of use in one application, while the same bearings may fail within a month of use in another application. It is believed that as much as over 40% of all motor failures may be attributed to bearing failures.

SUMMARY

[0004] In one aspect, the present application discloses a system including a first support, a shaft, a first inductive probe, a second inductive probe, and at least one vibration sensor. The first support is configured to hold a bearing. The shaft defines an axial direction along a length of the shaft. The shaft is coupleable to a race of the bearing to apply an axial mechanical loading on the bearing. The first inductive probe and the second inductive probe are inductively coupleable with the shaft at respective probe locations. The respective probe locations are spaced apart along the shaft. The second current probe is configured to measure a circulating current responsive to the first inductive probe inducing a current in the shaft. The at least one vibration sensor is disposed at the first support. The at least one vibration sensor is configured to provide a vibration signal responsive to sensing vibration concurrently with the circulating current being measured.

[0005] In another aspect, the present application discloses a method including steps of: (i) applying an axial mechanical loading to a bearing held by a first support, the axial mechanical loading being applied by a shaft coupled to a race of the bearing, the shaft defining an axial direction along a length of the shaft; (ii) inducing a current in the shaft using a first inductive probe; (iii) measuring a circulating current using a second inductive probe, the first inductive probe and the second inductive probe being inductively coupled with the shaft at respective probe locations, the respective probe locations being spaced apart along the shaft; and (iv) obtaining a vibration signal responsive to a vibration being sensed concurrently with the circulating current being measured, wherein the vibration signal is provided by at least one vibration sensor disposed at the first support.

[0006] The method may include determining a projected bearing degradation over a period of use based on the health state of the bearing after a period of accelerated testing, in which the period of accelerated testing is shorter than the period of use.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Various embodiments of the present disclosure will be described with reference to the following figures:

[0008] FIG. 1 is a schematic diagram of a system according to embodiments of the present disclosure;

[0009] FIG. 2 is a cross-sectional view showing various parts of a bearing;

[0010] FIG. 3 is a cross-sectional view of a mechanical load zone of the system;

[0011] FIG. 4 is a schematic block diagram of a control sub-system of the system;

[0012] FIGS. 5A to 5C show concept drawings of prototypes of the system and

FIG. 5D shows images of the prototype built; [0013] FIG. 6 is a schematic flow diagram of a method according to embodiments of the present disclosure;

[0014] FIG. 7A and FIG. 7B are images of a ball bearing and a part of a race of new bearings prior to testing;

[0015] FIG. 8A shows images of the ball bearing of FIG. 7A after testing;

[0016] FIG. 8B shows images of a part of the race of FIG. 7B after testing;

[0017] FIG. 9 are measured vibration signals after 60 hours of testing and after 120 hours of testing, using a prototype of the system;

[0018] FIG. 10 is an image of a side view of another prototype of the system;

[0019] FIG. 11 are measured vibration signals at day 1 , day 15, and day 30 of an evaluation program, measured along an x-axis of the system;

[0020] FIG. 12 are respective distribution graphs of the measured vibration signals of FIG. 11 ;

[0021] FIG. 13 are measured vibration signals at day 1 , day 15, and day 30 of test the evaluation program, measured along a y-axis of the system;

[0022] FIG. 14 are respective distribution graphs of the measured vibration signals of FIG. 13;

[0023] FIG. 15 are measured vibration signals at day 1 , day 15, and day 30 of the evaluation program, measured along a z-axis of the system;

[0024] FIG. 16 are respective distribution graphs of the measured vibration signals of FIG. 15;

[0025] FIG. 17 shows plots of the mean values and maximum values of the vibration signals; and

[0026] FIG. 18 shows plots of the standard deviation of the vibration signals.

DETAILED DESCRIPTION

[0027] The following detailed description is made with reference to the accompanying drawings, showing details and embodiments of the present disclosure for the purposes of illustration. Features that are described in the context of an embodiment may correspondingly be applicable to the same or similar features in the other embodiments, even if not explicitly described in these other embodiments. Additions and/or combinations and/or alternatives as described for a feature in the context of an embodiment may correspondingly be applicable to the same or similar feature in the other embodiments.

[0028] In the context of various embodiments, the articles “a”, “an” and “the” as used with regard to a feature or element include a reference to one or more of the features or elements.

[0029] In the context of various embodiments, the term “about” or “approximately" as applied to a numeric value encompasses the exact value and a reasonable variance as generally understood in the relevant technical field, e.g., within 10% of the specified value.

[0030] As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.

[0031] The word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments. As used herein, the singular ‘a’ and ‘an’ may be construed as including the plural “one or more" unless apparent from the context to be otherwise.

[0032] Terms such as “first” and “second” are used in the description and claims only for the sake of brevity and clarity, and do not necessarily imply a priority or order, unless required by the context. The terms "about" and "approximately" as applied to a stated numeric value encompasses the exact value and a reasonable variance as will be understood by one of ordinary skill in the art, and the terms “generally” and “substantially” are to be understood in a comparable manner, unless otherwise specified.

[0033] Some methods may be described in terms of steps merely to aid understanding and/or for convenient reference. The delineation between one step and another step may be merely for convenient reference in the present disclosure. It will be understood that in actual implementation there may not be a clear division or transition from one step to another subsequent step. There may be a certain amount of overlap among the steps and/or more than one step may occur or be performed concurrently in time, etc.

[0034] As used herein, the term “concurrent”, or “concurrently”, is used loosely to refer to two or more occurrences (or events) that at least partially overlap in time, in which the occurrences may not start at the same time instant and/or end at the same time instant.

[0035] As used herein, the terms “load” and “force” may be used interchangeably unless otherwise required by the context.

[0036] Motor drive systems incorporating high-speed switching devices produces time-varying high-amplitude common-mode (CM) voltage with a relatively rapid rate of change of voltage The CM voltage results in a CM current which is undesirable. The CM current circulates in/through the motor drive system. It is expected that the CM current will vary across differently configured motor drive systems and also vary over time as the condition of a motor drive system changes with use. The CM current also flows through the bearings (referred to as circulating bearing current) and this can result in various defects such as frosting and fluting at the races, and pitting on the rolling elements. In cases where the lubricant has worn off, the circulating bearing current can cause sparking or an electrical discharge that can result in pitting in the bearing.

[0037] System with electrical load zone

[0038] FIG. 1 is a schematic diagram of a system 100 according to some embodiments of the present disclosure. The system 100 can be used to provide a repeatable and quantifiable evaluation of potential bearing degradation in various applications, including but not limited to applications where the CM current is likely to be present.

[0039] The system 100 can be used to evaluate various types of bearings. For convenient reference and not to be limiting, the system 100 may be used to evaluate degradation performance of a bearing 900/902 such as one schematically illustrated in a cross-sectional view in FIG. 2. The bearing 900/902 may include a plurality of balls 910 spaced out by a cage 940. The balls 910 and the cage 940 are disposed between an outer race 920 and an inner race 930.

[0040] Referring again to FIG. 1 , the system 100 includes an electrical load zone 102 integrated with a mechanical load zone 103. The system 100 includes a first support 111 at which a bearing-under-test (BUT) 900 may be installed. In the example illustrated, the electrical load zone 102 and the mechanical load zone 103 are provided on opposite sides of the first support 111. In other examples, the electrical load zone 102 and the mechanical load zone 103 may be disposed on the same side of the first support 111.

[0041 ] A shaft 1 0 extends between the first support 111 and a second support 112. The second support 112 is spaced apart from the first support 111 along a reference axis or axial direction 101. The axial direction 101 may be defined by a shaft 140. A support bearing 902 (also referred to as a second bearing) is installed at the second support 112. The support bearing 902 is preferably selected to be of the same size as the BUT 900 to facilitate alignment of the shaft 140.

[0042] The shaft 140 extends beyond the second support to a drive end 141. The drive end 141 is operably coupled with a motor 200, e.g., an induction motor. Such that the motor 200 can drive rotation of the drive end 141 , and thus enable rotation of the shaft 140. In the example illustrated, the drive end 141 is part of a belt and pulley sub-system. In other examples, the drive end 141 may be coupled differently to the motor 200 such as, but not limited to, by a set of gears, etc.

[0043] Two inductive probes 340 (e.g., a current injection probe 342 and a current receiving probe 344) are disposed in the electrical load zone 102, between the first support 111 and the second support 112. In the present disclosure, the terms “probe”, “inductive coupling probe”, and “inductive probe” may be used interchangeably unless otherwise dictated by the context. The inductive probes (e g., injection probe, measurement probe, receiving probe, etc.) used may be physically similar but differently named to better illustrate the function of the respective probe in the context of the embodiment. Each inductive probe 340 may be clamped onto the shaft 140 or otherwise positioned to interface with the shaft at a probe location. In operation, the inductive probe 340 may be configured to induce a current in the shaft 140. When used in this mode, the inductive probe 340 may be described as an injection probe. Alternatively, in operation, a current may be induced in the inductive probe 340 and the induced current can be measured. When used in this mode, the inductive probe 340 may be described as a measurement probe.

[0044] One or more vibration sensors 310 are disposed at the first support 111. A discharge detector 350 is provided in proximity to the first support 111 , and more specifically, in proximity to the BUT 900. Optionally, a temperature sensor 330 is coupled to measure the temperature of/near the BUT 900.

[0045] Mechanical load zone

[0046] The shaft 140 further extends between the first support 111 and a third support 113. In this example, the first support 111 is axially aligned with and disposed between the second support 112 and the third support 113.

[0047] The shaft 140 may be engaged to the third support 113 in various ways. In this example, the shaft 140 extends beyond the third support 113 to an axial load end 143, and the axial load end 143 is configured to apply a mechanical load along the axial direction on the BUT 900. A load cell 320 may be coupled to the shaft 140 between the second support 112 and the first support 111. The load cell 320 is configured to measure the axial mechanical load applied to the BUT 900.

[0048] FIG. 3 provides a more detailed view of the mechanical load zone 103 according to one embodiment of the system 100. The axial load end 143 of the shaft 140 may be in a threaded engagement with an adjustable fastener 153. For example, a greater mechanical load may be applied to the BUT 900 by driving the adjustable fastener 153 towards the third support 113, and a smaller mechanical load may be applied to the BUT 900 by bringing the adjustable fastener 153 away from the third support 113. In the illustrated example, the adjustable fastener 153 and the axial load end 143 of the shaft 140 may form a nut-and-bolt pair. The adjustable fastener 153 may be manually or machine-actuated to “tighten” the threaded engagement and provide a greater axially-directed mechanical load on the BUT 900. The adjustable fastener 153 may be manually or machine-actuated to “loosen” the threaded engagement and provide a smaller axially-directed mechanical load on the BUT 900.

[0049] The load cell 320 may be provided in a load cell holder 322. The load cell holder 322 can be clamped about the shaft 140.

[0050] A tapered bearing 154 may be provided between the shaft 140 and an inner race 930 of the BUT 900 for transmission of axially-directed mechanical loads on the BUT 900. For example, the shaft 140 may present a tapered bearing to engage with the inner race of the BUT 900 and to concurrently push directly or indirectly in the axial direction 101 against the inner race 930 of the BUT 900. [0051] The outer race 920 of the BUT 900 is fixedly coupled to the first support 111 (which also serves as a bearing holder).

[0052] Control sub-system

[0053] In some embodiments, the system 100 may be at least partially manually configured and/or operated to perform a method of evaluating bearing degradation. In some other embodiments, the system 100 may be provided with a control subsystem 400 managed by a processor 410. The processor 410 may be in the form of one or more devices, such as but not limited to a computing device, a programmable device, an integrated chip, etc.

[0054] FIG. 4 is a schematic block diagram of one example of a control subsystem 400 of the system 100. The system 100 may include a processor 410 in operable signal communication with a memory 410 and a user interface 414. The processor 410 may be configured to perform a method of evaluating bearing degradation, e.g., by executing computer-readable instructions stored in the memory 412. Data collected by various sensors (generically designated as 300) may be stored in the memory 412, output via a user interface 414, and/or processed by the processor 410.

[0055] Based on measured and/or calculated parameters, the processor 410 may be in operable signal communication with a motor driver 420 to controllably rotate the shaft 140 at a selected speed in the course of the evaluation program. The processor 410 may further be in operable signal communication with an axial force control 430 to controllably apply an axial mechanical load at a selected load level. The processor 410 may be in operable signal communication with a pulse generator 440 to trigger the generation of a time series of high-voltages pulses fed to the inductive probe designated as the current injection probe 342. The processor 410 may be in operable signal communication with a heater 450 (e.g., a cartridge heater).

[0056] Method

[0057] To aid understanding, reference will be made to FIG. 1 to FIG. 6 in the following description of the proposed method 500. In particular, FIG. 5A to FIG. 5C show concept drawings of prototypes of the system 100, and FIG. 5D shows images of the prototype system 100 built and used in experiments. FIG. 6 is a schematic flow diagram of the method 500 according to various embodiments.

[0058] Electrical loading and axial mechanical loading

[0059] The method 500 includes a step of applying an electrical load (520) (also referred to as “electrical loading” 520) and a step of applying an axially-directed mechanical load (530) (also referred to as “axial mechanical loading” 530) to the BUT 900, in which the electrical loading 520 and the axial mechanical loading 530 are applied concurrently.

[0060] The method 500 includes electrical loading (520) concurrently with axial mechanical loading (530), in which the axial mechanical loading (530) includes provision of mechanical load forces at least having an axial component. The axial component of the mechanical load forces is parallel or substantially parallel to the shaft 140, e.g., parallel to the axial direction 101 . The shaft 140 may be supported by supports 110 (e.g., end support, bearing holders, etc.).

[0061] In the method 500, the electrical loading (520) and the axial mechanical loading (530) are concurrent with the BUT 900 in a state of use (e.g., in rotation 510). For the sake of brevity, a bearing in rotation refers to a state in which the outer race and the inner race of the bearing are in relative rotational motion to one another. In some examples, the BUT 900 may be further subjected to stress conditions (540), for example, including but not limited to, various temperature conditions, varying mechanical load conditions (in addition to the axial mechanical loading 530), etc.

[0062] In some examples, test data may be collected (step of data collection 550) with the bearing in rotation (510). The method 500 may further include a step of predicting a reliability or a lifespan (useful life) of the other bearings similarly designed and/or fabricated as the BUT 900 (560).

[0063] The concurrent events need not all start at the same time instant. In one example, the axial mechanical loading 530 may be applied to the BUT 900 (at the mechanical load zone 103) before the motor 200 starts to rotate the shaft 140. When the shaft 140 is rotating, the BUT 900 is in rotation (510). For example, the outer race 920 may be fixed by the first support 111 and the inner race 930 is rotated along with the shaft 140. When the BUT 900 is in rotation (510) and under axial mechanical loading (530), electrical loading (520) is then applied to the BUT 900. Test data is then collected in a step of data collection (550).

[0064] In another example, upon completion of the end of the data collection (550), the BUT 900 may be relieved of the electrical loading (520) before rotation of the shaft 140 is stopped. The BUT 900 may be in a stationary state before the axial mechanical loading (530) is removed. That is, the concurrent events need not all stop at the same time instant.

[0065] Pulsed electrical loading

[0066] In the present disclosure, the electrical loading 520 may be a pulsed electrical loading 520. For example, the electrical loading 520 may include multiple instances of a step of injecting (522) a voltage pulse to the shaft 140. In some examples, the electrical loading 520 applied over a period of time includes a step of injecting (522) a series of high-voltage pulses at a pulse frequency over the period of time.

[0067] In some examples, a high-voltage pulse generator 440 may be electrically connected to a first inductive probe 340. The pulse generator 440 may be configured to feed a pulsed current to the rotating shaft 140 via the first inductive probe 340 such that the first inductive probe 340 serves as an injection probe 342. This is observed to generate a pulsed bearing circulating current or CM current that passes through the BUT 900 (also referred to as a pulsed circulating bearing current). The pulsed current may be one with a controllable and varying amplitude to emulate the varying power rating conditions, for example, experienced in some motor drive systems.

[0068] The electrical loading 520 may further include a step of measuring (524) an induced bearing current. In some examples, a second inductive probe 340 is clamped onto the same shaft 140. The first inductive probe and the second inductive probe are coupled at respective probe locations. The probe locations are spaced apart along the shaft 140. The second inductive probe 340 can serve as a measurement probe 344 to monitor the induced current that flows through the BUT 900 (also referred to as an induced bearing current).

[0069] Other measurements [0070] Other probes 340 may be included. For example, an induced end-to-end shaft voltage may be measured using two spaced apart shaft voltage probes with their carbon fiber tips in contact with the shaft 1 0.

[0071] Data collection (550) may include acquiring signals from the measurement probe 344. Data collection (550) may include acquiring signals from the shaft voltage probes. Data collection (550) may include acquiring signals from the load cell 320). Data collection (550) may include measuring the temperature at/near the BUT 900, for example, using the temperature sensor 330. Data collection may include recording the number of discharges, using the discharge detector 350. Data collection (550) includes at least acquiring signals from the one or more vibration sensors 310, e.g., accelerometers, disposed at/on the first support 111 or the BUT 900.

[0072] The method 500 enables the acquisition of sufficient and relevant data to enable a practically useful estimate of the useful life of the BUT 900. This capability was not available previous to the present work.

[0073] Example 1

[0074] FIG. 7A and FIG. 7B are images of a ball 910 and a part of the races 920/930 of new bearings prior to use. The surface of the ball 910 and the inner surface of the races 920930 are smooth and free of visible defects. FIG. 8A and FIG. 8B shows images of the same ball 910 and races 920/930 of FIG. 7B after 120 hours of accelerated testing using a prototype of the system. The surface of the ball 910 in FIG. 8A show signs of wear and tear, including abrasion marks and scratches, as well as visible pitting 602 after the accelerated testing. Similarly, the surface of the races 920/930 in FIG. 8B show visible pitting 604 after the accelerated testing.

[0075] FIG. 9 shows plots of the vibration signals obtained after 60 hours of the accelerated testing and after 120 hours of the accelerated testing. The vibration signals (also referred to as the measured vibration signals) are measurements obtained from the one or more vibration sensors. It can be seen that, after 120 hours of the accelerated testing, the acceleration measurements which correspond to the extent of vibration exhibited by the BUT are characterized by an amplitude range exceeding the acceptable/predetermined upper limit and lower limit. The upper limit and the lower limit may be predetermined based on the vibration behaviour of the new bearings.

[0076] The bearing can undergo degradation similar to degradation that occurs in actual use of similar bearings. It is noteworthy that, using the proposed system, degradation can be seen in as short a time as 120 hours. In contrast, in actual use of similar bearings, a similar extent of degradation of similar bearings may require a few weeks to several months. It was further experimentally verified that the measured vibration signals correspond to the extent of degradation. In other words, the proposed system can be used to provide accelerated testing with meaningful and measurable outputs (e.g., measurable vibration signals).

[0077] Example 2

[0078] FIG. 10 is an image of a side view of another prototype of the system used in another evaluation of bearing degradation. In this example, the motor was controllable by a variable frequency driver (VFD) and the axial mechanical loading was a controllable axial force, controlled with the aid of an axial force control panel. A heat gun was used to controllably elevate the temperature of the BUT. A temperature sensor was provided near the BUT. The current injection probe and the current receiving probe were inductively coupled to spaced apart points on the shaft to measure the current/voltage across the BUT (also referred to as the bearing current/bearing voltage, for the sake of brevity). Vibration sensors were disposed on the bearing support or the first support. The electrical loading was provided via the current injection probe and measured via the current receiving probe. The mechanical load zone included stressed (preloaded and axially oriented) springs to apply the desired axial mechanical loading. A discharge detector was provided to monitor the number of discharges.

[0079] The present system and method may be used in various applications. For example, the present system and method were used as part of a product development process to evaluate newly developed bearings. The newly developed bearings were intended for use in a motor drive system, such as a motor drive system for an electric vehicle.

[0080] The test conditions may be selected or determined partly on the basis of actual operating conditions of the bearings in the motor drive system. For example, the BUT may be tested over a temperature range from about 20 °C to about 100 °C. The axial mechanical loading may be controllably provided in a range from zero (unloaded) to about 10 kN (kilonewton). The shaft rotation speed may be controlled by the motor in a range from zero (stationary) to about 2000 rpm (revolutions per minute).

[0081] The test conditions may be selected or determined partly on the basis of a target lifespan (maximum life expectancy) or a target useful life for the newly developed bearings. The electrical loading applied may be defined in terms of magnitude (peak current) and frequency of the injected current pulses (pulse injection frequency). The frequency of the injected current pulses is preferably (and optionally) set to be relatively high to subject the BUT to accelerated testing.

[0082] The vibration signals may be used as a health indicator. For example, the maximum and minimum values of the vibration signals of the new bearings (at day 1 ) may be selected as a reference for the purpose of comparison. The vibration signals may be measured with respect to any direction of interest. For convenient reference, some experimentally obtained results will be described with respect to the x-axis, y-axis, and z-axis of an orthogonal frame of reference, in which the y- axis is defined by the shaft and in which the BUT is disposed in the x-z plane.

[0083] FIG. 11 shows the measured vibration signals at day 1 , day 15, and day 30 of testing under an evaluation program, measured along the x-axis It may be noted that the maximum positive values and the maximum negative values of the vibration signals exhibit an increasing trend over time. Using the vibration signals ay day 1 as a reference, an upper limit and a lower limit may be defined (as shown in dashed lines in FIG. 11). At day 15, the vibration signals exhibited only a few excursions beyond the upper limit and the lower limit. At day 30, the vibration signals exceeded greater deviation beyond the upper limit and the lower limit.

[0084] The mean and the maximum values of the vibration signals were calculated based on the absolute values of the vibration signals. At day 1 , the mean was 2.65 mis²'- and the maximum value was 24.6 m/s². At day 15, the mean was 3.51 m/s² and the maximum value was 46.63 m/s². At day 1 , the mean was 5.23 m/s² and the maximum value was 75.26 m/s². [0085] While the mean and maximum values are useful, the present system and method advantageously offer the ability to further consider the distribution curves of the measured vibration signals. FIG. 12 shows the respective distribution graphs of the measured vibration signals of FIG. 11. FIG. 12 provides a more objective way of determining the upper limit and lower limit with reference to the new bearing, as well as a more objective way of determining when the performance of the BUT has degraded to a point where replacement of the bearing would be required.

[0086] FIG. 13 shows measured vibration signals at day 1 , day 15, and day 30 of testing, measured along the y-axis of the system. FIG. 14 shows respective distribution graphs of the measured vibration signals of FIG. 13.

[0087] While there is an increasing trend in the y-axis vibration with respect to time, the increase in vibration signal values is less than that of the x-axis.

[0088] FIG. 15 shows measured vibration signals at day 1 , day 15, and day 30 of testing, measured along the z-axis of the system. FIG. 16 shows respective distribution graphs of the measured vibration signals of FIG. 15. The vibration signals measured in the z-axis direction exhibit a similar trend as that measured in the x-axis direction.

[0089] FIG. 17 shows plots of the mean values and maximum values of the vibration signals of FIG. 11 , FIG. 13, and FIG. 15. FIG. 18 shows plots of the standard deviation of the vibration signals based on FIG. 12, FIG. 14, and FIG. 16. It can be appreciated that determining the extent of bearing degradation by the mean or the maximum values alone may be influenced by the direction in which the measurements are taken. In actual use, the path of the CM current may be so complex that it may not be clear which is the more critical direction (e.g., the direction in which the vibrations are larger and more indicative of pending bearing degradation). The standard deviation curves help to provide a clearer view of bearing degradation. It can be seen from FIG. 18 that there is an increase in the rate of degradation (increased rate of change of the standard deviation) after day 15. This may be used to suggest that, for example, that the bearing be replaced at day 15 in a critical use application.

[0090] Example 3 [0091] In another exemplary test, the test conditions used included a shaft rotation speed of 1500 rpm and at room temperature, with no axial mechanical force applied. A CM current (circulating bearing current) could be simulated across the BUT by injecting a 5 A (ampere) peak current at a pulse injection frequency of 1000 Hz (hertz). After running the test for a mere 120 hours (equivalent to five days’ of continuous operation), the data collected was sufficient for use in projecting an expected bearing life in actual use.

[0092] Further Examples

[0093] The system 100 can be used as a bearing test system to evaluate bearings across diverse applications, including but not limited to robotics, automated guided vehicles, electric vehicles, electric planes, and electric vessels. The tables below provide a summary of distinct test conditions for these applications, showing that a single unit of the proposed system 100 is capable of offering a thorough assessment of bearing performance in various operational scenarios.

[0094] In the field of robotics applications, the typical bearing may be subjected to operational conditions that vary significantly across different categories of robotics. For example, a low-power robot may be expected to handle a mechanical loading (axial mechanical loading) of up to 100 N, a medium-power robot may be expected to handle a mechanical loading (axial mechanical loading) in a range from about 100 N to about 500 N, and a high-power robot may be expected to handle a mechanical loading (axial mechanical loading) of about 500 N or higher.

Table 1. Robotics Applications [0095] As explained above, useful bearing performance test results should preferably include performance evaluation of the selected bearing in terms of both mechanical loading and electrical loading. The electrical loading is related to the common-mode voltage present in the robotic apparatus in operation. In practice, it would be costly to use an actual robot of each category solely to simulate the electrical loading. The proposed system 100 can be useful for obtaining useful bearing performance test results corresponding to subjecting the BUT 900 to different categories of robots, without requiring the use of the actual robotic apparatus.

[0096] In many application scenarios, it is useful for the bearing manufacturer or the product developer to estimate the useful life of a selected bearing. Unnecessary costs may be avoided by not replacing bearings too early, while timely maintenance, repair and/or replacement can be carried out before catastrophic failure is likely to occur. In products such as AGVs (autonomous guided vehicles), it can be appreciated that sudden failure of an AGV in mid-flight may potentially result in the AGV crashing and causing damage on impact with the ground.

[0097] Table 2 shows the various test conditions that can be configured in a prototype of the system 100 for testing a bearing and assessing its useful life when used in various categories of AGVs. In other examples, a realistic evaluation of the bearing performance can help inform the selection of bearings for different categories of AGVs.

Table 2. AGV Applications Bearings are fundamental engineering components with a critical role to play in broad range of applications. With the proliferation of electrically powered vehicles (land, air, and sea), there is a pressing need for useful and comparable bearing performance evaluation. Table 3 shows a non-exhaustive list of examples of electric vehicles with distinct or different operating conditions. Also shown in Table 3 are the test conditions that can be used to conduct accelerated testing for the different operating conditions or application scenarios.

Table 3. Electric Vehicle Applications [0098] In the examples presented in Table 1 to Table 3, “motor power rating” refers to the power rating at which the motor 200 of the system 100 is operated during the test, “rotational speed” refers to the shaft rotational speed or the speed at which the shaft 140 is rotated during the test, “axial load” refers to the axial mechanical loading 530. In the examples, “bearing operation temperature” refers to the temperature to which the BUT 900 is operating under. For example, the “bearing operation temperature” may refer to the temperature to which the BUT 900 is heated to using the heater 450 of the system. For example, the “bearing operation temperature" may refer to the temperature as measured by the temperature sensor 330. In the examples, “bearing current” may refer to the current injected at a probe location by an inductive probe 340 or to the current as measured by an inductive probe 340.

[0099] According to various embodiments of the present disclosure, the system 100 includes a first support 111 , a shaft 140, a first inductive probe 340, a second inductive probe 340, and at least one vibration sensor 310. The first support 111 is configured to hold a bearing 900 (e.g., BUT 900). The shaft 140 defines an axial direction 101 along a length of the shaft 140. The shaft 140 is coupleable to a race 920/930 of the bearing 900 to apply an axial mechanical loading 530 on the bearing 900. The first inductive probe 340 and the second inductive probe 340 are inductively coupleable with the shaft 140 at respective probe locations. The respective probe locations are spaced apart along the shaft 140. The second current probe 340 is configured to measure a circulating current responsive to the first inductive probe 340 inducing a current in the shaft 140. The at least one vibration sensor 310 is disposed at the first support 111. The at least one vibration sensor 310 is configured to provide a vibration signal responsive to sensing vibration concurrently with the circulating current being measured.

[00100] The system 100 may further include a motor 200, in which the motor 200 is coupled with the shaft 140 to enable a rotation of the shaft 140 at a selected shaft rotation speed. The system 100 may further include a pulse generator 440, in which the pulse generator 440 is coupled with the first inductive probe 340 and configured to generate a pulsed current characterized by a pulse frequency. The shaft 140 may be coupled to an inner race 930 of the bearing 900, in which the first support 111 is coupled to an outer race 920 of the bearing 900. The system 100 may further include a heater 450, in which the heater 450 is configured to heat the bearing 900 to a predetermined temperature. The system 100 may further include a discharge detector 350, in which the discharge detector 350 is configured to monitor a number of electrical discharges at the bearing 900.

[00101 ] The system may further include a processor 410, in which the processor 410 is configured to perform a method 500 including steps of: (i) acquiring the vibration signal from the at least one sensor 300; and (ii) determining a health state of the bearing 900 based on a comparison of the vibration signal acquired over a period of time. The processor 410 may be further configured to determine the health state of the bearing 900 based on a change in a standard deviation of the vibration signal over the period of time. The processor 410 may be further configured to determine a projected bearing degradation over a period of use based on the health state of the bearing 900 after a period of accelerated testing, in which the period of accelerated testing is shorter than the period of use.

[00102] According to various embodiments of the present disclosure, the method 500 includes steps of: (i) applying an axial mechanical loading 530 to a bearing 900 held by a first support 111 , the axial mechanical loading 530 being applied by a shaft 140 coupled to a race 920/930 of the bearing 900, the shaft 140 defining an axial direction 101 along a length of the shaft 140; (ii) inducing a current in the shaft 140 using a first inductive probe 340; (iii) measuring a circulating current using a second inductive probe 340, the first inductive probe 340 and the second inductive probe 340 being inductively coupled with the shaft 140 at respective probe locations, the respective probe locations being spaced apart along the shaft 140; and (iv) obtaining a vibration signal responsive to a vibration being sensed concurrently with the circulating current being measured, wherein the vibration signal is provided by at least one vibration sensor 310 disposed at the first support 111.

[00103] The method 500 may include a step concurrent with the electrical loading 520, in which the step includes rotating the shaft 140 at a selected shaft rotation speed. The inducing of the current in the shaft 140 may include injecting a pulsed current characterized by a pulse frequency. The pulse frequency may be based on an estimated number of electrical discharges at the bearing 900 in a state of actual use. The axial mechanical loading 530 may be applied to an inner race 930 of the bearing 900, in which the first support 111 is coupled to an outer race 920 of the bearing 900. The method 500 may further include heating the bearing 900 to a predetermined temperature. The method 500 may further include determining a health state of the bearing 900 based on a comparison of the vibration signal acquired over a period of time. The health state of the bearing 900 may be based on a change in a standard deviation of the vibration signal over the period of time. [00104] The method 500 may include determining a projected bearing degradation over a period of use based on the health state of the bearing 900 after a period of accelerated testing, in which the period of accelerated testing is shorter than the period of use.

[00105] All examples described herein, whether of apparatus, methods, materials, or products, including the examples presented in Tables 1 to 3, are presented for the purpose of illustration and to aid understanding, and are not intended to be limiting or exhaustive. Modifications may be made by one of ordinary skill in the art without departing from the scope of the claimed invention.

Claims

1 . A system comprising: a first support, the first support being configured to hold a bearing; a shaft, the shaft defining an axial direction along a length of the shaft, the shaft being coupleable to a race of the bearing to apply an axial mechanical loading on the bearing; a first inductive probe; a second inductive probe, the first inductive probe and the second inductive probe being inductively coupleable with the shaft at respective probe locations, the respective probe locations being spaced apart along the shaft, the second current probe being configured to measure a circulating current responsive to the first inductive probe inducing a current in the shaft; and at least one vibration sensor disposed at the first support, the at least one vibration sensor being configured to provide a vibration signal responsive to sensing vibration concurrently with the circulating current being measured.

2. The system as recited in claim 1 , further comprising: a motor, the motor being coupled with the shaft to enable a rotation of the shaft at a selected shaft rotation speed.

3. The system as recited in claim 1 or claim 2, further comprising: a pulse generator, the pulse generator being coupled with the first inductive probe and configured to generate a pulsed current characterized by a pulse frequency.

4. The system as recited in any one of claims 1 to 3, wherein the shaft is coupled to an inner race of the bearing, and wherein the first support is coupled to an outer race of the bearing.

5. The system as recited in any one of claims 1 to 4, further comprising a heater, the heater being configured to heat the bearing to a predetermined temperature.

6. The system as recited in any one of claims 1 to 5, further comprising a discharge detector, the discharge detector being configured to monitor a number of electrical discharges at the bearing.

7. The system as recited in any one of claims 1 to 5, further comprising a processor, the processor being configured to perform a method including: acquiring the vibration signal from the at least one sensor; and determining a health state of the bearing based on a comparison of the vibration signal acquired over a period of time.

8. The system as recited in claim 7, wherein the processor is further configured to determine the health state of the bearing based on a change in a standard deviation of the vibration signal over the period of time.

9. The system as recited in claim 7 or claim 8, wherein the processor is further configured to determine a projected bearing degradation over a period of use based on the health state of the bearing after a period of accelerated testing, and wherein the period of accelerated testing is shorter than the period of use.

10. A method comprising: applying an axial mechanical loading to a bearing held by a first support, the axial mechanical loading being applied by a shaft coupled to a race of the bearing, the shaft defining an axial direction along a length of the shaft; inducing a current in the shaft using a first inductive probe; measuring a circulating current using a second inductive probe, the first inductive probe and the second inductive probe being inductively coupled with the shaft at respective probe locations, the respective probe locations being spaced apart along the shaft; and obtaining a vibration signal responsive to a vibration being sensed concurrently with the circulating current being measured, wherein the vibration signal is provided by at least one vibration sensor disposed at the first support.

11. The method as recited in claim 10, comprising: concurrently with the electrical loading, rotating the shaft at a selected shaft rotation speed.

12. The method as recited in claim 10 or claim 11 , wherein the inducing of the current in the shaft comprises: injecting a pulsed current characterized by a pulse frequency.

13. The method as recited in claim 12, wherein the pulse frequency is based on an estimated number of electrical discharges at the bearing in a state of actual use.

14. The method as recited in any one of claims 10 to 13, wherein the axial mechanical loading is applied to an inner race of the bearing, and wherein the first support is coupled to an outer race of the bearing.

15. The method as recited in any one of claims 10 to 14, further comprising heating the bearing to a predetermined temperature.

16. The method as recited in any one of claims 10 to 15, further comprising determining a health state of the bearing based on a comparison of the vibration signal acquired over a period of time.

17. The method as recited in claim 16, wherein the health state of the bearing is based on a change in a standard deviation of the vibration signal over the period of time.

18. The method as recited in claim 16 or claim 17, further comprising determining a projected bearing degradation over a period of use based on the health state of the bearing after a period of accelerated testing, and wherein the period of accelerated testing is shorter than the period of use.