CommentaryDevelopment of Sensor Integrated Bearing“ Talking BearingsTM ”

Yasuyuki FUKUSHIMA*
Yosuke TOYOGUCHI*
Kohei MATSUBAYASHI*

Tomomi GOTO*
Daigo IKKE*

There has been a growing demand for equipment condition monitoring using
IoT technology to reduce equipment downtime and improve production
efficiency. NTN has developed Talking BearingsTM that integrate sensors,a power generation unit, and a wireless device to standard bearings, inorder to meet this demand. This paper introduces the features, structure, and performance test results of thedeveloped bearing.

1. Introduction
There has been an increased demand to reduce
equipment downtime as much as possible to increase
production efficiency1). Similar strong demands havebeen made to increase utilization even in power
generation facilities and infrastructure. To respond tothese demands, it is effective to monitor equipment
conditions to prevent sudden equipment stoppages
and plan for maintenance and part replacement
periods2) 3).
NTN has developed the “Condition Monitoring
System for Wind Turbines (Wind DoctorTM)”4), the“Sensor Integrated Bearing Unit” for Machine Tool
Spindles5), the “Bearing Diagnostic Application
for Industrial IoT Platforms”6), and the “PortableVibroscope”7) as shown in Fig. 1 to meet the needsof condition monitoring at this type of equipment.
We have also been releasing devices and analysis
software to the market for the purpose of bearing
condition monitoring.
It is important to provide devices that are extremely
useful and can detect bearing conditions with highsensitivity to achieve a condition monitoring service
that will bring a high level of satisfaction to users.
Rolling bearings are incorporated into all kinds ofmachines such as transport machinery, household
appliances and industrial machinery to support
rotation. Including sensors in rolling bearings is
considered to be an ideal data collection element formonitoring the condition of machines.
With this in mind, NTN has developed the sensor
integrated bearing “Talking BearingTM” with built-insensors, a power generation unit and wireless device
in a standard bearing**, without changing the bearing
size and load carrying capacity. This paper introduces
the structure of this developed product, its features,and results from performance tests.

The “Talking BearingTM” detects the bearing
condition using sensors and sends the sensor
information wirelessly so its name is derived fromthe fact that we can understand the condition of thebearing as though it is talking to us.
**Rolling bearings that comply with international standards interms of their boundary dimensions and type(a) Condition Monitoring System forWind Turbines「Wind DoctorTM」(b) For Machine Tool Spindles“Sensor Integrated Bearing Unit”(c) Portable
Vibroscope

Fig. 1 Products used for condition monitoring* New Product Development R&D Center

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Development of Sensor Integrated Bearing “Talking BearingsTM”
2. Features and structure
2.1 Features
This section provides the main features of thedeveloped product.
(1) Advanced condition monitoring and abnormality
diagnosis
The sensors are built into the bearing so they can
detect bearing conditions with greater sensitivity thanif the sensors had been installed on equipment. Thiscan diagnose abnormalities early.
(2) Compatibility
Sensors, a power generation unit and wireless device
have been built into a standard bearing withoutchanging the bearing dimensions or load carrying
capacity. This makes it easy to replace bearings used
on existing equipment.
(3) Very convenient
The sensors and wireless devices operate using thepower generated by bearing rotation to automaticallysend sensor information wirelessly. This requires nocables to supply power or transmit data.
2.2 Structure
2.2.1 Overall structure
The structure of the developed product is shownin Fig. 2. A power generator and electronic circuit
substrate are arranged at one end of the bearing
used at the inner ring rotation. A stator is fixed tothe bearing outer ring and coils are held in place bythe stator. A rotor (a magnetic ring that is alternately
magnetized by the N and S-poles) is also fixed tothe bearing inner ring. AC voltage is generated in thecoils by the action of electromagnetic induction as
the inner and outer bearing rings rotate relative toeach other. The electronic circuit substrate, which ismounted with circuits, sensors and wireless devices,
is fixed to the bearing outer ring via the stator andalso sealed with material that protects the electroniccircuit.
Electronic circuit
substrate

StatorRotor(Magnetic ring)

Material to protect
electronic circuit

Fig. 2 Structure of Sensor Integrated Bearing“Talking BearingsTM”

36

NTN TECHNICAL REVIEW No.89

2.2.2 Electronic circuit
A functional block diagram and power supply circuit
block diagram for the developed product are shown inFig. 3 and Fig. 4, respectively. AC voltage generated
by the power generator is input to the power supply
circuit. The power supply circuit rectifies AC voltage
into DC current, and also steps down any voltage
obtained beyond what is required to the designatedvoltage. Following this, a fixed voltage required forsensor and wireless module operation is obtainedusing a step-up/step-down DC-DC converter. The
fixed voltage activates the sensors, and the obtained
sensor signals are sent by radio waves through thewireless device.
Electronic circuit
Power generator

Power supply circuit

Sensors

Wireless device

Fig. 3 Functional block diagram for developed
product

Power supply circuit
Rectifier circuit

Voltage limiting circuit

Step-up/step-down
DC-DC converter

Fig. 4 Power supply circuit block diagram

3. Specifications
Table 1 shows the specifications for the developed
product. Such things as acceleration, temperatureand rotational speed are provided in the tablefor items to detect the condition of the bearing.
Among these items, rotational speed is obtained byprocessing the AC current waveform generated by thepower generator without using a dedicated sensor.
Furthermore, the operating temperature range is
set to -40 to 85 ℃ with consideration for the heat
resistant temperature of the electronic components
mounted in the circuit.
The wireless device uses Bluetooth Low Energy(2.4 GHz) telecommunication standard. Modes(monitoring mode and analysis mode) are selectedbased on the application to enable sensing.
Monitoring mode assumes that monitoring isperformed continuously and over an extended
period, and sends data obtained for temperature,acceleration and rotational speed at intervals of 0.1
seconds. During this time, acceleration sent in thismode is the RMS value. Analysis mode acquires andsends acceleration data for a given sample number toenable the frequency to be analyzed by the receiver.
In addition, switching between monitoring mode andanalysis mode can be done using dedicated software
installed on a computer.

Usage conditions

Communication

SensingBearing

Table 1 Specifications for Sensor Integrated Bearing“Talking BearingsTM”
TypeDeep Groove Ball Bearing

Number63-series, bore diameter code 14 orhigher

Acceleration

Radial detection direction
Detection range of ±50 G
Frequency band from 11 kHz (3 dB)
Sensitivity 40 mV/G

TemperatureC
Detection range of -50 to 150 °Rotational
speed

Resolution of 16.7 min-1

Standard

Bluetooth Low Energy(2.4 GHz)

Transmitted
data[Monitoring mode]
Temperature, acceleration(RMS value), rotational speed(communication interval: 0.1 second)[Analysis mode]
Acceleration

Allowablerotationalspeed

Conforms to bearing number

Rated load

Conforms to bearing number

Rotational
speed thatcan betransmitted

500 min-1 or more

Operatingtemperature
range

C-40 to 85 °and Fig. 7 show examples of displaying data formonitoring mode and analysis mode, respectively.
Monitoring mode displays the change over time foracceleration, temperature and rotational speed. Also,
when acquired data exceeds a pre-defined threshold,a warning will display. Analysis mode displays theacceleration time waveform and frequency analysis
results.
(1) Data is saved to a data logger then imported

Data logger

PC(2) Data is imported directly to a tablet or PC
Developedproduct
Tablet or PC

Fig. 5 Communication configuration examples

Fig. 6 Example of data displayed in monitoring mode

4. Examples of use
Fig. 5 shows communication configuration
examples for the developed product. When constantly
monitoring the equipment conditions for a long
period of time, the amount of received data will be
extremely large so it is best to send the data to adevice such as a data logger that can store a large
volume of data, and configure the device to ensure it
can import the data to a computer or similar terminal.
Moreover, when wanting to carry a computer or tablet
into the workplace each time to check the conditionof the equipment, a configuration that allows directcommunication with the computer or tablet iseffective. The developed product can communicate
with devices that comply with telecommunication
standards without needing to change the installed
communication program, enabling the appropriate
usage method to be selected as required.
The use of dedicated software enables thedeveloped product to communicate with a computeror similar device to display sensor data. Fig. 6Fig. 7 Example of data displayed in analysis mode

5. Performance test
5.1 Vibration detection performance
To check the vibration detection performance ofthe developed product, an abnormal bearing with adefect resembling spalling (simulated spalling) on the
raceway surface was used. This abnormal bearing wascompared with a normal bearing without any defects
to observe the vibration detected by the built-insensor. The vibration detection performance was also
compared using the acceleration sensor provided on
the outside of the bearing (hereafter, external sensor)
and the built-in sensor.

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Development of Sensor Integrated Bearing “Talking BearingsTM”
5.1.1 Test machine and test conditions
Fig. 8 shows a schematic drawing of the testing
equipment. The bearing being tested is rotated by ashaft fitted to the inner ring of the bearing. A radialload also acts on the bearing being tested througha stand that sways on a pivot point. The externalsensor is installed on the stand, and its specifications
are provided in Table 2. The external sensor iscompared with the built-in sensor (see Table 1), andtheir detection range is about the same. However,
the external sensor has a wider frequency band. The
acting radial load was set to 784 N. This load is quite
small when compared to the basic dynamic load
rating of 115 kN for deep groove ball bearing 6314.
Bearing being tested

Table 3 Specifications for the bearing being tested
Normal bearing

Abnormal bearing

Bearing

Deep groove ball bearing 6314

Seal

Non-contact type (one side)

GreaseThickening agent: Urea-based
Base oil: Poly-alpha olefin

SimulatedspallingNo1 location at the bottomof the groove on the outerring raceway surface
φ0.87 × depth of 0.1 mm

φ 0.87
Rotating shaft

0.1 mmRaceway
surface

Position of built-in
acceleration sensor
External sensor

Stand

Load

Position ofsimulated spalling

Simulatedspalling
Outer ring

Fig. 9 Schematic drawing of simulated spalling

Pivot

Fig. 8 Schematic drawing of testing equipment
5.1.2 Bearing being tested
Table 3 provides the specifications for the bearing
being tested and Fig. 9 shows a schematic drawingof the simulated spalling formed on the bearing
outer ring. Cylindrical-shaped simulated spalling wasformed at 1 location at the bottom of the groove on
the outer ring raceway surface, and its size was set
based on the size of the contact ellipse due to elastic
deformation of the bearing parts. More specifically,
the diameter of the simulated spalling was set to 0.87mm, which is twice the diameter of the contact ellipse
minor axis when the test radial load of 784 N wasapplied. Fig. 10 shows an external photo of actual
spalling that occurred during the damage end stage,as an example of spalling that occurs on a bearing. The
size of the simulated spalling was made sufficiently
small in comparison to end stage spalling with the aimof evaluating vibration detection performance during
the initial stages of damage.
Table 2 Specifications for the external sensor
Externalsensor

38

Detection range±60 G

Frequency band

3 Hz to 25 kHz（3 dB）

Sensitivity

100 mV/GNTN TECHNICAL REVIEW No.89

5 mm

Fig. 10 Example of spalling damage
5.1.3 Test results
Fig. 11 shows the built-in sensor output whenrotating the normal sensor and abnormal sensor at
2 000 min-1. Each time the rolling element passes
the simulated spalling on the abnormal bearing, anobvious spike in acceleration was detected. If a defectof about the same size as the simulated spalling
created this time occurs on the raceway, it would bepossible to detect an obvious abnormality with thedeveloped product.
Next, Fig. 12 shows a comparison between thebuilt-in sensor and external sensor for the acceleration
measured at the abnormal bearing. Fig. 12 shows
the results of conducting envelope processing andfrequency analysis (fast Fourier analysis) on the data
output in Fig. 13. Finally, Fig. 13 lists the rotational
speed (103 Hz) of the rolling element relative to theouter ring and the higher-order rotational speeds. The

sensor output when the rolling element passes thesimulated spalling is greater for the built-in sensor
in comparison with the external sensor. Frequency
analysis also shows that the built-in sensor is moresensitive and can better detect vibration at highfrequency.

1240-4-8-12020406080100Fig. 11 Comparison of normal bearing and abnormal
bearing built-in sensor output

128Acceleration G

Built-in sensor
External sensor

Bearing Rotational
speed 2 000 min-1

4 000303 000

202 000
Built-in (temperature sensor)
External (thermocouple)
Rotational speed

1002461 000

80Fig. 14 Comparison of temperature taken with thebuilt-in sensor and external thermocouple-4-80204060

80100Time ms

Fig. 12 Comparison of acceleration for built-in sensor
and external sensor with abnormal bearing

1Acceleration G

40Time h00.8

Built-in sensor
External sensor

103 Hz206 Hz0.6309 Hz

0.4412 Hz0.205 00004-12

Temperature ℃

Time ms50

Rotational speed min-1

Acceleration G

Abnormal bearing
Normal bearing

Bearing Rotational
speed 2 000 min-1

8and it was measured using the testing equipment
shown in Fig. 8. The rotational speed was taken as being
up to the allowable rotational speed of 4 600 min-1(value listed in the NTN catalog) for deep groove ballbearing 6314 (grease lubrication, non-contact seal).
Measurements were taken by repeatedly increasing
rotation and holding for two hours at increments ofaround 1 000 min-1. Measurement results are shownin Fig. 14. The results show that there is no significant
difference in the values measured with both sensors
in either the transient region after rotation wasincreased or the steady-state region when rotation
was held. Thus, the developed product has the same
temperature detection performance as when affixinga thermocouple to the bearing outer ring.

0200400600

800

1 000Frequency HzFig. 13 Comparison of frequency analysis for built-insensor and external sensor
5.2 Temperature detection performance
Measured values taken from a thermocouple affixedto the outer circumferential surface of the bearing
outer ring were compared with measured values takenfrom the built-in temperature sensor. The bearing
being tested was the normal bearing shown in Table 3,

5.3 Temperature increase characteristics
Fig. 15 shows the generated power and runningtorque of the developed product in relation torotational speed. Here, the generated power is thesum of the power consumed by the circuit and thepower loss from the power generator. Also, therunning torque is equivalent to the running torqueof the entire bearing with built-in sensor, including
the friction loss during bearing rotation and thegenerated power mentioned above. Fig. 15 shows
the values measured after holding for two hours at
each rotational speed. The generated power is small
at 1 to 2 % in contrast with the power loss of theentire bearing calculated from the running torqueand rotational speed, and incorporating the power
generator and circuit into the bearing is also estimatedto have a minor effect on the bearing temperature.
Fig. 16 shows the results measured for thetemperature on the actual bearing. The bearing
temperature was measured with a thermocouple
affixed to the outer ring outer circumferential surface
and the built-in sensor. Fig. 16 shows the value
increase from ambient temperature after holding fortwo hours at each rotational speed. There was no
significant difference between the standard bearing
and developed product, showing that the developed
product has the same temperature increasecharacteristics as the standard bearing.

NTN TECHNICAL REVIEW No.8939

Development of Sensor Integrated Bearing “Talking BearingsTM”

Running torque
Generated power

10040050200001 0002 000

6. Summary

600

3 000

4 0000
5 000

Generated power mW

Running torque mN･m

150

Rotational speed min-1

Rise in outer ring temperature ℃Fig. 15 Generated power and running torque for thedeveloped product20Standard bearing
Developed product

1510
500

1 000

2 000

3 000

4 000

5 000

Rotational speed min-1

Fig. 16 Temperature increase characteristics for thedeveloped product and standard bearing

To respond to efforts towards reducing downtime atmanufacturing sites, NTN has developed the Sensor
Integrated Bearing “Talking BearingTM” which hassensors, a power generation unit and wireless device
built into a standard bearing. The performance of
this product was verified in this paper. We predictthat demand for equipment condition monitoring will
increase in the near future, and further improvements
in functionality will be required. NTN will continue
to develop equipment condition monitoring andcontribute towards improving production efficiency
through its improvements in the function of “Talking
BearingTM” and releasing products in the market.
References
1) Japan Institute of Plant Maintenance, 2021
Maintenance Investigation Report Summary(June 2022)
2) Sohei Yamada, Shigetoshi Noritake, Investigation
to Optimize Manufacturing and Logistics Sites
Using Sensing Technology, Journal of The Japan
Society of Mechanical Engineers, Vol.123,No.1223(2020)19-21.
3) Hou Jinyama, Smart Equipment Condition
Monitoring & Diagnosis Technology in the IoT/AIAge, System/Control/Information, Vol.65, No.4
（2021）113-118.
4) Makoto Miyazaki, Wataru Hatakeyama,
Application of Condition Monitoring System forWind Turbines, NTN TECHNICAL REVIEW, No.86,(2018) 40-44.
5) Shohei Hashizume, Yusuke Shibuya, Daichi
Kondo, Yohei Yamamoto, Hiroyuki Iwanaga,
Development of Sensor Integrated Bearing Unit
for Machine Tool Spindles, NTN TECHNICALREVIEW, No.88 (2020) 33-37.
6) Hiroyuki Iwanaga, Development of Edge
Application for Bearing Diagnosis, Inspection
Technology, March 2022 Edition, 32-34.
7) Our Line of New Product, Portable Vibroscope,
NTN TECHNICAL REVIEW, No. 87 (2019) 106.

Photo of authors

40

Yasuyuki FUKUSHIMA

Tomomi GOTO

Yosuke TOYOGUCHI

Daigo IKKE

Kohei MATSUBAYASHINew ProductDevelopment R&D
Center

New ProductDevelopment R&DCenter

New ProductDevelopment R&DCenter

New ProductDevelopment R&DCenter

New ProductDevelopment R&DCenter

NTN TECHNICAL REVIEW No.89