U.S. patent application number 11/192096 was filed with the patent office on 2005-11-24 for rolling bearing device and ring with sensor for the rolling bearing device.
This patent application is currently assigned to NSK LTD.. Invention is credited to Endo, Shigeru, Fukuyama, Hiromasa, Morita, Kouichi, Shoda, Yoshio, Takahashi, Toshio, Takizawa, Takeshi.
Application Number | 20050259903 11/192096 |
Document ID | / |
Family ID | 27531705 |
Filed Date | 2005-11-24 |
United States Patent
Application |
20050259903 |
Kind Code |
A1 |
Takizawa, Takeshi ; et
al. |
November 24, 2005 |
Rolling bearing device and ring with sensor for the rolling bearing
device
Abstract
A rolling bearing with sensor includes an inner ring, an outer
ring, a plurality of rolling elements disposed between the inner
and outer rings, and a sensor having a detecting part detecting a
state of the rolling bearing and a circuit part connected to the
detecting part. The detecting part and the circuit part are
attached to the rolling bearing.
Inventors: |
Takizawa, Takeshi;
(Kanagawa, JP) ; Endo, Shigeru; (Kanagawa, JP)
; Morita, Kouichi; (Kanagawa, JP) ; Shoda,
Yoshio; (Kanagawa, JP) ; Fukuyama, Hiromasa;
(Kanagawa, JP) ; Takahashi, Toshio; (Kanagawa,
JP) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 PENNSYLVANIA AVENUE, N.W.
SUITE 800
WASHINGTON
DC
20037
US
|
Assignee: |
NSK LTD.
|
Family ID: |
27531705 |
Appl. No.: |
11/192096 |
Filed: |
July 29, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11192096 |
Jul 29, 2005 |
|
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|
09985921 |
Nov 6, 2001 |
|
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|
6948856 |
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Current U.S.
Class: |
384/448 |
Current CPC
Class: |
G01P 3/443 20130101;
F16C 2300/02 20130101; F16C 41/004 20130101; F16C 2226/30 20130101;
F16C 43/04 20130101; F16C 19/527 20130101; F16C 19/525 20130101;
F16C 41/007 20130101; F16C 41/008 20130101; F16C 19/06 20130101;
F16C 33/586 20130101 |
Class at
Publication: |
384/448 |
International
Class: |
F16C 041/04; F16C
032/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 6, 2000 |
JP |
P. 2000-338151 |
Jan 16, 2001 |
JP |
P. 2001-007792 |
Feb 22, 2001 |
JP |
P. 2001-046674 |
May 22, 2001 |
JP |
P. 2001-152805 |
Sep 27, 2001 |
JP |
P. 2001-298353 |
Claims
1-17. (canceled)
18. A rolling bearing with sensor, comprising; an inner ring; an
outer ring; a plurality of rolling elements disposed between said
inner and outer rings; a retainer for retaining said rolling
elements; a sensor having a detecting part detecting at least one
of a rotating speed, a vibration, a temperature and a humidity, a
transmitting part transmitting an output of said detecting part or
a signal obtained by processing said output, a control part
controlling said transmitting part based on the output of said
detecting part, and a power source for supplying a power to said
detecting part, said transmitting part and said control part; and a
receiving device disposed a part from said transmitting part
attached to said rolling bearing, for receiving said output or said
signal transmitted from said transmitting part.
19. The rolling bearing with sensor according to claim 18, wherein
said detecting part, said transmitting part and said control part
are disposed on one of said inner and outer rings, and said power
source is disposed on a member for fixing said one of said inner
and outer rings.
20. The rolling bearing with sensor according to claim 18, further
comprising: a shield for protecting a rolling surface of said inner
and outer rings and said rolling elements, wherein said detecting
part, said transmitting part and said control part are disposed on
said shield, and said power source is disposed on one of inner and
outer rings supporting said shield.
21. The rolling bearing with sensor according to claim 18, wherein
said detecting part, said transmitting part, said control part and
said power source are disposed on one of said inner and outer
rings.
22. The rolling bearing with sensor according to claim 18, further
comprising: a shield for protecting a rolling surface of said inner
and outer rings and said rolling elements, wherein said detecting
part, said transmitting part, said control part and said power
source are mounted on a printed circuit board to form a sensor
unit, and said sensor unit is disposed on one of said shield, said
inner ring and said outer ring, or both of said shield and one of
said inner and outer rings.
23. The rolling bearing with sensor according to claim 18, further
comprising: a shield supported on one of said inner and outer
rings, for protecting a rolling surface of said inner and outer
rings and said rolling elements, said shield including said
detecting part, said transmitting part, said control part and said
power source attached thereto; and a protecting cover attached to
said shield, for covering said transmitting part, said control part
and said power source.
24. The rolling bearing with sensor according to claim 18, further
comprising: a ring secured to one of said inner and outer rings,
for mounting said detecting part, said transmitting part, said
control part and said power source.
25. The rolling bearing with sensor according to claim 18, wherein
said transmitting part transmits a constant signal at predetermined
intervals, and said receiving device receives said constant signal,
for confirming that said sensor including said detecting part, said
transmitting part and said control part are functioned
normally.
26. The rolling bearing with sensor according to claim 25, wherein
said transmitting part transmits different kinds of identification
information including the signal transmitting when said detecting
part detects an abnormal operation and the signal transmitting at
said predetermined intervals when said sensor is normally
operated.
27. The rolling bearing with sensor according to claim 25, wherein
said power source supplies the power to said transmitting part when
said transmitting part transmits the radio wave.
28. A rolling bearing with sensor comprising: a plurality of
rolling elements; first and second rings rotating relative to each
other via said rolling elements; and an electric generator having
an annular magnet disposed on said first ring and an annular
conductor disposed on said second ring, said electric generator
generating an electric power by the relative rotation between said
first and second rings.
29. The rolling bearing with sensor according to claim 28, further
comprising: a sensor detecting a rotating speed of said bearing
based on an output of the electric power of said electric
generator.
30. The rolling bearing with sensor according to claim 28, wherein
said annular magnet has N and S poles which are alternately
arranged in a circumferential direction of said bearing, said
annular magnet rotates relative to said annular conductor to
generate an electromotive force, and wherein said bearing further
comprises a sensor detecting a relative rotating speed of said
first and second rings based on an output of said electromotive
force generated by said electric generator.
31. The rolling bearing with sensor according to claim 28, wherein
said magnet is annularly formed so that N and S poles are
alternately magnetized along the circumferential direction thereof
at equal intervals.
32. The rolling bearing with sensor according to claim 28, wherein
said conductor is annularly formed to extend along said magnet
while being meandered.
33. The rolling bearing with sensor according to claim 28, wherein
said conductor extends along said magnet while being meandered in
the radial direction of said bearing.
34. The rolling bearing with sensor according to claim 28, wherein
said conductor extends along said magnet while being meandered in
the axial direction of said bearing on a cylindrical surface
developed about a rotational axis of said bearing.
35. The rolling bearing with sensor according to claim 28, wherein
said conductor is meandered at pitches equal to that of an
arrangement of said magnetic poles of said magnet.
36. The rolling bearing with sensor according to claim 28, wherein
said conductor is rectangularly meandered.
37. The rolling bearing with sensor according to claim 28, wherein
said magnet is mounted on a first shield provided on said first
ring, and said conductor is mounted on a second shield provided on
said second ring.
38. The rolling bearing with sensor according to claim 37, wherein
said first shield is made of a magnetic material, and said second
shield is made of a non-magnetic material.
39. The rolling bearing with sensor according to claim 37, wherein
a third shield made of a magnetic material is provided at a
position opposite to said first shield, with said second shield
being interposed therebetween.
40. The rolling bearing with sensor according to claim 28, further
comprising: a seal for providing a closed space between said inner
and outer rings, wherein said magnet and said conductor of said
electric generator is disposed on said outside of said seal forming
said closed space.
41. The rolling bearing with sensor according to claim 28, further
comprising: a shield for providing a closed space between said
inner and outer rings, wherein said magnet and said conductor of
said electric generator is disposed on said outside of said shield
forming said closed space.
42. The rolling bearing with sensor according to claim 29, wherein
said sensor includes a detecting part further detecting at least
one of a vibration, a temperature and a humidity.
43. The rolling bearing with sensor according to claim 29, wherein
said sensor includes a transmitting part wirelessly transmitting a
detecting signal.
44. The bearing with sensor according to claim 29, further
comprising: a storage battery which charges and discharges an
electromotive force generated when said magnet and said conductor
rotate relative to each other.
45. A ring with sensor for a rolling bearing in which a pair of
raceway rings rotate relative to each other through rolling
elements disposed therebetween, wherein said ring with sensor is
disposed so as to rotate together with one of said raceway rings,
and wherein said ring with sensor comprises: a detecting part
detecting at least one of a rotating speed, a vibration, a
temperature and a humidity; a transmitting part transmitting an
output of said detecting part or a signal obtained by processing
the output; a control part controlling said transmitting part based
on the output of said detecting part; and a power source for
supplying a power to said detecting part, said transmitting part
and said control part.
46. The ring with sensor according to claim 45, wherein said
transmitting part transmits a constant signal at predetermined
intervals, and said constant signal is received by a receiving
device disposed a part from said transmitting part, for confirming
that said detecting part, said transmitting part and said control
part are functioned normally.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a rolling bearing device
having a sensor for detecting vibration (acceleration),
temperature, rotational speed, humidity (moisture) and the like,
and a ring with the sensor for used with the rolling bearing
device.
[0003] 2. Description of the Related Art
[0004] The rolling bearings, which are used for reducing rotation
resistance, have been used in various fields, such as industrial
equipment, vehicles, airplanes, and power plants. The rolling
bearing will be vibrated when the rotating shaft is eccentric and
be heated through the rotation friction. The vibration and
temperature will adversely affect the lifetime of the bearing. In
some of industrial machines, a water-soluble cutting lubricant is
frequently used in machining work. Accordingly, sometimes the
bearing part receives a splash of it, which contains water. When
the rolling bearing is mounted on a machine used outdoors, such an
automobile, a railroad car, or a construction machine, the bearing
is frequently splashed with water when it runs in the rain or on a
road with puddles. A measurement which has been taken for
preventing the rolling surfaces of the raceway and the rolling
elements from rusting is to use water-proof shields made of rubber
or the like, which is slidably fitted to the inner and outer rings.
Even in the case of the bearing having the water-proof shield, when
weather conditions change, in particular when temperature rapidly
changes, water enters the inside of the water-proof shield in the
form of vapor, so that dew condensation will form on the rolling
surfaces of the raceway and the rolling elements, sometimes.
[0005] Particularly, in the case of the rolling bearing, which is
mounted on a position where its inspection is difficult, e.g., a
device interior position, the vibration, temperature, rotational
speed or humidity sensors as general-purpose parts are separately
provided. A sensor suitable for a rolling bearing to be used is
selected from among those sensors, and attached to the outer
peripheral surface of the bearing. A signal derived from the sensor
thus attached is led out to a necessary part by way of a wire.
[0006] Specifically, a general-purpose vibration sensor including
an acceleration meter, a general-purpose temperature sensor
including a thermocouple, a rotational speed sensor including an
encoder and the like are connected, by wires, to an instrument
mounted on a housing which accommodates the rolling bearing device.
In this case, vibration, temperature and rotational speed of the
bearing are indirectly detected through the housing. There is a
proposal in which those general-purpose sensors are mounted on the
rolling bearing, and signals representative of vibration,
temperature and rotational speed are directly detected. In this
case, a space used for mounting the sensors is formed in advance in
the housing or the shaft.
[0007] Threshold values are set for the vibration and temperature.
When the measured vibration and temperature exceed the threshold
values, signals representative of those measured ones are output to
the instrument.
[0008] Those general-purpose sensors are large in size. Because of
this, a rolling bearing to which the sensors are mounted has a
large protruded part at which the sensors are mounted. The
protruded part is likely to restrict a freedom in laying out parts.
Allowing for this, it is necessary to determine a configuration of
the bearing and the layout of the sensors. The wiring ranging from
those sensors to the instrument is also required. To mount those
bearings with sensor, the machining work of the housing and the
shaft increases.
[0009] In a case where the existing equipment, e.g., industrial
equipment, is automated, it is essential to grasp a running status
of the automated equipment in a remote control manner. When
changing the bearing in the existing equipment into a bearing with
sensor, it is required to greatly alter the bearing and its vicinal
structure since the conventional bearing with sensor is not
interchangeable with another. Some types of shafts reject the
mounting of the sensors thereon. A case where the sensor is not
directly attached to the bearing but is located near the sensor,
suffers from some problems as described below.
[0010] The vibration sensor is constructed mainly with an
accelerometer, and its detection has a directivity. Accordingly,
when it is located apart from an object to be detected, the
detection is likely to contain noticeable noise. In the case of the
temperature sensor, with increase of a distance of the sensor to a
heat source, its thermal conduction time becomes longer, and the
sensing operation is affected by another heat source or sources,
resulting in producing an incorrect sensed value. Also for the
humidity detecting, it is necessary to detect humidity within the
bearing space located inside the bearing; otherwise, it is
impossible to correctly evaluate a degree of water entrance.
[0011] In addition, to detect a rotational speed of the rotating
shaft used in industrial equipment, machine tool, vehicle and the
like, an encoder is frequently attached to the shaft. In this case,
the encoder is used for a sensor for detecting a rotational speed
for the purpose of controlling the rotational speed of the shaft.
Further, a sensor for detecting vibration or temperature is
provided for monitoring an operating condition of the bearing and
the device including the bearing.
[0012] The encoder for detecting a rotational speed of the shaft
and the sensor for detecting vibration or temperature receive
electric power from a power source, which is separately provided.
Further, the detected signals of the rotational speed, vibration,
temperature and the like are outputted by wires.
[0013] In this case, wires must be used for supplying electric
power from the separately provided power source to the encoder for
detecting a rotational speed of the shaft and the sensor for
detecting vibration or temperature. Those wires must be taken out
every time the maintenance or replacement of the bearing and its
vicinal portion is carried out. A complicated mechanism is required
for supplying electric power to the sensor provided on the rotating
part.
[0014] To avoid this, the power source is preferably incorporated
into the bearing. An example of the bearing containing an electric
generator therein is disclosed in JP-A-6-200929. The electric
generator includes a comb-shaped iron core having a plurality of
threads radially arranged from the inner part of the bearing toward
the outer part, a coil wound around the bottoms each between the
adjacent threads, a plurality of magnets located while being
confronted with the bottoms of the iron core, and a ring which has
cuts arranged at intervals equal to the threads of the iron core
and rotates at a speed equal to that of the bearing between the
iron core and the magnets. When the ring rotates between the iron
core and the magnets, magnetic lines developed from the magnets are
induced into the ring to excite the threads of the iron core,
whereby the rotating speed is detected and electric power is
generated.
[0015] In the electric generator disclosed in JP-A-6-200929, since
the iron core extends over a part of the circumference, the
electromotive force generated by it is small. Further, the electric
power generated by the electromagnetic induction is caused by the
magnetic flux. Accordingly, an accuracy of the rotational speed
detection will be degraded by ring cutting accuracy, magnet layout
accuracy, non-uniformity of magnetic forces of the magnet,
dispersion of the gap between the iron core and the ring and
dispersion between the ring and the magnet, which is caused by an
eccentricity of the ring, and the like. Further, the electric power
generated is instable.
SUMMARY OF THE INVENTION
[0016] Accordingly, an object of the present invention is to
provide a rolling bearing with sensor and a ring with sensor for
the rolling bearing device which minimizes the formation of any
artificial part on a bearing mounting part of a bearing housing,
and which may easily be attached to an equipment that already
exists.
[0017] Another object of the present invention is to provide a
rolling bearing with sensor having a rotational speed sensor which
does not need to supply electric power from an external power
source, and is capable of detecting a rotational speed at high
accuracy.
[0018] To attain the above object, there is provided a rolling
bearing with sensor having inner and outer ring and rolling
elements, wherein a sensor in which a detecting part and a circuit
part are mounted on a printed circuit board, is provided on and
along the inner or outer ring. In a rolling bearing having shields,
a detecting circuit part is mounted on a printed circuit board, and
the printed circuit board is mounted on the shield. The invention
also provides a rolling bearing with sensor comprising: inner and
outer rings; rolling elements; a sensor having a detecting part
capable of detecting at least one of vibration, temperature,
rotational speed or humidity, and a circuit part; and the circuit
part being mounted on and along the inner or outer ring. In the
rolling bearing, the detecting part for detecting humidity is
provided within a space defined by the inner and outer rings and
the shield supported by the either of the inner and outer
rings.
[0019] In the rolling bearing, the circuit part includes a
transmitting part which converts a signal output from the detecting
part into a radio wave signal, and transmits the converted radio
wave signal. Further, it may include an ultrasonic wave generating
part which converts a signal detected by the detecting part into an
ultrasonic wave signal, and transmits the converted ultrasonic wave
signal.
[0020] Further, there is provided a rolling bearing with sensor,
including; an inner ring; an outer ring; a plurality of rolling
elements disposed between the inner and outer rings; a retainer for
retaining the rolling elements; a sensor having a detecting part
detecting at least one of a rotational speed, a vibration, a
temperature and a humidity, a transmitting part transmitting an
output of the detecting part or a signal obtained by processing the
output, a control part controlling the transmitting part based on
the output of the detecting part, and a power source for supplying
a power to the detecting part, the transmitting part and the
control part; and a receiving device disposed on a position apart
from the transmitting part, for receiving the signal transmitted
from the transmitting part.
[0021] Moreover, there is provided a ring with sensor for a rolling
bearing in which a pair of raceway rings rotate relative to each
other through rolling elements disposed therebetween, wherein the
ring with sensor is disposed so as to rotate together with one of
the raceway rings, and the ring with sensor includes: a detecting
part detecting at least one of a rotation speed, a vibration, a
temperature and a humidity; a transmitting part transmitting an
output of the detecting part or a signal obtained by processing the
output; a control part controlling the transmitting part based on
the output of the detecting part; and a power source for supplying
a power to the detecting part, the transmitting part and the
control part.
[0022] In addition, there is also provided a bearing with sensor
including: a plurality of rolling elements; first and second rings
rotating relative to each other via the rolling elements; and an
electric generator having an annular magnet disposed on the first
ring and an annular conductor disposed on the second ring, the
electric generator generating electric power by a relative rotation
between the magnet and the conductor.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1A is a sectional view showing a rolling bearing with
sensor, which is a first embodiment of the invention;
[0024] FIG. 1B is a sectional view taken on line I-I in FIG.
1A;
[0025] FIG. 2 is a sectional view showing a rolling bearing with
sensor, which is a second embodiment of the invention;
[0026] FIG. 3 is a sectional view showing a rolling bearing with
sensor, which is a third embodiment of the invention;
[0027] FIG. 4 is a sectional view showing a rolling bearing with
sensor, which is a fourth embodiment of the invention;
[0028] FIG. 5 is a sectional view showing a rolling bearing with
sensor, which is a fifth embodiment of the invention;
[0029] FIG. 6A is a sectional view showing a rolling bearing with
sensor, which is a sixth embodiment of the invention;
[0030] FIG. 6B is a side view showing the rolling bearing with
sensor of FIG. 6A;
[0031] FIG. 6C is a sectional view showing a rotation sensor
according to the sixth embodiment of the invention;
[0032] FIG. 7 is a sectional view showing the rolling bearing with
sensor of the first embodiment, which is fitted to a housing and to
a rotating shaft;
[0033] FIG. 8 is a sectional view showing a rolling bearing with
sensor, which is a seventh embodiment of the invention;
[0034] FIG. 9A is a plan view showing a detecting part of a sensor
to be mounted on the rolling bearing with sensor shown in FIG.
8;
[0035] FIG. 9 B is a sectional view taken on line IX-IX in FIG. 9A,
and a circuit diagram showing a transmitting circuit;
[0036] FIG. 10 is a sectional view, similar to FIG. 9B, showing
another sensor of the rolling bearing of FIG. 8;
[0037] FIG. 11 is a sectional view showing a rolling bearing with
sensor, which is an eighth embodiment of the invention;
[0038] FIGS. 12A to 12F are sectional views showing various types
of rolling bearings with sensor, each constituting a ninth
embodiment of the invention;
[0039] FIG. 13A is a sectional view showing a rolling bearing with
sensor, which is a tenth embodiment of the invention;
[0040] FIG. 13B is a side view showing the rolling bearing with
sensor shown in FIG. 13A;
[0041] FIG. 14 is an enlarged diagram showing a detecting part of a
humidity-detecting sensor shown in FIGS. 13A and 13B;
[0042] FIG. 15 is a block diagram showing the humidity-detecting
sensor of FIG. 13;
[0043] FIG. 16A is a sectional view showing a rolling bearing with
sensor, which is an eleventh embodiment of the invention;
[0044] FIG. 16B is a side view showing the rolling bearing with
sensor shown in FIG. 16A;
[0045] FIG. 17A is a sectional view showing a rolling bearing with
sensor, which is a twelfth embodiment of the invention;
[0046] FIG. 17B is a side view showing the rolling bearing with
sensor shown in FIG. 17A;
[0047] FIG. 18 is a sectional view showing a rolling bearing
device, which is a thirteenth embodiment of the present
invention;
[0048] FIG. 19 is a cross sectional view, taken on line XIX-XIX of
FIG. 18;
[0049] FIG. 20 is a block diagram showing an electrical expression
of a sensor of the rolling bearing device of FIG. 18;
[0050] FIG. 21A is a sectional view showing a rolling bearing
device, which is a fourteenth embodiment of the invention;
[0051] FIG. 21B is a side view taken on line XXI-XXI of FIG. 21A,
with a shield and a cover member being omitted;
[0052] FIG. 22A is a sectional view showing a rolling bearing
device, which is a fifteenth embodiment of the invention; FIG. 22B
is a side view, taken on line XXII-XXII of FIG. 22A;
[0053] FIG. 23A is a sectional view showing a rolling bearing
device, which is a sixteenth embodiment of the invention;
[0054] FIG. 23B is a side view, taken on line XXIII-XXIII of FIG.
23A;
[0055] FIG. 24A is a sectional view showing a rolling bearing
device, which is a seventeenth embodiment of the invention;
[0056] FIG. 24B is a side view, taken on line XXIV-XXIV of FIG.
24A;
[0057] FIG. 25A is a sectional view showing a rolling bearing
device, which is an eighteenth embodiment of the invention;
[0058] FIG. 25B is a side view, taken on line XXV-XXV of FIG.
25A;
[0059] FIG. 26A is a sectional view showing a rolling bearing
device, which is a nineteenth embodiment of the invention;
[0060] FIG. 26B is a side view, taken on line XXVI-XXVI of FIG.
26A;
[0061] FIG. 27A is a sectional view showing a rolling bearing
device, which is a twentieth embodiment of the invention;
[0062] FIG. 27B is a side view, taken on line XXVII-XXVII of FIG.
27A;
[0063] FIG. 28A is a sectional view showing a rolling bearing
device, which is a twenty-first embodiment of the invention;
[0064] FIG. 28B is a side view, taken on line XXVIII-XXVIII of FIG.
28A;
[0065] FIG. 29 is a sectional view showing a bearing device with
sensor, which is a twenty-second embodiment of the invention;
[0066] FIG. 30 is a cross sectional view, partly cut out, and taken
on line XXX-XXX in FIG. 29;
[0067] FIG. 31 is a block diagram showing the bearing device with
sensor of FIG. 29;
[0068] FIG. 32 is a perspective view showing apart of a structure
including a magnet and a conductor of the bearing device with
sensor of FIG. 29;
[0069] FIG. 33 is a sectional view showing a bearing device with
sensor, which is a twenty-third embodiment of the invention;
and
[0070] FIG. 34 is a perspective view showing a part of a structure
including a magnet and a conductor of the bearing device with
sensor of FIG. 33.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0071] A first embodiment of the present invention will be
described with reference to FIGS. 1A and 1B. A bearing 1 shown in
FIGS. 1A and 1B is a single-row deep groove ball bearing. The
bearing 1 includes an outer ring 2 and an inner ring 3, which are
examples of a bearing ring. An outer raceway 4, while being
recessed, is formed at a central part of the inner peripheral
surface of the outer ring 2. An inner raceway 5, while being
recessed, is formed at a central part of the outer peripheral
surface of the inner ring 3. A plurality of balls 6 as rolling
elements are retained with a retainer 7 in the circumferential
direction at equal intervals, while being equiangularly disposed
and in rolling contact with the outer raceway 4 and the inner
raceway 5. Shield mounting grooves 8a and 8b are respectively
provided at the inner peripheral surfaces of both ends 2a and 2b of
the outer ring 2 as viewed in the widthwise direction. Shields 9
are fitted to those grooves 8a and 8b.
[0072] An annular groove 10, as shown in FIGS. 1A and 1B, is
entirely provided on and along one side of the outer periphery edge
of the outer ring 2 as viewed from the widthwise direction. A
sensor 11 is circumferentially disposed on and along the bottom
surface 10a of the annular groove 10 in a state that the sensor 11
is located inside a prolongation of the side face 2c of the outer
ring 2, and inside a prolongation of the outer peripheral surface
2d. The sensor 11 is molded by using an insulting material, e.g., a
synthetic resin 12. To measure a temperature, it is preferable that
a heat conductivity of the synthetic resin 12 is equal to that of a
bearing member. The protective synthetic resin 12 for improving the
anti-dust, humidity and oil properties of the sensor 11 fills the
annular groove 10 and is formed in an annular shape. Its end faces
and outer peripheral surface are continuous to and flush with the
side face 2c and the peripheral surface 2d.
[0073] The sensor 11 for detecting vibration or temperature is
constructed such that a detecting part 15 for detecting vibration
or temperature and circuit components 14, such as resistors,
capacitors and IC, which form and a circuit part 16 for outputting
detected signals are mounted on a flexible printed circuit (FPC)
board 13.
[0074] A second embodiment of the invention will be described with
reference to FIG. 2. In the bearing 21 as shown in FIG. 2, an
annular groove 24 is formed entirely over the inner peripheral
surface of an inner ring 23, viz., the annular groove is not formed
in the outer ring 22. A sensor 11 is circumferentially disposed on
the bottom surface 24a of the annular groove 24 in a state that the
sensor 11 is located inside a prolongation of the side face 23a of
the inner ring 23, but outside a prolongation of the inner
peripheral surface 23b. The sensor 11 is molded by using an
insulating material, e.g., a synthetic resin 12. The protecting
synthetic resin 12 fills the annular groove 24, and is annular in
shape. Incidentally, the synthetic resin 12 is provided for
improving the performances of the dust-proof, water-proof and
oil-proof. The end face and the inner peripheral surface of it are
flush with the side face 23a and the inner peripheral surface 23b,
while being continuous to the latter. To measure a temperature, it
is preferable that a heat conductivity of the synthetic resin 12 is
equal to that of bearing member.
[0075] The remaining portion of the embodiment is substantially the
same as the corresponding one in the first embodiment, and hence
equivalent portions are designated by like reference numerals and
symbols used in the first embodiment, for simplicity of
explanation.
[0076] As described above, in each of the bearings 1 and 21 of the
first and second embodiments mentioned above, the sensor 11 is
disposed without outward extension, when comparing with the
conventional one. Therefore, there is no need for any special
machining of the bearing housing.
[0077] A third embodiment of the present invention will be
described with reference to FIG. 3. In the bearing 31 shown in FIG.
3, the sensor 11 is directly bonded to a bottom surface 10a of an
annular groove 10, which is formed in the outer ring 2. In this
case, an FPC (flexible printed circuit board) 13 of the sensor 11
is used as a bonding surface. The remaining portion of the
embodiment is substantially the same as the corresponding one in
the first embodiment, and hence equivalent portions are designated
by like reference numerals and symbols used in the first
embodiment, for simplicity of explanation.
[0078] A fourth embodiment of the invention will be described with
reference to FIG. 4. In the bearing 41 shown in FIG. 4, the sensor
11 is directly bonded to a bottom surface 24a of an annular groove
24, which is formed in the inner ring 23. In this case, an FPC 13
of the sensor 11 is used as a bonding surface. The remaining
portion of the embodiment is substantially the same as the
corresponding one in the second embodiment, and hence equivalent
portions are designated by like reference numerals and symbols used
in the second embodiment, for simplicity of explanation.
[0079] Also in each of the third and fourth embodiments, the sensor
11 is disposed within the annular groove 10 or 24. Accordingly,
those embodiments may achieve the object of the present invention
as the first and second embodiments do so. It is noted that in the
bearing device 31 (41) of the third (fourth) embodiment, the sensor
11 is bonded. This feature brings about the following advantages.
Its manufacturing is simpler than in the case where the sensor is
molded by using synthetic resin filling the annular groove 10 (24).
The manufacturing cost is reduced since the molding resin is not
used. Further, the sensor 11 may be additionally used if
necessary.
[0080] In each of the first to fourth embodiments, a power source
for the sensor 11 may be an external power source, and in this
case, the external power source is connected to the sensor 11 by a
power cable. Otherwise, a power source, together with the sensor
11, maybe located within the annular groove 10 (24), and in this
case, there is no need of using the power cable.
[0081] A fifth embodiment of the invention will be described with
reference to FIG. 5. A bearing 51 shown in FIG. 5 includes a
surface-opposed generator 52, which is located between the outer
ring 2 and the inner ring 3. The surface-opposed generator 52
includes a coil 53 and a magnet 54. A shield 9 is fitted into a
groove 8a, which is formed in the inner peripheral surface in an
end 2a of the outer ring 2 in the widthwise direction, and
corresponds to the location of the annular groove 10. And, the coil
53 is mounted on the inner side (=surface facing balls 6) of the
shield 9. The magnet 54 is mounted on a holding plate 55, while
being disposed in association with the coil 53. The holding plate
55 is fitted into a holding-plate mounting groove 56, which is
formed in the outer peripheral surface of an end 3a of the inner
ring 3 in the width direction.
[0082] The generator 52 generates electricity and supplies it to
the sensor 11. The remaining portion of the embodiment is
substantially the same as the corresponding one in the first
embodiment, and hence equivalent portions are designated by like
reference numerals and symbols used in the first embodiment, for
simplicity of explanation.
[0083] Where the generator 52 is thus used, it supplies electric
power to the sensor 11 even in such a case that it is difficult to
supply electric power from an external power source to the sensor
11 or that it is difficult to locate a power source together with
the sensor 11, within annular groove 10.
[0084] In the fifth embodiment of the invention, the sensor 11 is
provided on the outer ring 2 as in the first embodiment. If
required, it may be provided on the inner ring 23 as in the second
embodiment. In this case, the coil 53 of the generator 52 is
mounted on the holding plate 55 that is fitted to the inner ring
23, and the magnet 54 is mounted on the shield 9 that is fitted to
the outer ring 22. As in the third and fourth embodiments, the
sensor 11 may be bonded for fixation without molding.
[0085] A sixth embodiment of the invention will be described with
reference to FIGS. 6A, 6B and 6C. A bearing device 61 shown in
FIGS. 6A and 6B includes a recessed part 63 formed by cutting a
part of the end face of an outer ring 62, which is fitted to the
fixed housing A. Also, a rotational speed sensor shown in FIG. 6C
includes a rotational speed detecting part 18 and a detected part
17. The detected part 17 is constructed by a permanent magnet
attached to an inner ring shoulder portion of a race side with
respect to the shield 9, and an outer surface of said permanet
megnet is alternately magnetized to have N poles and S poles. The
rotational speed detecting part 18 is constructed by a hall element
for detecting change of magnetic flux, attached to an inner surface
of the shield 9 disposed on the same side as the detected part
17.
[0086] The detected part 17 may be made of any one of a plastic
magnet, a rubber magnet or a sintered magnet, and further may be
made of a gear wheel or a pulser-ring, instead of the permanent
magnet. The rotational speed detecting part may be of an active
type such as MR, GMR or hall IC, or of a passive type with a coil.
Further, when outer ring rotates, the rotational speed sensor can
be structured such that the detected part 17 is attached to the
outer ring 62 and the rotational speed detecting part 18 is
attached to the inner surface of the shield 9 secured to the inner
ring 3.
[0087] A detecting part 15 of a sensor 64, which is for detecting a
signal representative of vibration, temperature or like of the
bearing device 61, is mounted on the recessed part 63. The
detecting part 15 is disposed such that it is located inside a
prolongation of the side face 62a of the inner ring 62, but outside
a prolongation of the outer peripheral surface 62b. The detecting
part 15 may be mounted on the recessed part 63 in such a manner
that it is molded by using an insulating material, e.g., synthetic
resin 12, as in the first and second embodiments, or that it is
insulatedly bonded to a bottom surface 63a of the recessed part 63
as in the third and fourth embodiments. A circuit part 16 of the
sensor 64, while being insulated, is directly bonded to one of
shields 9, which are fitted into shield-mounting groove 8a and
shield-mounting groove 8b formed respectively in both ends 62c and
62d of the outer ring 62 in the widthwise direction.
[0088] The sensor 64 is constructed such that circuit components 14
and the like are mounted on an arcuate FPC 65 formed conforming to
a shape of the shield 9. The detecting part 15 and the circuit part
16 are provided on one continuous FPC 65. Otherwise, the detecting
part 15 and the circuit part 16 may be mounted on separate FPCs,
respectively, and interconnected by wires. A power source may be an
external power source connected to the sensor 64 by a power cable.
Otherwise, a power source together with the sensor 64 may be
located on the shield 9, and in this case, there is no need of
using the power cable. Further, a surface-opposed generator 54 as
described in the fifth embodiment may be used. The remaining
portion of the embodiment is substantially the same as the
corresponding one in the first embodiment, and hence equivalent
portions are designated by like reference numerals and symbols used
in the first embodiment, for simplicity of explanation.
[0089] The mounting part of the sensor 64 is not limited to the
above-mentioned one, but in a case where the outer ring serves as a
rotating ring and the inner ring serves as a stational ring, a
recess formed by cutting a part of the side face 3a of the inner
ring 3 may be used for the sensor mounting part. In this case, a
shield mounting groove (recess) is formed at the end 3b of the
inner ring 3, and the shield is fitted into the groove, and the
sensor 64 is mounted thereon.
[0090] As described above, the bearing device 61 of the sixth
embodiment may be formed by merely cutting a part for mounting the
detecting part 15 of the sensor 64. Accordingly, there is no need
of machining work of the housing A and the shaft S to which the
bearing device 61 is to be mounted, whereby, the rolling bearing
with sensor 61 requires the least machining work of the
bearing.
[0091] A description will be given of how to take a signal out of
the sensor in each of the first to sixth embodiments with reference
to FIG. 7. To detect vibration, temperature or the like of the
outer ring 2 as a stational ring, a rolling bearing with sensor 1
of the first embodiment is mounted on the housing A as shown in
FIG. 7. The housing A is static and at least one of the ends of the
housing is opened. The rotating shaft S is inserted through the
inner ring 3 of the rolling bearing 1, fixed thereto to be
rotatable. A wire W and a power cable E are connected to the sensor
11, which is fastened to the annular groove 10 of the outer ring 2
as the stational ring by molding.
[0092] The rolling bearing with sensor 1 may be the bearing 31 of
the third embodiment. In a case where the outer ring serves as a
rotating ring, and the inner ring serves as a stational ring whose
vibration, temperature or the like are detected, the bearing 21 or
41 of the second or fourth embodiment is used and the wire W is
connected thereto, so that vibration, temperature or the like of
the inner ring 23 may be detected.
[0093] In the bearing 61 of the sixth embodiment, the wire W and
the power cable E derived from the circuit part 16 of the sensor 64
mounted on the shield 9 are wired along the housing A or the shaft
S as a stational part.
[0094] As a result, the bearing can output a signal, which is
converted by the circuit part 16 of the sensor 11 (64). A power
source (not shown) may be located outside by using the wire W and
the power cable E as well. When the power source together with the
sensor 11 is located in the annular groove 10 (in the sixth
embodiment, the sensor 64 is located on the shield 9), or when the
surface-opposed generator 52 is provided as in the bearing device
51 of the fifth embodiment, there is no need of using the power
cable E, to thereby reduce the number of wires extended from the
rolling bearing with sensor 1.
[0095] A seventh embodiment of the invention will be described with
reference to FIGS. 8 through 10. In a rolling bearing with sensor
71 shown in FIG. 8, an outer ring 22 is fitted to a housing A, and
a rotating shaft S is fitted into an inner ring 23. The housing A
is opened at at least one end thereof. A sensor 72, which is
mounted on the rotating ring of the bearing 71, i.e., on an annular
groove 24 of an inner ring 23, includes a detecting part 15 for
detecting vibration, and a transmitting part (radio wave generator
part) 73 which converts a detecting signal into a radio wave R, and
transmits it outside. A power source 74 for the sensor 72 is
mounted in the annular groove 24.
[0096] The detecting part 15 includes conductive electrodes 15b
mounted on a movable part 15c and a fixed part 15d of a detecting
main part 15a made of an elastic insulating material shown in FIG.
9A in such a manner as to oppose to each other. The movable part
15c has an elastic modulus selected so that the conductive
electrodes 15b come in contact with each other when it receives a
predetermined vibration acceleration. The transmitting part 73, as
exemplarily shown in FIG. 9B, includes circuit components 14 such
as a capacitor 73a, a coil 73b, a variable resistor 73c, a variable
capacitance diode 73d and the like. When the conductive electrodes
15b of the detecting part 15 come in contact with each other under
a predetermined vibration acceleration, a current from the power
source 74 to the transmitting part 73 is generated, and the current
is outputted as a radio wave.
[0097] A composite capacitance value C of the capacitor 73a and the
variable capacitance diode 73d is varied, when the reverse voltage
applied to the variable capacitance diode 73d is varied by varying
a resistance value of the variable resistor 73c. And, an
oscillation frequency defined by the capacitance value C and a
reactance value L of the coil 73b may be selected. In other words,
even when a plurality of rolling bearings with sensor 71 are
concurrently used, the signals produced from those bearings may be
detected discriminately.
[0098] The seventh embodiment may use a transmitting part 75
including a capacitor 75a and a coil 75b as shown in FIG. 10, and
the transmitting circuit part 75 is of the fixed frequency type in
which a capacitance value of the capacitor 75a and a reactance
value of the coil 75b are arbitrarily selected for each rolling
bearing 71. Accordingly, the transmitting circuit part 75 can be
reduced in size. It is evident that the transmitting parts 73 and
75 are an example of the transmitting part, and those may be
realized by other circuit arrangements. The detecting main part 15a
may be structured by a thermostat, and then, the sensor emits a
radio wave R when a predetermined temperature is detected. If the
FPC 13 is configured like the FPC 65 in the sixth embodiment, the
sensor 72 includes the transmitting circuit part 73 (75), and is
applicable to the bearing 61 of the sixth embodiment. The remaining
portion of the embodiment is substantially the same as the
corresponding one of the rolling bearing with sensor 21 in the
second embodiment, and hence equivalent portions are designated by
like reference numerals and symbols used in the second embodiment,
for simplicity of explanation.
[0099] In the seventh embodiment, although the sensor 72 is molded
by using the synthetic resin 12, the sensor 72 may be
circumferentially bonded onto and along the bottom surface 24a of
the annular groove 24 as in the bearing device 41 of the fourth
embodiment. In a case where the outer ring serves as a rotating
ring whose vibration, temperature or the like is detected and the
inner ring is a stational ring, the sensor 11 of the rolling
bearing with sensor 1, 31 or 51 of the first, third or fifth
embodiment (the sensor 64 in the bearing device 61 of the sixth
embodiment) is substituted by the sensor 72, and, in the rolling
bearings with sensor land 31, a power source is located in the
annular groove 10 (on the shield 9 in the sixth embodiment). By so
doing, a detecting signal may be transmitted while being carried on
a radio wave R. The transmitted signal is received by an antenna 76
located at a remote position, and transmitted through a demodulator
77 to a related control system.
[0100] Since the rolling bearing 71 of the seventh embodiment
transmits a detected signal as a radio wave R, there is eliminated
the wires extended from the rolling bearing 71. Accordingly,
vibration, temperature or the like of the rolling bearing may be
detected in such a simple manner that the rolling bearing is
mounted as in mounting the conventional one. The rolling bearing
with sensor 71 of the embodiment may be used for detecting
vibration, temperature or the like of the stational ring as well as
those of the rotating ring.
[0101] An eighth embodiment of the invention will be described with
reference to FIG. 11. A bearing device 81 shown in FIG. 11 includes
an outer ring 2 fitted to the inner surface of a housing Al tightly
closed and an inner ring 3 fitted into a rotating shaft S. An
annular groove 10 is formed in the outer ring 2. A sensor 82 is
circumferentially fastened to the bottom surface 10a of the annular
groove 10 by molding. The sensor 82 includes a detecting part 15
for detecting vibration, temperature or the like, and an ultrasonic
wave output circuit part (ultrasonic wave generating part) 83 which
converts a detecting signal into an ultrasonic wave signal U and
outputs the converted one. If the FPC 13 is configured like the FPC
65 in the sixth embodiment, the sensor 82 can include the
ultrasonic wave output circuit part 83 applicable to the bearing 61
of the sixth embodiment. The remaining portion of the embodiment is
substantially the same as the corresponding one of the bearing 51
of the fifth embodiment, and hence equivalent portions are
designated by like reference numerals and symbols used in the fifth
embodiment, for simplicity of explanation.
[0102] In the eighth embodiment, the sensor 82 and a power source
(not shown) may be put in the annular groove 10, instead of the
generator 52. In a case where the outer ring serves as a rotating
ring, and the inner ring serves as a stational ring being an object
to be detected, viz., its vibration, temperature or the like are
detected, the rolling bearing with sensor 21 of the second
embodiment is used for the bearing 81, the sensor 11 of the rolling
bearing 21 is used for the sensor 82, or a power source is put in
the annular groove 24 or a surface-opposed generator 52 is used as
in the fifth embodiment. By so doing, detected signals
representative of vibration, temperature or the like may be sent in
the form of an ultrasonic wave U. The ultrasonic wave signal U is
received by an ultrasonic wave receiver 84. In this case, the
ultrasonic wave receiver 84 is detachably mounted in a closed
manner on an ultrasonic wave detecting surface provided on the
outer surface of the housing A'. The received ultrasonic wave
signal is transmitted to a related control system, by way of a
demodulator 85.
[0103] Thus, in the rolling bearing with sensor 81 of the eighth
embodiment, the sensor 82 can output detecting signals
representative of vibration, temperature or the like in the form of
the ultrasonic wave signals U even when the bearing device 81 is
covered with the housing A'.
[0104] In the sensors 11, 72 and 82 of the first to fifth, seventh
and eighth embodiments are fastened to the bottom surfaces 10a and
24a of the annular grooves 10 and 24 by bonding or molding. In the
sensor 64 of the sixth embodiment, the detecting part 15 is
fastened to the raceway by molding or bonding, and the circuit part
16 is mounted on the shield 9. In either case, the detecting part
15 is mounted at a position inside an area surrounded by the
prolongation of the end faces of the outer ring and the inner ring,
a prolongation of the outer peripheral surface of the outer ring,
and a prolongation of the inner peripheral surface of the inner
ring. Therefore, there is no need for any special machining of the
housing.
[0105] A ninth embodiment of the invention will be described with
reference to FIGS. 12A to 12F. In rolling bearings with sensor 91
shown in FIGS. 12A to 12F, sensors 11, 64, 72 and 82 are directly
bonded to the surfaces of the outer ring 92 and the inner ring 93,
by using FPCs 13 and 65 as bonding surfaces. For the details of the
sensors, reference is made to the first embodiment for the sensor
11, the sixth embodiment for the sensor 64, the seventh embodiment
for the sensor 72, and the eighth embodiment for the sensor 82. The
rolling bearing with sensor 91 of this embodiment requires a less
machining work of the housing when comparing with the conventional
one.
[0106] A tenth embodiment of the invention will be described with
reference to FIGS. 13A through 15. In the embodiment, like
reference numerals and symbols will be used for designating like or
equivalent portions in the first to ninth embodiments.
[0107] A rolling bearing with sensor 101 shown in FIG. 13A includes
an outer ring 102, an inner ring 103, and a sensor 105 for sensing
a humidity in a space K surrounded preferably by water-proof
shields 104. In the rolling bearing 101, the outer ring 102 is
fitted into the opened end of a housing A and fastened by a fixing
ring 106. The inner ring 103 is fitted to the outer peripheral
surface of the rotating shaft S. A recess 107, as shown in FIG.
13B, is formed in a part of the end face of the outer ring 102,
while extending in the circumferential direction.
[0108] The sensor 105 includes a detecting part 108 and a circuit
part 109, and receives electric power from a power source (e.g., a
button shaped battery) 110 by way of a power cable E. The
water-proof rubber shields 104 is fitted to the outer ring 102 and
is slidably contacted with the inner ring 103, and the detecting
part 108 is mounted on the inner surfaces 104a of the water-proof
shields 104, viz. within a space K surrounded by the outer ring
102, the inner ring 103 and the water-proof shields 104. The
circuit part 109 is disposed so that it is not protruded out of a
recess 107 formed in the outer ring 102. The recess 107 to which
the circuit part 109 has been mounted may be molded by using
synthetic resin. The circuit part 109 may be mounted on an FPC, as
in the sensors 11, 64, 72 and 82 in the first to ninth embodiments.
Fabricating of the circuit part into an integrated circuit is more
preferable since remarkable size reduction of it is realized.
[0109] The electric power 110 is placed in a recess 111 formed at a
part of the housing A in insulating and water-tight fashion.
Grooves 112a and 112b for receiving the power cable E, are formed
in the housing A and the fixing ring 106, while ranging from the
recess 107 to the recess 111.
[0110] The detecting part 108 of the sensor 105 includes two
electrodes 113a and 113b formed in a comb shape, and a
moisture-absorbing conductor 114 located between those electrodes
113a and 113b as shown in FIG. 14. The two electrodes 113a and 113b
and the conductor 114 are mounted on an insulating substrate 115.
Terminals 116a and 116b are mounted on the electrodes 113a and
113b, respectively. The moisture-absorbing conductor 114 is formed
with a thin film made of porous ceramics, e.g., calcium phosphate,
by coating sintering and drying process or vacuum deposition
process. When the conductor 114 absorbs atmospheric moisture,
electric resistance value between the two electrodes 113a and 113b
varies. A variation of the electric resistance value in the
detecting part 108 is detected in the form of a signal of a
variation of humidity. To this end, a fixed voltage Vcc is applied
to the electrode 113a of the detecting part 108, and a resistor "r"
earthed is connected to the electrode 113b. A voltage V1 passing
through the detecting part 108 is detected as a signal proportional
to the humidity.
[0111] The circuit part 109 shown in FIG. 15 includes a comparator
circuit 109a for processing a signal derived from the detecting
part 108, and a transmitting part 109b for generating a radio wave.
A voltage V1 derived from the detecting part 108 is input to the
comparator circuit 109a as an object voltage for comparison.
Further, a reference voltage Vs is applied to the comparator
circuit part 109a. When the detecting part 108 absorbs atmospheric
moisture and the moisture-absorbing conductor 114 of the detecting
part 108 reduces its resistance value, the voltage V1 is relatively
increased. The comparator circuit compares a threshold value
defined by the reference voltage Vs with the voltage V1 whose value
varies in accordance with a degree of moisture absorption by the
detecting part 108. When the voltage varies to exceed the threshold
value, the comparator circuit 109a outputs a signal to the
transmitting circuit part 109b. Accordingly, the sensor 105
transmits a radio wave when the detected humidity exceeds the
predetermined threshold value. The threshold value may be adjusted
by changing the resistor "r", the reference voltage Vs and the
like. Thus, the circuit part 109 operates such that a signal output
from the detecting part 108 is compared with the threshold value,
and a radio wave R is transmitted to a receiver (not shown) located
outside on the basis of the comparison result. It is evident that
the circuit arrangement of the circuit part 109 is not limited to
that shown in FIG. 15.
[0112] As described above, the tenth embodiment thus constructed is
capable of detecting a humidity in the space surrounded by the
outer ring 102, the inner ring 103 and the water-proof shields 104
of the rolling bearing with sensor 101. In the rolling bearing with
sensor 101, the special machining work of the bearing mounting
part, e.g., the bearing housing A, may be minimized, and the
rolling bearing with sensor may readily be mounted on the existing
equipment.
[0113] An eleventh embodiment of the present invention will be
described with reference to FIGS. 16A and 16B. Like reference
numerals and symbols will be used for designating equivalent
portions in the first to tenth embodiments.
[0114] In a rolling bearing with sensor 121 shown in FIG. 16A, an
outer ring 122 is fitted into the end of the housing A, and an
inner ring 103 is fitted to the outer peripheral surface of the
rotating shaft S. The bearing 121 includes a sensor 105 for
detecting a humidity. The circuit part 109 of the sensor 105 is
mounted on an outer surface 104b of the water-proof shield 104,
viz., a surface opposite to the inner surface 104a to which the
detecting part 108 is mounted. As shown in FIG. 16B, a circuit part
109 includes a comparator circuit 109a for comparing a signal
output from a detecting part 108 with a predetermined threshold
value, and a transmitting circuit part 109b for transmitting a
radio wave in response to a signal output from the comparator
circuit 109a. The circuit part is mounted on the water-proof
shields 104 along the circumferential direction thereof. The
detecting part 108 and the circuit part 109 of the sensor 105 are
interconnected by a wire W, which passes through the water-proof
shields 104 in a watertight manner. The circuit part 109 may be
mounted on an FPC, as in the sensors 11, 64, 72 and 82 in the first
to ninth embodiments, or fabricated into an integrated circuit for
further remarkable size reduction.
[0115] Electric power of the sensor 105 is supplied from the power
source 110 placed in the recess 111 of the housing A through the
power cable E. To arrange the power cable E in the range from the
power cable E to the circuit part 109, the grooves 112a and 112b
are formed in the housing A and the fixing ring 106, and a stepped
part 112c is formed at a part of the outer ring 122. If the power
cable E does not interfere with the fixing ring 106, the stepped
part 112c of the outer ring 122 may be omitted, and hence no
machining work is required for the outer ring 122.
[0116] Thus, the eleventh embodiment is capable of detecting the
humidity in the within a space K surrounded by the outer ring 122,
the inner ring 103 and the water-proof shields 104 of the bearing
121. In this rolling bearing with sensor, the special machining
work of the bearing mounting part, e.g., the bearing housing A, may
be minimized, and the rolling bearing with sensor may readily be
mounted on the existing equipment. Further, since the detecting
part 108 and the circuit part 109 of the sensor 105 are both
mounted on the water-proof shield 104, the assembling of the
bearing 121 is easy.
[0117] A twelfth embodiment of the invention will be described with
reference to FIGS. 17A and 17B. Like reference numerals and symbols
will be used for designating equivalent portions in the first to
eleventh embodiments.
[0118] A rolling bearing with sensor 131 shown in FIG. 17A includes
a sensor 105 for detecting the humidity, as in the tenth and
eleventh embodiments. The circuit part 109 of the sensor 105, as
shown in FIG. 17B, is mounted on the water-proof shield 104 as in
the eleventh embodiment. The circuit part 109 may be mounted on an
FPC, as in the sensors 11, 64, 72 and 82 in the first to ninth
embodiments. Further, the circuit part may be fabricated into an
integrated circuit for size reduction.
[0119] The power source 110 is a solar battery. At a part of the
raceway ring (an outer ring 132 in this case) to which the
water-proof shields 104 are fastened, a stepped part 133 is formed
to be flush with the outer surface 104b of the water-proof shields
104. The power source 110 of the solar battery is mounted over an
area including the stepped part 133 and the water-proof shield 104.
If the solar battery is configured along the circumferential
direction of the water-proof shield 104, there is no need of
forming the stepped part 133 of the outer ring 132.
[0120] As described above, the twelfth embodiment is capable of
detecting the humidity within a space K surrounded by the outer
ring 132, the inner ring 103 and the water-proof shields 104 of the
bearing 131. In this rolling bearing with sensor, the special
machining work of the bearing mounting part, e.g., the bearing
housing A, may be minimized, and the rolling bearing with sensor
may readily be mounted on the existing equipment. Since the solar
battery is used for the power source 110, no care must be taken of
the occurrence of a worn battery.
[0121] In the tenth to twelfth embodiments, the detecting part 108
of the sensor 105 is located outside the space K defined by the
outer ring 102 (122, 132), the inner ring 103, and the water-proof
shields 104. The detecting part 108 maybe located within the space
K as in the cases of FIGS. 12A and 12C in the ninth embodiment, if
the size of it allows such doing of the detecting part.
Specifically, it may be located on the inner peripheral surface of
the outer ring 102 (122, 132) facing the space K or the outer
peripheral surface of the inner ring 103 facing the space K. The
detecting part 108 may be constructed so as to detect vibration,
temperature or humidity.
[0122] In the respective embodiments, the single-row deep groove
ball bearing is used for the rolling bearing. It will readily be
understood that also when the invention is applied to other types
of rolling bearings, such as a cylindrical roller bearing or a
thrust ball bearing.
[0123] As seen from the foregoing description, in the rolling
bearing with sensor of the invention, the special machining work of
the bearing mounting part, e.g., the bearing housing, is minimized,
and the rolling bearing with sensor may readily be mounted on the
existing equipment. In the invention, the sensor is mounted on the
bearing whose vibration, temperature, humidity or the like is
detected. Therefore, vibration, temperature, humidity or the like
may be detected quickly and accurately.
[0124] Further, the sensor includes the radio wave generating part
or an ultrasonic wave generating part. The bearing assembling work
is free from troublesome work of wiring or the like. Accordingly,
the invention provides an easy-to-handle rolling bearing with
sensor.
[0125] A thirteenth embodiment of the present invention will be
described with reference to FIGS. 18 through 20. A rolling bearing
device 201 shown in FIG. 18 is provided between a housing A as a
stational part and a rotating shaft S. The rolling bearing device
201 includes an outer ring 202 and an inner ring 203, which are
examples of a raceway ring and, in particular, detects a vibration,
a temperature, a rotational speed or the like of the outer ring 202
fitted to the housing A. The outer ring 202 is fitted to the end of
the housing A, and held with a fixing ring 204 for preventing it
from falling off. A recessed outer raceway 202a is formed at a
central part of the inner peripheral surface of the outer ring 202.
A recessed inner raceway 203a, is formed at a central part of the
outer peripheral surface of the outer ring 203. A plurality of
balls 205 as rolling elements are retained with a retainer 206 in
the circumferential direction at equal intervals while being in
rollably contacted with the outer raceway 202a and the inner
raceway 203a. Shield mounting grooves 202b are respectively
provided on both ends of the outer ring 202 as viewed in the
widthwise direction, at locations closer to the inner ring. Shields
207 are respectively fitted to and supported by the shield mounting
grooves 202b in order to protect the rolling surfaces of the outer
raceway 202a, the inner raceway 203a, and the balls 205.
[0126] An arcuate recess 208, which continuously extends in the
circumferential direction of the outer ring 202, is provided at a
part of an end face of the outer ring 202. A sensor 209 is mounted
within the arcuate recess 208 in such a fashion that the sensor 209
is not protruded out of the arcuate recess 208. The sensor 209, as
shown in FIG. 19, includes a detecting part 210 for detecting an
acceleration, temperature or rotational speed, a transmitting part
211 for transmitting a radio wave signal, and a control part 212
for controlling the transmitting part 211. The sensor 209 is
supplied with electric power from a power source 213, e.g., a
button-shaped battery, by way of a wire W. The power source 213 is
placed within a recess 214 formed at a part of the housing A. A
groove 215 is provided ranging from the arcuate recess 208 to the
recess 214, and the wire W will be laid in the groove 215.
[0127] The detecting part 210 includes an acceleration sensor 216,
a temperature sensor 217 and a rotating speed sensor 218. The
acceleration sensor 216 is provided mainly for sensing a vibration,
and may be a piezoelectric element which produces a potential
difference in accordance with an acceleration variation caused by a
vibration, or a strain gauge stuck onto a plate spring. The
temperature sensor 217 may be a thermistor whose electric
resistance varies with a temperature variation. The detecting part
210 may include either of the acceleration sensor 216, the
temperature sensor 217 or the rotating speed sensor 218 according
to uses of the rolling bearing device 201. The arcuate recesses 208
may be formed at a plurality of locations of the end face of the
rolling bearing device 201. In this case, the sensors 209 may be
independently located in those recesses 208, or the detecting parts
210 maybe located in those recesses 208.
[0128] As described above, the arcuate recess 208 is provided on
the static side, and the sensor 209 and the power source 213 are
placed in the recess 208 such that the sensor 209 and the power
source 213 are not protruded out of the outer surfaces of the
housing A and the rolling bearing device 201. Therefore, there is
no need of providing any special space for the mounting of the
sensor 209 in the housing A or the shaft S. Accordingly, the
rolling bearing device 201 may be interchanged with a conventional
bearing. Further, the least amount of machining is required for the
rolling bearing device 201.
[0129] In the block diagram of FIG. 20, a signal derived from the
acceleration sensor 216 of the detecting part 210 is input to a
comparator 220a in the control part 212, and is compared with a
predetermined acceleration in the comparator. A signal derived from
the temperature sensor 217 is input to a comparator 220b, and
compared with a predetermined temperature by the comparator 220b.
Either of the signals derived from the sensors exceeds a threshold
value, the control part 212 judges that something is wrong with the
bearing (or the device using the bearing). Upon the judgement being
an abnormality, a transmitting part controller 222 first turns on
(closes) a switch 224, which is inserted in a path for supplying
electric power to the transmitting part 211, in order to enable the
transmitting part 211 to operate. Subsequently, the transmitting
part controller 222 sends to the transmitting part 211 a signal for
transmitting a radio wave signal R indicating that the acceleration
sensor 216 or the temperature sensor 217 detected an abnormality of
the bearing or the like. Then, the rotating speed at the detecting
time of the abnormality may be simultaneously transmitted. Upon
receipt of the signal, the transmitting part 211 transmits a radio
wave signal R indicating that the acceleration sensor 216 or the
temperature sensor 217 detected an abnormality of the bearing or
the like. The radio wave signal R is received by a receiving device
219, which is located at a position spaced a part from the
transmitting part 211.
[0130] Thus, the rolling bearing device 201 operates such that when
the acceleration sensor 216, the temperature sensor 217 or the
rotating speed sensor 218 detects an abnormality of the bearing or
the like, the transmitting part 211 sends a radio wave signal R
indicating the abnormality occurrence, but when the acceleration
sensor 16 or the temperature sensor 217 produces a normal output
signal, the transmitting part 211 does not emit a radio wave signal
R indicating the normality.
[0131] Sensor-function checking device is further provided for
informing that the sensor normally functions; it sends a radio wave
signal R indicating that the sensor normally functions, at a fixed
time interval (of e.g., 24 hours). Therefore, even in such a case
that the sensor abnormally functions and fails to output an
abnormality signal, there is no chance of making such a
misjudgement that it normally functions.
[0132] One may discriminate between a normally operating sensor and
an abnormally operating sensor in such a manner that different
identification signals, such as audio signals different in
frequency from each other, obtained when the sensor normally
operates and when the sensor abnormally operates are incorporated
into a radio wave R. The same thing is true for the discrimination
between the radio wave signal R transmitted when the acceleration
exceeds the threshold value of acceleration and the radio wave
signal R transmitted when the temperature exceeds the threshold
value of temperature.
[0133] In the embodiment, the transmitting part 211 sends a radio
wave R in only the following cases: 1) the sensor 209 detects an
abnormality; and 2) the sensor 209 normally operates. When no radio
wave R is transmitted, the switch 224 for supplying electric power
to the transmitting part 211 is in an OFF (open) state.
Accordingly, no electric power is consumed in the transmitting part
211. Therefore, in a case where the power source 213 is a battery,
the power consumption is lessened, and hence the battery once
mounted is used for a long time.
[0134] The sensor 209 may be further reduced in size and power
dissipation by fabricating the detecting part 210, the control part
212 and the transmitting part 211 into an integrated circuit.
[0135] In the embodiment of the invention, the bearing abnormality
is judged by comparing an output signal of the acceleration sensor
216 with the threshold value of acceleration, and comparing an
output signal of the temperature sensor 217 with the threshold
value of temperature. In an alternative, the output signals of the
acceleration sensor 216, the temperature sensor 217 and the
rotating speed sensor 218 are converted into digital signals.
Variations of the acceleration and temperature, or the correlation
between variations of the acceleration and temperature are judged
to determine that the bearing (or the device using the bearing) is
abnormal. A radio wave signal R indicating the result of the
determination is transmitted from the transmitting part 211.
[0136] The detecting part 210 forming the sensor 209, those
circuits 220a, 220b and 222, and the power source 213 may be
individually connected by the wire W, and insulated and bonded to
the recess 208 of the outer ring. Those may be mounted on the
flexible printed circuit board to form a sensor unit, to thereby
facilitate the bonding work for fixing. It should be understood
that the sensor 209 of the embodiment is presented by way of
example, and an electrical arrangement of the sensor is not limited
to that of block diagram shown in FIG. 20 A fourteenth embodiment
of the invention will be described with reference to FIGS. 21A and
21B. In the embodiment, equivalent portions are designated by like
reference numerals used in the thirteenth embodiment.
[0137] A bearing device 231 shown in FIG. 21A is arranged such that
an outer ring 202 is fitted to the inner side of the end of a
housing A as a stational part, and an inner ring 203 is fitted to
the outer side of the end of a rotating shaft S. The bearing device
231 thus constructed serves as a rolling bearing device for
detecting an acceleration, temperature or rotating speed of the
inner ring 202.
[0138] As shown in FIG. 21B, a recess 232 is formed in a part of
the end face of the inner ring 203 along the circumferential
direction of the inner ring 203. A sensor 209 is mounted in the
recess 232. The power source 213 for supplying electric power to
the sensor 209 is mounted on the end 233 of the shaft S,
preferably, in a recess 234 formed at the center of the shaft S. A
groove 235 is formed between the recess 232 of the inner ring 203
to which the sensor 209 is attached and the recess 234 in which the
power source 213 is fitted, and a wire W is placed in the groove
235. A cover member 236 covering the end 233 of the shaft S is
attached in order to prevent the inner ring from falling off, as
shown in FIG. 21A. The cover member 236 also has a function to
protect the power source 213, the wire W and the sensor 209. While
the power source 213 and the wire W are arranged in the recess 234
and the groove 235 formed in the end 233 of the shaft S, those may
be put in a recess and a groove formed in the inner side of the
cover member 236, so that no machining of the shaft S is
required.
[0139] In the bearing device 231 thus constructed, there is no need
of machining the housing A, and is required less machining of the
shaft S for the attachment of the bearing device to the shaft. The
bearing device 231 thus constructed is capable of detecting an
acceleration and a temperature of the inner ring 203 that is fitted
to the rotating shaft S. As in the thirteenth embodiment, since the
sensor 209 includes sensor-function checking device, the bearing
device of the embodiment is capable of periodically and easily
checking as to if the sensor 209 normally functions.
[0140] A fifteenth embodiment of the present invention will be
described with reference to FIGS. 22A and 22B. In the embodiment,
equivalent portions are designated by like reference numerals used
in the thirteenth and fourteenth embodiments.
[0141] A bearing device 241 shown in FIG. 22A is arranged such that
an outer ring 202 is fitted to the inner side of a housing A as a
stational part, and an inner ring 203 is fitted to the outer side
of an intermediate part of a rotating shaft S. The bearing device
241 thus constructed serves as a rolling bearing device for
detecting an acceleration or temperature of the inner ring 203.
[0142] A recess 232 is formed in a part of the inner ring 203 while
being opened to the inner peripheral surface of the inner ring 203.
The recess 232 has a width extending along the circumferential
direction and being longer than the depth of the inner ring 203. A
sensor 209 is mounted in the recess 232. As shown in FIGS. 22A and
22B, a power source 213 for supplying electric power to the sensor
209 is placed in a recess 243 formed in a part of the inner surface
of a sleeve 242. A groove 244 for connecting the recess 243 to the
recess 232 of the inner ring 203 is formed in the end 242a of the
sleeve 242. A wire W for electrically connecting the power source
213 to the sensor 209 is placed in the groove 244. The power source
213 and the sensor 209, as shown in FIG. 22A, are protected by the
sleeve 242.
[0143] The bearing device 241 thus constructed is capable of
detecting an acceleration, a temperature or a rotating speed of the
inner ring 203 fitted to the shaft S, and may be provided at the
intermediate part of the shaft S. The bearing device 241 does not
require any special machining of the housing A and the shaft S. In
this respect, the bearing device is readily applied to the already
existing bearing. Further, as in the thirteenth embodiment, since
the sensor 209 includes sensor-function checking device, the
bearing device of the embodiment is capable of periodically and
easily checking as to if the sensor 209 normally functions.
[0144] A sixteenth embodiment of the present invention will be
described with reference to FIGS. 23A and 23B. In the embodiment,
equivalent portions are designated by like reference numerals used
in the thirteenth to fifteenth embodiments.
[0145] A bearing device 251 shown in FIGS. 23A and 23B is arranged
such that an outer ring 202 is fitted to the end of a housing A as
a stational part, and an inner ring 203 is fitted to the outer side
of an intermediate portion of a rotating shaft S. In the sensor
209, a detecting part 210 includes a temperature sensor 217, and
has a function similar to that of the thirteenth embodiment. In
this case, a part of the sensor 209 is protruded out of the outer
surface of the bearing device 251. In this case, the protruded part
of the sensor 209 usually faces the space, and is not protruded out
of a prolongation of the outer surface of the fixing ring 204. As
shown in FIGS. 23A and 23B, the detecting part 210, the control
part 212 and the transmitting part 211, while being arranged along
the circumferential direction, are mounted on the shields 207 which
is fitted to and supported by the outer ring 202. Accordingly, the
power source 213 is provided on the housing A as in the thirteenth
embodiment. On the other hand, the shields 207 are supported on the
inner ring 203, it is preferable that a sleeve 242 is provided as
in the fifteenth embodiment, and that the power source 213 is
located on the shaft S side.
[0146] In the bearing device 251 thus constructed, any special
machining of the bearing device is not required, and it may be
mounted on the housing A with less machining of it. The bearing
device 251 is capable of detecting a temperature of the bearing
device 251. Further, as in the thirteenth embodiment, since the
sensor 209 includes sensor-function checking device, the bearing
device of the embodiment is capable of periodically and easily
checking as to if the sensor 209 normally functions.
[0147] A seventeenth embodiment of the present invention will be
described with reference to FIGS. 24A and 24B. In the embodiment,
equivalent portions are designated by like reference numerals used
in the thirteenth to sixteenth embodiments.
[0148] A bearing device 261 shown in FIG. 24A is arranged such that
the outer ring 202 is fitted to the inner side of the housing A as
a stational part, and the inner ring 203 is fitted to the outer
periphery side of the rotating shaft S as a rotating part. As shown
in FIGS. 24A and 24B, a sensor 209 is mounted in a recess 208 which
is circumferentially formed at a part of the end face of the outer
ring 202. The sensor is used for sensing an acceleration and a
temperature of the outer ring 202.
[0149] A power source 213 for supplying electric power to the
sensor 209 is a small battery so configured as to be adaptable for
its installing place and, together with the sensor 209, is mounted
in the recess 208. Accordingly, in the embodiment, unlike the
thirteenth embodiment, there is no need of mounting the power
source 213 on the housing A, and hence of machining the housing A
for its mounting. Further, the sensor 209 and the power source 213
are mounted so as not to be protruded out of the recess 208.
Therefore, the bearing device 261 may easily be applied to an
already existing apparatus by merely replacing a conventional
bearing with the bearing device of the invention.
[0150] As in the thirteenth embodiment, since the sensor 209
includes sensor-function checking device, the bearing device of the
embodiment is capable of periodically and easily checking as to if
the sensor 209 normally functions. Incidentally, to detect an
acceleration and a temperature of the inner ring 203, a recess is
formed at a part of the end face of the inner ring 203 along the
circumferential direction, and the sensor 209 and the power source
213 are mounted in the recess.
[0151] An eighteenth embodiment of the present invention will be
described with reference to FIGS. 25A and 25B. In the embodiment,
equivalent portions are designated by like reference numerals used
in the thirteenth to seventeenth embodiments.
[0152] A bearing device 271 shown in FIG. 25A is arranged such that
the outer ring 202 is fitted to the inner side of the housing A as
a stational part, and the inner ring 203 is fitted to the outer
peripheral side of the rotating shaft S. As shown in FIG. 25A, the
sensor 209 is provided on the shields 207 supported on the outer
ring 202, while being arranged in the circumferential direction as
shown in FIG. 25B. A power source 213 for supplying electric power
to the sensor 209 is a small battery so configured as to be
adaptable for its installing place and, together with the sensor
209, is mounted in the recess 207. Accordingly, in the embodiment,
unlike the sixteenth embodiment, there is no need of mounting the
power source 213 on the housing A, and hence of machining the
housing A for its mounting. Therefore, the bearing device 271 may
easily be applied to an already existing apparatus by merely
replacing a conventional bearing with the bearing device of the
invention. The shields 207 may be supported on the inner ring
203.
[0153] Further, as in the thirteenth embodiment, since the sensor
209 includes sensor-function checking device, the bearing device of
the embodiment is capable of periodically and easily checking as to
if the sensor 209 normally functions.
[0154] A nineteenth embodiment of the present invention will be
described with reference to FIGS. 26A and 26B. In the embodiment,
equivalent portions are designated by like reference numerals used
in the thirteenth to eighteenth embodiments.
[0155] A bearing device 281 shown in FIG. 26A is arranged such that
an outer ring 202 is fitted to the intermediate part of a housing A
as a stational part, and an inner ring 203 is fitted to the outer
peripheral side of an intermediate part of a shaft S as a rotating
part. A detecting part 210 of a sensor 209 includes an acceleration
sensor 216 and a temperature sensor 217, and is mounted in a recess
282 of the outer ring 202. As shown in FIG. 26B, the control part
212 and the transmitting part 211 of the sensor 209 are mounted on
a shield 207 which is fitted to and supported on the outer ring 202
in such a manner as to arranged circumferentially. That is, in the
sensor 209, the acceleration sensor 216 and the temperature sensor
217 for sensing an acceleration and a temperature are placed at a
location to be detected. Incidentally, in a case where the location
to be detected is the inner ring 203, a recess is formed in the
inner ring 203. The detecting part 210 is mounted in the recess,
and the control part 212 and the transmitting part 211 are
circumferentially mounted on the shield 207 which is fitted to and
supported on the inner ring 203.
[0156] A power source 213 is a small battery so configured as to be
adaptable for its installing place and, together with the control
part 212 and the transmitting part 211, is mounted on the shield
207. A protecting member 283 is provided on the shield 207, for
covering the control part 212, the transmitting part 211 and the
power source 213. The protecting member 283 is preferably made of a
material permitting radio wave to pass therethrough, such as a
plastic material. Where the protecting member 283, as shown in FIG.
26A, is protruded from the outer ring 202 and the inner ring 203, a
cover, preferably a ring-like protecting cover (referred to as a
protecting ring) is provided. Specifically, an outer-ring
protecting ring 284 is provided on the outer ring side, and an
inner-ring protecting ring 285 is provided on the inner ring side.
The outer-ring protecting ring 284 and the inner-ring protecting
ring 285 are each wider than the width of the protruded part of the
protecting member 283. Those are brought into engagement with the
outer ring 202 and the inner ring 203 with steps being formed
therebetween. Accordingly, the detecting part 210 located in the
recess 282 is covered with and protected by the outer-ring
protecting ring 284. If required, the outer ring 202 and the inner
ring 203 are previously selected in width so as to prevent the
outer-ring protecting ring 284 from protruding out of the end faces
of the outer ring 202 and the inner ring 203.
[0157] Thus constructed bearing device, the mounting of the bearing
device 281 may be carried out without machining the housing A and
the shaft S. Therefore, a conventional bearing may easily be
replaced with the bearing device 281. The bearing device of the
embodiment is excellent in durability since the sensor 209 and the
power source 213 are protected by the protecting member 283 and the
outer-ring protecting ring 284.
[0158] Further, as in the thirteenth embodiment, since the sensor
209 includes sensor-function checking device, the bearing device of
the embodiment is capable of periodically and easily checking as to
if the sensor 209 normally functions.
[0159] The inside of the protecting member 283 is preferably molded
of an insulating filling member, e.g., a synthetic resin, whereby
the control part 212, the transmitting part 211, the power source
213 and the like are stably fixed. In an environment where the
sensor 209 is constantly irradiated with external light, it is
preferable to use a material to allow light to transmit
therethrough for the protecting member and the filling material,
and a solar battery for the power source 213. By so doing, no care
must be taken of electric power consumption.
[0160] In a case where the object to be detected is a vibration,
temperature and the like of the inner ring 203, the shield 207 is
provided so as to be fitted to the inner ring 203 on which the
detecting part 210 is mounted. The control part 212 and the
transmitting part 211 of the sensor 209 and the power source 213
are mounted on the shield 207.
[0161] Next, a twentieth embodiment of the present invention will
be described with reference to FIGS. 27A and 27B. In the
embodiment, equivalent portions are designated by like reference
numerals used in the thirteenth to nineteenth embodiments.
[0162] A bearing device 291 shown in FIG. 27A is arranged such that
an outer ring 202 is fitted to the inner side of an intermediate
part of a housing A as a stational part, and an inner ring 203 is
fitted to the outer side of the intermediate part of a shaft S as a
rotating part. A ring for outer ring 292, which is fastened to the
outer ring 202 in a unitary form, is mounted on the end face of the
outer ring 202. A ring for inner ring 293, which is fastened to the
inner ring 203 in a unitary form, is mounted on the end face of the
inner ring 203. In the embodiment, the ring for inner ring 293 of
which the width is equal to that of the ring for outer ring 292, is
used. If required, this ring 93 for inner ring may be omitted.
[0163] The ring for outer ring 292 includes a flange 94 formed
integrally therewith, which extends toward the ring for inner ring
293 so as to cover the shield 207. The control part 212 and the
transmitting part 211 of the sensor 209 and the power source 213
for supplying electric power to the sensor 209, as shown in FIG.
27B, are disposed along the circumferential direction in which the
flange 294 expands, on a surface of the flange 294, which faces the
shield 207, i.e., an inner surface 294a. The detecting part 210 of
the sensor 209 is mounted in a recess 295, which is formed in a
part of the ring 292 for outer ring.
[0164] The ring 292 for outer ring is preferably made of a
material, which permits the radio wave R emitted from the
transmitting part 211 to pass therethrough, such as a plastic
material. An antenna for transmitting the radio wave R may be
mounted on the reverse side, i.e., an outer surface 294b, of the
flange, which is a counterpart of the side of the flange on which
the transmitting part 211 is mounted.
[0165] The mounting of the bearing device 291 thus constructed may
be carried out without machining the housing A and the shaft S.
Therefore, the bearing of an existing apparatus may easily be
replaced with the bearing device 291 to which the sensor 209 for
sensing the vibration and temperature is mounted. Since the sensor
209 is mounted on the side of the ring 292 for outer ring, which
faces the shield 207 and is protected against the outside, its
durability is good.
[0166] The control part 212 and the transmitting part 211 of the
sensor 209, and the power source 213 may be mounted on an arcuate
board, which is curved along the shape of the flange 294, viz., a
flexible printed circuit board, and then stuck to the flange 294.
The detecting part 210, together with the control part 212 and the
transmitting part 211, may be mounted on the flange 294.
[0167] In a case where a location to be detected is the inner ring
203, a flange is formed integral with the ring for inner ring 293,
while extending toward the ring for outer ring 292. The control
part 212 and the transmitting part 211, and the power source 213
are mounted on the flange. The detecting part 210 of the sensor 209
is mounted in the recess formed at a part of the ring for inner
ring 293.
[0168] Also in the twentieth embodiment, the sensor 209 includes
sensor-function checking device, as in the thirteenth embodiment.
Therefore, the bearing device of the embodiment is capable of
periodically and easily checking as to if the sensor 209 normally
functions.
[0169] In the thirteenth to twentieth embodiments, the single-row
deep groove ball bearing is used for a typical example of the
rolling bearing. It will readily be understood that also when the
invention is applied to other types of rolling bearings, such as a
thrust ball bearing and a cylindrical roller bearing, rolling
bearings each containing a sensor for sensing a vibration or a
temperature, may be realized.
[0170] A twenty-first embodiment of the present invention will be
described with reference to FIGS. 28A and 28B. In the embodiments,
equivalent portions are designated by like reference numerals used
in the thirteenth to twentieth embodiments.
[0171] A ring for outer ring 302 serving as a ring with sensor 301
shown in FIG. 28A is interference fitted to a housing A to which an
outer ring 202 of a bearing 300 is interference fitted, and the
ring with sensor 301 is movable together with the outer ring 202.
As in the twentieth embodiment, a ring for inner ring 303 is
provided in the end face of the inner ring 303. A flange 304
protruding toward the shaft S is formed on the inner periphery of a
ring with sensor 301. As shown in FIG. 28B, a control part 212 and
the transmitting part 211 of the sensor 209, and the power source
213 for supplying electric power to the sensor 209 are mounted on a
surface of the flange 304 which faces the shields 207 of the
bearing 300, i.e., an inner surface 304a, while being arranged in
the circumferential direction in which the flange 304 expands. A
detecting part 210 of a sensor 209, which includes an acceleration
sensor 216 for sensing a vibration and a temperature sensor 217 for
sensing a temperature, is mounted in a recess 305 formed at a part
of the outer ring 301.
[0172] An arcuate opening 306 is formed in the flange 304. The
opening 306 expands in the circumferential direction in which the
flange expands, and passes through the flange 304. An antenna 307
for emitting a radio wave signal R which is output from the
transmitting part 211, is mounted on the inner surface 304a, while
aligning with a position of the opening 306. Accordingly, in the
embodiment, the ring with sensor 301 may be made of a metallic
material. In a case where the opening 306 is not formed in the
flange 304, the ring with sensor 301 is preferably made of a
material permitting radio wave to pass therethrough, such as a
plastic material or the antenna 307 is mounted on an outer surface
304b of the flange 304.
[0173] The detecting part 210 may be mounted on the inner surface
304a of the flange 304. The sensor 209, the power source 213 and
the antenna 307 may be mounted on a flexible printed circuit board,
and then stuck to the inner surface 304a. The sensor 209, the power
source 213 and the antenna 307 may be molded of non-conductive
resin, whereby, the protection of the sensor 209 is secured.
[0174] With the ring with sensor 301 thus constructed, there is no
need of machining the housing A or the shaft S with the bearing 300
mounted thereon. Further, the existing bearings may be used as they
are, and the bearings used for the conventional apparatus may have
useful effects as those by the thirteenth to twentieth embodiments
described above. The sensor 209, the power source 213 and others
are mounted on the inner surface 304a of the flange 304, and those
are protected against the outside. In this respect, its durability
is excellent.
[0175] When a location to be detected is the inner ring 203, the
ring with sensor having the flange projected toward the housing A
is interference fitted to the shaft S to which the inner ring 203
is interference fitted, and the ring with sensor and the outer ring
202 are movable together with each other. The control part 212, the
transmitting part 121 and the power source 213 are mounted on the
flange of the ring with sensor, and the detecting part 210 of the
sensor 209 is mounted in the recess formed at a part of the ring
with sensor.
[0176] Also in the twenty-first embodiment, since the sensor 209
includes sensor-function checking device as in the thirteenth
embodiment, the bearing device of the embodiment is capable of
periodically and easily checking as to if the sensor 209 normally
functions.
[0177] In the twenty-first embodiment, the single-row deep groove
ball bearing is used for a typical example of the rolling bearing,
and the ring 301 having the sensors for sensing a vibration and
temperature is discussed. It will readily be understood that also
when the invention is applied to other types of rolling bearings,
such as a thrust ball bearing and a cylindrical roller bearing,
rolling bearings each containing a sensor for detecting a vibration
or a temperature, may be realized.
[0178] As seen from the foregoing description, the invention
succeeds in providing a rolling bearing device and a ring with
sensor for the rolling bearing device in which there is no need of
specially forming a large space for mounting the sensor in the
housing or the shaft, and the least working of the bearing is
required. When the sensor normally functions, a radio wave
indicating that the sensor is normal is transmitted at fixed time
intervals. Accordingly, one can readily know that the sensor
normally functions.
[0179] A bearing device with sensor 401 according to a
twenty-second embodiment will be described with reference to FIGS.
29 through 31. As shown in FIG. 29, the rolling bearing with sensor
401 includes a plurality of balls 402 as rolling elements, and a
pair of raceways, that is, an inner ring 403 being a first raceway
and an outer ring 404 being a second raceway, those raceways
rotating relative to each other via the balls 402 being interposed
therebetween. The balls 402 are arranged in the circumferential
direction Q at equal intervals within a retainer 405 (FIG. 30). A
recessed inner raceway 403b is formed at a central part of the
outer peripheral surface 403a of the inner ring 403. The balls 402
are in rolling contact with the inner raceway 403b. A recessed
outer raceway 404b is formed at a central part of the outer
peripheral surface 404a of the outer ring 404. The balls 402 are in
sliding contact with the outer raceway 404b. The outer ring 404 is
secured to the housing A, and the inner ring 403 supports the
rotating shaft S.
[0180] A first groove 406 is formed in one of the ends 403c of the
outer peripheral surface 403a of the inner ring 403 as viewed in
the width direction (in a direction P along the axial line of the
shaft S), while extending over the entire circumference thereof. A
first shield 407 is fitted to the first groove 406 thus formed. The
first shield 407 is annularly formed while expanding in the radial
direction and in the circumferential direction Q of the inner ring
403. Second shields 409 are respectively fitted into second grooves
408, which are formed in both ends 404c of an inner peripheral
surface 404a of the outer ring 404. The second shields 409 are
annularly formed in a state that it overlaps with the first shield
407 in the direction P along the axis of the shaft S, and expands
in the radial direction and in the circumferential direction Q of
the outer ring 404.
[0181] The annular magnet 410 is mounted on an outer peripheral
surface 407a (opposite to a surface facing the balls 402) of the
first shield 407, which is perpendicular to the axial line of the
shaft S. The magnet 410 extends along a direction of the outer
peripheral surface 407a. The magnet 410 is magnetized to have N
poles 410n and S poles 410s, which are alternately arranged in the
circumferential direction Q of the inner ring 403 at equal
intervals. The magnet 410 may be any one obtained by molding a
rubber magnet and a plastic magnet containing ferrite powder, a
rare earth magnet or a ferrite magnet, if it is a permanent magnet
magnetized to have N poles and S poles being arranged in the
circumferential direction Q. Further, in the first shield 407, when
a magnetic circuit is formed by using a magnetic material in
cooperation with the magnet 410 so as to intercept the magnetic
lines, its magnetic influence on the rolling bearing with sensor
401 is lessened.
[0182] The conductor 411 is mounted on the inside surface 409a of
the second shield 409, which is confronted with the magnet 410,
while being spaced from the latter by a fixed distance from the
magnet 410 in the axial direction P of the shaft S. The conductor
411 is extended annularly along the magnet 410 in the
circumferential direction Q, while being meandered to form
rectangular parts radially arranged at intervals each equal to the
pole-to-pole distance of the magnet 410.
[0183] A recess 412 is formed in a part of the outer peripheral
edge 404c of the outer ring 404, which corresponds to the second
shield 409 to which the conductor 411 is mounted. A sensor 413 is
mounted on a flat surface 412a of the recess 412, which is
perpendicular to the axial line of the shaft S. The sensor 413 may
be mounted on a flexible printed circuit board, and arranged along
the cylindrical surface 412b of the recess 412. The recess 412 may
be molded of resin and the like.
[0184] The sensor 413, as shown in FIG. 31, includes a detecting
part 414 for detecting vibration or temperature, a transmitting
part 415 for transmitting a radio wave signal R, and a control part
416 for controlling the transmitting part 415 in accordance with
the output signal of the detecting part 414. The control part 416
is connected to both ends 411a of the conductor 411, and a storage
battery 417 which, together with the sensor 413, is placed in the
recess 412, and includes a power source circuit (not shown).
[0185] A specific example of the detecting part for detecting
vibration is a vibration sensor having an acceleration sensor,
which is constructed by a piezoelectric element or strain gauge. A
specific example of the detecting part for detecting temperature is
a temperature sensor containing a thermistor, a temperature sensing
resister, a thermocouple or the like, or an IC temperature sensor,
which, together with the circuit, is fabricated into an integrated
circuit.
[0186] An operation of the rolling bearing with sensor 401 thus
constructed will be described. The outer ring 404 is fixed to the
housing A and the inner ring 403 is rotated together with the shaft
S. That is, when the inner ring 403 and the outer ring 404 rotate
relative to each other, the magnet 410, together with the inner
ring 403, rotates with respective to the conductor 411, as shown in
FIG. 32. The conductor 411 is meandered at intervals each equal to
the pitch of the magnetic poles of the magnet 410. The conductor
may be considered as a semicircular coil in which the winding
directions of the rectangularly bent parts 411a of the conductor
are alternately inverted. Accordingly, when the magnet 410 rotates,
a magnetic field H formed around the magnet 410 moves together with
the magnet 410. As a result, a direction of the magnetic field H
crossing the meandering faces of the conductor 411 alternately
changes with respective to the conductor 411.
[0187] Accordingly, an electromotive force is generated so that
current flows in such a direction as to cancel the magnetic field
H, which passes through a space within each the rectangularly bent
part 411a, viz., in a direction W at a moment shown in FIG. 32. The
magnetic field H alternately varies with respective to the
conductor 411. Accordingly, an electromotive force generated in the
conductor 411 also alternately varies. And hence, an AC
electromotive force appears at both ends 411a of the conductor 411.
In this respect, the magnet 410 and the conductor 411 cooperate to
form an electric generator 418; viz., when the magnet and the
conductor 411 rotate relative to each other, an electromotive force
is generated.
[0188] Then, since the magnet 410 and the conductor 411 are
respectively provided in an annular shaped and rotate relative to
each other, the electromotive force generated at both ends of the
conductor has little variation even when the dimensional uniformity
is lost to some extent as to the circularity of each of the magnet
and the conductor, distance between them, pole-to-pole distance,
meandering interval, and the like. Accordingly, a stable electric
power is generated.
[0189] Since conductor 411 is meandered in the radial direction,
when it rotates relative to the magnet 410, an electromotive force
is generated. When the conductor is meandered at intervals each
equal to the pole-to-pole distance in the present invention
embodiment, the electromotive force generated in the conductor 411
is uniform in phase, so that a more stable outputting of it is
secured. Further, the conductor 411 is meandered while
rectangularly bent in the embodiment, it crosses the magnetic field
H developed by the magnet 410 over a broader area. As a result, a
larger electromotive force is produced.
[0190] The conductor 411 may be formed on a printed circuit board
or a flexible printed circuit board by etching. In this case, it
may be formed in the form of a multiple of layers. If either of
coils formed as below is used, an electromotive force generated is
large: a coil in which a conducting wire is plurally wound along
the outer surface of the second shield in such a manner that it is
meandered, while rectangularly bent, at intervals each equal to the
pole-to-pole distance of the magnet; and a coil in which solenoids
are arranged in the circumferential direction Q and along the outer
surface of the magnet 410, each solenoid being such that the
winding direction of the conducting wire is inverted at intervals
each equal to the pole-to-pole distance of the magnet 410. If a
ferromagnetic member, e.g., iron core, is located within each
rectangularly bent part of the conductor or at the center of the
solenoid, the generated electromotive force is further
increased.
[0191] There is a chance that eddy current is generated in the
second shield 409 on which the conductor 411 is mounted since a
magnetic field whose direction is inverted every pole of the magnet
410 successively passes through the second shield annularly shaped
when the magnet 410 rotates relative to the second shield. To avoid
this, it is preferable to make the second shield of a non-magnetic
material, e.g., plastic or resin.
[0192] When the magnet 410 rotates relative to the conductor 411, a
frequency of the AC electromotive force appearing at both ends 411a
of the conductor 411 is proportional to the rotational speed of the
bearing. This implies that the rotational speed of the bearing can
be detected in a manner that a frequency of the electromotive force
is detected by the control part 416, and the rotational speed of
the bearing is obtained based on an output variation of the
frequency.
[0193] In this case, since the magnet 410 and the conductor 411 are
annular in shape and rotate relative to each other, the
electromotive force appearing at both ends 411a of the conductor
411 has little variation even when the dimensional uniformity is
lost to some extent as to the circularity of each of the magnet and
the conductor, distance between them, pole-to-pole distance,
meandering interval, and the like. Accordingly, the accuracy of
detecting the rotational speed of the bearing, which is measured
based on the electromotive force, has little variation.
[0194] The AC electromotive force generated is rectified by a
rectifying circuit contained in the control part 416, and the
resultant is utilized for the electric power for the sensor 13.
Information of vibration or temperature, detected by the detecting
part 414 of the sensor 413, together with frequency information of
the electromotive force generated in the conductor 411, is
signal-processed by the control part 416, and subjected to
comparison judging process, and the resultant is sent from the
transmitting part 415 in the form of radio wave R. Accordingly,
information about a operating state of the rolling bearing with
sensor 401 may be obtained when the radio wave R is received by a
receiver, which is separately provided at a location remote from
the rolling bearing with sensor 401. Further, it is noted that the
detecting information is output in a wireless manner. Because of
this feature, there is eliminated troublesome work of connecting
and disconnecting the wires every time the shaft S to which the
rolling bearing with sensor 401 is mounted and its vicinal
structure are disassembled or assembling.
[0195] The storage battery 417, which, together with the sensor
413, is placed in the recess 412, is charged by an electric power
generated through the rotation of the magnet 410 relative to the
conductor 411, under control of a power source circuit of the
control part 416. When the rotational speed of the rolling bearing
with sensor 401 decreases, and an electric power generated through
the rotation of the magnet 10 relative to the conductor 411 is
insufficient for the power consumption by the sensor 413, the
storage battery 417 discharges electric power to make up for the
deficiency of the electric power. Thus, even when the electric
power generated through the rotation of the magnet 410 relative to
the conductor 411 is insufficient, the rolling bearing with sensor
401 is able to carry out the detecting operation reliably and
accurately.
[0196] A third shield (not shown) made of a magnetic material may
be located as a back yoke at a position opposite to the first
shield 407 with respective to the second shields 409. Then, since
the influence of the external magnetic field on it is lessened even
when the rotational speed is slow and the electromotive force is
small, the rotational speed can be detected more accurately. In
this case, it is preferable that the third shield is rotated with
the inner ring on which the magnet 410 is supported, to avoid such
an unwanted situation that eddy current is generated in the third
shield and the shield is heated.
[0197] A bearing device with sensor 421 according to a twenty-third
embodiment will be described with reference to FIGS. 33 and 34. In
those figures, equivalent portions are designated by like reference
numerals used in the twenty-second embodiment.
[0198] A magnet 422 of the bearing device with sensor 421 shown in
FIG. 33 is annularly shaped while extending in a circumferential
direction Q of the bearing device with sensor 421. Its outer
peripheral surface 422a is supported on the first shield 407. As
shown in FIG. 34, a conductor 423 extends in a circumferential
direction Q of the bearing device with sensor 421, while being
rectangularly meandered along a cylindrical surface developed about
the rotational axis of the inner ring 403 and at intervals each
equal to the pole-to-pole distance of the magnet 410. Specifically,
the conductor 423 annularly extends while being spaced from the
inner peripheral surface 422b of the magnet 422 by a fixed gap. In
the twenty-third embodiment, the conductor 423 is located on the
inner side of the magnet 422 as radially viewed. If required, the
conductor 423 may be located on the outer side thereof.
[0199] In the bearing device with sensor 421 of the single-row deep
groove ball bearing type as shown in FIG. 33, the magnet 422 and
the conductor 423 may be assembled at a good concentricity.
Accordingly, if the magnet 422 and the conductor 423 are radially
disposed in a state that the cylindrical surfaces of those members
are confronted with each other, a variation of an electric power
generated through the rotation of the magnet 422 relative to the
conductor 423 is reduced.
[0200] In the bearing device with sensor of the thrust ball bearing
type, it is preferable to dispose the magnet 410 and the conductor
411 along the rotating shaft as in the twenty-second embodiment. If
so disposed, a variation of the electric power output is
reduced.
[0201] In the twenty-second and twenty-third embodiments, the first
shield 407 on which the magnet 410 (422) of the rolling bearing
with sensor 401 (421) is mounted, together with the shaft S, is
fitted to the rotating inner ring 403, and the second shields 409
on which the conductor 411 (423) is mounted is fitted to the outer
ring 409 fixed to the housing A. However, in case that the sensor
413 which needs the electric power is mounted on the inner ring
403, the magnet 410 (422) is provided fixed to the outer ring 404
and the conductor 411 (423) is provided so as to rotate with the
inner ring 403.
[0202] As described above, in the rolling bearing with sensor 401,
the conductor 411 (423) is fixed to the raceway on which the sensor
413 is mounted, and the magnet 410 (422) is disposed so as to
rotate relative to the conductor 411 (423). With such a mechanical
arrangement, an electromotive force appears between the both ends
411a of the conductor 411, and is supplied to the sensor 413, and
the detecting information by the sensor 413 is sent by a radio wave
R. In the rolling bearing with sensor, the wiring from the rolling
bearing with sensor 401 to exterior is not used, viz., a power
cable E for operating the sensor, a communication cable for
transmitting the information detected by the sensor, and the like
are not used. Therefore, there is eliminated troublesome work of
connecting and disconnecting the wires in the
assembling/disassembling of the rolling bearing with sensor 401 and
its vicinal structure. Accordingly, the cost of the
assembling/disassembling work of the structure in the vicinity of
the rolling bearing with sensor 401 and replacing the wires is
reduced.
[0203] When the rolling bearing with sensor 401 (421) of the
twenty-second (twenty-third) embodiment is applied to a spindle,
e.g., main shaft, of a machine tool, a spindle unit with rotating
speed sensor is provided which does not require the reconnection of
the power source every time the tool is replaced with another.
[0204] Further, in the rolling bearing with sensor 401 (421) of the
twenty-second (twenty-third) embodiment, the sensor 413 is not
protruded out of a region defined by the both end faces, and the
outer and inner peripheries of the rolling bearing with sensor 401
(412). Therefore, the bearing device may easily be replaced with
the existing bearing if any machining work is not done for its
mounting.
[0205] A frequency of AC electromotive force generated by the
rolling bearing with sensor 401 (421) in the twenty-second
(twenty-third) embodiment is proportional to a rotational speed of
the shaft to which the rolling bearing with sensor 401 (421) is
mounted, and an amplitude of the AC electromotive force is also
proportional to the rotational speed of the shaft. Accordingly, if
the rolling bearing with sensor 401 (421) is incorporated into an
electric generator to be controlled in rotational speed, there is
no need of using a frequency generator (FG) or a tachogenerator,
which is provided separately from the electric generator for the
purpose of detecting the rotational speed. This results in cost and
size reduction of the electric generator.
[0206] In the rolling bearing with sensor 401 (421), the magnet 410
and the conductor 411 are disposed over the entire circumference.
Accordingly, an AC electromotive force generated for each phase is
averaged. Accordingly, even if error factors of the AC
electromotive force exist, an frequency error of the AC
electromotive force with respective to the rotational speed of the
bearing is very small. Those error factors are magnetizing pitch
(interval at which it is magnetized to N and S poles) of the magnet
410, magnetizing intensity, irregularity of magnetizing pitch
(interval at which the conductor is meandered) of the magnet 410,
misalignment of the magnet 410 with the conductor 411, and
others.
[0207] An electric generator, which is small in rotational speed
irregularity, and low in cost and size, may be realized if the
rolling bearing with sensor 401 (421) is provided on the rotating
shaft of an electric generator or the like, a frequency of an AC
electromotive force generated by the rolling bearing with sensor
401 (421) and a reference frequency produced by a quartz vibrator
are input to a PLL (phase locked loop) circuit, and a rotational
speed of the electric generator is controlled in accordance with a
phase difference.
[0208] Where the dust- and water-proof seals are used for the
rolling bearing with sensor, the first and second shields or first
to third shields as electric generators may be disposed outside the
seals. In a case where a position near zero rotation of the shaft
to which the rolling bearing with sensor is attached is detected,
it is preferable to use an active type rotational speed sensor,
such as a Hall element (IC) or an MR element, additionally. Also
when the rotational speed is not measured, the electric generator
that is constructed with the annular magnet and conductor is stable
in the frequency and amplitude of an AC electromotive force
generated. Accordingly, it may be used as a stable source capable
of supplying quality electric power.
[0209] The mounting position of the power source 413 in each
embodiment is not limited to the recess 412 formed at a part of the
outer ring 404. If required, a recess is formed at a part of the
inner ring 403. Further, it may be attached to the end face of the
inner or outer ring.
[0210] It should be understood that the present invention is not
limited to the above-mentioned embodiments, but may variously be
modified, altered and changed within the scope of the
invention.
[0211] As seen from the foregoing description, the invention
succeeds in providing a rolling bearing with sensor having an
electric generator and a sensor. The electric generator includes a
bearing having a pair of raceway rings being rotatable relative to
each other with the aid of rolling elements being interposed
therebetween, an annular magnet supported on the first raceway ring
of the bearing, N and S poles being alternately disposed in the
circumferential direction of the bearing, and an annular conductor
supported on the second raceway of the bearing, the annular
conductor rotating relative to the magnet, thereby generating an
electromotive force. The sensor detects a rotational speed of the
first raceway ring relative to the second raceway ring on the basis
of electric power output from the electric generator. In the thus
constructed rolling bearing with sensor, the magnet and the
conductor cooperate to provide a function of the electric
generator, and also a function of a sensor for detecting a
rotational speed of the bearing. Accordingly, the rolling bearing
does not need the supply of electric power from an external power
source in order to operate the sensor, and is capable of detecting
a rotational speed of the bearing.
[0212] In the electric generator, the magnet is magnetized so as to
have the N and S poles being arranged alternately and in the
circumferential direction, is annular in shape and preferably
arranged at equal intervals. The conductor, annularly shaped,
extends, while being meandered, in a direction in which the
conductor crosses the magnetic lines developed from the magnet,
specifically, in the radial direction of the bearing or in the
axial direction of said bearing and along said magnet and a
cylindrical surface developed about the rotational axis of the
bearing. The magnet and the conductor are annularly shaped.
Accordingly, when the magnet and the conductor rotate relative to
each other, an electromotive force is always generated irrespective
of their rotational positions. The electromotive force appearing at
both ends of the conductor a little varies even when the
dimensional uniformity is lost of the circularity deviation and
concentricity of each of the magnet and the conductor, distance
between them, pole-to-pole distance, meandering interval, and the
like. Thus, the outputting of the electromotive force generated
through the relative rotation of the magnet to the conductor is
stabilized, and a rotational speed measured based on the
electromotive force may be detected at high accuracy.
* * * * *