Electricity: measuring and testing – Electrical speed measuring – Including speed-related frequency generator
Reexamination Certificate
2001-07-25
2004-05-25
Snow, Walter E. (Department: 2862)
Electricity: measuring and testing
Electrical speed measuring
Including speed-related frequency generator
C324S207120, C384S448000
Reexamination Certificate
active
06741073
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a bearing provided with a rotation sensor, and more specifically, it relates to the structure of a bearing employed for a general-purpose motor requiring a rotation detecting function.
The present invention also relates to a bearing provided with a rotation sensor, and more specifically, it relates to a method of extracting a signal from a bearing provided with a rotation sensor.
The present invention further relates to a bearing provided with a rotation sensor, and more specifically, it relates to a bearing provided with a rotation sensor having a function of detecting the number of rotations or a rotational direction.
The present invention further relates to a bearing provided with a rotation sensor and a motor employing the same, and more specifically, it relates to a bearing provided with a rotation sensor supporting a shaft requiring a rotation detecting function. More particularly, the present invention relates to a bearing provided with a rotation sensor used in the vicinity of a general-purpose motor or the like generating a large magnetic field.
2. Description of the Prior Art
First Prior Art
The structure of a bearing
500
provided with a rotation sensor according to first prior art is described with reference to FIG.
26
.
FIG. 26
is a sectional view showing the structure of the bearing
500
provided with a rotation sensor. This bearing
500
provided with a rotation sensor, forming an antifriction bearing, comprises an outer ring
1
, an inner ring
3
and rolling elements
2
. A shielding member is provided between the outer ring
1
and the inner ring
3
.
When the inner ring
3
is employed as a rotating bearing ring, a pulser ring
4
is fixed to the inner ring
3
with a mandrel
5
. When the outer ring
1
is employed as a fixed bearing ring, a magnetic sensor
8
is fixed to the outer ring
1
with a sensor case
7
and a sensor case fixing ring
6
. The bearing
500
provided with a rotation sensor having the aforementioned structure, which is compact and strong with no requirement for assembly control, is applied to a support bearing for the rotary shaft of a motor.
Problem of First Prior Art
FIG. 27
shows the bearing
500
provided with a rotation sensor having the aforementioned structure in a state assembled into a motor.
FIG. 27
is a sectional view showing the structure of the motor into which the bearing
500
provided with a rotation sensor is assembled. A motor rotor
11
assembled into a rotary shaft
12
is supported in a housing
13
by a front bearing
14
and a rear bearing
15
, and a motor stator
10
is also fixed to the housing
13
. In the motor shown in
FIG. 27
, the rear bearing
15
stores a rotation sensor.
When a large current is fed to the motor stator
10
, the flow of a magnetic flux cannot be ignored. A magnetic loop is generated to pass through the motor rotor
11
, the rotary shaft
12
, the inner ring
3
, the outer ring
1
and the housing
13
and return to the motor stator
10
as shown by arrows in FIG.
27
. At this time, a nonmagnetic part occupies most part of the space between the inner ring
3
and the outer ring
1
, except the rolling elements
2
. The magnetic rolling elements
2
are in point contact with the inner ring
3
and the outer ring
1
, and arranged only on about six portions of a circumference. Therefore, a path through the inner ring
3
, the rolling elements
2
and the outer ring
1
has high magnetic resistance.
Consequently, the bearing
15
exhibits high magnetic resistance, readily leading to leakage of a magnetic flux. The leaking magnetic flux flows to the sensor case fixing ring
6
and the mandrel
5
, which are magnetic members, to disadvantageously exert bad influence on the magnetic sensor
8
and disturb a sensor signal.
Second Prior Art
Another type of bearing provided with a rotation sensor has a rotating element provided with a sensor target such as a magnetic pattern and a fixed element provided with a sensor element for detecting relative rotational movement of the sensor target with respect to the sensor element and outputting an electric signal.
FIGS. 28 and 29
show the sectional structures of bearings
600
a
and
600
b
provided with rotation sensors according to second prior art. Each of the bearings
600
a
and
600
b
provided with rotation sensors has an inner ring
601
, an outer ring
603
and rolling elements
602
provided in an annular space defined between the inner ring
601
and the outer ring
603
. When the inner ring
601
is employed as a rotating element, an encoder ring
604
serving as a sensor target is fixed to the inner ring
601
. When the outer ring
603
is employed as a non-rotating element, a rotation detecting sensor
605
detecting rotation of the encoder ring
604
is fixed to the outer ring
603
.
Problem of Second Prior Art
In order to extract an output signal from the rotation detecting sensor
605
, a cable must be extracted from a circuit board into which the rotation detecting sensor
605
is assembled. When the outer diameter of the bearing
600
a
or
600
b
is larger than 30 mm, a cable
610
can be extracted from an axial end surface of the bearing
600
a
provided with a rotation sensor as shown in
FIG. 28
or from the outer peripheral surface of the bearing
600
b
provided with a rotation sensor as shown in FIG.
29
.
If the outer diameter of the bearing
600
a
or
600
b
is smaller than 30 mm, however, no space for extracting the cable
610
is defined but it is difficult to extract a signal from the rotation detecting sensor
605
.
Third Prior Art
FIG. 30
is a sectional view showing a bearing provided with a rotation sensor according to third prior art. Referring to
FIG. 30
, this bearing provided with a rotation sensor is an antifriction bearing formed by an outer ring
701
, an inner ring
703
and rolling elements
702
, and a pulser ring
704
is fixed to the rotating element (the inner ring
703
, for example) while a magnetic sensor
705
is fixed to the non-rotating element (the outer ring
701
, for example) through a sensor case
706
. A magnetic encoder is formed on the surface of the pulser ring
704
. Such a bearing provided with a rotation sensor, which is miniature and strong with no requirement for assembly control, is utilized for supporting a motor or the like.
Alternatively, the outer ring
701
and the inner ring
703
may be employed as a rotating element and a non-rotating element respectively.
The sensor of such a bearing provided with a rotation sensor generates an analog output shown in
FIG. 31A
or a rectangular wave output shown in FIG.
31
B. An analog output type sensor must have repetitive reproducibility of a sinusoidal waveform, and hence uniformity of magnetization intensity is important for the magnetic encoder. A rectangular wave output type sensor utilizes an output signal in a saturated waveform, and hence large magnetization intensity is more strongly required as compared with uniformity of the magnetization intensity. When the magnetization intensity is large, magnetic field strength steeply changes to advantageously improve pitch accuracy or increase a sensor gap.
Problem of Third Prior Art
In general, anisotropic magnetic powder is employed for the magnetic encoder regardless of the output signal. When anisotropic magnetic powder is employed for an analog output type encoder, however, the amplitude of a sinusoidal wave output is disadvantageously largely dispersed.
Fourth Prior Art
FIG. 32
is a longitudinal sectional view of a bearing provided with a rotation sensor according to fourth prior art. Referring to
FIG. 32
, the bearing provided with a rotation sensor is an antifriction bearing formed by an outer ring
801
, an inner ring
803
and rolling elements
802
, and a pulser ring
804
is fixed to a rotating side (the side of the inner ring
803
, for example) through a mandrel
805
while a magnetic sensor
808
is fixed to a non-rotating side (the side of the outer ring
801
, for example
Iwamoto Ken-ichi
Koike Takashi
Nagano Yoshitaka
McDermott & Will & Emery
NTN Corporation
Snow Walter E.
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