Electricity: measuring and testing – Magnetic – Displacement
Reexamination Certificate
2000-11-02
2002-07-02
Lefkowitz, Edward (Department: 2862)
Electricity: measuring and testing
Magnetic
Displacement
C324S207250
Reexamination Certificate
active
06414482
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a rotational angle sensor to be used for detecting a rotational angle of an object, and more particularly to a non-contact type rotational angle sensor for detecting a rotational angle of an object in non-contact therewith by converting the rotational angle to a change in magnetic force, and a sensor core used in the non-contact type rotational angle sensor.
2. Description of Related Art
Conventionally, there have been known contact type rotational angle sensors using a potentiometer. This potentiometer is constructed such that a wiper slides on a resistance element, thereby changing electrical resistance values. Accordingly, dust particles resulting from friction between the resistance element and the wiper may be generated in a sliding portion therebetween. The dust particles would cause detection errors in the resistance values. Furthermore, a frictional resistance in the sliding portion may become an operating resistance to an object to be detected, which affects the operating responsivity of the object.
As a rotational angle sensor to resolve the above disadvantages of the contact type rotational angle sensor, a non-contact type with no sliding member or portion has been developed. One of such the non-contact type rotational angle sensors is constructed to detect a rotational angle of an object in non-contact therewith by converting the rotational angle to a change in magnetic force. Japanese patent No. 2,842,482 and Japanese patent unexamined publication No. 8-35809 disclose an example of the non-contact type rotational angle sensor of this kind.
FIG. 25
shows main parts of the rotational angle sensor disclosed in Japanese patent No. 2,842,482. This rotational angle sensor is provided with a cylindrical case
51
and a connecting shaft
52
disposed rotatably in the center of the case
51
. A first member
53
is fixed on the inner peripheral surface of the case
51
. The first member
53
is constituted of two semicircular rings
53
A and
53
B, both made of a soft magnetic material. Between the semicircular rings
53
A and
53
B there are provided two sub-air-gaps
54
. An electric coil
56
is arranged in one gap
54
, and a Hall probe is arranged in the other gap
54
. A second member
57
made of a soft magnetic material is fixed on the connecting shaft
52
. A tubular magnet
58
constructed of two thin members
58
A and
58
B is fit on the outer periphery of the second member
57
. The tubular magnet
58
is made of mold samarium-cobalt formed and magnetized in a tubular shape. A main-air-gap
59
is disposed between the tubular magnet
58
and the first member
53
. The main-air-gap
59
is desired to be as narrow as possible. In the above publication, if the average inner diameter of the second member
57
is 5 mm and the thickness of the tubular magnet
58
is 1 mm, then the width of the main-air-gap
59
is of the order of 0.2 mm. Thus, a magnetic field is generated between the first member
53
and the tubular magnet
58
and the second member
57
. When the second member
57
and the tubular magnet
58
are rotated together with the connecting shaft
52
, the magnetic field is rotated, thereby changing the density of magnetic flux passing through the Hall probe
56
and the electric coil
55
. The change in the magnetic flux density is output in the form of electric signals.
FIG. 26
shows main parts of the rotational angle sensor disclosed in Japanese patent unexamined publication No.8-35809. This rotational angle sensor is provided with a tubular yoke
61
and a driven shaft
62
disposed in the center of the yoke
61
, both being integrally configured. A tubular permanent magnet
63
is fixedly provided on the inner peripheral surface of the tubular yoke
61
made of a soft magnetic material. The tubular magnet
63
has been magnetized in a radial direction in cross-section. Around the driven shaft
62
, two separated tubular stators
64
A and
64
B are fixedly disposed. The driven shaft
62
is allowed to rotate in a central area surrounded by the stators
64
A and
64
B. A Hall element
66
is provided in a gap
65
between the two stators
64
A and
64
B. The tubular yoke
61
and the tubular magnet
63
are arranged rotatably with respect to the stators
64
A and
64
B. An annular air-gap
67
is produced between the tubular magnet
63
and the stators
64
A and
64
B. Thus, a magnetic field is generated between the tubular yoke
61
, the tubular magnet
63
, and the stators
64
A and
64
B. Accordingly, rotation of the tubular magnet
63
together with the tubular yoke
61
causes rotation of the magnetic field, thereby changing the density of magnetic flux passing through the Hall element
66
. The change in the magnetic field density is output in the form of electrical signals.
In the rotational angle sensor of Japanese patent No. 2,842,482, however, the tubular magnet
58
is made of mold samarium-cobalt formed and magnetized in a tubular shape with a very small thickness of about 1 mm, which would be very physically brittle and hard to manufacture. In addition, the tubular magnet
58
after fit on the outer periphery of the second member
57
has to be assembled with the shaft
52
while keeping the extreme narrow main-air-gap
59
with respect to the first member
53
. Therefore, in assembling, even a slight inclination of the tubular magnet
58
or the first member
53
may bring them into contact, which would easily damage the tubular magnet
58
. This results in difficulty in manufacturing the rotational angle sensor and deterioration in the accuracy of detection of a rotational angle.
In the rotational angle sensor of Japanese patent unexamined publication No. 8-35809, on the other hand, there is a problem that it is difficult to manufacture the tubular magnet
63
. In addition, the tubular magnet
63
has to be fixed on the inner peripheral surface of the tubular yoke
61
and, inside of the magnet
63
, the stators
64
A and
64
B are needed assembling with the air-gap
67
of a predetermined dimension. During assembly, contact between the tubular magnet
63
and the stators
64
A and
64
B would cause damage to them. This makes it difficult to manufacture the rotational angle sensor and also causes deterioration in the accuracy of detection of a rotational angle.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above circumstances and has an object to overcome the above problems and to provide a non-contact type rotational angle sensor capable of providing enhanced productivity of magnets, sensor cores with the magnets, and rotational angle sensors, and improved assembling property of parts and elements to enhance the accuracy of detection of a rotational angle, and a sensor core used in the sensor.
Additional objects and advantages of the invention will be set forth in part in the description which follows and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the purpose of the invention, there is provided a sensor core used in a non-contact type rotational angle sensor for detecting a rotational angle of an object in non-contact therewith by converting the rotational angle to a change in magnetic force, the sensor core including: a stator core provided with two blocks made of a magnetic material; a mover core provided with two blocks made of a magnetic material, disposed coaxially with the stator core; a first gap produced between the stator core and the mover core; a second gap produced between the two stator blocks; a third gap produced between the two mover blocks; and a rectangular parallelepiped magnet disposed in the third gap and magnetized in a direction across the third gap to connect the mover blocks.
In the above sensor core, preferably, a shape of one of the stator core and the mover cor
Aisan Kogyo Kabushiki Kaisha
Kinder Darrell
Lefkowitz Edward
Oliff & Berridg,e PLC
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