Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
1999-09-28
2001-03-27
Mullins, Burton (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S261100, C310S268000
Reexamination Certificate
active
06208055
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an improved electromagnetic transducer which includes a rotor and a coil, and which reciprocally transduces kinetic energy generated due to rotation of the rotor to electrical energy generated in the coil. More particularly, the present invention provides an electromagnetic transducer with improved energy conversion efficiency and to electronic devices which employ the improved transducer.
2. Description of the Related Art
Heretofore, an electromagnetic transducer has been utilized which transduces changes in magnetic flux due to rotation of a rotor into electrical energy, or conversely transduces electrical energy into rotary power. Examples of such an electromagnetic transducer employed in a multipolar power generator are described in, e.g., Japanese Unexamined Patent Publication Nos. 8-75874 and 9-211152, and in a paper in Proceedings of The Swiss Society of Chronometry reported by Asulab S. A. on Oct. 2, 1997.
Each of these multipolar power generators comprises a plurality of magnets rotatably supported about a predetermined axis and arranged on a plane perpendicular to the predetermined axis with N and S poles arrayed alternately in the direction of rotation, a rotor having a back yoke made of soft iron supporting the plurality of magnets, and a coil made up of windings and arranged near the rotor. With this type of multipolar power generator, when the rotor is rotated with a mechanical energy source, such as a barrel main spring, the magnetic flux near the coil is changed with the rotation of the rotor, and an induced current flows through the coil windings by electromagnetic induction.
The above-described multipolar power generator is suitable as a power supply source for, e.g., a speed-governing control circuit of an electronically controlled watch or the like because inductive electromotive forces can be generated with stability by such an arrangement where the plurality of magnets are arranged with N and S poles arrayed alternately in the direction of rotation. Also, compared with a conventional power generator which comprises a rotor, a metal-made core arranged near the rotor, and a stator including a coil wound over another portion of the core, a power generator producing no iron loss and having higher efficiency of power generation can be realized by not employing a metal core. Alternatively, by not arranging a metal-made core near the rotor, a power generator having a small cogging torque and very excellent startability can be achieved.
However, the following problems are experienced in the electromagnetic transducer described above.
(1) Because the rotor includes the back yoke made of soft iron and the plurality of magnets arranged on the back yoke as described above, the rotor has increased weight. Accordingly, a rotor shaft supporting those components is required to have a diameter of sufficient size and durability to accommodate the increased weight. An increase in diameter of the rotor shaft increases the contact area between the shaft, a main plate and a bearing support seat which hold the rotor shaft. Correspondingly, the rotation of the rotor is restricted and the power generation efficiency of the multipolar power generator is reduced.
(2) To rotate the more weighty rotor with stability, a bearing portion formed in the main plate, etc. must be an anti-vibration bearing, which has been used in conventional mechanical watches, for the purpose of improving anti-vibration ability and anti-impact ability. This results in increased thickness of the multipolar power generator.
The above problems are also similarly encountered when an electromagnetic transducer is employed as a motor using electrical energy as a power source.
SUMMARY OF THE INVENTION
Objects of the Invention
Therefore, it is an object of the present invention to overcome the aforementioned problems.
Another object of the present invention is to provide an electromagnetic transducer with improved conversion efficiency by reducing the weight of the rotor and thinning the rotor shaft, thereby resulting in reduction of both size and weight.
To achieve the above objects, the present invention provides an electromagnetic transducer comprising a rotor and a coil which reciprocally transduces kinetic energy generated by rotation of the rotor to electrical energy generated in the coil. The rotor comprises a rotor shaft serving as the center of rotation, and a back yoke including a magnetic body with N and S poles arrayed in the direction of rotation of the rotor, with the magnetic body being held in close contact with the back yoke. The back yoke is formed with reduced volume regions, each of which is aligned with one of the poles based on distribution of magnetic force lines generated inside the back yoke. The back yoke can be reduced to such an extent that the magnetic flux is not saturated at a close contact portion between the back yoke and the magnetic body. More concretely, the volume and weight of the back yoke can be reduced by forming cutouts in the circumferential edge of the back yoke, or by forming recesses in the back yoke, or by forming holes in a portion of the back yoke inward of the magnetic body.
Here, the term “electromagnetic transducer” includes a power generator for converting mechanical energy in a rotating rotor, supplied from a driving mechanism such as a main spring, to electrical energy in a coil, and a motor for applying electrical energy, supplied from an electrical source, to a coil to rotate a rotor and generate mechanical energy.
Also, the magnetic body is only required to satisfy such an arrangement that N and S poles are arrayed in the direction of rotation of the rotor. For example, the magnetic body can be constructed by magnetizing a surface of an annular magnetic body into a plurality of poles, or by incorporating a plurality of magnets with N and S poles arrayed alternately on the back yoke.
With the above features of the present invention, the back yoke is reduced to such an extent that the magnetic flux inside the back yoke is not saturated, thereby its weight and hence the overall weight of the rotor. Correspondingly, the rotor shaft can be thinned, and the efficiency of power generation and the driving efficiency of the motor can be improved. In addition, a reduction in the weight of the rotor contributes to simplifying and downsizing the structure of an antivibration bearing, thus resulting in a further reduction of both size and weight of the electromagnetic transducer.
When the magnetic body is constructed by magnetizing a surface of an annular magnetic body into a plurality of poles, a multipolar rotor can be formed just by magnetizing one magnetic body, and the rotor as one component of the electromagnetic transducer can be manufactured with ease.
When the magnetic body is constructed by a plurality of magnets with N and S poles arrayed alternately on the back yoke, the magnets are only required to be in the least necessary portions; that is, the magnets need only occupy a small portion
35
of the total area in which the magnets may be placed and still be operative. Therefore, the weight of the rotor can be further reduced.
The following arrangements may be used to realize the above feature where the volume and weight of the back yoke is reduced based on magnetic force lines.
(1) The reduction can be accomplished by forming cutouts in the back yoke extending from an outer periphery of the back yoke toward the center of the rotation and aligned with the centers of the poles of the magnetic body in one-to-one relation.
(2) The reduction can also be accomplished by forming recesses in one surface of the back yoke in one-to-one relation to the centers of the poles of the magnetic body with the other surface being held in contact with the magnetic body.
(3) When the magnetic body is constructed by a plurality of magnets with N and S poles arrayed alternately on the back yoke, the volume and weight of the back yoke can be reduced by forming cutouts in an outer peripheral edge
Gabrik Michael T.
Mullins Burton
Seiko Epson Corporation
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