Photography – Camera detail – Shutter
Reexamination Certificate
2002-01-16
2004-03-16
Fuller, Rodney (Department: 2851)
Photography
Camera detail
Shutter
C396S508000
Reexamination Certificate
active
06705776
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an electromagnetic actuator that generates a driving force by an electromagnetic force. More specifically, the present invention relates to an electromagnetic actuator that generates a rotational driving force by rotating by a predetermined angle range and that is employed for driving a camera shutter or the like, and the present invention relates to a camera shutter unit using this electromagnetic actuator.
BACKGROUND ART
A conventional electromagnetic actuator is made up of, for example, a rotor magnetized with different polarities (the N pole and the S pole), a pair of arcuate magnetic pole parts disposed in such a way as to surround a part of the outer circumferential surface of the rotor, a yoke (magnetic-path forming member) that magnetically connects the magnetic pole parts to each other and forms a magnetic path (magnetic circuit), a magnetizing coil wrapped around a part of the yoke, etc.
However, since this structure has a disadvantage in the fact that a magnetic attraction force by which the rotor is maintained at an initial position (resting position) is weak in a current-stopped state in which an electric current is not passed through the coil, a technique is employed in which, for example, the relationship between the pair of magnetic pole parts and the magnetization angle of the rotor is changed, or a magnetic gap between the outer circumferential surface of the rotor and the magnetic pole parts is narrowed, in order to strengthen the magnetic attraction force and raise the maintaining force. Without being limited to the situation of the initial position (resting position), this technique is likewise applied to a situation in which the rotor is maintained at the maximum rotational position where the rotor has rotated angularly to the maximum.
In order to raise the maintaining force according to techniques like the aforementioned one, there arises a need to set an actuating voltage (lowest actuating voltage) required to actuate the rotor at a high level in any technique, thus bringing about an increase in power consumption. On the other hand, in order to set the lowest actuating voltage at a low level, there is a technique of, for example, extending an area where the outer circumferential surface of the rotor faces the magnetic pole part. However, if this technique is employed, a magnetic attraction force (rotational urging force) that prompts rotation will be oppositely lowered, thereby bringing about a decrease in the maintaining force serving to urge it in a predetermined rotational direction and maintain it.
As a conventional electromagnetic actuator, one of U.S. Pat. No. 5,689,746 is known. In this electromagnetic actuator, yokes, which form magnetic pole parts and are opposite to each other with a rotor therebetween, branch into two parts to each be linear, and one of them holds a coil. However, if these yokes are disposed around the opening of a camera and are used as driving sources of a shutter unit, a space cannot be efficiently exploited, thus leading to the enlargement of the unit.
The present invention has been made in consideration of the problems of the conventional techniques, and an object of the present invention is to provide an electromagnetic actuator capable of giving a desired rotational urging force to a rotor and maintaining the rotor at a predetermined position, and capable of heightening a driving force when rotated, while aiming for structural simplification or size reduction without raising an actuating voltage, i.e., under the state of controlling power consumption. Another object is to provide a camera shutter unit that employs this electromagnetic actuator.
DISCLOSURE OF INVENTION
An electromagnetic actuator according to a first aspect of the present invention includes a magnetizing coil; a rotor that is magnetized with different polarities and rotates by a predetermined angle range between an initial position taken when an electric current is stopped and a maximum rotational position where the rotor rotates angularly to the maximum when an electric current is applied, thereby outputting a driving force; and a first magnetic pole part and a second magnetic pole part that are disposed so as to face an outer circumferential surface of the rotor and that generate mutually different magnetic poles through a magnetic path when an electric current is passed through the coil; in which the rotor has a projection that is magnetized with one of the different polarities and that projects outward in its radial direction, and, in the vicinity of the first magnetic pole part, an auxiliary magnetic pole piece is provided that is disposed so as to be close to or be in contact with the projection when the rotor is located at the initial position and that generates the same magnetic pole as the first magnetic pole part when a current is applied.
According to this structure, when the rotor is located at the initial position in the current-stopped state, a strong magnetic attraction force acts between the projection of the rotor and the auxiliary magnetic pole piece, and the rotor is infallibly maintained at the initial position. On the other hand, in the current-running state, the same magnetic pole as the magnetic pole with which the rotor projection is magnetized occurs in the auxiliary magnetic pole piece, and a strong repulsion force occurs, thereby rotating the rotor swiftly in a predetermined direction.
An electromagnetic actuator according to a second aspect of the present invention includes a magnetizing coil; a rotor that is magnetized with different polarities and rotates by a predetermined angle range between an initial position taken when an electric current is stopped and a maximum rotational position where the rotor rotates angularly to the maximum when an electric current is applied, thereby outputting a driving force; and a first magnetic pole part and a second magnetic pole part that are disposed so as to face an outer circumferential surface of the rotor and that generate mutually different magnetic poles through a magnetic path when an electric current is passed through the coil; in which the rotor has a projection that is magnetized with one of the different polarities and that projects outward in its radial direction, and, in the vicinity of the first magnetic pole part, a first auxiliary magnetic pole piece is provided that is disposed so as to be close to or be in contact with the projection when the rotor is located at the initial position and that generates the same magnetic pole as the first magnetic pole part when a current is applied, and, in the vicinity of the second magnetic pole part, a second auxiliary magnetic pole piece is provided that is disposed so as to be close to or be in contact with the projection when the rotor is located at the maximum rotational position and that generates the same magnetic pole as the second magnetic pole part when a current is applied.
According to this structure, in addition to the same action as the aforementioned one, when the rotor is located at the maximum rotational position, a strong magnetic attraction force acts between the projection and the second auxiliary magnetic pole piece, and the rotor is infallibly maintained at the maximum rotational position. On the other hand, when a current is applied in an opposite direction in this state, the same magnetic pole as the magnetic pole with which the rotor projection is magnetized occurs in the second auxiliary magnetic pole piece, and a strong repulsion force occurs, thereby rotating the rotor swiftly in the opposite direction and returning it to the initial position.
In the aforementioned structure, the auxiliary magnetic pole piece may be formed by bending a planar magnetic member so as to be close to or be in contact with the projection.
According to this structure, the auxiliary magnetic pole piece can be formed to have a wide area while aiming for structural simplification and weight reduction, and a magnetic attraction force or repulsion force acting between the projection and
Dalakis Michael
Fuller Rodney
Nidec Copal Corporation
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