Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
1999-04-13
2001-01-09
Ramirez, Nestor (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S049540, C310S06700R, C310S153000, C310S091000, C310S262000, C310S265000
Reexamination Certificate
active
06172439
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of Invention
The present invention relates to a motor, and more particularly to a high-speed rotating motor for uses as a rotating apparatus for a rotative polygonal mirror or the like.
2. Related Art
The motor for use as an apparatus for rotating a rotative polygonal mirror has a rotor case on which the rotative polygonal mirror is mounted, a frame for rotatively supporting the rotor case, a rotor magnet fixed to the rotor case through a yoke and an armature fixed to a frame such that the armature is positioned opposite to the rotor magnet.
The rotor case has a cylindrical portion which creates a space in which the armature is disposed. The cylindrical yoke is fixed to the inner surface of the cylindrical portion, while the cylindrical rotor magnet is fixed to the inner surface of the yoke. When the yoke and the rotor magnet are fixed to each other, the conventional method is performed such that the overall outer surface of the yoke is bonded to the inner surface of the cylindrical portion. Moreover, the overall outer surface of the rotor magnet is bonded to the inner surface of the yoke.
The rotor case is usually made of aluminum alloy having excellent machinability. On the other hand, in general, the yoke is manufactured by pressing a thin rolled plate and the rotor magnet is manufactured by sintering.
The motor structured as described above has the rotor case made of aluminum alloy and the yoke made of steel. Therefore, the rotor case has a thermal expansion coefficient larger than that of the yoke. It leads to a fact that the cylindrical portion of the rotor case greatly expands in radial direction as compared with the yoke when the ambient temperature has been raised. Since the conventional motor has the structure that the overall outer surface of the cylindrical yoke is bonded to the inner surface of the cylindrical portion, smooth expansion of the cylindrical portion of the rotor case is, however, prevented by the yoke. As a result, distortion of the cylindrical portion occurs. Thus, there arises a problem in that imbalance of the rotor case occurs.
The rotor magnet has a thermal expansion coefficient which is considerably smaller than that of the yoke. Therefore, when the yoke is expanded by heat, the rotor magnet cannot follow the expansion of the yoke. However, the conventional motor has the structure that the overall outer surface of the cylindrical rotor magnet is bonded to the inner surface of the cylindrical yoke. Therefore, when the yoke has been expanded, great force is exerted on the rotor magnet. Thus, there arises a problem in that brittle fracture of the rotor magnet occurs. When the cylindrical portion of the rotor case and the yoke have been deformed outwards in the radial direction during high speed rotation of the rotor case, the rotor magnet cannot be deformed by centrifugal force exerted on the rotor magnet. The reason for this is that the rotor magnet is a brittle member molded by sintering or the like. Since the conventional motor has the structure that the overall-outer surface of the cylindrical rotor magnet is bonded to the inner surface of the cylindrical yoke, the rotor magnet is pulled outwards in the radial direction through the yoke. Thus, there is a probability that brittle fracture occurs.
SUMMARY OF INVENTION
Accordingly, an object of the present invention is to provide a structure of a motor which is manufactured by bonding members made of materials having different physical properties to one another and with which excess stress is not exerted on a specific member in a case of thermal expansion or during high speed rotation.
An aspect of the present invention, there is provided a motor comprising:
a rotor case having a cylindrical portion;
a cylindrical yoke fixed to an inner surface of said cylindrical portion said yoke made of a magnetic material;
a cylindrical rotor magnet fixed to an inner surface of said yoke;
a frame for rotatively supporting said rotor case;
an armature fixed to said frame, said armature being opposite to said rotor magnet;
a yoke separating slit for permitting enlargement of a diameter of said yoke when said yoke separating slit expands in a circumferential direction of said yoke;
a plurality of yoke bonding portions where an-outer surface of said yoke is bonded to the inner surface of said cylindrical portion, said yoke bonding portions being apart from one another in the circumferential direction; and
the inner surface of said cylindrical portion and the outer surface of said yoke being permitted to separate from and contact to one another between adjoining yoke bonding portions.
As described above, the motor according to the present invention has the yoke which is provided with yoke separating slit for separating the yoke in the circumferential direction. Therefore, if force for enlarging the diameter of the yoke is exerted, the yoke separating slit is widened. Thus, the diameter of the yoke can be enlarged. Therefore, if the ambient temperature is raised, the cylindrical portion of the rotor case is expanded greatly as compared with the yoke because the thermal expansion coefficient of the rotor case is larger than that of the yoke. In the foregoing case, the yoke separating slit is widened such the yoke separating slit is pulled by the cylindrical portion of the rotor case. Therefore, the yoke is deformed to follow the deformation of the cylindrical portion of the rotor case. Thus, excess force is not exerted on the cylindrical portion of the rotor case. As a result, distortion of the rotor case can be prevented. Thus, imbalance of the rotor case can be prevented.
REFERENCES:
patent: 3500090 (1970-03-01), Baermann
patent: 3828212 (1974-08-01), Harkness et al.
patent: 4012651 (1977-03-01), Burson
patent: 4423345 (1983-12-01), Nilsson
patent: 4996613 (1991-02-01), Hishida
patent: 5331238 (1994-07-01), Johnsen
patent: 5396134 (1995-03-01), Mochizuki
patent: 5402023 (1995-03-01), Nakanishi et al.
patent: 60-139140 (1985-07-01), None
Kabushiki Kaisha Sankyo Seiko Seisakusho
Perez Guillermo
Ramirez Nestor
Sughrue Mion Zinn Macpeak & Seas, PLLC
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