Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
1999-07-27
2001-03-13
Waks, J (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C029S596000
Reexamination Certificate
active
06201324
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a stator structure of a claw pole stepping motor and, more particularly, to an improvement in performance, and reduction in diameter and production cost attained by improvement in construction of the stator.
2. Description of the Prior Arts
Recently, remarkable progress has been made for various devices in performance and particularly in miniaturization. Accordingly, various devices have adopted a plurality of specific motors as required for their functions. Stepping motors are best suited in particular for requirement of positioning control. However, they have not been adopted due to limitations on the miniaturization of motors.
FIG. 1A
is a partly sectional perspective view showing a stator structure of a conventional claw-pole stepping motor, and
FIG. 1B
is an enlarged perspective view showing pole teeth of the stator structure.
Referring to
FIG. 1A
, a motor is mounted on an upper flange
1
and an outer yoke
2
has, at the inner circumference thereof, pole teeth
4
that are made of a soft magnetic steel plate processed by sheet metal working. An inner yoke
3
also has, at the inner circumference thereof, pole teeth
4
that are made of a soft magnetic steel plate processed by sheet metal working. The yokes
2
and
3
are arranged such that a coil
6
with magnetic wires wound around a bobbin
5
is arranged therebetween and that the pole teeth
4
provided at the inner circumference of the yokes
2
and
3
face are combined with each other to constitute a pancake
15
. Two pancakes
15
each with the yokes
2
and
3
and the coil
6
thus arranged are positioned back to back to constitute a stator. The outer yoke
2
of the lower pancake
15
as shown is provided with a lower flange
7
with a bearing
8
arranged at the center thereof. A sleeve
10
connects a rotor magnet
9
to a shaft
11
that provides the rotation center of the rotor.
FIG.2
is a cross-sectional view showing the pancake of the claw pole stepping motor shown is FIG.
1
A.
Particularly referring to the structure of the pole teeth
4
in the pancake
15
shown in
FIG.2
, it will be understood that the pole teeth
4
are subject to stress caused by a sheet metal working process, and are thin in thickness, because the pole teeth
4
are formed by such process at the inner circumference of the yokes
2
and
3
, respectively. Accordingly, the pole teeth
4
are liable to develop warping or bending as well.
As mentioned in the foregoing, a claw pole stepping motor has yokes
2
,
3
, and the pole teeth
4
manufactured in unitary structure. The smaller the diameter of the motor, the thinner the thickness of the material plate needed to secure a space for the coils and workability, and the shorter the height of the pole teeth as well. This might cause manufacturing difficulty and degradation of motor characteristics as well, thereby resulting in limiting the reduction in the diameter up to an outer diameter of 8 mm. This has resulted in provision of an encoder as a position detector in a DC motor for positioning control which results in an extremely expensive structure. However, considering the current environment regarding stepping motors, high-performance magnets such as the rare earth magnet have been developed for use in rotor magnets facing stators. This has laid the cornerstone for possibly improving the characteristics of the motor only if the stators can be worked properly and thus raised requirements for an appropriate method for manufacturing the stator.
SUMMARY OF THE INVENTION
The present invention has been made in view of the foregoing problems and its object is to provide a stator structure that enables the claw pole motor to be reduced in diameter and provide highly enhanced performance.
In order to achieve the foregoing object, a claw pole stepping motor comprising a stator that constitutes a magnetic circuit in yokes made of a soft magnetic steel plate by sheet metal working and a rotor disposed inside the stator for rotation, is characterized in that pole teeth made of soft magnetic material which face rotor magnets are provided as separate parts independent of the yokes.
Furthermore, the stator structure of the present invention is characterized by holding the pole teeth at the inner circumference of a bobbin made of polymeric material.
Furthermore, the stator structure of the present invention is characterized by having a relationship of T1≧T2 between the thickness T1 of a pole tooth and the plate thickness T2 of a yoke.
Furthermore, the stator structure of the present invention is characterized by having the relationship of L≧D/2 between the length L of a pole tooth in the axial direction and the diameter D of the rotor.
Furthermore, the bobbin according to the stator structure of the present invention is characterized by having guide slots for positioning and holding a plurality of pole teeth arranged at the inner circumference of the bobbin, and guide portions for positioning and holding yokes and pole teeth on the end faces.
Furthermore, the stator structure of the present invention is characterized by providing stoppers for guide slots such that the length of a guide slot is shorter than that of a pole tooth in order to allow stable contact between the pole teeth and the yokes and also to obtain a good magnetic performance.
Furthermore, the stator structure of the present invention is characterized in that the guide portion serves as a holding portion for the pole teeth as well.
Furthermore, the stator structure of the present invention is characterized by forming the pole teeth in unitary structure with a bobbin by the insert molding.
Furthermore, the stator structure of the present invention is characterized in that the pole teeth is pressed into the yokes.
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Fujitani Sakae
Kagawa Masaki
Suzuki Yuzuru
Fay Sharpe Fagan Minnich & McKee LLP
Minebea Co. Ltd.
Waks J
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