Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2000-08-30
2002-11-26
Waks, Joseph (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S156450, C310S257000
Reexamination Certificate
active
06486576
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a permanent magnet type stepping motor, and more particularly to a permanent magnet type stepping motor adapted to exhibit increased rotational angle accuracy and static angle accuracy and minimize a reduction in static torque.
A typical two-phase permanent magnet type stepping motor which has been conventionally known in the art is generally constructed in such a manner as shown in
FIGS. 4 and 5
, wherein
FIG. 4
is a development view of the stepping motor and
FIG. 5
shows relationship between pole teeth of a stator and magnetic poles of a rotor.
In
FIG. 4
, reference numeral
1
designates a rotor including a cylindrical permanent magnet element
7
securely mounted on a cylindrical bushing
5
fixed on a revolving shaft
3
. The revolving shaft
3
is supported by two bearings (not shown). The permanent magnet element
7
is constructed into a cylindrical configuration so as to permit n (n: a positive integer of
4
or more) N magnetic poles and n S magnetic poles to alternately appear at equal pitches thereon in a circumferential direction of the revolving shaft
3
. The conventional stepping motor also includes a stator
9
arranged on an outer periphery of the rotor
1
while being mounted in a housing (not shown). The stator
9
includes a first claw pole type yoke unit
11
and a second claw pole type yoke unit
25
. The first and second claw pole type yoke units
11
and
25
are arranged in juxtaposition to each other in an axial direction of the revolving shaft
3
. The first and second claw pole type yoke units
11
and
25
are shifted from each other in the circumferential direction by a distance one quarter (¼) as large as predetermined pitches P between the magnetic poles of the permanent magnet element
7
. The first claw pole type yoke unit
11
includes a first yoke
13
and a second yoke
17
respectively including n pole teeth .
15
and
19
arranged opposite to the permanent magnet element
7
at a predetermined interval in a radial direction of the revolving shaft
3
and positioned at predetermined pitches P in the circumferential direction. The first claw pole type yoke unit
11
also includes an exciting winding
21
constructed so as to permit the n pole teeth
15
of the first yoke
13
and the n pole teeth
19
of the second yoke
17
to be excited at polarities different from each other, respectively. The exciting winding
21
is wound on a bobbin
23
.
The second claw pole yoke unit
25
likewise includes a first yoke
27
and a second yoke
31
respectively including n pole teeth
29
and
33
arranged opposite to the permanent magnet element
7
at a predetermined interval in the radial direction of the revolving shaft
3
and positioned at predetermined pitches P in the circumferential direction. The second claw pole type yoke unit
25
also includes an exciting winding
35
constructed so as to permit the n pole teeth
29
of the first yoke
27
and the n pole teeth
33
of the second yoke
31
to be excited at polarities different from each other, respectively. The exciting winding
35
is likewise wound on a bobbin
37
.
In the conventional permanent magnet type stepping motor thus constructed, as shown in
FIG. 5
, the pitch P between each adjacent two of the pole teeth
15
, that between each adjacent two of the pole teeth
19
, that between each adjacent two of the pole teeth
29
, that between each adjacent two of the pole teeth
33
, and that between two magnetic poles of the permanent magnet element
7
are typically set to be identical with each other or to have the same angle.
Unfortunately, the conventional permanent magnet type stepping motor thus constructed is deteriorated in rotational angle accuracy and static angle accuracy as compared with a hybrid type stepping motor. In order to eliminate such a problem, a variety of techniques were proposed as disclosed in, for example, Japanese Patent Application Laid-Open Publication No. 245929/1995, Japanese Patent Application Laid-Open Publication No. 245930/1995, Japanese Patent Application laid-Open Publication No. 127024/1998, Japanese Patent Application Laid-Open Publication No. 248232/1998 and the like. The techniques proposed are generally constructed so as to vary a configuration of pole teeth or shift one of two yokes from the other yoke at a predetermined pitch in a circumferential direction of a revolving shaft, to thereby reduce a detent torque, resulting in eliminating the above-described problem. Alternatively, in the proposed techniques, it is employed that a correction pole magnet of a phase opposite to a high frequency contained in electromotive force induced due to relative movement between a rotor and a stator is arranged on a magnetic pole of the rotor to suppress a high-frequency component, to thereby eliminate the problem. In the prior art, pitches between pole teeth of each of yokes of claw pole type yoke units are rendered constant.
As described above, those skilled in the art attempted to solve the above-described problem while rendering the pitches between the pole teeth of each of the yokes of the claw pole type yoke units constant. However, this fails to increase rotational angle accuracy and static angle accuracy. Also, the conventional rotor having the correction magnetic poles provided thereon causes a problem of substantially reducing a composite or synthesized static torque.
SUMMARY OF THE INVENTION
The present invention has been made in view of the foregoing disadvantage of the prior art.
Accordingly, it is an object of the present invention to provide a permanent magnet type stepping motor which is capable of exhibiting both increased rotational angle accuracy and static angle accuracy and minimizing a reduction in static torque.
In accordance with the present invention, a permanent magnet type stepping motor is provided. The permanent magnet type stepping motor includes a rotor having a permanent magnet element fixed on a revolving shaft and a stator including two or more claw pole type yoke units juxtaposed to each other in an axial direction thereof. The permanent magnet element is constructed into a cylindrical configuration so as to permit n (n: a positive integer of 4 or more) N magnetic poles and n S magnetic poles to alternately appear at equal pitches thereon in a circumferential direction of the revolving shaft. The claw pole type yoke units each include first and second yokes and an exciting winding. The first and second yokes each include n pole teeth arranged opposite to the permanent magnet element at a predetermined interval in a radial direction of the revolving shaft and positioned at predetermined pitches in the circumferential direction. The exciting winding is constructed so as to permit the n pole teeth of the first yoke and the n pole teeth of the second yoke to be excited at polarities different from each other. The first and second yokes are combined with each other so that the n pole teeth of the first yoke and the n pole teeth of the second yoke are engaged with each other while being kept from being contacted with each other or are alternated with each other while being kept uncontacted with each other.
In the present invention, the respective adjacent two pole teeth of the claw pole yoke unit are arranged at constant pitches. Supposing that a magnetic pole center-magnetic pole center length between each adjacent two magnetic poles of the n N magnetic poles or n S magnetic poles of the rotor is defined to be one pitch (“pitch between centers of homopolar magnetic poles”, “magnetic pole center-magnetic pole center pitch between homopolar magnetic poles” or “homopolar magnetic pole center-magnetic pole center pitch”) or a sum of magnetic pole widths of the N and S magnetic poles adjacent to each other is defined to be one pitch (“heteropolar magnetic pole width pitch”), the pitches are not defined to be constant at 360°
but defined to be two or more pitches different from each other which are within a range of between more than 270°
and less than 450°
. It
Koike Akira
Yura Tsunao
Rankin, Hill Porter & Clark LLP
Sanyo Denki Co. Ltd.
Waks Joseph
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