Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2000-01-26
2001-02-20
Nguyen, Tran N (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S254100
Reexamination Certificate
active
06191509
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.
A typical two-phase permanent magnet type stepping motor which has been conventionally known in the art is constructed in such a manner as shown in
FIGS. 8 and 9
. In
FIG. 8
, 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 juxtaposed 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 by a distance one quarter (¼) as large as predetermined pitches P between the magnetic poles of the permanent magnet element
7
in the circumferential direction. 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 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. 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 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 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. The exciting winding
35
is likewise wound on a bobbin
37
.
In the conventional permanent magnet type stepping motor thus constructed, the pitch P between each adjacent two of the pole teeth
15
, a pitch P between each adjacent two of the pole teeth
29
, a pitch P between each adjacent two of the pole teeth
33
and the above-described pitch P between each adjacent two of the pole teeth of the permanent magnet element
7
are typically set to be identical with each other.
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 and Japanese Patent Application Laid-Open Publication No. 127024/1998. 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 or decrease or remove a specific harmonic component contained in a waveform of induced electromotive force, resulting in eliminating the above-described 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.
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.
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 of the revolving shaft. 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 n pole teeth of the first yoke of each of the claw pole type yoke units are so arranged that pitches between the n pole teeth of the first yoke adjacent to each other are not set to be constant at 360°
but set at two or more different pitches which are larger than 270°
and smaller than 450°
. It is of course that a total sum of the n pitches between the n pole teeth adjacent to each other is 360°. A basic concept of the present invention is to separate from or abandon a conventional idea that pitches between pole teeth of a yoke of a claw pole type yoke unit is maintained constant. Thus, the present invention is so constructed that pitches between the pole teeth of the first yoke of at least one claw pole type yoke unit are rendered different from each other within the above-described angular conditions. The construction of the prior art that pitches between pole teeth of each of yokes of the claw pole type yoke units are rendered constant causes phases of partial static torques partially occurring between the pitches to be coincident with each other. The prior art attempts to permit a synthesized static torque which is obtained due to synthesis of the partial static torques to approach a sinusoidal wave by varying a configuration of the pole teeth or the like to vary characteristics of the partial static torques. On the contrary, in the present invention, the pitches between the pole teeth of at least the first yoke are rendered nonconstant or varied to shift a phase of each of the partial static torques, to thereby permit characteristics of the synthesized static torque to approach a sinusoidal wave. When it is possible to approac
Koike Akira
Yura Tsunao
Nguyen Tran N
Pearne & Gordon LLP
Sanyo Denki Co. Ltd.
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