Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
1999-12-16
2001-06-19
Enad, Elvin (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S051000, C310S216006, C310S256000
Reexamination Certificate
active
06249066
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a stepping motor, and, more particularly, to a hybrid-type stepping motor used in, for example, an inkjet printer or a scanner.
2. Description of the Related Art
An example of a known conventional hybrid-type stepping motor is illustrated in FIG.
7
.
The stepping motor
1
includes a three-phase six-pole stator
6
; a pair of brackets
7
a
and
7
b
, one externally fitted to each end portion of the stator
6
in an axial direction thereof; and a rotor
9
inserted in the inner peripheral side of the stator
6
and rotatably supported by the pair of brackets
7
a
and
7
b
through bearings
8
a
and
8
b.
The rotor
9
comprises a rotary shaft
10
; a disc-shaped permanent magnet
11
secured to the rotary shaft
10
; and gear-like rotor cores
12
a
and
12
b
, each of which is secured to a corresponding end of the permanent magnet
11
in an axial direction thereof.
The rotor core
12
a
is separated from the rotor core
12
b
by half a pitch in a peripheral direction thereof, and is positioned so that a toothed pole (not shown) of the rotor core
12
b
is disposed between adjacent toothed poles (not shown) of the rotor core
12
a
. In
FIG. 7
, reference numeral
15
denotes a bolt for securing the pair of brackets
7
a
and
7
b
to the stator
6
.
It is well known that hybrid-type stepping motors have a high noise level and vibrate considerably. In reality, however, a technology which allows effective reduction of such noise and vibration has not yet been proposed.
The present inventors have analyzed the causes of noise and vibration in hybrid-type stepping motors. It was found that for a standard hybrid-type stepping motor with an air gap of 50 &mgr;m, when the generated tangent force that turns into torque was
1
, the radial attraction/repulsion force (the vibration force) between the stator
6
and the rotor
9
was over
10
, while the axial force (the magnetic repulsion force between the stator steel plates) was about 0.1. By suppressing vibration of the stator in a radial direction thereof caused by the radial vibration force, noise and vibration can be effectively reduced.
OBJECTS OF THE INVENTION
Therefore, it is an object of the present invention to overcome the aforementioned problems.
The present invention has been achieved based on this knowledge and has as its object the provision of a stepping motor which makes it possible to reliably and effectively reduce noise and vibration by suppressing vibration of a stator in a radial direction thereof caused by a radial vibration force between a stator and a rotor.
SUMMUARY OF THE INVENTION
To achieve this object according to one aspect of the present invention, the stepping motor comprises a stator including a stator core and a winding, the stator core having a plurality of magnetic poles formed on an inner peripheral portion thereof, at a predetermined interval in a peripheral direction thereof, each magnetic pole including a support and a small-toothed portion, and the winding being placed upon the magnetic poles; a rotor which is inserted in the inner peripheral side of the stator and which is rotatably supported through a pair of bearings; and a pair of brackets, one fitted to each end portion of the stator in an axial direction thereof. The stepping motor further comprises: a pair of internally fitted members, one disposed at each end portion of the stator in the axial direction thereof, each internally fitted member having a first fitted portion internally fitted to an inner peripheral surface of the corresponding end portion of the stator.
The stator is sandwiched in a radial direction thereof by the first fitted portions of the internally fitted members and second fitted portions of the brackets, each second fitted portion being externally fitted to an outer peripheral surface of the corresponding end portion of the stator in the axial direction thereof. The internally fitted members and the brackets are separately formed in order not to limit the freedom with which the brackets are positioned with respect to the internally fitted members in a radial direction thereof.
According to this means, vibration of the stator in a radial direction thereof caused by a vibration force in the radial direction which is about 100 times larger than the axial force can be suppressed from both the inside diameter side and the outside diameter side of the stator, so that noise and vibration can be effectively reduced.
The positioning of the brackets with respect to the outside diameter of the stator, and the positioning of the internally fitted members with respect to the inside diameter of the stator can be performed separately. Therefore, the stator can be sandwiched between the internally fitted members and between the brackets, respectively, with high precision, and thus be reliably sandwiched in the radial direction of the stator from both the inner peripheral surface and the outer peripheral surface thereof.
According to another aspect of the present invention, friction reducing means is provided for reducing friction between the surfaces of the brackets and the surfaces of the internally fitted members that they contact each other in an axial direction thereof According to this means, when the brackets are being mounted, they can be slid with respect to the internally fitted members. Therefore, it is possible to prevent the internally fitted members from limiting the freedom with which the brackets are positioned; to facilitate assembly of the brackets; and to separately sandwich and position the stator from the inner side and outer side thereof.
According to a further aspect of the present invention, a vibration absorbing member is interposed between the surfaces of the brackets and the surfaces of the internally fitted members that contact each other in the axial direction thereof. According to this means, vibration at the side of the internally fitted members and vibration at the side of the brackets do not interfere with each other, so that noise/vibration can be effectively reduced.
According to an additional aspect of the present invention, the pair of brackets are secured to the stator with a bolt, on a line extending from the support of the corresponding magnetic pole of the stator. According to this means, vibration transmitted from the supports in a radial direction thereof can be suppressed at a location where the bolts are secured, so that noise/vibration can be reduced more effectively.
According to yet another aspect of the present invention, the bearing is mounted to the internally fitted members. According to this means, compared to the case where a bearing is supported by brackets, the inside diameter of the stator and the rotary shaft of the rotor can be brought closer to a position where axes coincide, so that a uniform air gap can be formed between the rotor and the stator.
According to yet further aspect of the present invention, a rib for reinforcing the second fitted portions is provided on the pair of brackets. According to this means, the rigidity of the second fitted portions of the brackets is increased, so that the stator can be sandwiched more reliably between the second fitted portions and the first fitted portions of the internally fitted members in a radial direction thereof.
Other objects and attainments together with a fuller understanding of the invention will become apparent and appreciated by referring to the following description and claims taken in conjunction with the accompanying drawings.
REFERENCES:
patent: 5386161 (1995-01-01), Sakamoto
patent: 5945759 (1999-08-01), Tanaka et al.
patent: 6057613 (2000-05-01), Trago
patent: 3041034 (1997-06-01), None
patent: 3054582 (1998-09-01), None
Ikegami Akihiko
Koike Yoshikazu
Enad Elvin
Jones Judson H.
Seiko Epson Corporation
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