Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
1995-09-21
2002-05-28
Budd, Mark O. (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S043000
Reexamination Certificate
active
06396189
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a stator assembly of a rotary electric device and a method of assembling the same and, more particularly, it relates to a stator assembly of a stepping motor and a method of assembling the same.
2. Description of the Prior Art
A stepping motor has a wide variety of applications including OA device and computer peripheral devices and, in most cases, it is an indispensable component of such devices.
While stepping motors are classified into PM, VR and HB types depending on the structure of the rotor, they commonly comprise a rotor that revolves inside and which is borne by a stator assembly having a number of stationary magnetic poles.
FIG. 8
of the accompanying drawings is an exploded perspective view of a known stepping motor. Referring to
FIG. 8
, it comprises a bottomed cylindrical stator assembly
51
having an inner structure as will be described in detail hereinafter. The stator assembly
51
carries a terminal section
53
on the outer periphery. A number of wires (not shown) are soldered to the terminal section
53
to connect the motor to external circuits. The stator assembly has yokes
55
made from magnetic metal plates as outer peripheral members thereof, upper and lower exposed magnetic poles
57
and
59
arranged respectively on the upper and lower halves of the inner periphery thereof and a number of alignment projections
61
arranged on the top of the assembly for centering.
The stepping motor also comprises a rotor
63
designed to revolve inside the stator assembly
51
and carrying on the outer periphery thereof N and S magnetic poles and a top plate rigidly secured to the top of the stator assembly
51
. A bearing
69
for carrying the rotary shaft
67
of the rotor
63
is rigidly fitted to the center of the top plate
65
. Alignment through bores
71
are arranged on an imaginary circle around the bearing
69
at positions corresponding to respective alignment projections. Each of the alignment through bores
71
is provided with a projection
73
for welding a resistor there standing downward toward the stator assembly
51
at a position away from the bearing
69
along the periphery thereof.
FIG. 9
is a sectional side view of the stepping motor of
FIG. 8
having the above described components The stator assembly of the stepping motor additionally comprises an upper stator coil
75
and a lower stator coil
77
. For assembling the stator assembly
51
, a subassembly consisting of a pair of cup-shaped yokes
55
carrying a number of stationary magnetic poles and an upper stator coil
75
arranged inside the yokes and another subassembly consisting of a pair of cup-shaped yokes
55
carrying a number of stationary magnetic poles and a lower stator coil
77
arranged inside the yokes are laid one on the other in an injection molding type metal mold and then synthetic resin is injected into the inside so that the stator assembly
51
is assembled and produced as a unitary entity. A number of alignment projections
61
are formed with synthetic resin at the same time. Note that reference numeral
79
in
FIG. 9
denotes synthetic residual resin remaining in the injection port of the metal mold and reference numeral
81
denotes a bearing held in position by a block of synthetic resin
83
injected into the stator assembly. As seen from
FIGS. 8 and 9
, the stator assembly
51
is realized by bonding an upper stator subassembly A and a lower stator subassembly B, which will be described in detail hereinafter.
FIG. 10
is an exploded perspective view of the above described stator assembly
51
. The illustrated components are identically formed and laid one of the other to produce vertically arranged mirror images before they are bonded together to make a unitary entity. As seen from
FIG. 10
, the lower stator subassembly B comprises a lower cup
60
provided with a plurality of lower stationary magnetic poles
59
a
standing upward from the bottom thereof and a lower stator coil
77
arranged in the inside thereof. A yoke plate
55
a
provided with a plurality of suspended lower stationary magnetic poles
59
b
and projections
59
c
is secured to the top of the lower cup
60
from above with the projections
59
c
fitted into corresponding recesses. Under this condition, a terminal section
53
of the lower coil
77
comes engaged with a deepest central section
60
c
of a notch
60
a
of the lower cup
60
. Note that the yoke plate
55
a
is provided with an alignment bore
55
b
and an alignment projection
55
c
. The upper stator subassembly A is assembly in much the same way as the lower stator subassembly B.
FIG. 11
is a plan view of the lower stator subassembly B.
For aligning a yoke plate
55
a
with a lower cup
60
of a rotary electric device having a configuration as described above and fitting the former into the latter, the alignment projection
59
c
of the yoke plate
55
a
is fitted into the notch
60
a
of the lower cup
60
and projections
59
d
of the yoke plate
55
a
are engaged with the deepest central section
60
c
of the lower cup
60
. Then, for placing the upper stator subassembly A on the lower stator subassembly B in position, the alignment projection
55
c
arranged on the yoke plate of the upper stator subassembly A if fitted into the alignment bore
55
b
formed in the yoke plate of the lower stator subassembly B and the alignment bore
55
b
formed in the yoke plate of the upper stator subassembly A is engaged with the alignment projection
55
c
on the yoke plate of the lower stator subassembly B.
With the above arrangement, the alignment projection
59
c
of the yoke plate
55
a
of the lower cup
60
and the matching notch
60
a
of the lower cup
60
have respective tolerances, while the alignment projection
59
d
of the yoke plate
55
a
and the matching deepest section
60
c
of the lower cup
60
have respective tolerances. On the other hand, the alignment projection
55
c
of the yoke plate of the upper stator subassembly A and the matching bore
55
b
of the yoke plate of the lower stator subassembly B have respective tolerances, while the alignment projection
55
c
of the yoke plate of the lower stator subassembly B and the matching bore
55
b
of yoke plate of the upper stator subassembly A have respective tolerances.
Thus, when the upper and lower stator subassemblies are bonded together with synthetic resin in a mold, the above tolerances can add up to a significantly large error for the positions of the stationary magnetic poles and a reduced alignment accuracy of the components that can by turn result in a poor performance of the rotary electric device.
SUMMARY OF THE INVENTION
In view of the above identified problems and other problems of conventional electric motors of the type under consideration, it is therefore the object of the present invention to provide a stator assembly comprising stationary magnetic poles arranged with an enhanced positional accuracy as compared with those of conventional electric motors and a method of assembling the same in a simple manner.
According to the invention, the above object is achieved by providing a stator assembly of the rotary electric device comprising a yoke provided with a plurality of stationary magnetic poles and a yoke plate bonded to said yoke by means of synthetic resin in a mold to form an integral unit for enclosing a stator coil, characterized in that it has small holes formed by alignment pins in the molded synthetic resin.
According to the present invention, there is also provided a method of assembling a stator assembly of a rotary electric device comprising a yoke provided with a plurality of stationary magnetic poles and a yoke plate bonded to said yoke by means of synthetic resin in a mold to form an integral unit for enclosing a stator coil, characterized in that it comprises a step of bringing an alignment pin arranged on a jig for combining the yoke and the yoke plate into engagement with a corresponding alignment sections of the yoke and the yoke plate to put
Matsushita Kunitake
Muramatsu Kazuo
Sano Hiroshi
Yamawaki Takayuki
Minebea Co. Ltd.
Staas & Halsey , LLP
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