Stator structure that removes metal particles from the stator structure

An object of the present invention is to provide a novel stator structure in an electrical rotating machine which has a stator to one end of which an end plate provided with a bearing is fixedly mounted and a rotor rotatably supported by the bearing, in which unwanted metal particles produced during welding of the end plate to the stator are prevented from entering between the stator and the rotor. Positioning protrusions 61 are formed extending axially from the one end of the stator and positioning apertures 71 are provided in the end plate 65 for corresponding to and engaging with the positioning protrusions 61. Also, welding projections to be melted by resistance welding are arranged as located substantially on straight lines respectively extending from the rotation shaft 67 across the positioning protrusions 61 and on the outer side of the positioning protrusions 61. The end plate 65 is joined to the one end of the stator by welding at welding points 14. Unwanted metal particles produced during the resistance welding are blocked by the positioning protrusions 61 and will hardly flow towards the rotor 63.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an electrical rotating machine and more 
specifically, a stator structure in a stepping motor. 
2. Description of the Prior Art 
Stepping motors are widely used in OA machines, computer peripherals, and 
other industrial apparatuses and enjoy their major role in drive 
application. The stepping motors are classified into PM, VR, and HB types 
depending on the structure of their rotators. Each stepping motor includes 
a bearing mechanism for supporting the shaft of a rotor which rotates in a 
stator magnet assembly provided with a given number of coils. 
FIG. 6 is an exploded perspective view of a conventional stepping motor. As 
shown, a stator assembly 51 is made of a cylindrical form having a bottom 
and its interior will be explained later in more detail. The stator 
assembly 51 has a terminal 53 provided at the side thereof. Leads are 
soldered to the terminal 53 for connection to an external circuit but are 
not shown. An annular body of the stator assembly 51 is composed of yokes 
55 of a magnetic conductive metal. There are two rows of upper stator 
magnetic poles 57 and lower stator magnetic poles 59 projecting inwardly 
from the yoke 55. A plurality of positioning protrusions 61 are provided 
on the top of the stator assembly 51. 
Denoted by 63 is a rotor which rotates in the stator assembly 51 as 
magnetized to have N and S poles. An end plate 65 is mounted to the top of 
the stator assembly 51. The end plate 65 has a bearing 69 provided in the 
center thereof for supporting a rotating shaft 67 of the rotor 63. There 
are positioning apertures 71 arranged about the bearing 69 in the end 
plate 65 to correspond to the positioning protrusions 61 of the stator 
assembly 51. Also, projections 73 to be melted by resistance welding are 
provided about the bearing 69 inwardly of the positioning apertures 71 as 
extending downwardly or towards the stator assembly 51. The projections 73 
may be located between the positioning apertures 71. Denoted by 74 are 
alignment raised portions which extend downwardly from the end plate 65 to 
be fitted into a center or rotor 63 opening of the stator assembly 51 for 
centering the bearing 69. 
FIG. 7 is a longitudinal cross sectional view of the conventional stepping 
motor. As shown in FIG. 7, there are upper stator coils 75 and lower 
stator coils 77. The stator assembly 51 is fabricated by coupling the two 
yokes 55 of a bowl shape in cross section having magnetic poles, one 
containing the upper stator coils 75 and the other containing the lower 
stator coils 77, in a set of molds loaded in an injection machine, and 
filling the yokes 55 with an amount of resin material. During injection of 
the resin material, the positioning protrusions 61 are simultaneously 
formed. Denoted by 79 are burrs remaining in an injection resin inlet of 
the molds. Also shown is a lower bearing 81 secured in a bottom resin 83. 
Motor mounting tubs 85 and anchoring slots 87 are shown in FIG. 6. 
As shown in FIG. 7, the assembling of the stepping motor or electrical 
rotating machine starts with placing the end plate 65 on the stator 
assembly 51 so that the positioning protrusions 61 are accepted in the 
positioning apertures 71 of the end plate 65, and applying a pulse current 
to heat up the projections 73 while pressing the end plate 65 against the 
yokes 55. As the result of the resistance welding, the end plate 65 is 
securely joined at welding points 89 shown in FIG. 8 to the stator 
assembly 51. It is, however, likely to allow particles of metal produced 
during the resistance welding to enter between the end plate 65 and the 
yoke 55 and between the stator assembly 51 and the rotor 63. Upon 
energizing the electrical rotating machine, the metal particles between 
the end plate 65 and the yoke 55 start flowing due to resultant vibration. 
Some of the metal particles are attracted by the action of a magnetic 
force on the rotor 63, thus traveling deep into a small clearance between 
the rotor 63 and the stator assembly 51. This will interrupt the smooth 
rotation of the rotor 63 or create rotation noises. At worse, the rotor 63 
may be jammed and stop. 
SUMMARY OF THE INVENTION 
It is an object of the present invention, for eliminating the above 
disadvantage, to provide a novel stator structure in an electrical 
rotating machine which has a stator to one end of which an end plate 
provided with a bearing is fixedly mounted and a rotor rotatably supported 
by the bearing, characterized in that particles of metal produced during 
welding of the end plate to the stator are prevented from entering between 
the stator and the rotor. 
For achievement of the above object of the present invention, a stator 
structure in an electrical rotating machine which has a stator to one end 
of which an end plate provided with a bearing is fixedly mounted and a 
rotor rotatably supported by the bearing is provided in that positioning 
protrusions are formed extending axially from the one end of the stator, 
positioning apertures are provided in the end plate for corresponding to 
and engaging with the positioning protrusions, and welding points are 
determined for fixedly Joining the end plate to the one end of the stator 
by welding. In particular, the welding point is located substantially on a 
straight line extending from the center of rotation across the positioning 
protrusion and on the outer side of the positioning protrusion. 
While the positioning protrusions are provided extending axially from the 
one end of the stator, the corresponding positioning apertures in which 
the positioning protrusions are accepted are arranged in the end plate. 
Also, the welding projections which are melted for coalescing by 
resistance welding are provided substantially on their respective straight 
line extending from the center of rotation across the positioning 
protrusions and on the outer side of the positioning protrusions 
respectively. Upon the welding projections being melted, the end plate is 
joined to the stator. As unwanted metal particles produced during the 
resistance welding are blocked by the positioning protrusions, they will 
hardly flow towards the rotor.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Embodiments of the present invention will be described in more detail 
referring to the accompanying drawings. FIG. 1 is a cross sectional view 
of an end plate of a stepping motor according to one embodiment of the 
present invention. FIG. 2 is a front view of the same. Like components are 
denoted by like numerals as described in the prior art and will be 
explained in no more detail. As shown, the endplate of the embodiment is 
denoted by 10. The end plate 10 has a bearing 69 provided in the center 
thereof for supporting a rotating shaft 67. The end plate 10 also has 
positioning apertures 71 provided therein about the rotating shaft 67, 
similar to those in the prior art. 
The positioning apertures 71 are so located as to correspond to positioning 
protrusions 61 provided upwardly on the top of a stator assembly 51. Each 
of the positioning apertures 71 is associated with a welding projection 12 
which is to be heated by resistance welding. The welding projection 12 is 
located on just the outer side of the positioning aperture 71 and on a 
straight line L extending from the center of the bearing 69, by which the 
rotating shaft 67 is supported, across the positioning aperture 71 in 
which the positioning protrusion 61 is accepted. 
The end plate 10 is joined to the stator assembly 51 by placing the end 
plate 10 on the stator assembly 51 with its positioning apertures 71 
accepting the positioning protrusions 61, and while pressing the end plate 
10 against the yokes 55, applying a pulse current to heat up the welding 
projections 12 for coalescing. As the result of the resistance welding, 
the end plate 10 is securely joined at its welding points 14 shown in FIG. 
3 to the top of the stator assembly 51. During the resistance welding, 
particles of metal may be produced and dispersed in all directions from 
the projections 12. A part of the metal particles which tends to flow 
towards the rotor 63 is blocked by the positioning protrusions 61 of the 
stator assembly 51. The remaining metal particles about the welding points 
12 are also prevented from entering between the stator assembly 51 and the 
rotor 63. It is a good idea that surface regions of the end plate 10 just 
outside the projections 71 are slotted down at an angle .theta. as shown 
in FIG. 1 so that the metal particles are removed outwardly along the 
slots 17 as shown in FIG. 3. 
The welding projections 12 of the previous embodiment are formed on the end 
plate 10. In another embodiment, welding projections 16 are provided on 
the upper yoke 55 of the stator assembly 51 as shown in FIG. 4. Each 
projection 16 is located outwardly of the positioning protrusion 61 and on 
a straight line extending from the center of the rotating shaft opening 
across the positioning protrusion 61. 
As shown in FIG. 5, the slots 17 for removal of unwanted metal particles 
are arranged on the yoke 55 although they are on the end plate 10 
outwardly of the positioning apertures 71 in the previous embodiment. It 
is understood that the present invention is applicable not only to the 
stepping motors but also to other small-sized motors and generators. 
As set forth above, the stator structure in an electrical rotating machine 
which has a stator to one end of which an end plate provided with a 
bearing is fixedly mounted and a rotor rotatably supported by the bearing, 
according to the present invention is provided in that the positioning 
protrusions are formed extending axially from the one end of the stator, 
the positioning apertures are provided in the end plate for corresponding 
to and engaging with the positioning protrusions, and the welding 
projections to be melted by the resistance welding are arranged 
substantially on their respective straight lines extending from the center 
of rotation across the positioning protrusions and on the outer side of 
the positioning protrusions. Accordingly, unwanted metal particles 
produced during the resistance welding of the end plate to the stator are 
blocked by the positioning protrusions and will hardly flow towards the 
rotor. This allows the stator assembly to be free from such traditional 
disadvantages as sneaking of metal particles into a clearance between the 
stator magnetic poles and the rotor which may result in generation of 
noise and interruption of the rotation.