Electric rotating machine

An electric rotating machine can be constructed by mass production techniques, can sustain large axial loads, and can be formed out of a portion of the chassis of a portable electronic device. The electric rotating machine, which can be a duplex micromotor, comprises a base plate, at least one rotor assembly each including a rotor shaft, a rotor magnet disposed on the shaft and having radial pole faces, a pair of bearings supporting opposite ends of the shaft, and a worm, spur gear, or other such element situated on the shaft. A field yoke is favorably formed as a box-like structure of magnetic material with a field magnet therein having pole faces facing radially towards the rotor magnet. The field yoke has an open side mating with the base plate. Upstanding ears are formed on the base plate to seat the rotor bearings when the latter are inserted therein in an assembly direction perpendicular to the axis of the rotor shaft. Preferably, to facilitate automated assembly, the maximum diameter of the rotor magnet is smaller than the minimum axial distance parallel to the base plate separating the opposite magnetic pole faces of the field magnet. To better support axial loads, the bearings are preferably pivot bearings.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to electric rotating machines, and is more 
particularly directed to small electric devices, such as micromotors, 
which can be incorporated into miniaturized electronic apparatus, such as 
miniature tape players and the like. 
2. Description of the Prior Art 
Micromotors or other miniature DC motors are presently used in miniature 
electronic apparatus as an alternative to solenoid plungers and are 
employed, for example, in a small portable cassette tape recorder player 
to establish its mode. 
Coventional micromotors are constructed as brush-type DC motors including a 
housing, with field permanent magnets disposed within the housing; a rotor 
constituted by a shaft, a wound armature, and a commutator affixed on the 
shaft; and a brush assembly formed of an end plate for closing off the 
housing, brushes, and a bearing for one end of the shaft. 
Assembly of such a conventional micromotor tends to be troublesome, and 
does not lend itself to automation. More specifically, in carrying out 
assembly of the conventional micromotor, the rotor is fitted axially into 
the housing, and then the brush assembly is fitted over the shaft. 
Difficulties are often encountered in spreading the brushes while the 
brush assembly is slid axially into place. These difficulties hinder 
attempts to automate the assembly of the motor, and cause mass-production 
jigs for motor assembly to be complex and cumbersome. 
Also, when the micromotor is to be used in place of a solenoid plunger, a 
screw or worm is included on the rotor shaft to engage a claw for carrying 
out axial longitudinal displacement. However, because of the axial 
assembly required for conventional micromotors, journal type bearings must 
be used, and such bearings are severely limited as to the maximum axial 
load which can be placed on the motor. 
Accordingly, it has been desired to provide structure for an electric 
rotating machine which is easily adaptable to automated assembly, and 
which enables the machine to withstand increased axial loads. 
OBJECTS AND SUMMARY OF THE INVENTION 
It is an object of this invention to provide an electric rotating machine, 
such as a micromotor, whose structure facilitates the assembly procedure 
therefore, and thus lends itself to automatic assembly and mass 
production. 
Another object of this invention is to provide an electric rotating machine 
which can sustain greater axial loads than devices of the prior art. 
A further object of this invention is to provide an electric rotating 
machine of simple construction which can be constructed as a portion of 
the chassis of a portable tape player or other device into which it is 
incorporated. 
A still further object of this invention is to provide an electric rotating 
machine which can be constructed as narrow as possible in the radial 
direction so that miniature devices incorporating such an electric 
rotating machine can be constructed of exceedingly small size. 
According to an aspect of this invention, an electric rotating machine 
comprises a base plate, a rotor assembly including a rotor shaft, a rotor 
magnet disposed on the shaft and having radial pole faces, a pair of 
bearings supporting opposite ends of the shaft, and a rotary motion 
transmitting element, such as a worm, disposed on the shaft. A field yoke 
is favorably formed as a box-like structure of magnetic material and has 
at least one field magnet disposed therein with opposite magnetic pole 
faces facing radially toward the rotor magnet, and also has an open side 
to mate with the base plate. Bearing receiving structure, for example, 
structure including upstanding tabs or ears, is formed on the base plate 
to receive the rotor bearings when the latter are inserted therein in an 
assembly direction perpendicular to the axial direction of the rotor 
shaft. Preferably, to facilitate assembly, the maximum radial dimension of 
the rotor magnet is smaller than the minimum distance separating the 
magnetic pole faces across the rotor in the direction parallel to the base 
plate. 
In a favorable embodiment, the electric rotating machine can be constructed 
as a duplex motor including a pair off independently rotatable rotor 
assemblies having a common axis. In such a duplex motor, a single pivot 
bearing can be provided to support the inboard ends of both rotor shafts. 
Also, because the worms or other motion transmitting elements are 
force-fit onto the rotor shafts prior to assembly, pivot bearings can also 
be used to support the outboard ends of the rotor shafts, so that the 
duplex motor can withstand large axial loads.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
For purposes of background and for emphasizing the advantageous features of 
this invention, a micromotor according to the prior art will initially be 
discussed with reference to FIG. 1. 
The conventional micromotor has a cylindrical housing 1 containing within 
it a stator yoke with permanent stator magnets (not shown) disposed 
therein. A rotor assembly 2 is inserted into the housing 1 into a bearing 
4 formed in an end wall thereof, and an end plate 3, which also serves a 
brush assembly, is then fitted over an open end of the cylindrical housing 
1. 
The rotor assembly 2 includes a rotor shaft 5 and an armature formed of a 
slotted armature core 6 and armature windings 7. Commutators 8 are 
disposed on the shaft 5 at one side of the armature core 6. 
The end plate 3 is formed of a disc-shaped bearing member 9 with a pair of 
brushes 10 formed thereon. The bearing member 9 is usually formed of a 
nonconductive material, such as thermosetting plastic resin. The brushes 
10 are formed with a U-shaped cross-section, as viewed in the axial 
direction, with free ends thereof arranged to contact the commutator 8. 
Construction of the conventional micromotor is complicated by a number of 
factors. First of all, because a permanent field magnet is contained in 
the housing 1, the rotor assembly 2 must usually be inserted by hand. 
Further, the brushes 10 must be spread by some externally-applied force 
prior to fitting the bearing member 9 over the shaft 5 of the rotor 
assembly 2. 
Moreover, in a conventional micromotor as illustrated in FIG. 1, if a power 
transmitting device, such as a worm, pulley, or spur gear, is to be 
attached to the shaft 5, this must be done after the housing 1, rotor 
assembly 2, and end plate 3 of the micromotor have been assembled. If a 
pivot bearing is used in place of the bearing 4 in the housing 1, such 
pivot bearing is subjected to breakage forces when the shaft 5 is 
force-fit into the bore of the worm or other power transmitting device. As 
a result, pivot bearings are not used for the bearing 4. Accordingly, the 
maximum axial loads that can be accommodated by the shaft 5 of the 
conventional micromotor are substantially limited. 
A control motor embodying the present invention will now be discussed 
initially with reference to FIGS. 2-4. This control motor 11 is a duplex 
control motor of the type having a pair of independently rotatable rotor 
assemblies 13 and 14, so that the control motor 11 comprises a combination 
of two electrically independent motors. Of course, the principles of the 
present invention are also applicable to a single-rotor motor, or to one 
with any arbitrary number of rotors. 
As is shown in FIGS. 2-4, the control motor 11 also includes a base plate 
15 and a box-shaped field yoke 16 disposed thereon. Bearings 17a, 17b, and 
17c, to be described in detail hereinafter, support respective rotor 
shafts 18a and 18b of the rotor assemblies 13 and 14. Respective worms 19a 
and 19b are mounted on the respective shafts 18a and 18b. 
In the duplex control motor 11, the rotor shafts 18a and 18b, whose inboard 
ends are in proximity to one another, are supported on a common one of the 
bearings 17b, while the other, or outboard ends of the shafts 18a and 18b 
are each supported by one of the other bearings 17a and 17c. 
As shown in FIG. 5 (and perhaps better illustrated in FIG. 12) the base 
plate 15 has a pair of support tabs 20a and 20b bent perpendicular to the 
base plate 15 at positions radially across from each other at a position 
corresponding to the position of the inboard ends of the shafts 18a and 
18b. The base plate 15 also has end support ears 21a and 21b bent at right 
angles thereto at the positions of the outboard ends of the shafts 18a and 
18b, respectively. Each of the support ears 21a and 21b has a pair of 
upstanding prongs 22a and 22b, repsectively, each defining a U-shaped 
recess 23a and 23b into which the respective bearings 17a and 17c can be 
received and supported. 
Also shown in FIG. 5 and FIG. 12 is a brush assembly 24 including a support 
plate 25 arranged to be mounted on the base plate 15. The support plate 25 
is formed of an insulator material, preferably thermosetting plastic 
resin. The plate 25 has recesses 26a and 26b formed therein to mate with 
the tabs 20a and 20b to position and hold down the plate 25. The support 
25 can be affixed mechanically, by bending the tabs 20a and 20b, or can be 
cemented in place or affixed by caulking. 
Two pairs of brushes 27a, 27b, and 28a, 28b, are mounted on the support 
plate 25 for supplying electric drive current to the respective rotor 
assemblies 13 and 14. These brushes 27a, 27b, 28a, and 28b are each formed 
of a U-shaped member with the free-end thereof elongated and extending 
generally downward towards the support plate, and arranged radially across 
from the associated brush of that pair. 
A support member 29 for the bearing 17b is mounted at a central part of the 
support plate 25, and has upstanding fingers 29a, 29b defining a U-shaped 
recess 30 open at the top and into which the bearing 17b is fitted. 
The field yoke 16, as shown in FIGS. 2, 6, and 9, is formed generally as a 
box-shaped member with top and opposite sides arranged radially around the 
rotor assemblies 13 and 14. The field yoke 16 generally forms a U-shaped 
section across the axis of the rotor assemblies 13 and 14, with the sides 
of the yoke 16 defining legs of the U-shaped section, and being 
substantially perpendicular to to the base plate 15. The open end of the 
U-shaped section abuts the base plate 15. 
First and second field magnets 32a and 32b are arranged inside the 
box-shaped field yoke 16 and are affixed to respective ones of the sides 
thereof. These field magnets 32a and 32b each have a concave cylindrical 
surface facing the rotor 13 or 14 and have complementary magnetic 
polarities (i.e., one north and one south). 
As shown in FIGS. 7-9, the rotor assembly 13 has a slotted stacked armature 
core 33 with three pole faces disposed at separations of 120 mechanical 
degrees. Three slots separate adjacent ones of the faces of the armature 
core 33. A longitudinal opening 34 is provided on the top of the 
box-shaped field yoke at a position corresponding to the position of the 
armature core 33, and a similar longitudinal opening 35 is provided in the 
base plate 15. These openings 34, 35 enable the motor assembly to be 
constructed as compactly as possible without the base plate 15 and field 
yoke 16 interfering with the rotation of the rotor assemblies 13 and 14. 
Also, in order to facilitate assembly, as illustrated in FIG. 7, the 
diameter y of the armature core 33 should be at least slightly less than 
the smallest distance x, in the radial direction parallel to the base 
plate 15, separating the field magnets 32a and 32b. 
As shown in FIG. 9, magnetic flux is carried by the ferromagnetic material 
of the base plate 15 and field yoke 16 along paths (dashed lines) around 
the longitudinal openings 34 and 35. Thus, a magnetic flux return circuit 
is provided between the two field magnets 32a and 32b. 
As shown in FIG. 8, three-phase armature windings 36a, 36b, and 36c are 
wound in the slotted core 33. Commutator bars 37a, 37b, and 37c are 
disposed on the shafts 18a, 18b and are electrically connected to the 
windings 36a, 36b, and 36c. 
The assembly process for constructing the control motor 11 can be explained 
with reference to FIGS. 10, 11, and 12. 
As shown in FIG. 10, the worm 19a or 19b is force-fitted over the outboard 
end of the rotor shaft 18a or 18b. During this stage of the assembly, the 
opposite, or inboard end of the shaft 18a or 18b is held against a flat 
surface 38 of an assembly jig. 
The tight friction fit between the bore of the worm 19a or 19b and the 
associated rotor shaft 18a or 18b is usually sufficient to prevent mutual 
rotation therebetween. However, a spline or keyway could be cut into the 
shaft, with mating structure in the core of the worm 19a or 19b. 
Once the work 19a or 19b is installed on the associated rotor assembly 13 
or 14, the bearing member 17a or 17c is fitted over the outboard end of 
the shaft 18a (or 18b) and the bearing member 17b is fitted over the 
inboard end thereof. 
As shown in FIG. 11, each of the bearing members 17a-17c is a pivot bearing 
and is formed generally as a cylindrical bushing having an annular groove 
39a, 39b or 39c extending around the circumferential surface thereof. The 
upstanding prongs 22a, 22b of the end support ears 21a and 21b 
respectively engage the annular grooves 39a and 39c, while the support 
member 29 engages the annular groove 39b. Thus, the U-shaped recesses 23a 
and 23b and the U-shaped recess 30 act as bearing seats to position and 
support the respective bearing members 17a, 17b, and 17c. 
As shown in FIG. 12, the brush assembly 24 is installed in place engaging 
the support ears 20a and 20b. Then, the rotor assemblies 13 and 14, with 
the bearing members 17a, 17b, and 17c in place thereon, are lowered 
vertically for mounting onto the base plate 15. That is, unlike 
conventional motors, the shaft with the bearings thereon is installed in 
the direction perpendicular to the axial direction of the rotor shaft 18a 
or 18b. 
An adhesive cement or other securing means can be used to fasten the 
bearings 17a and 17b to the support ears 21a and 21b, and to secure the 
bearing member 17b to the support member 29. 
Once the rotor assemblies 13 and 14 are so installed, the field yoke 16 can 
be lowered vertically over the rotor cores 33 so that the open end of the 
field yoke 16 engages the base plate 15. Then the field yoke 16 and the 
base plate 15 can be fixed together by any convenient securing means, such 
as a spot-weld, machine screws, or adhesive cement. 
Because the diameter y of the rotor core 33 is slightly less than the 
minimum separation distance x between the field magnets 32a and 32b, the 
field yoke 16 can be brought into place against the base plate 15 over the 
rotor assemblies 13 and 14 without any particular difficulty. 
However, if for some particular purpose a higher-torque motor is desired, 
the air gap between the rotor core 33 and the magnets 32a and 32b can be 
made narrow by reducing this minimum separation distance x. In such case, 
if this distance x is less than the diameter y, the field yoke 16 can be 
assembled axially over the rotor assemblies 13 and 14, and then the field 
yoke 16 and rotor assemblies 13 and 14 can be brought together vertically 
down for installation on the base plate 15. 
FIGS. 13 and 14 show alternative constructions of the rotor assembly 13 of 
a similar motor embodying this invention. In the variation of FIG. 13, a 
pulley 41 is affixed to the outboard end of the shaft 18, while the worm 
19a is omitted. In the variation of FIG. 14, a spur gear 42 is affixed to 
the outboard end of the shaft 18a. In each of these variations, because 
the load imparted to the shaft 18a by means of the pulley 41 or the spur 
gear 42 is a radial load rather than an axial load, the bearing member 17a 
is preferably formed as a journal bearing, or radial bearing, rather than 
a pivot bearing, or axial bearing. 
Also, similarly to the rotor shaft 13 of the embodiment of FIGS. 2-12, the 
pulley 41 or spur gear 42 is fitted onto the the rotor shaft 18a prior to 
assembly of the rotor 13 onto the base plate 15. Since the rotor assembly 
13 is brought to its mounting position by movement vertically, i.e., 
perpendicular to the axial direction thereof, the rotor 13 can be 
assembled onto the base plate 15 without any particular difficulty, even 
if the outside diameter of the pulley 41 of the spur gear 42 is greater 
than the outside diameter of any of the other portions of the rotor 
assembly 13. 
FIG. 15 shows an alternative arrangement of a base plate suitable for use 
with electric rotating machines embodying this invention. Elements shown 
therein corresponding to elements in the foregoing embodiments are 
identified with similar reference characters, but primed. In this base 
plate 15', like that of FIG. 5, the support ears 21a' and 21b', have 
U-shaped recesses 23a' and 23b' respectively formed therein. However, in 
this base plate 15', the support ears 21a' and 21b' are formed inside of 
the longitudinal opening 35' in the base plate 15' by bending at a right 
angle. This base plate can thus be formed from a portion of the chassis of 
a tape recorder or other similar device. 
FIG. 16 illustrates a portion of another embodiment of this invention, in 
which similar elements are identified with the same reference characters. 
Here, a bearing 43 having a radial projection 44 thereon is used to 
support one end of the shaft 18a of the rotor assembly 13. An aperture 45 
is cut out of the base plate 15 to receive the projection 44 of the 
bearing member 43. Thus, in this embodiment, the bearing member can be 
assembled onto the shaft 18a, and then the rotor assembly 13 together with 
the bearing member 43 can be assembled vertically onto the base plate 15. 
The projection 44 can be secured into the aperture 45 by cement, thermal 
deformation, caulking, or other convenient means. 
It should be understood that this invention is not limited to the 
brush-type DC motor is described hereinabove but can be applied with great 
facility to any of various types of electric rotating machines, including, 
but not limited to, brushless DC motors, generators, alternators, 
synchronous motors, stepper motors, and tachometers. 
Also, although in the above-described embodiment, the rotor assemblies 13 
and 14, with the bearing members 17a, 17b, and 17c thereon are mounted by 
installing the same vertically with respect to the base plate 15, it 
should be understood that electric rotating machines embodying this 
invention could also be constructed with the rotor assemblies thereof 
installed along a diagonal direction or along a lateral direction with 
respect to the base plate 15, so long as the direction of installation is 
generally perpendicular to the axis of the rotor assembly 13 or 14. 
Furthermore, although a single pair of bearings 17a, 17b, or 17c is 
associated with each respective rotor shaft 18a or 18b, an additional 
bearing or bearings can be provided on each such rotor shaft. In fact, if 
a large radial load is expected to be applied to the shaft, it is 
preferable to include a plurality of bearings for each shaft to support 
the radial load. If additional bearings are so provided, additional 
supports therefor, such as the support ears 21a or 21b, can be easily 
formed in the base plate 15. The provision of additional bearings will not 
present any particular problem in the assembly of the motor, as all the 
bearings can be installed in the same direction on their respective 
supporting members. 
In addition, although the bearing members 17a, 17b, and 17c are illustrated 
as having axial grooves 39a, 39b, and 39c therein to engage their 
respective supporting members, it is apparent that other equivalent 
structure could be substituted. For example, the bearings 17 and 17b could 
be affixed to the support ears 21a and 21b by means of an adhesive cement. 
In such case, it may be preferable to increase the axial width of the 
U-shaped recesses 23a and 23b to approximately the width of the respective 
bearing members 17a and 17b. 
Moreover, terms of orientation as used herein, such as "vertical" or 
"lateral", are used for purposes of explanation, rather than limitation, 
and are to be taken with reference to the base plate 15 as shown in the 
drawings. It is apparent that electric rotating machines incorporating the 
features of this invention could assume any arbitrary orientation. 
Although particular embodiments of this invention have been described in 
detail hereinabove, it is apparent that many modifications and variations 
can be effected therein by those skilled in the art, without departing 
from the scope or spirit of this invention as defined in the appended 
claims.