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Description  |
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BACKGROUND OF THE INVENTION
The invention relates to a small sized electric motor and more particularly
relates to a small sized electric motor which is sectionally non-circular
and may be used in various machines and apparatuses and which has the
fulcrums of brushes arranged in the direction lengthwise of the section of
motor, so that brushes of sufficient length may be used in the small sized
electric motor.
The conventional small sized electric motor 1 is generally non-circular in
the section thereof as shown in FIG. 3 because a motor of such outer
configuration may be more easily attached to the machines and other
apparatus. In FIG. 3, the conventional small sized electric motor 1
(called a motor hereinafter) has a sectionally rectangular housing 2, in
which a pair of magnets 3, 4 are oppositely arranged in the direction
lengthwise thereof and a rotor 5 is rotatably positioned between the two
magnets. FIG. 3 shows a triplepolar motor 1 as an example of multipolar
motors, in which the rotor 5 is composed of a rotor shaft 7, rotatably
journalled in the housing 2, a rotor core structure 8 which is assembled
integral with the core shaft 7 and formed with cores 8a, 8b, 8c providing
winding carrier parts 8d, 8e, 8f respectively, a winding 9 sequentially
wound around the winding carrier parts 8d, 8e, 8f, connector terminals 10
provided between the winding carrier parts respectively and extending
radially of the rotor shaft 7. The terminals each having connected thereto
the initial and last ends of the winding 9 wound around the winding
carrier parts 8d, 8e, 8f, and a commutator 11 mounted on the rotor shaft 7
and providing conductive parts 11a, 11b, 11c and nonconductive parts 11d,
11e, 11f.
The core structure 8 has the winding carrier parts 8d, 8e, 8f arranged
around the rotor shaft 7 with a space of 120.degree. therebetween, and
accordingly the connector terminals 10a, 10b, 10c are arranged on the
commutator 11 with a space of 120.degree. therebetween. Similarly the
commutator 11 has the nonconductive parts 11d, 11e, 11f each arranged
between the adjacent winding carrier parts 8d, 8e, 8f with a space of
120.degree. therebetween around the rotor shaft 7.
The winding 9 has the initial end anchored, for example, to one 10a of the
connector terminals 10 of the commutator 11, and then is wound a
predetermined number of times around the winding carrier part 8b of the
cores. The wound end 9b is anchored to the next connector terminal 10b
where the initial end 9c of the winding 9 starts again to be wound around
the next winding carrier part 8f of the cores. After the winding 9 has
been wound the predetermined times around the winding carrier part 8f, the
wound end 9d is then anchored to the next connector terminal 10c where the
initial end 9e of the winding 9 starts again to be wound around the next
winding carrier part 10c. After the winding 9 has been wound the
predetermined number of times around the winding carrier part 10c, the
wound end 9f is then anchored to the initial connector terminal 10a. Then
the initial and wound ends of the winding 9 are each welded to the
respective connector terminals
A pair of linear brushes 12, 13, which are passed against the commutator 11
on the opposite sides thereof with the an elasticity of their own, have
the respective base ends 12a, 13a secured to the associated fulcrums 14,
15 which are provided with a predetermined space therebetween on one side
of the housing 2 in a direction laterally thereof. Therefore the brush
terminals (not shown), which are to be connected to a power supply (not
shown), are designed to outwardly project side by side from the side of
the housing 2 in the direction laterally thereof.
The brushes 12, 13 are adapted to cooperate with the nonconductive parts
11d, 11e, 11f of the commutator 11 as the rotor 5 is rotated to thereby
change over the direction of electric current flowing through the winding
9 wound around the winding carrier parts 8d, 8e, 8f of the cores 8a, 8b,
8c, i.e. to determine the electric displacement position of the commutator
11, so that the rotor 5 may be continuously rotated. In this case, the
nonconductive parts 11d, 11e, 11f are positioned in alignment with the
center axes of the respective winding carrier parts 8d, 8e, 8f of the core
structure 8, and accordingly the electric displacement position of the
commutator 11 is 0.degree. with respect to the magnetic line of force M of
the magnets 3, 4. Namely if the rotor 5 is rotated in the direction as
shown by an arrow A, the direction of electric current flowing through the
winding 9 on the winding carrier part 8e is changed over when the
nonconductive part 11f of the commutator 11 contacts the brush 12. When
the nonconductive part 11 e contacts the brush 13, the direction of
electric current flowing through the winding 9 of the winding carrier part
8d is changed over, and when the nonconductive part 11 d contacts the
brush 12, the direction of electric current flowing through the winding 9
of the winding carrier part 8c is changed over. Thus the rotor 5 is
continuously rotated.
Now according to the conventional motor 1, since the brushes 12, 13 are
arranged extending in parallel with each other from one side of the casing
2 in the direction laterally thereof in such a manner as to transverse the
magnetic line of force M of the magnets 3, 4, the length of the brushes
12, 13 is extraordinarily delimited with respect to the commutator 11.
Namely in the prior art, since the distance is very short between the
fulcrum of each brush and a point of the commutator where the brush
contacts the commutator, the pressing variation of the brush is
accordingly large to the extent that the contact of the brush with the
commutator is not stabilized, and therefore the output of the motor is
lowered. Further as the brushes and commutator come to be worn down, the
contact angle of brushes with respect to the commutator will be remarkably
varied, and accordingly the electric displacement position is varied. As
the result, the output of the motor is further lowered. Still further, in
the assembling operation, it is almost impossible to avoid the variations
of angle with which the brushes are attached to the fulcrums. Such
variations of attaching angle will inevitably result in variations of
pressure with which the brushes contact the commutator. The foregoing
disadvantages have been typical in the small sized electric motor.
BRIEF SUMMARY OF THE INVENTION
The present invention has been provided to eliminate such disadvantages of
the prior art. It is therefore a primary object of the invention to
provide an improved small sized electric motor in which the distance is
made as long as possible between the fulcrums to which the brushes are
attached and the points at which the brushes contact the commutator so as
to reduce the pressure variation of brushes with respect to the commutator
to thereby cause the brushes to constantly follow the commutator, thus to
prevent the output of the motor from being deteriorated. It is another
object of the invention to maintain a constant contact angle of the
brushes to the commutator even if the brushes and commutator are worn down
during the practical use of the motor, to thereby maintain the constant
electric displacement position of the commutator, thus to prevent the
output of the motor being deteriorated. It is still another object of the
invention to solve the problem caused by displacement of the electric
displacement position resulting from the elongation of brushes according
to the invention, simply by properly displacing the anchoring positions of
the winding on the rotor core structure without changing the position of
the commutator relative to the rotor core structure.
In short, the invention has been made to provide a small sized electric
motor of a sectionally non-circular housing having a pair of magnets
oppositely located therein in the lengthwise direction thereof and a rotor
positioned between the magnets, said rotor being composed of a rotor
shaft, a core structure, a commutator and a plurality of connector
terminals, said electric motor comprising a pair of fulcrums oppositely
located on the housing in the lengthwise direction with respect to a cross
section thereof; a pair of elongated brushes each having one end part
secured to each of the fulcrums and having the other end part elastically
pressed against the commutator at a point thereof with a predetermined
angle displaced with respect to the magnetic line of force which is caused
by the magnets, to thereby determine a predetermined electric displacement
position thereat; and a winding wound around the core structure, said
winding having the initial ends and the wound ends each connected to each
of the connector terminals with a predetermined angle displaced with
respect to the commutator corresponding to the predetermined angle of each
brush, wherein the displacement of the electric displacement position is
compensated by the specific connections of the winding on the rotor. More
precisely, the motor is a triplepolar electric motor and has the pair of
elongated brushes each having one end part secured to each of the fulcrums
and having the other end contacting the commutator at a point thereof with
the angle 120.degree. displaced with respect to the magnetic line of force
caused by the magnets, and the winding having the initial ends and the
wound ends each connected to each of the connector terminals with the
angle 120.degree. displaced accordingly with respect to the commutator.
Another aspect of the invention is to provide a method for producing a
small sized electric motor of a sectionally non-circular housing having a
pair of magnets located therein in the lengthwise direction with respect
to cross section thereof and a rotor positioned between the magnets, said
rotor being composed of a rotor shaft, a core structure, a commutator and
a plurality of connector terminals, said method comprising the steps of
positioning a pair of fulcrums opposite to each other on the housing in
the lengthwise direction with respect to a cross section thereof; securing
a pair of elongated brushes each at one end part to each of the fulcrums
and elastically pressing the brushes each at the other end part against
the commutator at a point thereof with a predetermined angle displaced
with respect to the magnetic line of force which is caused by the magnets,
to thereby determine a predetermined electric displacement position
thereat; and winding a winding around the core structure in a manner that
the initial ends and the wound ends are each connected to each of the
connector terminals with a predetermined angle displaced with respect to
the commutator corresponding to the predetermined angle of each brush,
wherein the displacement of the electric displacement position is
compensated by the specific connections of the winding on the rotor. More
precisely, the method is to produce a triplepolar electric motor, said
method securing the pair of elongated brushes each at one end part to each
of the fulcrums and contacting the brushes each at the other end part
against the commutator at a point thereof with the angle 120.degree.
displaced with respect to the magnetic line of force, and winding the
winding around the core structure in a manner that the initial ends and
the wound ends are each connected to each of the connector terminals with
the angle 120.degree. displaced accordingly with respect to the
commutator.
BRIEF DESCRIPTION OF THE DRAWINGS
The other features and advantages of the invention will be apparent from
the following description of preferred embodiments in reference to the
attached drawings, in which:
FIG. 1 is a plan view of a small sized electric motor of a sectionally
non-circular housing according to the invention;
FIG. 2 is an end view of the electric motor as shown in FIG. 1;
FIG. 3 is a sectioned view of the conventional small sized electric motor
of a sectionally non-circular housing;
FIG. 4 is a sectioned end view of the electric motor as shown in FIGS. 1
and 2;
FIG. 5 is a perspective view of a rotor of the electric motor as shown in
FIG. 4;
FIG. 6 is a diagrammatic end elevational view of the electric motor of the
invention showing the relation between the brushes and the commutator.
FIG. 7 is a diagrammatic end elevational view of a second embodiment
according to the invention; and
FIG. 8 is a diagrammatic end elevational view of a third embodiment
according to the invention.
DETAIL DESCRIPTION OF THE INVENTION
In reference to FIGS. 4 to 6 showing a preferred embodiment of the
invention with the same reference numerals as those in FIGS. 1 to 3 being
attached to the parts thereof common to those of the conventional motor,
but the the parts of inventiveness being indicated with different
reference numerals. the embodiment of the invention would be fully
understood with the explanation only as to the parts thereof different
from those of the conventional motor.
A motor 20 has a pair of fulcrums 21, 22 positioned opposite to each other
on the housing 2 in the lengthwise direction thereof and on the magnetic
line M of force caused by the magnets 3, 4. A pair of elongated brushes
23, 24 have each one end part 23a (24a) secured to each of the fulcrums
21, 22 and have each the other end part elastically pressed against the
commutator 11. Accordingly a pair of brush terminals 6, as shown in FIGS.
1 and 2 to be connected to a power supply (not shown), are arranged on
opposite sides of the rotor 5 in the lengthwise direction of the housing 2
with respect to a cross section thereof and are projected out therefrom.
As shown, in this case the point at which each brush 23(24) contacts the
commutator 11 varies by the angle 60.degree. compared with the
conventional case as shown in FIG. 3, with each brush 23 (24) being
displaced by the angle 30.degree. with respect to the magnetic line M of
force. Accordingly there arises a problem that the electric displacement
position of the commutator 11 varies by the angle 120.degree..
This problem will however be solved by changing the connecting positions of
a winding 25 with respect to the commutator 11. Namely at first the
initial end 25a of the winding 25 is anchored, for example, to one 10a of
the connector terminals 10 and then the winding 25 is wound a
predetermined number of times around the winding carrier part 8d of the
core 8a of the core structure 8. The wound end 25b of the winding 25 is
then anchored to the connector terminal 10b which is displaced 120.degree.
from the connector terminal 10a. Then from the next initial end 25c the
winding 25 is wound around the winding carrier part 8e of the core 8b and
the wound end 25d is then anchored to the connector terminal 10c which is
displaced 120.degree. from the connector terminal 10b. Then from the next
initial end 25e the winding 25 is wound around the winding carrier part 8f
of the core 8c and the wound end 25f is then anchored to the connector
terminal 10a which is displaced 120.degree. from the connector terminal
10c. Then the initial ends and the wound ends are welded to the connector
terminals 10a, 10b, 10c respectively.
With the structure of the invention as mentioned above, the operation is as
follows: In reference to FIGS. 4 to 6, if the brush terminals 6 in FIG. 1
are connected to the power supply (not shown), the commutator 11 is
energized through the brushes 23, 24, and therefore the cores 8a, 8b, 8c
of the core structure 8 are energized through the winding 25, and then the
rotor 5 is rotated, for example, in the direction indicated by an arrow
mark A in relation with the magnetic line M of force which is caused by
the magnets 3, 4. While the rotor 5 is rotated, the winding carrier part
8e of the core 8b is positioned in alignment with the magnetic line M of
force when the nonconductive part 11 d of the commutator 11 comes into
contact with the brush 24. It is this time that the electric current
flowing through the winding 25 on the winding carrier part 8e is changed
over. Namely the electric current is changed over with the electric
displacement position of the commutator 11 being displaced by the angle
120.degree. with respect to the magnetic line M of force as advanced in
the rotational direction of the rotor 5 because of the initial end 25c and
the wound end 25d of the winding 25 being connected to the connector
terminals 10b and 10c respectively. Thus the electric displacement
position for the core 8b is unchanged in effect from that of the prior art
as shown in FIG. 3. Similarly if the nonconductive part 11f of the
commutator 11 comes to contact the brush 23, the direction of the electric
current flowing through the winding 25 on the core 8a is changed over, and
if the nonconductive part 11e of the commutator 11 comes to contact the
brush 24, the direction of the electric current flowing through the
winding 25 on the core 8c is changed over. Thus the rotor 5 is
continuously rotated.
As is understood from the foregoing explanation, since the fulcrums 21, 22
are positioned opposite to each other across the rotor 5 in the lengthwise
direction of the sectioned housing 2 and on the magnetic line M of force
caused by the magnets 3, 4, there may be used the brushes 23, 24 which are
remarkably longer than the conventional ones to thereby reduce the
pressure variation of brushes accordingly to the extent that no angular
variation of brushes is substantially caused if the brushes and the
commutator are worn down. Further according to the invention, the winding
25 may be easily wound around the winding carrier parts 8d, 8e, 8f with a
repeated operation cycle such as firstly anchoring the initial 25a, for
example, of the winding 25 to the connector terminal 10a and then rotating
the core structure 8 by the angle 60.degree. in one direction to wind the
winding 25 around the winding carrier part 8d, and then rotating the core
structure 8 in the opposite direction by the angle 180.degree. to anchor
the wound end 25b of the winding 25 to the connector terminal 10b.
In reference to FIG. 7 showing a second embodiment of the invention having
the same reference numerals attached to the parts thereof which are common
with those of the first embodiment as mentioned above, a motor 30 has the
fulcrums 21, 22 oppositely arranged across the rotor 5 in the lengthwise
direction of the housing 2. A pair of elongated torsion springs 31, 32
twisted in one direction have each a twisted end 31a (32a) secured to each
of the fulcrums 21, 22 and a free end bent into a recess 31b (32b). A pair
of brush elements 33, 34 are fixedly positioned in the recesses 31b, 32b
respectively and are pressed against the commutator 11 opposite to each
other diametrically thereacross due to the elasticity of the torsion
springs 31, 32.
In reference to FIG. 8 showing a third embodiment of the invention having
the same reference numerals attached to the parts thereof which are common
with those of the second embodiment as mentioned above, a motor 40 has a
pair of elongated torsion springs 41, 42 provided therein. The torsion
springs 41, 42 are each twisted in the direction opposite to the twisted
direction of the torsion springs in the second embodiment, and have each a
twisted end 41a (42a) secured to each of the fulcrums 21, 22 and a free
end bent into a recess 41c (42c). The brush elements 33, 34 are fixedly
positioned in the recesses 41c, 42c respectively. The torsion springs 41,
42 are each bent at a point 41b (42b) thereof with a predetermined angle
directed away from the magnetic line M of force so that the brush elements
33, 34 may be pressed against the commutator 11 opposite to each other
diametrically thereacross with the electric displacement position being
maintained at the angle 120.degree. displaced with respect to the magnetic
line M of force.
The second and third embodiments of the invention are each slightly
modified from the first embodiment, but the effect is substantially same.
The invention has been explained in reference to the embodiments of a
triplepolar motor, but is not limited to this type of motor. The invention
may, of course, be applied to the motor of four or more poles. For
example, as to the four-pole motor, the brushes will be extended in
parallel with the magnetic line of force so as to obtain the electric
displacement position displaced the angle 90.degree. with respect to the
magnetic line of force, and the winding wound around the core structure
will have the initial ends and the wound ends each connected to the
connector terminals 10 of the commutator 11 with the angle 90.degree.
being displaced with respect to the commutator 11.
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