Vibration motor

Details Vibration motor Vibration motor

2001-12-21

2004-05-11

Le, Dang (Department: 2834)

Electrical generator or motor structure

Dynamoelectric

Rotary

C310SDIG006, C310S248000, C310S229000, C310S081000

Reexamination Certificate

active

06734594

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a vibration motor suitable for a communication apparatus notifying a user of incoming calls and, more particularly, to a vibration motor having an improved brush of a stator contacting a commutator of a rotor in order to maintain line contact between the brush and the commutator and to stabilize the vibration motor.
2. Background Art
One of essential functions in a communication apparatus is a notifying function to notify a user of incoming calls. Both a vibration mode for vibrating the communication apparatus and a sound mode for generating melody sound or bell sound have been used for the notifying function in the communication apparatus.
In accordance with the user's preference of the notifying function, one of the vibration mode and the sound mode is activated to notify the user of the incoming calls
The vibration mode has been used for preventing noise generation and avoiding offensive influences exerted on a group of people by the sound generated in the sound mode.
Generally, in the sound mode, one of a variety of melody sound stored in the communication apparatus is generated from a speaker mounted in the communication apparatus, and the user may be notified by the one of the melody sound generated from the speaker. In the vibration mode, vibration generated from a vibration motor mounted in the communication apparatus propagates to an outer casing of the communication apparatus.
A conventional vibration mode is performed by a vibration motor mounted inside the communication apparatus. The vibration motor having a coin type or a pan cake type in shape and having a diameter greater than a height of the vibration motor is shown in
FIGS. 1 and 2
.
The vibration motor includes a cover plate
100
, a bore
100
a
formed on a central portion of cover plate
100
and raised from cover plate
100
by a predetermined height, a stationary shaft
140
having a low portion forcibly inserted into bore
100
a
of cover plate
100
, and a first printed circuit board (PCB)
110
disposed on cover plate
100
and coupled to an external power source.
A ring-shaped magnet
130
inserted around shaft
140
is disposed on first PCB
110
and includes N and S magnetic field poles alternatively arranged around shaft
140
to form a ring shape.
A pair of brushes
120
is disposed within a central hole formed on ring-shaped magnet
130
and includes a first end connected to first PCB and a second end upwardly extended and raised from the first end. Brushes
120
are spaced-apart from each other.
A cylindrical case
150
having a circular plate, a circumferential cylindrical side extended from the circular plate, and an opening defined by the circumferential cylindrical side and facing cover plate
100
is coupled to circumferential peripheral side of cover plate
100
to cover an upper side of cover plate
100
. A support hole
150
a
is formed on a central portion of the circular plate of case
150
. A low portion of stationary shaft
140
is supported by bore
100
a
while an upper portion of shaft
140
is supported by supporting hole
150
a
of cylindrical case
150
when cylindrical case
150
is coupled to cover plate
100
.
A stator of the vibration motor includes cover plate
100
, shaft
140
supported by both cover plate
100
and cylindrical case
150
, first PCB
110
disposed on cover plate
100
, ring-shaped magnet
130
, the pair of brushes
120
, and cylindrical case
150
. An eccentric rotor
200
of the vibration motor disposed between ring-shaped magnet
130
and the circular plate of case
150
includes a bearing b rotatably inserted around shaft
140
, a second PCB coupled bearing b, a plurality of coils
240
, and a commutator
220
.
Second PCB
210
is supported by bearing b and rotates about shaft
140
. A plurality of commutator
220
is integrally formed on a bottom surface of second PCB facing first PCB. A segment of commutator
220
comes into contact with the second end of brushes
120
coupled to first PCB
110
. The external electric power is transmitted to coils
240
through first PCB
110
, brushes
120
, and commutator
220
.
Second PCB
210
includes an insulator
250
filled between coils of rotor
200
. Insulator
250
is integrally formed on second PCB
210
with commutator
220
and coils
240
by insert molding. A weight
230
is disposed between two adjacent coils
240
in order to increase the amount of eccentric force.
When the external electric power is fed to first PCB
110
, the electric power is supplied to coils
240
through the first ends of the pair of brushes
120
coupled to first PCB
110
, commutator
220
being contact with the second ends of brushes
120
. Therefore, the interaction between a first magnetic field generated by coils
240
and a second magnetic field generated from ring-shaped magnet
130
rotates rotor
200
about shaft
140
.
Since rotor
200
is eccentrically supported by shaft
140
, the eccentric rotation of rotor
200
propagates to cover plate
100
and case
150
through shaft
140
and causes case
150
to vibrate. This vibration of case
150
is used for silently notifying a user of incoming calls.
However, brushes
120
in the conventional vibration motor come into unstable contact with commutator
220
. Therefore, the unstable contact between brushes
120
and commutator
220
causes electric spark and noise which not only shorten the life time of brushes
120
and commutator
220
of the vibration motor but deteriorate the notifying function of the communication apparatus.
Brushes
120
having an arcuate shape are arranged around opposite sides of shaft
140
as shown in
FIGS. 3 and 4
. Each of brushes
120
includes a first bending portion
121
bent in a vertical direction from a predetermined portion of the first end, a second bending portion
122
upwardly extended from first bending portion
121
and being slant with respect to both first bending portion
121
and commutator
220
, a curved portion
123
extended from second bending portion
122
and being contact with commutator
220
.
Curved portion
123
of brushes
120
is bent in both a radial direction a and an arcuate direction while being slant with respect to commutator
220
. Since curved portion
123
is bent in lengthwise about the contact between commutator
220
and brushes
120
, brushes
120
shows differences h
1
, h
2
between bending curvatures of an inside portion and an outside portion of brushes around the contact. This difference cause curved portion
123
of brushes
120
does not come to uniform contact with commutator. The amount of the contact varies along the width w of brushes
120
between the inside portion and the outside portion of brushes
120
as a gap P varies along the width w of curved bending portion
123
of brushes where curved bending portion
123
is contact with commutator
220
.
Therefore, brushes
120
come into partial point contact with commutator
220
because of the differences h
1
, h
2
formed along the width w of curved portion
123
of brushes
120
. Non-uniform scratches are formed on commutator
220
as shown in FIG.
6
. The non-uniform scratches affect the contact between commutator
220
and brushes
120
.
The contact between brushes
120
and commutator
220
becomes irregular because brushes
120
does not come to uniform contact with commutator
220
but come to point contact with commutator.
A lowered current wave lower than a reference current wave d is shown in
FIG. 7
in a predetermined period of operation time after the vibration motor operates. As the non-uniform contact between brushes
120
and commutator
220
gradually increases, instantaneous sparks are frequently generated between brushes
120
and commutator
220
due to the increment of current density and instant current density. The abrasion of brushes
120
deteriorates reliability of the vibration motor.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved vibration motor able to prevent

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