Flat type vibration motor

Details Flat type vibration motor Flat type vibration motor

2003-11-12

2004-10-19

Le, Dang (Department: 2834)

Electrical generator or motor structure

Dynamoelectric

Rotary

C310S220000, C310S248000

Reexamination Certificate

active

06806603

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a vibration motor, and more particularly, to an improved vibration motor which can minimize mechanical friction and electric spark between brushes for receiving electric current and a commutator arranged in a rotor in order to prolong the lifetime of the motor as well as to enhance the reliability thereof.
2. Description of the Related Art
As well known in the art, a communication device generally uses a bell and a vibrator to inform a user of call incoming. A vibration mode typically actuates a small-sized vibration motor transferring driving force into a housing of the communication device to vibrate the communication device.
The vibration motor currently applied to a mobile telephone is discriminated into a flat type vibration motor (or coin type vibration motor) and a cylinder type vibration motor. The flat type vibration motor has a relatively simple vibration structure, e.g., of rotating a weight of high specific gravity which is placed inside the motor. The flat type vibration can be fabricated thin so that components of a mobile phone can be readily miniaturized. Owing to these advantages, application of the flat type vibration motor is gradually spreading.
FIG. 1
is a sectional view of a conventional flat type vibration motor, and
FIGS. 2A and 2B
are plan and bottom views of a rotor of the flat type vibration motor. As shown in
FIGS. 1 through 2B
, the conventional flat type vibration motor
300
generally comprises a stator assembly
100
functioning as a stationary member (hereinafter will be referred to as “stator”) and a rotor assembly
200
functioning as a rotary member (hereinafter will be referred to as “rotor”).
The stator
100
includes a disk-like lower plate
110
having a cylindrical shaft holder
115
projected to a predetermined height from an upper central portion of the lower plate
110
for fixing the lower end of a shaft
140
via insert press. The stator
100
also includes a lower board
120
which is integrally attached to the upper face of the lower plate
110
and on which a circuit pattern is printed. A terminal unit
125
is mounted on a distal portion of the lower board
120
and connected with an external power supply (not shown).
An annular magnet
130
is mounted on the upper outer periphery of the lower plate
110
, and has N and S poles in the outer periphery of the magnet
130
which are alternatingly magnetized to an equal interval.
The stator
100
also includes a pair of brushes
160
spaced from each other at a predetermined angle and arranged adjacent to an upper central portion of the lower board
120
. Each of the brushes
160
is electrically connected with each of input and output terminals of the terminal unit
125
.
A cylindrical housing
150
is coupled from above with the outer periphery of the lower plate
110
in order to protect the stator
100
and the rotor
200
. A shaft hole
155
is formed in a central portion of the underside of the housing
150
to axially support the upper end of the shaft
140
.
The rotor
200
is arranged rotatable about the stator
100
via the bearing member
145
of the shaft
140
, and includes an upper plate
210
, a commutator
220
, a weight
230
and a pair of winding coils
240
.
The upper plate
210
is arranged in the underside of an insulator
250
, and the weight
230
and the winding coil
240
are integrally contained within the insulator
250
via insert injection molding. The commutator
220
has a number of segments which are buried in the underside of the upper board
210
around the center of rotation at a predetermined interval, exposing contact faces thereof. The segments are electrically connected with the upper ends of the brushes
160
through elastic contact.
The weight
230
is arranged between the winding coils
240
in order to maximize eccentricity in actuation of the motor, and made of high specific gravity material such as tungsten.
The winding coils
240
are opposed to each other on a common radius of rotation which is substantially equal to that of the magnet
130
placed under the winding coils
240
. One of the winding coils
240
is supplied with electric current of a polarity, which is different from that of the other one of the winding coils
240
by the commutator
220
in contact with the brushes
160
.
In the conventional vibration motor
300
of the above construction, when the lower plate
120
is supplied with electric current from the external power supply via the terminal unit
125
, electric current is introduced into the commutator
220
, which is arranged in the upper board
210
in elastic contact with the upper ends of the brushes
160
, via the brushes
160
having lower ends electrically connected with the lower plate
120
. Then, electric current is supplied from the commutator
220
via the circuit pattern printed on the upper board
210
into the winding coils
240
.
In this case, magnetic fields created from the winding coils
240
and the magnet
130
interact with each other to generate electromagnetic force thereby rotating the rotor
200
in a direction. The commutator
220
periodically alternates the polarity of electric current supplied to the winding coils
240
as the winding coils
240
of the rotor
200
relatively change positions in respect to the magnet of the stator
100
.
The rotor
200
having the weight
230
arranged eccentrically therein is rotated eccentrically in one direction around the shaft
140
as the center of rotation. Eccentric rotation of the rotor
200
is transferred via the shaft
140
to the lower plate
110
and the housing
150
to create vibration so that the vibration motor
300
can be used as a silent call device of a mobile communication device.
However, the above conventional vibration motor
300
has drawbacks that the brushes
160
cause mechanical abrasion or generate electric spark while passing through gaps G of the segments of the commutator
220
during rotation of the rotor
200
. Then, byproducts such as black powder may be created to deteriorate the stability of electric contacts between the brushes
160
and the commutator
220
, functioning as a major factor of degrading the performance of the vibration motor as well as creating noise. Such problems also resultantly shorten the lifetime of the vibration motor.
SUMMARY OF THE INVENTION
The present invention has been made to solve the foregoing problems and it is therefore an object of the present invention to provide an improved flat type vibration motor which can minimize mechanical friction and electric spark from brushes for conducting electric current between a stator and a rotor in order to prolong the lifetime of the motor as well as to prevent deterioration of motor performance thereby enhancing the reliability of an article.
According to an aspect of the invention for realizing the above objects, there is provided a flat type vibration motor for generating vibration in energization. The flat type vibration motor comprises: a stator including a lower board with a terminal unit, the terminal unit being supplied with electric current from an external power supply, and a magnet having N and S poles alternatingly magnetized in a periphery of the magnet; a shaft having a lower end fixedly pressed into an upper central portion of the stator and an upper end assembled into a lower central portion of a housing; a rotor rotatably assembled between the stator and the housing, wherein the rotor includes an insulator of eccentric mass, which integrally contains at least one winding coil corresponding to the magnet and a weight arranged eccentrically adjacent to the winding coil, and an upper board mounted on an underside of the insulator; a plurality of brushes electrically connected with the terminal unit and having lower ends fixed to the stator; a plurality of annular slip rings arranged in an underside of the upper board to have an axis concentric with the shaft, each of the rings contacting an upper end of each of the brushes; and an Integrat

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