1. Field of the Invention
The present invention relates to a vibration motor having brushes with different osculatory tracks, and more particularly to a vibration motor having brushes with different osculatory tracks, which reduces the abrasion of a commutator and has an elongated life span.
2. Description of the Related Art
Generally, communication apparatuses essentially require an incoming-call notification function. The above incoming-call notification function may take the form of sound, such as a melody or bell, or vibration.
The vibration is mainly used to prevent the melody or bell from being transmitted to the outside through a speaker, thereby not annoying other persons. In order to generate the vibration, a small-sized vibration motor is driven to transmit its driving force to a case of an apparatus, thereby vibrating the apparatus.
Vibration motors, which are recently applied to portable phones, are divided into coin type vibration motors having a small thickness and bar type vibration motors having a long shape according to shapes of the motors.
Regardless of the type of vibration motor, the vibration motor uses electromagnetic induction, in which electromagnetic force perpendicular to a magnetic field is generated by flowing current in the magnetic field, to which a conductor is positioned perpendicular.
The coin type vibration motor generates vibration in a simple manner such as by rotating a counter weight positioned therein.
Particularly, the coin type vibration motor has a small thickness and minimizes the number of components of a portable phone, thereby being increasingly used now.
FIG. 1 is an exploded perspective view of a conventional coin type vibration motor. With reference to FIG. 1, the coin type vibration motor 100 will be described in detail, as follows.
The coin type vibration motor 100 comprises a stator assembly 110 serving as a fixed member, and a rotor assembly 120 serving as a rotary member.
The stator assembly 110 includes a bracket 111 having a circular flat plate shape, a lower substrate 112 attached to an upper surface of the bracket 111, and a magnet 113 having a disk shape attached to an upper surface of the lower substrate 112.
The upper surface of the bracket 111 is sealed by a case 150, and is connected to the case 150 by a central shaft 130.
The rotor assembly 120 is rotatably connected to the shaft 130, and includes a bearing 121, coil assemblies 122, a counter weight 123, a commutator 124, an upper substrate 125 and an insulator 126.
The upper substrate 125 is a circular printed circuit board, and supplies current having opposite polarities to the coil assemblies 122 through patterns formed on upper and lower surfaces of the upper substrate 125 when power from the commutator 124 attached to the lower surface of the upper substrate 125 is supplied thereto.
The commutator 124 is buried under the lower surface of the upper substrate 125 such that a plurality of segments of the commutator 124 form a circle centering on a rotary center and a contact surface of the commutator 124 is exposed to the outside.
Each of the coil assemblies 122 includes at least one coil so that the coils have the same rotating radius as the magnet 113, and the powers having opposite polarities are supplied to the coil assemblies 122 by the upper substrate 125.
The counter weight 123 is made of a material having a high specific gravity, such as tungsten, and is attached on the surface of the upper substrate 125, on which the coil assemblies 122 are positioned, thereby determining the eccentricity of the vibration motor 100.
The insulator 126 serves to firmly attach the bearing 121, the coil assemblies 12 and the counter weight 123 to the upper substrate 125, and to insulate the bearing 121, the coil assemblies 12 and the counter weight 123 from the upper substrate 125.
Here, lower ends of the stator assembly 110 and the rotor assembly 120 are fixed to the lower substrate 112, and upper ends of the stator assembly 110 and the rotor assembly 120 are electrically interconnected by a brush 140 contacting the commutator 124.
FIG. 2 is a cross-sectional view of a conventional bar type vibration motor. With reference to FIG. 2, the bar type vibration motor 200 will be described in detail, as follows.
The bar type vibration motor 200 comprises a stator assembly 210 and a rotor assembly 220.
The stator assembly 210 includes a body 211, a cap 212 fixed to one side of the body 211, and a magnet 213. The body 211 has a hollow cylindrical shape, and the magnet 213 is fixed to the inside of the body 211.
The rotor assembly 220 includes an eccentric poise 223, a plurality of commutators 224 divisionally fixed to one surface of a fixing body 225, and a plurality of coil assemblies 222 fixed to the fixing body 225.
The commutators 224 include a plurality of flat segments on the lower surface of the fixing body 225, and the coil assemblies 222 are electrically connected to the commutators 224 respectively.
Here, one end of a shaft 230 is connected to the eccentric poise 223, and the other end of the shaft 230 is connected to the fixing body 225. The shaft 230 is rotatably supported by bearings 221 installed in the body 211.
Further, a lower substrate (not shown), provided with a pair of brushes 240 fixed thereto, is mounted on the fixing cap 212. The brushes 240 are connected to a lead wire 215 for supplying power therethrough, and contact the commutators 224, thereby applying current.
The above-described vibration motors, in which the brushes contact the commutators to supply current, are referred to as “brush type vibration motors”. In order to achieve the commutating action of such brush type vibration motors, it is important to maintain proper stress of the brushes and to make the brushes contact the commutators constantly.
Hereinafter, types of the brushes of the coin-type vibration motor will be described.
With reference to FIG. 1, one end of the brush 140 is fixed to the lower substrate 112 by welding, and the uppermost tip of the other end of the brush 140 contacts the commutator 124 so as to apply current. The brush 140 serves to electrically connect the stator assembly 110 and the rotor assembly 120.
The brushes 140 are prepared in a pair, which are symmetrically designed for transmitting positive and negative power, and are located on the same osculatory track.
The brushes 140 are mainly made of a copper alloy, and the uppermost tips of the brushes 140 contacting the commutators 124 are coated with gold or other precious metal so as to obtain electric conductivity.
Regardless of which of the above-described types of vibration motors or types of brushes are used, left and right brushes 141 and 142 of the brush unit 140, as shown in FIG. 3, which are symmetrically positioned on the same osculatory track (R), contact the commutators along the same osculatory track (R).
That is, since contact portions of the commutators 124 contact the left and right brushes 141 and 142, the contact portions of the commutators are abraded twice per cycle (hereinafter, a track of the brush contacting the rotating surface of the commutator is referred to as an “osculatory track”).
Accordingly, the contact portions of the commutators are worn out, thus shortening the life span of the vibration motor.
Accordingly, in order to solve the above problems, a vibration motor having brushes with different osculatory tracks has been required in the art.