1. Field of the Invention
The present invention relates to a small vibration motor for generating vibrations, which is built in an electronic apparatus, such as a mobile telephone, a PDA and the like, and to a method of manufacturing the same.
2. Description of Related Art
Conventionally, an electronic apparatus such as the mobile telephone, the PDA and the like includes a mechanism of a so-called silent mode to notify an incoming call through vibrations, and an alarm to notify a predetermined time through vibrations, and the like. As a mechanism for generating a vibration, a vibration actuator is built into such an electronic apparatus.
FIG. 14A is a schematic view showing the inner structure of a mobile telephone in which a vibration motor serving as a conventional vibration actuator is built. FIG. 14B is a schematic view showing the appearance of the vibration motor. As shown in FIG. 14A, printed circuit boards (motherboards) 101, 102 are mounted within the mobile telephone 100. A speaker 103 and a vibration motor 104 are connected to the side of the printed circuit board 101. The vibration motor 104 is driven by a driver IC 105 mounted on the printed circuit board 101. On the other hand, a power supply IC 110, a converter IC 111, an MPU 112, a memory IC 113 and the like are mounted on the side of the printed circuit board 102.
The illustrated vibration motor 104 is a motor with a brush. As shown in FIG. 14B, a weight 125 is fixed around an output shaft 120. When the vibration motor 104 is driven, the output shaft 120 is rotated, and the weight 125 is eccentrically rotated. The eccentric rotation of the weight 125 causes rotationally unbalanced energy to be generated as a vibration component.