Electric toothbrush

Abstract

The invention provides an electric toothbrush capable of changing a resonant frequency and vibration amplitude of an eccentric shaft. An electric toothbrush of the present invention includes a motor, an eccentric shaft with one end fixed to a rotation shaft of the motor, and a stem serving as a vibration transmitting component having a bearing for supporting the other end of the eccentric shaft for transmitting vibration generated in accordance with rotation of the eccentric shaft to a brush portion. In the electric toothbrush, eccentric shaft is formed so that a gravity center position is movable at least in one direction among a direction in which a distance to a shaft center is changed and an axial direction.

1 . An electric toothbrush, comprising:
 a motor;   an eccentric shaft with one end fixed to a rotation shaft of the motor; and   a vibration transmitting component for transmitting vibration generated in accordance with rotation of the eccentric shaft to a brush portion, wherein   the eccentric shaft is formed so that a gravity center position is movable at least in one direction among a direction in which a distance to a shaft center is changed and an axial direction.   
     
     
         2 . The electric toothbrush according to  claim 1 , wherein the eccentric shaft includes a plurality of weights positioned so that gravity centers are shifted from the shaft center, and at least one of the plurality of weights is provided rotatably relative to an eccentric shaft main body. 
     
     
         3 . The electric toothbrush according to  claim 2 , comprising:
 a first weight fixed to the eccentric shaft main body and positioned so that a gravity center is shifted from the shaft center; and   a second weight positioned so that a gravity center is shifted from the shaft center with a rotation range regulated so that rotation relative to the eccentric shaft main body is permitted within a fixed range, wherein   a regulated position of the second weight in a rotation direction is differentiated by a rotation direction of the eccentric shaft.   
     
     
         4 . The electric toothbrush according to  claim 1 , wherein the eccentric shaft includes a weight positioned so that a gravity center is shifted from the shaft center, and the weight is provided movably in the axial direction relative to an eccentric shaft main body. 
     
     
         5 . The electric toothbrush according to  claim 4 , wherein a male screw is formed in the eccentric shaft main body, and
 a female screw to be screwed onto the male screw is formed in the weight.   
     
     
         6 . The electric toothbrush according to  claim 4 , wherein the weight is fitted to the eccentric shaft main body slidably in the axial direction. 
     
     
         7 . The electric toothbrush according to  claim 1 , wherein the eccentric shaft includes:
 a first weight fixed to an eccentric shaft main body and positioned so that a gravity center is shifted from the shaft center; and   a second weight positioned so that a gravity center is shifted from the shaft center, the second weight being adapted to be rotatable relative to the eccentric shaft main body, and   the first weight and the second weight are arranged in line in the axial direction so that a plurality of teeth provided in an end surface of the first weight and a plurality of teeth provided in an end surface of the second weight are meshed with each other, thereby forming a ratchet mechanism.   
     
     
         8 . The electric toothbrush according to  claim 1 , wherein the eccentric shaft includes:
 an eccentric shaft main body;   a weight positioned so that a gravity center is shifted from the shaft center; and   a coil spring with one end fixed to the eccentric shaft main body and the other end fixed to the weight.   
     
     
         9 . The electric toothbrush according to  claim 1 , wherein the eccentric shaft includes:
 an eccentric shaft main body; and   a weight positioned so that a gravity center is shifted from the shaft center, and the eccentric shaft main body and the weight are arranged in line in the axial direction while a fluid is placed between the eccentric shaft main body and the weight.   
     
     
         10 . The electric toothbrush according to  claim 1 , wherein a bearing for supporting the other end of the eccentric shaft is provided in the vibration transmitting component.