Electric toothbrush

Abstract

An electric toothbrush is provided with a brush portion, a motor including a rotary shaft, a battery, which supplies the motor with power supply voltage, and an eccentric shaft, which rotates together with the rotary shaft. The eccentric shaft has a center of gravity located at a position deviated from an axis of the rotary shaft of the motor. An oscillation transmission mechanism transmits oscillations generated by the rotation of the eccentric shaft. An oscillation amplitude regulation circuit regulates an oscillation amplitude of the brush portion to be constant regardless of changes in the power supply voltage in a state in which the brush portion is free from external loads.

1 . An electric toothbrush comprising:
 a brush portion;   a motor including a rotary shaft;   a battery which supplies the motor with power supply voltage;   an eccentric shaft which rotates together with the rotary shaft, in which the eccentric shaft has a center of gravity located at a position deviated from an axis of the rotary shaft of the motor;   an oscillation transmission mechanism which transmits oscillations generated by the rotation of the eccentric shaft to the brush portion; and   an oscillation amplitude regulation circuit which regulates an oscillation amplitude of the brush portion to be constant regardless of changes in the power supply voltage in a state in which the brush portion is free from external loads.   
   
   
       2 . The electric toothbrush according to  claim 1 , wherein the oscillation amplitude regulation circuit includes a pulse generation circuit which supplies the motor with the power supply voltage in pulses of a predetermined pulse duration period set to regulate the oscillation amplitude of the brush portion to be constant in accordance with the value of the power supply voltage supplied from the battery. 
   
   
       3 . The electric toothbrush according to  claim 1 , wherein the oscillation amplitude regulation circuit converts the power supply voltage supplied from the battery into constant voltage for regulating the oscillation amplitude of the brush portion to be constant, and supplies the motor with the constant voltage. 
   
   
       4 . The electric toothbrush according to  claim 2 , wherein the oscillation amplitude regulation circuit:
 detects load current applied to the motor when external load is applied to the motor; and   supplies the motor with the power supply voltage in pulses of the predetermined pulse duration period set to regulate the oscillation amplitude of the brush portion to be constant in accordance with both the value of the power supply voltage supplied from the battery and the value of the detected load current.   
   
   
       5 . The electric toothbrush according to  claim 2 , wherein the oscillation amplitude regulation circuit:
 detects rotation speed of the motor when external load is applied to the motor; and   supplies the motor with the power supply voltage in pulses of the predetermined pulse duration period set to regulate the oscillation amplitude of the brush portion to be constant in accordance with both the value of the power supply voltage supplied from the battery and the detected rotation speed.   
   
   
       6 . The electric toothbrush according to  claim 2 , wherein the oscillation amplitude regulation circuit:
 detects back electromotive force of the motor when external load is applied to the motor; and   supplies the motor with the power supply voltage in pulses of the predetermined pulse duration period set to regulate the oscillation amplitude of the brush portion to be constant in accordance with both the value of the power supply voltage supplied from the battery and the value of the detected electromotive force.   
   
   
       7 . The electric toothbrush according to  claim 2 , wherein the pulse generation circuit includes:
 a memory which stores the value of the power supply voltage supplied from the battery in association with the predetermined pulse duration period set to regulate the oscillation amplitude of the brush portion to be constant; and   a switch element which functions in accordance with a pulse signal having a pulse duration period stored in the memory;   wherein the power supply voltage is supplied in pulses to the motor via the switch element.