Koki Holdings Co., Ltd.

Kyouichi Nakayama

Yuuki Takeda

A rectifier circuit for rectifying an AC voltage supplied from a commercial power supply into a DC voltage, a smoothing capacitor for smoothing the output of the rectifier circuit, and an electrically powered tool for supplying the smoothed pulsating DC voltage to a motor by an inverter circuit, wherein when the motor is driven while no load is being applied to a tip tool, the smoothed DC voltage repeatedly generates a maximal value and a minimum value so as to synchronize with the fluctuation in the AC voltage. During no-load rotation, control is performed so that driving is performed at a value that is less than a threshold value Dfor the duty ratio at which the generation of a gear sound starts in any of the speed dial setting values 1-6. It is thereby possible to suppress a gear sound generated by a power transmission mechanism during no-load rotation.

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Ibaraki, Japan

Kyouichi Nakayama