| 摘要 |
An electric toothbrush has a balanced mass provided on a shaft extension that rotates freely about a longitudinal axis, inside a cavity in a brush head The shaft extension and the brush head are flexibly coupled to a drive shaft and to a remote end of a shank respectively. When the shaft is rotated by an electric motor in a handle, of the toothbrush, an off-set stub axle, effectively at a remote end of the shaft extension and fitted to a bearing in the brush head, causes the brush head to vibrate. The shank is not caused to vibrate to any extent.
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