| 摘要 |
A gear mechanism includes a sun gear, a planetary gear, an internal gear and a cam gear. The planetary gear is disposed so as to continuously engage the sun gear. When the gear mechanism is operated, the planetary gear revolves around the sun gear while rotating on its own axis. The internal gear is disposed so as to be movable in a direction perpendicular to the axis of the sun gear so as to engage the planetary gear. The internal gear is kept apart from the planetary gear when the gear mechanism is non-operated and engages the planetary gear when the gear mechanism is operated. The cam gear rotatably supports the planetary gear. Upon receiving an external driving force, the cam gear moves the internal gear in a direction perpendicular to the axis of the sun gear so as to engage the internal gear with the planetary gear. The cam gear is rotated so as to revolve the planetary gear around the sun gear.
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