| 摘要 |
A fall board structure is provided for a keyboard instrument having a keyboard, in which a plurality of keys are arranged between side arms, to actualize light, comfortable and safe operations of a fall board. The fall board structure is basically constructed by arms, torque shaft units and rotation members. Herein, the arm is fixed to a side end of the fall board, so that it rotates in response to rotary movement of the fall board, while the torque shaft unit is fixed to the side arm of the keyboard, wherein it has a shaft portion which rotates in accordance with the rotary movement of the fall board. The rotation member is constructed by a clutch portion and a in lever portion, which is brought into contact with a lower edge portion of the arm at a contact point. The shaft portion of the torque shaft unit engages with the clutch portion of the rotation member equipped with a one-way clutch mechanism such that the clutch portion locks the shaft portion when the shaft portion rotates in a counterclockwise direction corresponding to a close operation direction of the fall board while the clutch portion releases the shaft portion when the shaft portion rotates in a clockwise direction corresponding to an open operation direction of the fall board. Thus, only in a close operation mode of the fall board, the torque shaft unit produces resistance force, which is transmitted to the arm via the contact point.
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