| 摘要 |
An overhead control for raising and lowering garage doors and other cyclically operated devices which utilizes a unidirectional electric motor which drives an endless chain in only one direction. A follower rides on a rail and is coupled to the endless chain by a gear which engages the chain on one side so as to move the follower in a first direction. When the follower reaches the end of the rail, the gear of the follower rotates 180 DEG so as to engage the opposite side of the chain and thus move the follower in the opposite direction. The tension may be adjusted so that a door will stop or reverse when it meets resistance sufficiently firm to shift the gear of the follower.
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