| 摘要 |
A drawing board is mounted on a support column slidably guided by a vertical pedestal structure and is supported by a cable passing over a pulley which is urged upwardly by a gas cylinder to counterbalance the weight of the drawing board. Opposed brake shoes mounted by toggle linkage on an inner support member are biased into engagement with inner surfaces of the support column by springs acting on sliding pivots of the toggle linkage. The normally engaged brakes are releasable by a foot pedal connected by a rod with a sliding yoke on which the sliding pivots are mounted. The rod is connected with the yoke by engaging in a notch in an edge of the yoke. In the event of breakage of the cable or failure of the counterbalancing cylinder, a safety device is actuated to disconnect the rod from the sliding yoke and thereby permit spring actuation of the brakes to prevent the drawing board from falling.
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