| 摘要 |
A spindle to be intermittently driven by a continuously rotating belt is journaled on mounting arm which is swingable on a supporting rail about a pivotal axis parallel to the spindle axis. A lever fulcrumed on the spindle carries two rollers coacting with an encircling track fixed to the rail, the two rollers defining with respective recesses in the track a pair of stable positions in which the lever can be indexed by a toggle mechanism articulated to the mounting arm and the lever. A torsion spring anchored to the rail and to the mounting arm tends to swing the latter into the first stable position in which a whorl on the spindle engages the driving belt for frictional entrainment thereby; in the alternate stable position the spindle is decoupled from the belt.
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