| 摘要 |
In order to be able in a simple manner to supply one or more suction pick-up devices periodically moved relative to the surface of a stack with driving energy, the suction pick-up device is connected to an air volume or source having substantially constant negative pressure over overpressure, and a valve assembly that periodically connects the suction pick-up device to the outside air. The valve assembly is incorporated in the connecting line between the suction pick-up device and the air volume. The valve assembly may be embodied with a control piston that is subject to the action of a restoring force, by a pneumatic multi-way valve having a regulattable frequency, or by a magnetic valve connected to a regulattable frequency generator. With the aid of a regulating device for the cross section of the vent opening, it is possible to generate an amplitude of the suction pick-up device movement that becomes progressively smaller from stroke to stroke after the movable suction pick-up device has been switched on, until it attains a complete standstill.
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