The two ends of the cord-like object are respectively fixed on one side of the rolling part and the jettison device.
以及索状物，其一端固定于所述收卷部件的一侧，另一端则固定于所述弹性装置上；
The jettison device is a spring. The utility model has the advantage of reducing the subpressure loss of the vacuum in the process of perforation, and saving energy.
本实用新型的优点是减少在打孔时的真空的负压损失，节约能耗。
The jettison device is a spring. The utility model has the advantage of reducing the subpressure loss of the vacuum in the process of perforation, and saving energy.
本实用新型的优点是减少在打孔时的真空的负压损失，节约能耗。
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