The two ends of the cord-like object are respectively fixed on one side of the rolling part and the jettisondevice.
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；
2
The jettisondevice 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.