| 摘要 |
<p>Apparatus for cutting a running web of paper or the like has a rotary disk-shaped first knife and a driven counterknife. The first knife is rotatable on a shaft which constitutes the piston rod of a double-acting pneumatic cylinder and piston unit. The cylinder of such unit is connected with a second piston rod forming part of a single-acting cylinder and piston unit. The control system for the two units includes a shutoff valve which can admit compressed air to the single-acting unit whereby the pressure in a first conduit which connects the source of compressed air with the single-acting unit rises when the second piston rod reaches an end position in which the marginal portion of the first knife overlaps but is remote from the marginal portion of the counterknife. A second conduit thereupon admits compressed air to the double-acting unit in order to move the first knife axially against the counterknife. The second conduit contains a valve which is responsive to increased pressure of air in the first conduit to insure that the first knife is shifted against the counterknife only when the second piston rod reaches its end position. The double-acting unit holds the first knife away from the counterknife while the single-acting unit moves the second piston rod to its end position.</p> |
