| 摘要 |
<p>A system for accurate web feeding in conjunction with a rotary die cutter or printer where the length of web treated per revolution of the treatment roll is substantially less than the peripheral length of the treatment roll at its effective diameter wherein scrap between treated areas is eliminated through a "net pull-back" of the web during the portion of the cycle when the web is free of the treatment means. In die cutting the system accommodates all the inherent overfeed including that generated by die engagement and disengagement from the web both respectively before and beyond the aligned centers of the impression and complementary rolls thus permitting two-stage cutting of blanks on successive rotations of the impression roll as is frequently required by the most efficient layout pattern on the treatment rolls. In die cutting the impression roll is maintained at constant peripheral velocity and the web, while engaged by the die, travels at the peripheral velocity of the impression roll. As the trailing edge of the die approaches the nip formed by the impression and complementary rolls, one or both of the feed rolls driven by the web is clutched into a cam mechanism for positive driving at a constant velocity equal to the die-induced velocity of the web. This constant velocity driving of the web jointly by the die and feed rolls continues until the die releases the web beyond the aligned centers of the treatment rolls when the web comes under exclusive control of the feed rolls. The camcontrolled velocity of the feed rolls and web then decreases to zero, is maintained at zero velocity for a period of time dependent upon the peripheral distance between the die trailing edge and die leading edge, and is then driven in a reverse direction for a fixed distance and accelerated forward to the peripheral velocity of the impression roll at which point, during the constant velocity motion of the feed rolls as induced by the cam mechanism, the leading edge of the die engages the web at the exact point of disengagement of the trailing edge of the die on the previous cycle. While still in the constant velocity portion of the feed roll drive cycle, the clutch is disengaged and the feed rolls freed for web induced travel, the web itself now being driven by the die engaged therewith.</p> |
