Method of an apparatus for equalizing longitudinal stresses in an advancing web

摘要

A broad textile web, on its way to a processing station such as a rotary-screen printer, passes around a set of closely juxtaposed but independently rotatable feed rollers that are individually driven via respective differential gear trains each having a first input connected to a common drive shaft and a second input connected to an ancillary stepping motor. Each feed roller engages a strip zone of the web which is scanned by an associated sensor upstream of the roller, the latter detecting the leading and trailing edges of recurrent transverse web sections-e.g. of pile fabric-mechanically, electrically or optically distinguishable from intervening sections. Unequal longitudinal tensions in the several strip zones actuate the sensor-controlled stepping motors for different time periods so as to cancel any relative deformation. The lateral edges of a rising web portion are guided between separately driven roller pairs supported by parallelogrammatic linkages which rise or fall according to whether these rollers rotate too slow or too fast in comparison with the web speed, thereby controlling switches which either accelerate or decelerate the corresponding drive motors to keep the web edges straight.