Magnetic feeding device

摘要

Means are provided for accurate incremental feeding of web material from a supply to a work station by a combination of intermittent drive means for advancing the web and electrically controlled magnetic brake means for clamping and stopping the web after a desired increment thereof has been fed from the supply to the work station. In one embodiment the intermittent drive means comprises a second magnetic brake means reciprocated through advance and retraction strokes of predetermined length which is actuated and deactuated in phase opposition with the first brake means to effect the incremental advance of the web. In another the embodiment intermittent drive means is comprised of sequential feed rolls which nip the web material over a predetermined circumferential extent of the rolls to effect a given incremental advance. If the web carries registration marks defining the exact increment of advance desired then a photodetector is used to trigger one or both brake means when the proper increment of advance has been achieved. In this event the intermittent drive means is set to advance the web in slightly larger increments than those desired and the photodetector thus controls the final incremental length of the web presented to the work station. Both of these embodiments are adapted to heavier materials or those requiring greater gripping force by dual magnets having opposed core and coil assemblies of opposite polarities.