Apparatus for intermittently advancing a sheet of indeterminate length

摘要

An apparatus for the division-true, intermittent feed of a sheet of indeterminate length has a sheet supply roll; a table for receiving the sheet from the supply roll; a sheet tensioning device disposed between the supply roll and the table; an advancing device for advancing the sheet in each operational cycle through a forward feed stroke that is greater than the divisional distance defined by spaced markings on the sheet; a cutting device for cyclically severing a length from the sheet subsequent to the forward feed stroke; a reversing device for retracting the sheet in each operational cycle through a centering stroke subsequent to the forward feed stroke. The reversing device includes a force-exerting arrangement-constituted solely by the tensioning device-for imparting to the sheet a force for executing the centering stroke, a sensor head cooperating with the moving sheet for responding to the presence or absence of the sheet markings; a solenoid assembly having a solenoid and being connected with the sensor head for changing the state of energization of the solenoid as a function of the response of the sensor head to the sheet markings and an armature cooperating with the solenoid and the sheet for selectively immobilizing or releasing the sheet as a function of the state of energization of the solenoid.