Indexing roll drive system

Abstract

A short dwell indexing drive system for intermittently moving a web of thermosealing material through a bag machine includes a conjugate cam defined by a pair of disc cams on a continuously driven input or cam shaft which engage cooperating groups of cam followers on an intermittently driven output shaft that yields one web draw/dwell cycle for each revolution of the cam shaft. In the preferred embodiment the contour of the cams smoothly index the web by first accelerating the output shaft from zero velocity through a relatively low peak velocity and thereafter decelerating the web to zero velocity at a point in the cycle in excess of 180.degree. before the output shaft is held stationary to the end of the cycle during a dwell period. Belt drives and an adjustable jackshaft which allows the use of different pulley ratios are connected between the output shaft and a web engaging draw roll for amplifying or reducing motion of the output shaft and for providing articles such as bags of different sizes. If articles such as heat sealed thermoplastic pouches are to be made from webs of thermosealing material or laminate, the drive system may be modified by changing the cam configuration to provide a long dwell that requires in excess of 180.degree. of each cycle of operation with the remaining portion of the cycle being used to advance the web.