AUTOMATICALLY REPOSITIONABLE OUTPUT STACK RETENTION SYSTEM

In a sheet ejection and stacking system, such as for a document handler output, in which an upper sheet feeding and ejection unit with a she et ejection path is repositionable between an open and a closed position relati ve to a lower sheet stacking unit which is providing a sheet stacking tray for the ejected sheets, here a platen cover unit. The sheet stacking tray has an automatically adjusting sheet stacking registration edge wall defining syste m which is automatically maintained closely adjacent to the sheet ejection pos ition of the upper unit. This system is defined by upstanding stack retaining wall members movably mounted to the sheet stacking tray and a plurality of aligni ng post members integral the upper unit which automatically engage and move the stack retaining members into alignment with the upper unit, into a proper sh eet receiving position therewith, when the upper unit is closed Yet, the retaini ng members retain the ejected sheets substantially in their desired stacking po sition when the upper unit is opened. The aligning post members overlap and mate within the stack retaining members in the closed position to fully block mov ement of ejected sheets into or under the upper unit. Considerable mounting or oth er misalignment tolerances are automatically compensated for between the two units with this system.