a checkpoint system , wheeled bins for a checkpoint system , and methods for conveying articles in wheeled bins through a checkpoint system . each bin has four wheels that do not extend below the bin &# 39 ; s flat bottom . in this way , the bin can be slid on its bottom along a shallow , troughed divesting table while it is being filled and conveyed on its bottom through a checkpoint and rolled on its wheels along a deeper troughed discharge lane . a bin return beneath the discharge lane returns bins to a bin storage queue beneath the divesting table . a sorter at the output of the checkpoint selectively diverts bins to one or more discharge lanes , such as individual lanes for cleared and for suspect bin contents .