Mailbox or sorter bin use sensing system

In a multi-bin sheet collecting system for a reproduction apparatus, in which printed sheets may be directed to selected bins of an array of said bins for job separation, sorting, and/or user mailboxing, to stack on a tray member in said selected bin, the improvement wherein the removal of printed sheet from individual said bins may be sensed to indicate the availability of individual bins for the direction of further printed sheets therein, comprising:

• one individual integral optical transmitter/receiver unit mounted in one aperture in each said bin tray member, in an area of said tray member to be overlaid by sheets stacked thereon;
• each said integral optical transmitter/receiver unit having a light transmitting element for transmitting a first light beam in a first direction towards another said optical transmitter/receiver unit in a next adjacent said bin of said array in said first direction;
• each said integral optical transmitter/receiver unit also having a light beam receiving element for receiving a second light beam from another said optical transmitter receiver unit in another next adjacent said bin of said array;
• said light beam receiving element generating an electrical bin empty signal in response to receiving said second light beam unless said second light beam is blocked by sheets in said tray member of said another next adjacent bin;
• and a controller operatively connected to said integral optical transmitter/receiver units to indicate which said bins are empty and available in response to said respective electrical bin empty signals and to indicate which said bins have unremoved printed sheets therein and are unavailable in response to the absence of said respective electrical bin empty signals.