Recirculating document feeder with stack weight determined pressurized air/vacuum levels and method

An improved recirculating document feeder for presenting sheets from a document sheet stack individually to a station of a reproduction apparatus for reproducing information contained on such sheets, said improved recirculating document feeder comprising:

• means for supporting a document sheet stack;
• means, defining a feed path extending away from and then back to said document stack supporting means, for directing sheets from a document sheet stack on said document stack supporting means into association with said reproduction apparatus station and then back to such stack;
• vacuum assisted friction feed means, operatively associated with sad document stack supporting means, for feeding respective sheets from the stack seriatim;
• means for directing a flow of pressurized air at a document sheet stack on said document sheet stack supporting means to facilitate separation of individual document sheets in such stack;
• and
• control means for regulating pressurized air and vacuum levels to facilitate sheet separation and feeding reliability based on the weight of a document sheet stack on said document sheet stack supporting means, said control means including means for counting the total number of individual document sheets in such document sheet stack, means for determining the height of the original topmost document sheet of such stack at a particular point in time, means for counting the number of individual document sheets fed from such stack from such particular point in time, means for computing the weight of each individual document sheet based on the counted number of document sheets from such particular point in time, means for calculating the total weight of such stack based on the weight of each individual document sheet and the total number of documents sheets in the such stack, and means for adjusting the pressurized air and vacuum levels to predetermined levels based on the calculated total weight of such stack within an operating window whereby induced air flow is sufficiently high to prevent multi-sheet feeds yet sufficiently low to prevent sheet stack dishevelment.