Method and apparatus for charging for printing mixed sheet sizes on an electrophotographic printing machine

A method of enabling a self-service printing machine having an external customer interface device to bill for printing jobs having mixed size sheets, comprising the steps of:

• programming different billing rates in the printing machine for different size sheets through use of a user interface;
• receiving a signal from the external customer interface device indicating customer credits therein, wherein said external customer interface device is independent of said user interface;
• controlling the printing of sheets fed to the printing machine, comprising:
• feeding a sheet to the printing machine;
• determining the size of said sheet;
• sending a signal to the external customer interface device corresponding to the billing rate amount programmed for said sheet size;
• deducting said billing rate amount from said customer credits contained within the external customer interface device;
• determining whether customer credits remain in the external customer interface device after deducting said billing rate amount from said customer credits;
• disabling the printing machine in response to the external customer interface device indicating that no customer credits remain within the external customer interface device;
• and
• sending an enable signal from the external customer interface device to the printing machine if credits remain within the external customer interface device;
• and
• repeating said controlling step until printing is terminated.