Epm having a system for detecting fault conditions of the thermal

Abstract

In an electronic postage meter which has a thermal printer and a control system for causing the thermal printer to print a postage indicia, the thermal printer includes a linear array of thermal elements. The electronic postage meter control system is comprised of a print control circuit for producing lengthwise and serially, during a first mode of operation, a composite image having alphanumeric characters and graphic data. The image is divided into a plurality of widthwise sections. A first widthwise section has highly critical alphanumeric character information and graphic information. A second widthwise section of the image having less critical alphanumeric character information. The control system has a second mode of operation for producing serial test data coupled to the thermal elements such that the thermal print elements are selectively responsive to the serial test data for developing for each of the thermal elements an associated test signal during each second mode of operation. A comparison of each test signal for each of the thermal elements against an associated predetermined reference signal is performed in order to automatically generate an associated failure signal when a defective thermal element is detected during a second mode of operation. If, the failure is associated with first widthwise section and no failure are associated with the second widthwise section, than the image is shifted to avoid the failure, otherwise print is stopped. If the failure is associated with the second widthwise section and the failures are less that a predetermined number than the thermal printer continues to print, otherwise printing stop.