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Method and Device to Alert Service that a Thermal Print Head Needs Replacement Disclosure Number: IPCOM000014262D
Original Publication Date: 2000-Sep-01
Included in the Prior Art Database: 2003-Jun-19

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As thermal printer speeds increase the thermal print head is being stressed to its limits. Some print heads are designed with thermal gradients so large that the glass over coatings crack on the frequently used elements. This condition gradually degrades print quality until a subjective limit is exceeded and the print head is replaced. Some applications are very sensitive to missing dots bar code printing for example. This leads to the need for a method and device for identifying bad print elements so that appropriate maintenance can be scheduled. In the case of bar code printing, one missing element might require print head replacement. In another application, a "soft" failure could be recorded so that print head replacement might be scheduled at some convenient time. All of this is possible with this invention. Figure 1 shows a schematic circuit of a printer that scans the print head and records burned out elements. A device (Hexsense from International Rectifier) monitors the current through each print element as each is scanned by the microprocessor. This scanning is done at a time when no printing is done, possibly after a power on reset. The pulse length (maybe 25 microseconds or shorter) can be much shorter than a normal print pulse length (typically 300 microseconds) so that no dots are printed on the thermal paper. The circuit is simple and straightforward. 1 2