System and method for automatically detecting defective...

B - Operations – Transporting – 41 – J

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Details

CPC

314/41, 101/43

IPC codes

B41J 7/96 (2006.01) B41J 2/35 (2006.01) B41J 2/365 (2006.01)

Type

Patent

Patent number

CA 1241567

Description

SYSTEM AND METHOD FOR AUTOMATICALLY DETECTING DEFEC- TIVE THERMAL PRINTHEAD ELEMENTS Abstract of the Disclosure A system and method are disclosed for automatically detecting any defective elements in a linear array of thermal printhead elements of a ther- mal printer and for automatically correcting for at least one defective thermal printhead element. In a preferred embodiment of the invention an ON/OFF line from a microprocessor is turned OFF to turn off a voltage regulator, thereby preventing the thermal printhead elements from printing. With the voltage regulator OFF, a diode is forward biased to enable a voltage divider to be formed between a sensing resis- tor and any one of the thermal printhead elements that is activated at any given time. To accomplish this, test data, containing only one 1 state bit at any given time, is selectively applied from the micropro- cessor for storage in a shift register. The test data is then latched into a latch circuit and, upon the occurrence of a STROBE pulse used to activate only one of the elements at any given time via the one 1 state bit. By using the voltage divider, an initial refer- ence sense voltage is determined for that element and then digitized and stored in a non-volatile RAM. This sense voltage corresponds to the resistance of that element being measured. Similarly, subsequent initial reference sense voltages are selectively determined for the remaining elements and their digitized values stored in the non-volatile RAM. In each of subsequent test periods, the resistances of the elements are selectively measured and compared with the correspon- ding initial resistance measurements stored in the non-volatile RAM. When a subsequent sense voltage (or resistance measurement) of an element exceeds the value of the initial reference sense voltage for that element by a predetermined amount, that element is detected as a defective element. A software subrou- tine, in the microprocessor is then utilized to change the position of serial data bits carrying data to be printed such that the detected defective thermal element is not utilized during a normal printing operation.

Application Number

486398

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