System for detecting defective thermal printhead elements

Details System for detecting defective thermal printhead elements System for detecting defective thermal printhead elements

1984-08-14

1986-06-17

Goldberg, E. A.

Recorders

Thermal recording

400 54, 400120, 219216, G01D 1510

Patent

active

045959358

ABSTRACT:
A system and method are disclosed for automatically detecting any defective elements in a linear array of thermal printhead elements of a thermal 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 resistor and any one of the thermal printhead elements that is activated at any given time. When a subsequent sense voltage (or resistance measurement) of an element exceeds the value of the initial reference sense voltage for that by a predetermined amount, that element is detected as a defective element. A software subroutine, 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.

REFERENCES:
patent: 4284876 (1981-08-01), Ishibashi et al.
patent: 4321610 (1982-03-01), Moore et al.
patent: 4364063 (1982-12-01), Anno et al.
patent: 4453166 (1984-01-01), Enoto
patent: 4500893 (1985-02-01), Sakura et al.

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