Ncr Canada Ltd.

Arvindkumar C Vyas

Ralf M Brooks

Brian P Connell

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.

System for detecting defective thermal printhead elements

A variable impact printing mechanism includes a supporting magnetic structure having a plurality of circumferential coils mounted thereon and having a central bore in which a magnetic hammer element is positioned for linear movement to cooperate with a type member positioned adjacent to one end of the bore in order to effect printing on a record member positioned between the hammer and the type member. A controller is provided to energize drivers for the various coils in predetermined sequences to vary the velocity achieved by the hammer element at the end of its printing movement in accordance with varying printing requirements.

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Waterloo, Canada

Arvindkumar C Vyas