May Sau Ho

US Patent:

51092344, Apr 28, 1992

Filed:

Sep 14, 1990

Appl. No.:

7/583297

Inventors:

David R. Otis - Somerville MA
May F. Ho - La Mesa CA

Assignee:

Hewlett-Packard Company - Palo Alto CA

International Classification:

B41J 2365
B41J 238

US Classification:

346 11

Abstract:

A thermal technique for reducing print density shifts due to print wait time in thermal ink jet printers. The ink jet firing resistors of the printhead are driven with warming pulses having a pulse width insufficient to cause ink drop firing at the warming pulse frequency. They are driven for an interval that depends on the amount of time that has elapsed since printing by the printhead last occurred, or an interval that depends on the amount of decrease in the printhead temperature since printing stopped. In a particular embodiment of the printhead warming technique, the warming pulses have the same amplitude as the ink drop firing pulses, and a higher frequency.