Christopher James Shultz

US Patent:

56821832, Oct 28, 1997

Filed:

Oct 31, 1994

Appl. No.:

8/332544

Inventors:

John M. Wade - Poway CA
Christopher J. Shultz - San Diego CA
Betsy C. Huntingdon - West Lafayette IN

Assignee:

Hewlett-Packard Company - Palo Alto CA

International Classification:

B41J 2195
B41J 29373

US Classification:

347 7

Abstract:

Disclosed is a method of determining imminent ink exhaustion in a thermal inkjet print cartridge based on the discovery that ink drop volume falls at a faster rate at high frequency firing rates than at low frequency firing rates as ink supply diminishes. The method includes warming the print cartridge printhead and ink to a predetermined temperature; then operating the print cartridge printhead at a first firing frequency to eject a volume of ink, said operating step including heating the ink and printhead, carrying away heat in the ejected volume of ink, and conveying a volume of cooler ink to the printhead to replace the ejected volume; and monitoring a first temperature change from the predetermined temperature. Then warming the same print cartridge printhead and ink to a predetermined temperature; operating the print cartridge printhead at a second firing frequency which is different than the first firing frequency to eject a volume of ink, said operating step including heating the ink and printhead, carrying away heat in the ejected volume of ink, and conveying a volume of cooler ink to the printhead to replace the ejected volume; and monitoring a second temperature change from the predetermined temperature. The first and second temperature changes are compared to indicate a low ink supply.