The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Oct. 28, 1997
Filed:
Oct. 31, 1994
John M Wade, Poway, CA (US);
Christopher J Shultz, San Diego, CA (US);
Betsy C Huntingdon, West Lafayette, IN (US);
Hewlett-Packard Company, Palo Alto, CA (US);
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. The method is quickly and readily performed by a printer before printing or between printing intervals. The indication of low ink supply can be used to develop printer shutdown, or use of a reserve print cartridge, or an operator warning, or a combination of these tactics.