US 5,699,090 A · Out of ink detector for a thermal inkjet printer

Abstract

When a thermal inkjet print cartridge operates to eject ink, three things happen at once: (1) heating by the heating resistor with flow of heat into the ink chamber; (2) cooling by heat drain toward the reservoir, print cartridge body and to ambient; and (3) cooling by carrying away of heat in the ink drops and replacement by cooler ink from the reservoir. The present invention is a method of detecting a depleted ink supply by monitoring the temperature of the printhead substrate with a temperature sensitive resistive trace on the printhead surface. When the print cartridge is warmed with warming pulses to a temperature higher than its normal operating temperature: and then firing pulses are implemented to eject ink, the temperature measured by the thermal sense resistor will decrease if the print cartridge is ejecting its normal, or nearly normal, amount of ink. If the print cartridge is ejecting less than its normal amount of ink the temperature will decrease less, stay the same, or even increase. It is this temperature increase or decrease that is used as an ink ejection detector. The method is quickly and readily performed by a printer before printing or between printing intervals. The indication of a depleted 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.

Claims20

Dependent claims

A method for operating a thermal-ink jet printer including a printhead having ink-firing heater resistors responsive to pulses provided to the printhead, said method including detection of an out-of-ink condition in the printer and comprising the steps of:

directing to the printhead ink-nonfiring warming pulses to warm the printhead to a temperature that is higher than a temperature that would be produced pursuant to ink-firing pulses;
then directing to the printhead ink-firing pulses;
sampling the temperature of the printhead while the ink-firing pulses are directed to the ink-firing resistors to produce a set of temperature samples;
determining a temperature approximation equation for a curve that is fitted to the temperature samples, wherein the approximation equation defines temperature as a function of time, the temperature approximation having a slope associated therewith;
determining the slope of the determined temperature approximation equation;
ascertaining from the determined slope of the temperature approximation equation whether an out-of-ink condition exists;
and
holding, in a nonvolatile memory, automatically readable instructions for automatic performance of the above-enumerated steps.

5 more elements

A method for operating a thermal-inkjet facsimile machine, said machine being for unattended operation overnight and on weekends, and said machine including a printhead having ink-firing heater resistors responsive to pulses provided to the printhead;

said method including detection of an out-of-ink condition in the facsimile machine, and comprising these steps:
while the facsimile machine is operating unattended overnight and on weekends, directing to the printhead ink-nonfiring warming pulses to warm the printhead to a temperature that is higher than a temperature that would be produced pursuant to ink-firing pulses;
then, while the facsimile machine continues operating overnight and on weekends, directing to the printhead ink-firing pulses;
sampling the temperature of the printhead while the ink-firing pulses are directed to the ink-firing resistors to produce a set of temperature samples;
then, while the facsimile machine continues operating overnight and on weekends, determining a temperature approximation equation for a curve that is fitted to the temperature samples, wherein the approximation equation defines temperature as a function of time, the temperature approximation having a slope associated therewith;
then, while the facsimile machine continues operating overnight and on weekends, determining the slope of the temperature approximation equation;
then, while the facsimile machine continues operating overnight and on weekends, ascertaining from the determined slope of the temperature approximation equation whether an out-of-ink condition exists;
and
then, while the machine continues operating overnight and on weekends, applying the ascertained out-of-ink condition to automatically bring into service a different printhead.

6 more elements

Dependencies are inferred from the claim text.

Out of ink detector for a thermal inkjet printer

Life of this patent

Out of ink detector for a thermal inkjet printer

Life of this patent

Abstract

Claims20