Recognition of ink expiry in an ink jet printing head

摘要

In ink jet printers in which the printing head (33) is connected to an ink reservoir (16), such as may be used in teleprinter or facsimile apparatuses, it is necessary to foresee the expiry of the ink in the reservoir in order to be able in due time to replace the printing head or the pertinent cartridge. A logic circuit (40) is used to count the number of drops gradually expelled, and, with any necessary correction, compares this number with the maximum number of drops equivalent to a known volume of ink contained on average in the reservoir. Expiry of the ink is indicated in in dependence on the result of the comparison.