Importance

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Abstract

A color ink jet printing device has an off-board ink reservoir for each color being printed. Each reservoir comprises at least two separately replaceable cartridges from which ink is supplied under positive pressure to refill replaceable printhead cartridges. A visual indicator is provided for each off-board cartridge to indicate when the cartridge is empty and this indicator is turned on if the ink supply in the cartridge is exhausted during a refill operation. Printing is not stopped until all off-board cartridges holding one color of ink are empty. At this time the empty cartridges that held any color ink, are replaced. After each operator intervention to replace empty cartridges, the volume of each color ink will be (N-1)/N of maximum reservoir capacity where N is an integer greater than one and represents the number of cartridges in the reservoir. The empty status of a reservoir cartridge is determined by sensing the level of ink in the printhead cartridge a fixed time interval after initiation of a refill operation from the reservoir cartridge.

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First Claim