A typical ink jet printer has a pen that reciprocates over a printable surface such as a sheet of paper. The pen includes a print head having an array of numerous orifices through which droplets of ink may be expelled onto the surface to generate a desired pattern. Some ink jet printers have a replaceable ink supply mounted to a stationary position on the printer, and connected to a reciprocating print head by a conduit. This permits the use of a larger ink supply, and avoids the need to replace the print head each time the supply of ink is depleted. Color ink jet printers generally have several ink supply cartridges each containing a different color of ink, or a multi-chamber cartridge.
Printers with remote or "off axis" ink supplies are normally shipped with the ink supplies and print head removed. The ink conduit is empty, open to ambient air, or in a "dry" condition. This avoids potential leakage of the ink and shelf life reduction that begins when the seal of an ink supply cartridge is penetrated. More significantly, if ink were to remain in the ink conduit for an extended period between manufacturing and first use, air may be absorbed by the ink, and water evaporated. This would undesirably change the consistency of the ink beyond normal parameters. In addition, the print head may be protected in special packaging against potential shocks during shipping. When printers are shipped "dry, " the ink conduits are empty, except for the presence of ambient air.
When setting up such a printer for its first use, as ink flows from the ink supply to the print head and its on-board reservoir, the air volume within the ink tube is forced into the print head reservoir. If the reservoir is sufficiently large, this can be readily accommodated, but leaves a substantial air volume in the reservoir. Thereafter, ambient pressure or temperature variations, such as caused by changing weather or air travel, can generate pressure changes in the air bubble that undesirably force ink from the orifices. The consequences of such leakage or "drool" include user inconvenience, printer damage, and impaired printing.
The present invention overcomes the limitations of the prior art by providing an ink jet printer with a body defining a paper path and a carriage operable to reciprocate across the paper path. An ink supply receptacle on the body is spaced apart from the carriage, and an ink conduit extends between the ink supply receptacle and the carriage. A suction apparatus on the carriage has an expandable chamber with an inlet connected to the conduit, and moves between a collapsed position and an expanded position, such that ink may be drawn from an ink supply connected to the receptacle to displace at least some of the air from the tube. The chamber may be spring biased to the expanded position, and constrained to the collapsed position during shipping, so that removal of the constraint after installation of ink supplies will draw ink into the conduit to displace air. The suction apparatus may also be installed in a position on the carriage later to be occupied by the print head.