Patent ID: 7331661

Claim:
An ink refill unit for an ink cartridge, the ink cartridge having a negatively pressurized ink storage compartment that supplies ink to a printhead assembly, and an interface for releasably receiving the refill unit, the refill unit comprising: a body containing a quantity of ink; a docking portion with an ink outlet; and a constriction actuator configured to actuate a constriction mechanism of the ink storage compartment as the ink refill unit engages the interface and release the constriction mechanism as the ink refill unit disengages the interface, thereby causing constriction and relaxation of a flexible wall of the ink storage compartment by the constriction mechanism, wherein, the docking portion is configured to establish fluid communication between the body and the ink storage compartment through the ink outlet when the ink refill unit engages the interface, such that ink is drawn from the body into the cartridge because of the negative pressure in the ink storage compartment caused by said constriction.