Ink refill unit with keyed connection ink cartridge

1. An ink refill unit for replenishing an ink cartridge in an inkjet printer, the ink cartridge having an interface for engaging the ink refill unit to an ink storage compartment of the ink cartridge, the ink refill unit comprising:

a body containing a quantity of colored ink; and,

an ink outlet for engaging an ink inlet in the interface; wherein

a valve actuator of the ink refill unit has a complementary shape only to a valve aperture of the interface of an ink cartridge of the same color ink as the colored ink contained in the refill unit such that the valve actuator and the corresponding valve aperture have a keyed connection with each other.

2. An ink refill unit according to claim 1 , wherein:

the ink storage compartment is negatively pressurized, supplies ink to a printhead assembly, and has an interface for receiving the refill unit, the interface having an inlet valve biased to its closed configuration; and

the refill unit further comprises engagement formations for releasably engaging the interface and the valve actuator is configured to open the inlet valve via the valve aperture as the refill unit engages the ink interface so that the ink in the body is in fluid communication with the ink storage compartment.

3. An ink refill unit according to claim 1 , wherein:

the ink storage compartment is negatively pressurized ink storage and supplies ink to a printhead assembly via a normally open outlet valve; and

the refill unit further comprises engagement formations for releasably engaging the ink storage compartment and an outlet valve actuator for closing the outlet valve as the refill unit engages the ink storage compartment.

4. An ink refill unit according to claim 1 , wherein:

the ink storage compartment supplies a printhead assembly with an array of nozzles, wherein during use, the ink storage compartment is maintained at a negative pressure to avoid inadvertent ink leakage from the nozzles;

the refill unit further comprises an ink outlet and a repressurizing arrangement;

upon engagement of the refill unit with the ink storage compartment, the repressurizing arrangement causes part of the ink storage compartment to be inwardly depressed as the ink from the body is drawn into the ink storage compartment through the ink outlet by the negative pressure until pressure equalization; and

upon subsequent disengagement of the refill unit from the ink storage compartment, the repressurizing arrangement releases the inwardly depressed part of the ink storage compartment to re-establish the negative pressure.

5. An ink refill unit according to claim 1 , wherein:

the interface releasably engages with the refill unit and has valves for controlling ink flows into, and out of, the storage compartment; and

the refill unit further comprises an ink outlet and valve actuators for actuating the valves when the refill unit engages the interface, such that the valve actuators actuate the valves in a predetermined sequence.

6. An ink refill unit according to claim 1 , wherein:

the ink cartridge forms part of the inkjet printer which has a printhead, control circuitry and an interface for releasably engaging the refill unit;

the refill unit further comprises an ink outlet and a memory circuit for storing information relating to at least one characteristic of the ink; and

during use, the memory circuit being interrogated by the control circuit to verify that the ink in the refill unit is suitable for the printer.

7. An ink refill unit according to claim 1 , further comprising:

an ink storage compartment;

a docking portion for engaging the interface of the cartridge, the docking portion having a base plate with the ink outlet for connection to the ink inlet on the interface; and

engagement formations for releasably engaging the interface, the engagement formations being formed on a transverse centre line of the base plate, a centre of the ink outlet being spaced from the transverse centre line.

8. An ink refill unit according to claim 1 , further comprising:

an ink outlet for engaging a complementary ink inlet in the cartridge; and

a visual indicator to provide a visual indication when a predetermined quantity ink has flowed from the refill unit into the cartridge.

9. An ink refill unit according to claim 1 wherein the valve actuator comprises a spigot extending from the body for insertion in the valve aperture in the interface; wherein,

the lateral cross section of the spigot is keyed to the shape defined by the valve aperture at only one orientation of the refill unit with respect to the interface.

10. An ink refill unit according to claim 9 wherein the spigot has a tri-star cross section.

11. An ink refill unit according to claim 10 wherein the spigot is tapered.