Ink refill unit for docking with an ink cartridge

1. 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.

2. A refill unit according to claim 1 , wherein:

the interface has an inlet valve biased to its closed configuration; and

the refill unit comprises engagement formations for releasably engaging the interface and an inlet valve actuator for opening the inlet valve 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. A refill unit according to claim 1 , wherein:

the refill unit interfaces with the ink storage compartment 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. A refill unit according to claim 1 , wherein:

the printhead assembly has an array of nozzles, and 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. A refill unit according to claim 1 , wherein:

the interface has valves for controlling ink flows into, and out of, the storage compartment; and

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

6. A refill unit according to claim 1 for refilling an ink cartridge that forms part of an inkjet printer, the printer also having a printhead, control circuitry and an interface for releasably engaging the refill unit,

wherein 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

wherein, during use, the memory circuit allows the control circuit to interrogate it to verify that the ink in the refill unit is suitable for the printer.

7. A refill unit according to claim 1 , wherein:

the docking portion has a base plate with an ink outlet for connection to an inlet port on the interface;

the refill unit further comprises engagement formations for releasably engaging the interface, the engagement formations being formed on the transverse centre line of the base plate; and

the centre of the ink outlet is spaced from a transverse centre line.

8. A refill unit according to claim 1 , wherein the ink refill unit further comprises:

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

a spigot extending from the body for insertion in an aperture in the interface, and

wherein the lateral cross section of the spigot is keyed to the shape defined by the aperture to ensure the ink refill is correctly matched to the cartridge.

9. A 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.

10. An ink refill unit according to claim 1 wherein the docking portion has valve actuator formations and the interface has a normally closed inlet valve and a normally open outlet valve, such that the ink outlet forms a sealed connection with the inlet valve upon releasable engagement of the docking portion with the interface.

11. An ink refill unit according to claim 10 wherein the valve actuator formations close the outlet valve and subsequently opens the inlet valve upon releasable engagement of the docking portion with the interface.

12. An ink refill unit according to claim 11 wherein the valve actuator formations are two spigot like projections with a tri star cross section.

13. An ink refill unit according to claim 12 wherein the ink outlet has a normally closed valve that is configured to open as the ink outlet forms a sealed connection with the inlet valve of the interface.