Ink refill unit with ink level indicator

1. An ink refill unit for replenishing an ink cartridge in an inkjet printer, the ink refill unit comprising:

a body containing ink;

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,

wherein the body has a fiexible bag for storing the ink, and the visual indicator is a strip of flexible material fixed to the flexible bag and slidingly retained on a rigid part of the body so that when the flexible bag collapses as the ink is used, the strip slides relative to the rigid part of the body.

2. An ink refill unit according to claim 1 for refilling a negatively pressurized ink storage compartment that supplies ink to a printhead assembly, the ink storage compartment having an interface for receiving the refill unit, the interface having an inlet valve biased to its closed configuration, wherein the refill unit further 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. An ink refill unit according to claim 1 , wherein:

the ink cartridge has a negatively pressurized ink storage compartment that supplies ink to a printhead assembly, and an interface for receiving the refill unit, the interface having a normally closed inlet valve and a normally open outlet valve, both in fluid communication with the ink storage compartment; and

the refill unit further comprises a docking portion having an ink outlet and valve actuator formations, wherein during use, the docking portion releasably engages the interface to actuate the inlet and the outlet valves so the cartridge fills with ink from the body because of the negative pressure in the ink storage compartment.

4. An ink refill unit according to claim 1 for refilling a negatively pressurized ink storage compartment that supplies ink to a printhead assembly via a normally open outlet valve, wherein 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.

5. An ink refill unit according to claim 1 for refilling an ink storage compartment supplying 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,

wherein the refill unit further comprises 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.

6. An ink refill unit according to claim 1 for refilling an ink storage compartment with an interface for releasably engaging with the refill unit, the interface having valves for controlling ink flows into, and out of, the storage compartment,

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

7. 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 a memory circuit for storing information relating to at least one characteristic of the ink; and

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.

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

the ink cartridge has an interface for engaging the ink refill unit; and

the ink refill unit further comprises:

an ink storage compartment;

a docking portion for engaging the interface of the cartridge, the docking portion having a base plate with an ink outlet for connection to an inlet port 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, the centre of the ink outlet being spaced from the transverse centre line.

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

the ink cartridge has an interface for engaging the ink refill unit, an ink storage compartment partially defined by a tubular flexible wall, and a constriction mechanism for constricting the flexible tubular wall by a predetermined amount; and

the ink refill unit further comprises a docking portion for engaging the interface of the cartridge, the docking portion having an ink outlet for connection to an inlet port on the interface, and a plurality of constriction actuators for actuating the constriction mechanism as the ink refill unit engages the interface and releases the constriction mechanism as the ink refill unit disengages the interface.

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

the ink cartridge has an interface for engaging the ink refill unit; and

the ink refill unit further comprises a spigot extending from the body for insertion in an aperture in the interface, the lateral cross section of the spigot being keyed to the shape defined by the aperture to ensure the ink refill is correctly matched to the cartridge.

11. An ink refill unit according to claim 1 wherein the visual indication is a differently colored part of the strip as it slides past a point on the rigid part of the body.

12. An ink refill unit according to claim 11 wherein both ends of the strip are fixed to the flexible bag and retained for sliding past a window in the rigid part of the body, so that the visual indication is the differently colored part appearing in the window.

13. An ink refill unit according to claim 12 wherein the visual indication is an indication that the refill unit is empty.