Printer comprising priming pump and downstream expansion chamber

1. A printer comprising:

an inkjet printhead having an ink inlet, an ink outlet and an array of nozzles;

an ink chamber having an outlet port connected to said ink inlet via an upstream ink conduit;

an air pump having a pump outlet communicating with a headspace in said ink chamber, said pump being configured to positively pressurize said headspace during a printhead priming operation; and

a downstream ink conduit connected to said ink outlet, said downstream ink conduit communicating with a pump inlet of said pump,

wherein said downstream ink conduit includes an expansion box for accommodating a volume of ink, thereby inhibiting said ink from reaching said pump inlet, and

wherein said expansion box comprises:

at least one expansion chamber, said expansion chamber having a respective chamber inlet defined in a base thereof, said chamber inlet being connected to said downstream ink conduit;

a common air chamber having an air outlet defined in a base thereof, said air outlet being connected to said pump inlet via a pump inlet conduit; and

a cover for said expansion chamber and said common air chamber, said cover defining a roof of said expansion box, said cover having at least one air channel defined therein, said air channel providing fluid communication between said at least one expansion chamber and said common air chamber.

2. The printer of claim 1 , wherein said air channel is a serpentine channel for minimizing transfer of ink from said expansion chamber to said common air chamber.

3. The printer of claim 2 , wherein said air channel is hydrophobic.

4. The printer of claim 2 , wherein said air channel comprises at least one ink-trapping stomach.

5. The printer of claim 1 , wherein said air channel terminates at a channel outlet defined in a roof of said air chamber, said channel outlet being positioned to deposit ink into said air chamber.

6. The printer of claim 5 , wherein said channel outlet is offset from said air outlet.

7. The printer of claim 6 , wherein a snorkel extends from said air outlet towards said roof, thereby maximizing an effective ink-collecting volume of said air chamber.

8. The printer of claim 1 , wherein said cover has an air vent defined therein.

9. The printer of claim 8 , wherein said cover has one or more air vents defined therein, the number of air vents regulating a pressure in said expansion box.

10. The printer of claim 1 , comprising a timing circuit for controlling operation of said pump during printhead priming.

11. The printer of claim 1 , comprising an ink sensor for sensing ink in said expansion chamber, said sensor cooperating with said pump such that said pump is shut off when said sensor senses ink.

12. The printer of claim 11 , wherein said expansion chamber is configured to promote expansion and bursting of ink bubbles entering said chamber, thereby minimizing phantom sensing of ink in said chamber.

13. The printer of claim 1 , wherein said air pump is reversible for effecting both priming and depriming operations.

14. The printer of claim 1 , further comprising a conduit junction, said conduit junction comprising:

a plurality of junction outlets, each junction outlet being connected to a headspace port of each ink chamber;

a junction inlet connected to said pump outlet.

15. The printer of claim 14 , wherein said conduit junction comprises an air vent such that each headspace is open to atmosphere.

16. The printer of claim 1 , wherein said downstream ink conduit comprises any one of:

an inline electronically-controlled valve; and

a loop section passing below a level of ink in said ink chamber.

17. The printer of claim 1 , wherein said ink chamber maintains a predetermined level of ink when said pump is switched off.

18. The printer of claim 1 , wherein said ink chamber comprises a float valve cooperating with an ink reservoir for maintaining said predetermined level of ink.