Patent ID: 8393696

Claim:
An inkjet printing system comprising: an ink reservoir configured to contain a supply of ink and an air space above the supply of ink; an air pressure device fluidly coupled to the air space above the supply of ink, the air pressure device having a negative pressure source configured to withdraw air from the air space above the supply of ink, a positive pressure source configured to inject air into the air space above the supply of ink, and a valve configured to couple either the negative pressure source or the positive pressure source to the air space above the supply of ink; at least one ink ejection device fluidly coupled to the ink reservoir, the at least one ink ejection device configured to receive ink from the supply of ink and to eject ink droplets onto an image receiving surface; and a controller coupled to the valve of the air pressure device, the controller being configured to operate the valve to selectively couple either the negative pressure source or the positive pressure source to the air space above the supply of ink to produce a pressure in the ink reservoir that corresponds to a pressure setpoint, the pressure in the ink reservoir alone changing a mass of the ink droplets ejected by the at least one ink ejection device in response to the controller activating the at least one ink ejection device.