Patent ID: 7841706

Claim:
An ink supply device for supplying ink from an ink tank to a print head, the ink supply device comprising: detection means for detecting an ink pressure in the print head; pressure application means for selectively applying a negative pressure or a positive pressure to an interior of the print head, the pressure application means being installed in an ink supply path for supplying ink from an interior of the ink tank to the interior of the print head; predetermined negative pressure application means installed in the ink supply path to apply a predetermined negative pressure to the print head; and control means for controlling the pressure application means based on the ink pressure detected by the detection means to adjust the pressure applied to the interior of the print head; wherein the detection means is installed near the print head to detect the ink pressure in the print head without a pressure loss and, along with the print head, forms a print unit, wherein the pressure application means applies the negative pressure to the interior of the print head by a delivery force acting on the ink in the ink supply path in a direction from the print head toward the ink tank, and applies the positive pressure to the interior of the print head by a delivery force acting on the ink in the ink supply path in a direction from the ink tank toward the print head, and wherein the control means controls the pressure application means based on the ink pressure detected by the detection means in a way that selects the negative pressure or the positive pressure as the pressure applied to the interior of the print head, and controls the selected negative pressure or positive pressure so as to maintain the ink pressure in the print head within a predetermined negative pressure range during a printing operation in which the print head applies ink supplied thereinto onto a print medium to print an image.