"In addition, a pressure controller connected to the ink chamber of the sub-tank is usually provided in the ink supply device to adjust the pressure within the ink chamber. For example, it reduces the inner pressure of the ink chamber by sucking air from the inside of the ink chamber to set the print head at a state of slight negative pressure. The pressure adjustment becomes difficult if ink flows into the connector channel connecting the sub-tank and the pressure controller, and a dripping problem is likely to occur. Thereby, when, for example, the ink level excesses an upper limit in the ink chamber, it is controlled to prevent ink from the main tank from being supplied to the sub-tank.
"As aforementioned, the nozzle face of the print head is capped for achieving the suction of ink, however, if for example there is a displacement between the nozzle face and the rubber cap, suction force may be reduced because air enters through a space between the nozzle face and the rubber cap. In this case, ink residual within the print head is sucked and removed, but new ink is hardly supplied to the print head so that the print head tends to be in a state containing (air) bubbles and consequently being not filled with ink. If the ink is ejected from the nozzles in this state, there is a problem that it is difficult to achieve stable ejection of ink because defective ejection occurs in which air bubbles not ink are ejected from the nozzles.
"To precisely detect the ink level by the float which floats on the ink to move straight in the vertical direction according to the changes of the ink level in the sub-tank, it is required to use a large float, for example, corresponding to the volume of the ink chamber. If such a large float is used, it is possible to detect precisely the ink level in the sub-tank, but there is a problem of limiting the volume for ink storage.
"Besides, the float used for detecting the ink level in the sub-tank may stick to the internal wall of the ink chamber, which makes it impossible to correctly detect the ink level. In this case, it is difficult to control the ink supply which is based on the correct detection of the ink level, and the ink is undesirably supplied to excess the predetermined upper limit. There is a problem that, when the ink is supplied over the predetermined upper limit to the ink chamber, the excessively supplied ink may flow to the side of the pressure controller (such flow of ink is referred to thereafter as 'backflow'), making difficult the pressure adjustment within the ink chamber."
As a supplement to the background information on this patent, VerticalNews correspondents also obtained the inventor's summary information for this patent: "According to one aspect of the present invention, an ink supply device for an inkjet printer includes a sub-tank and a main tank. The sub-tank has an ink chamber to store liquid ink and is connected to a print head configured to eject the liquid ink via a head-side supply passage. The sub-tank has a plurality of supply holes which connect the ink chamber and the head-side supply passage. At least two of the plurality of supply holes have their openings on the ink chamber side formed at different heights. The main tank is connected to the sub-tank and contains the liquid ink to be supplied to the ink chamber."
For additional information on this patent, see: Tamaki, Kazutaka. Ink Supply Device for Inkjet Printer and Inkjet Printer. U.S. Patent Number 8506060, filed
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