1. Technical Field
The disclosure relates to an ink circulation type inkjet printer.
2. Related Art
Japanese Unexamined Patent Application Publication No. 2008-162262 describes an ink circulation type inkjet printer that performs printing by ejecting ink from an inkjet head while circulating the ink.
The ink circulation type inkjet printer includes an inkjet head, a positive pressure tank disposed upstream of the inkjet head, and a negative pressure tank disposed downstream of the inkjet head. A positive pressure is applied to the positive pressure tank and a negative pressure is applied to the negative pressure tank, thereby causing circulation of ink. The pressures of the positive pressure tank and the negative pressure tank are set so that a nozzle pressure of the inkjet head is appropriate for ejection of ink.
However, during circulation of ink, a variation in the liquid levels of ink of the positive pressure tank and the negative pressure tank causes a variation in the pressures of the positive pressure tank and the negative pressure tank. Consequently, due to a variation in the nozzle pressure, an appropriate pressure may not be achieved.
To address this, there has been proposed a technique in which a variation in the pressures of the positive pressure tank and the negative pressure tank due to a variation in liquid level is reduced by using the positive pressure tank and the negative pressure tank provided with sufficiently increased air capacities, and thereby a variation in the nozzle pressure is suppressed.
Also, a technique is known which uses a pressure regulator including a mechanical damper to suppress a variation in the pressures of the positive pressure tank and the negative pressure tank, and thus suppress the variation in the nozzle pressure.
In some inkjet printers, the positive pressure tank is disposed at a position higher than the inkjet head so that a positive pressure (hydraulic head pressure) is generated by the difference in height. In such an inkjet printer, the positive pressure tank is opened to the atmosphere during circulation of ink. Since the positive pressure tank is opened to the atmosphere, a variation in the pressures of the positive pressure tank is suppressed, and thus the variation in the nozzle pressure may be suppressed
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