1. Field of the Invention
The present general inventive concept relates to an apparatus to remove bubbles from a printhead of an inkjet printer, and more particularly, to a bubble removing apparatus usable with a line printing type array printhead.
2. Description of the Related Art
Generally, an inkjet printer is a device that prints a desired image by ejecting droplets of ink onto paper. FIGS. 1 and 2 illustrate a conventional inkjet printer. Referring to FIG. 1, the conventional inkjet printer includes a printhead 10 ejecting ink droplets through nozzles 11a, feed rollers 20 feeding paper (P) below the printhead 10, and ejecting rollers 30 ejecting the paper (P) to a tray 40 after printing. When the feed rollers 20 feed the paper (P) below the printhead 10, the printhead 10 ejects the ink droplets through nozzles 11a formed in a chip 11 to print the desired image, and the ejecting rollers 30 eject the paper (P) to the tray 40 after printing.
Examples of the printhead 10 include a shuttle type printhead and a line printing type printhead. The shuttle type print head prints each lateral line of the desired image while reciprocating in a width direction of paper (P). The line printing type printhead has a width corresponding to the width of paper (P), such that the line printing type printhead can simultaneously print one line of an image at a fixed position. The line printing type printhead is also referred to as an array type printhead, is preferred over the shuttle type print head because the array type printhead provides a high speed printing characteristic.
In the conventional inkjet printer, the ink droplets are ejected through the nozzles 11a formed in the chip 11 of the printhead 10. Therefore, if the nozzles 11a are clogged by bubbles, the ink droplets are not properly ejected, and thus the desired image is not properly formed. To solve this problem, various conventional methods are used to remove the bubbles from ink. In a representative method of the various conventional approaches, a suction cap is put on the chip 11 of the printhead 10, and the nozzles 11a are sucked using a pump to remove the bubbles from the nozzles 11a together with a little amount of the ink. Although this method can be effectively used for the shuttle type printhead having a small number of the chips 11 and a small size, it is difficult to use this method for the array type printhead since the chips 11 of the array type printhead are widely arranged across the width of the paper (P). That is, since the array type printhead includes a plurality of the chips 11 with the nozzles 11a arranged in the width direction of the paper (P) to entirely cover the width of the paper (P), it is difficult to precisely put caps on all the chips 11 for a hermetic or airtight seal. Further, it is difficult to apply a uniform pressure to the nozzles 11a to suck the bubbles from the nozzles 11a. To solve these problems, another method illustrated in FIG. 2 is used to remove the bubbles from the array type printhead. Referring to FIG. 2, an ink circulation line 60 is provided between the printhead 10 and an ink tank 50, and if necessary, ink is circulated between the printhead 10 and the ink tank 50 using a diaphragm pump 70. That is, when the ink reaches the ink tank 50 during circulation, the bubbles are removed from the ink due to a specific gravity difference between the bubbles and the ink.
Although the bubbles can be removed from a channel of the printhead 10 using the ink circulation method of FIG. 2, that is, although the bubbles can be removed from the ink before the ink flows into the chips 11 of the printhead 10, the bubbles cannot be removed from the ink that has already entered the chips 11 of the printhead 10 since the ink that has entered the chips 11 is not circulated through the ink circulation line 60. The bubbles are removed from the ink that has entered the chips 11 through purging. In a purge process, a valve 80 of the ink circulation line 60 is closed, and the diaphragm pump 70 is intensively operated two or three times to apply a large pressure to the printhead 10, such that the bubbles can be pushed out of the chips 11 of the printhead 10 together with a little amount of the ink. That is, both the circulation and purging must be performed to remove the bubbles from the ink in the array type printhead 10.
However, the conventional inkjet printer requires two motors, a circulation motor (M1) 71 and a purging motor (M2) 72, in the diaphragm pump 70 to perform the circulation and purging since the circulation and purging requires different operating conditions. FIGS. 3A and 3B are characteristic graphs respectively illustrating a pump output in the circulation process for removing the bubbles and a pump output in the purge process for removing bubbles for the conventional bubble removing apparatus. During the circulation process, the diaphragm pump 70 is slowly operated to continuously generate a pressure of about 2 kpa as illustrated in FIG. 3A. However, during the purging process, the diaphragm pump 70 is operated one or two times to generate an instantaneous pressure larger than 7 kpa, as illustrated in FIG. 3B. For this reason, the two motors 71 and 72 with different output powers are used.
However, because of the two motors and power transmitting structures for connecting the two motors to the diaphragm pumps, the inkjet print has a complicated structure and a heavy weight. Therefore, there is a need for an apparatus that has a more simplified structure and can smoothly perform the circulation and purging processes.