Incremental printing of symbolic information – Ink jet – Fluid or fluid source handling means
Reexamination Certificate
1999-02-04
2001-05-15
Le, N. (Department: 2861)
Incremental printing of symbolic information
Ink jet
Fluid or fluid source handling means
Reexamination Certificate
active
06231174
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ink jet recording device for printing by ejecting ink droplets, and more particularly to a configuration for removing air bubbles from within ink channels running between an ink tank and a print head of the ink jet recording device.
2. Description of the Related Art
Ink jet recording devices print characters and other images by ejecting droplets of ink from a print head according to an inputted signal. Ink jet recording devices eject ink droplets by pressurizing ink in the print head using various types of actuators. For example, piezoelectric elements and electrode restrictive elements can be deformed according to the inputted signal to apply pressure to ink in the print head. Also, thermal elements can be energized according to the inputted signal to selectively generate heat to boil a portion of ink in the print head. The boiled ink forms expanding bubbles that increase pressure in the ink, thereby ejecting ink droplets.
The actuators are disposed in actuator chambers of the print head. Ink is supplied to the actuator chambers through a channel defined by side walls. Sometimes, for various reasons, air bubbles cling to the side walls of the ink channel. The air bubbles can enter actuator chambers where the actuators are located. Because the bulk modulus elasticity of air is extremely small compared to that of ink, the air bubbles in the actuator chambers absorb pressure generated by the actuator, so that pressure in the actuator chamber can not be properly increased. As a result, ink droplets can not be properly ejected. When ink droplets can not be properly ejected, print quality suffers greatly.
Japanese Patent-Application Publication (Kokai) No. SHO-56-75867 discloses a circulation purge operation for preventing air bubbles from entering actuator chambers. A circulation channel is provided between an ink tank and a manifold for distributing ink to actuators in the print head. The circulation channel includes a first channel for guiding ink from the ink tank to the manifold and a second channel for returning ink from the manifold to the ink tank. During the circulation purge operation, air bubbles clinging to the inner side walls and the like of the ink channels are removed by forcibly circulating ink through the circulation channel.
SUMMARY OF THE INVENTION
Air bubbles clinging to the side walls of the circulation channel can be more effectively removed when the ink circulates through the circulation channel at a high flow velocity. However, when the flow velocity of the ink in the circulation channel is increased, the pressure of ink in the circulation channel also increases. The menisci formed in nozzles by surface tension can be disrupted so that ink can leak out of the nozzles. Therefore, ink can only be forced through the circulation channel at a slow flow velocity, which is insufficient for completely removing air bubbles.
It is an objective of the present invention to overcome the above-described problems and to provide an ink jet recording device capable of effectively removing air bubbles clinging to side walls of ink channels.
According to a first aspect of the present invention, an ink jet recording device includes a print head, a circulation channel, and an ink circulation unit. The print head has a plurality of actuators for ejecting ink to perform printing operations.
The circulation channel includes a manifold, an ink tank containing ink, a supply channel, and a collection channel. The manifold is in fluid communication with the plurality of actuators. The supply channel supplies ink from the ink tank to the manifold. The collection channel returns ink from the manifold to the ink tank.
The ink circulation unit performs circulation purge to remove bubbles from the circulation channel by changing flow direction of ink in the circulation channel.
According to the first aspect of the present invention, when circulation purge is performed, flow velocity of ink can be greatly changed by changing flow direction of ink. Air bubbles clinging to the side walls of the ink channel can be greatly loosened by this large change in flow velocity. As a result, air bubbles can be easily removed by the flow of ink. Bubbles removed by the flow of ink are collected in the ink tank and so do not enter the print head. Even though changing the flow direction of ink greatly increases the difference in the flow velocity, and so sufficiently loosens clinging air bubbles, this does not increase pressure in the ink channel as much as when air bubbles are loosened by simply increasing flow velocity of ink. As a result, ink is less likely to leak from the nozzles of the print head.
It is desirable that the ink circulation unit be provided with a reversibly rotatable ink circulation pump provided along the supply channel. With this configuration, flow direction of ink can be changed using a simple control operation of changing rotational direction of the ink circulation pump. Clinging air bubbles can be loosened by simply changing flow direction of ink in the circulation channels.
It is desirable that during circulation purge, the ink circulation unit circulate ink in a circulation direction and, for a shorter time than in the circulation direction, in a reverse direction opposite the circulation direction. With this configuration, ink bubbles removed by reversing flow of ink can be quickly removed and transported to the ink tank when the ink is circulated for a longer time in the normal circulation direction. There is no danger that the removed air bubbles will flow back to the ink channels or remain stationary in the ink channels.
According to a second aspect of the present invention an ink jet recording device includes a print head, a circulation channel, an ink circulation unit, and a vibration application unit. The print head and the circulation channel are the same as in the first aspect of the present invention.
On the other hand, the ink circulation unit performs circulation purge by circulating ink through the circulation channel. The vibration application unit applies vibration to the ink during circulation purge.
It should be noted that no particular limitations are placed on the amplitude or frequency of vibration applied by the vibration application unit. Any vibration source is sufficient as long as it is capable of vibrating the ink to shock or otherwise loosen the air bubbles clinging to the side walls of the ink channels.
According to this configuration, during circulation purge, the vibration application unit applies vibration to the circulating ink. This vibration is propagated through the ink and loosens air bubbles clinging to the side walls of the ink channels. Therefore, air bubbles can be more easily removed by flow of ink during circulation purge. Accordingly, ink bubbles are removed by flow of ink and collected in the ink tank, and so will not enter the print head. Because the air bubbles are loosened up merely by application of vibration to the circulating ink, the pressure in the ink channels need not be increased as much as when air bubbles were removed by simply increasing flow velocity of the ink. Therefore, there is less danger of ink leaking from the nozzles of the print head.
It is desirable that the vibration application unit be provided in the supply channel. With this configuration, during circulation purge, vibration can be applied to the supply channel and air bubbles can be collected by being transported to the collection channel. Therefore, very few air bubbles will be included in the ink supply to the print head. Situations wherein bubbles prevent printing can be reduced.
It is desirable that either the first or the collection channels be configured from a flexible tube and that the vibration application unit apply vibration to the flexible tube. With this configuration, ink circulating within the flexible tube is vibrated so that air bubbles clinging to the flexible tube will be loosened up, so that the air bubbles can be effectively removed from the circ
Brother Kogyo Kabushiki Kaisha
Le N.
Nghieu Michael
Oliff & Berridg,e PLC
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