Incremental printing of symbolic information – Ink jet – Fluid or fluid source handling means
Reexamination Certificate
2000-04-17
2001-12-04
Le, N. (Department: 2861)
Incremental printing of symbolic information
Ink jet
Fluid or fluid source handling means
Reexamination Certificate
active
06325496
ABSTRACT:
This application is based on patent application Ser. Nos. 11-118722 (1999) filed Apr. 26, 1999 in Japan, 11-228926 (1999) filed Aug. 12, 1999 in Japan and 2000-078813 (2000) filed Mar. 21, 2000 in Japan, the content of which is incorporated hereinto by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to an ink-jet printing apparatus. More particularly, the invention relates to an ink-jet printing apparatus which has an air buffering vessel in an ink supply system supplying an ink to a printing head.
2. Description of the Related Art
Nowadays, various printing systems have been developed as printing apparatus. Amongst, an ink-jet printing system has been widely employed for superiority in gentleness, capability of high speed and high density printing for non-contacting with a printing medium, and easiness of colorization and down-sizing.
One system of the conventional ink-jet printing apparatus is constructed to reciprocate a printing head mounted on a carriage and perform printing on the printing medium by ejecting an ink from the printing head. In such conventional ink-jet printing apparatus, it is necessary to increase capacity of an ink tank in order to reduce frequency of exchanging of the ink tank. However, an integral type of the printing head and the ink tank, when the capacity of the ink tank is increased, inertial mass on the carriage is inherently increased. Therefore, in order to avoid increasing of inertial mass, the ink tank is arranged at stationary or fixed position without requiring movement and supplies the ink to the printing head on the carriage through a tube or the like by means of various pumps.
On the other hand, in the ink-jet printing apparatus, for avoiding dripping of ink from the printing head except for driving for printing, the inside of the printing head is constantly maintained in a slight negative pressure state lower than an atmospheric pressure. By this, ejection upon driving for printing and prevention of unnecessary dripping other than driving for printing can be achieved.
However, when the carriage is moved reciprocally in the ink-jet printing apparatus for printing, the ink within the tube connecting the printing head and the ink tank flows to cause fluctuation of an ink ejection amount by pushing out and pulling back the ink within the printing head, resulting in fluctuation of printing or ejection failure.
Accordingly, as a measure for such fluctuation of printing or ejection failure, there has been known a technology, in which an air buffering vessel having an air storing portion is arranged between the tube and the printing head in the vicinity of the printing head for buffering pressure variation due to flow of the ink within the tube utilizing elastic property of the air to stabilize ejection.
Such an air buffering vessel defines an air storing portion in the upper portion and an ink storing portion in the lower portion thereof. The air storing portion also has a function for separating air from the ink admixing the air within the tube to accumulate within the air storing portion for feeding only ink to the printing head. Accordingly, so as to avoid penetration of the air into the printing head from the ink storing portion due to waving of a liquid level of the ink storing portion by reciprocal motion of the carriage, the height of the liquid level in the ink storing portion has to be maintained at a predetermined height.
On the other hand, even in an ink-jet printing apparatus of the type performing printing by feeding a printing medium without moving a carriage, namely a printing head, a similar vessel is arranged for separating the air admixed in the ink. The internal ink storing portion in the vessel is required to certainly maintain the height of the liquid level at the predetermined height for the purpose of air separation in either of the carriage scanning type and the stationary printing head type printing apparatus.
However, the height of the liquid level tends to be gradually lowered due to penetration of air from a tube wall surface or degassing of dissolved gas in the ink. Therefore, in order to continuously maintain the predetermined liquid level height, there is a known method, in which two tubes are used to connect one ends of respective tubes to the bottom surface position and the predetermined liquid level height position of the ink storing portion respectively and the other ends to a separate stationary ink tank to circulate the ink by the pump.
However, in the conventional method for maintaining the liquid level height using two tubes, number of tubes connecting the printing head mounted on the carriage and the stationary ink tank which is not movable, must be increased. Particularly, in the case of a color printer of a plurality of colors, problems that an arrangement of the tubes becomes complicate, a driving resistance of the carriage due to increasing of stiffness increases and the parts assembling cost elevates, can be encountered.
The foregoing problems will not be encountered when using a single tube having low air permeability. However, at present, an appropriate material having no air permeability in the tube having bending ability and flexibility, is hardly available. Accordingly, it is difficult to maintain the predetermined liquid level height over a long period of time without liquid level height adjusting function employing a single low cost tube.
SUMMARY OF THE INVENTION
The present invention has been worked out for solving the problems in the prior art. It is therefore an object of the present invention to provide an ink-jet printing apparatus which can maintain a liquid level height in an ink storing portion in an air buffering vessel at a predetermined height and can simplify an associated mechanism for connection between a scanning carriage and a stationary ink tank while a low cost single tube is employed.
It is another object of the present invention to provide an ink-jet printing apparatus having a pressure reduction vessel which can prevent ejection failure due to carriage scanning and prevent penetration of air into a printing head.
A further object of the present invention is to provide an air buffering vessel or a pressure reduction vessel which can maintain a liquid level height in an ink storing portion at a predetermined height and prevent penetration of air into a printing head.
In order to accomplish the above-mentioned objects, in a first aspect of the present invention, there is provided an ink-jet printing apparatus comprising:
means for printing on a printing medium by ejecting an ink from a printing head with varying relative position between the printing head and the printing medium by either of scanning the printing head or feeding the printing medium;
an ink storage tank disposed at a position not being interfered by scanning of the printing head or feeding of the printing medium;
an air buffering vessel connected to the printing head; and
means for supplying the ink to the printing head from the ink storage tank through the air buffering vessel,
wherein the air buffering vessel has one ink supply opening from the ink storage tank and at least two suction and discharge openings located at mutually different height in a vertical direction, an upper opening of the at least two suction and discharge openings is constructed for air suction and discharge, a lower opening of the at least two suction and discharge openings is constructed for ink supply and discharge, and the upper opening and the lower opening are communicated with a connection opening to the printing head.
Here, an ink-jet printing apparatus may assume that flow resistances of the one ink supply opening, the upper opening and the lower opening of the air buffering vessel may be Rt, Ra and Ri, respectively, a relationship of three flow resistances may be Ra<Rt<Ri.
The flow resistance may be set by at least one flow rate restricting filter member.
At least one of the flow resistances may be set by a flow rate restricting movable lid which is in open posit
Kageyama Tetsuto
Sasaki Toshihiro
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Le N.
Nghiem Michael
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