Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
1999-09-15
2002-04-02
Le, N. (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S029000, C347S036000
Reexamination Certificate
active
06364449
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an ink jet recording apparatus comprising a carriage which travels in a widthwise direction of a recording sheet or the like; and a recording head mounted on the carriage for jetting ink droplets to record an image on the recording sheet in accordance with print data. Particularly, the present invention relates to a cleaning control technique which shortens a suction time required for maintenance of the recording head or for refilling the recording head with ink, and promotes removal of ink, whose viscosity has been increased, and air bubbles from an ink channel extending from an ink reservoir to the recording head.
Since owing to the development of personal computers graphic processing can be performed relatively easily, a demand exists for recording apparatuses that can, for example, output high quality hard copies of color images displayed on screens. In response to this demand, recording apparatuses in which ink jet recording heads are mounted are being produced. Since during printing the noise made by such ink jet recording apparatuses is relatively low, and since the apparatuses can deposit small dots at a high density, the apparatuses are presently being used to perform a variety of different types of printing, to include color printing.
Such an ink jet recording apparatus comprises: ink jet recording heads, for receiving ink from ink cartridges; and a paper feeding mechanism, for moving a recording sheet relative to the recording head. During the printing process, the recording heads, which are carried along by a carriage while it moves the width of a recording sheet, eject ink droplets that are deposited on the recording sheet. Mounted on the common carriage are a black recording head for ejecting black ink, and color recording heads for ejecting yellow, cyan and magenta inks, for example, so that not only can text be printed in black ink, but also full color printing can be performed by changing the ratio of the inks to be ejected.
Since the ink jet recording heads perform printing by pressurizing ink in a pressure generating chamber and then ejecting that ink through nozzles as ink droplets, a print failure can be caused by an increase in the viscosity of the ink or the solidification of the ink due to the evaporation of a solvent through nozzle orifices, by the attachment of dust particles, or by the entry of air bubbles.
Therefore, the ink jet recording apparatus further comprises a cap for sealing the nozzle orifices of the recording head while printing is not being performed, and a wiping blade for cleaning a nozzle plate as needed. The cap not only serves as a lid for protecting ink at the nozzle orifices from being dried out when printing is not being performed, but when the nozzle orifices are clogged, it also seals a nozzle plate and induces a flow of ink through the nozzle orifices so as to resolve an ink ejection failure that is caused by the clogging of the nozzle orifices due to the solidification of ink, or due to air bubbles that have entered an ink channel.
The forcible ink suction process, which is performed to prevent the clogging of the recording head or the entry of air bubbles into an ink channel, is normally called a cleaning operation. The cleaning operation is begun when printing is restarted after the apparatus has been halted for a long time, or when a user manipulates a cleaning switch to resolve the degrading of the quality of a recorded image. For this process, ink droplets are drawn out through the nozzle orifices by the application of a negative pressure, and the wiping blade, constituted by an elastic rubber plate, wipes the surface of the recording head.
The capping member also has a capability of discharging ink droplets by application to the recording head of a drive signal that is irrelevant to printing. This function is called a flushing operation. The flushing operation is performed at predetermined cycles for the purposes of: recovering meniscuses, which are irregularly formed in the vicinity of nozzle orifices of the recording head as a result of wiping action of the wiping blade during the cleaning operation; preventing mixture of colors, which would be removed by the capping member applying weak suction to the ink at the nozzle orifices; and preventing clogging in the nozzle orifices from which a small amount of ink droplets is ejected during a printing operation, which would otherwise be caused by an increase in the viscosity of ink.
There has recently been provided an ink jet recording apparatus which uses at least six colors of ink; that is, dark magenta, light magenta, dark cyan, light cyan, yellow, and black, in order to improve the quality of a print at the time of color printing.
The ink jet recording apparatus that uses multiple colors of ink requires at least six rows of nozzle orifices. In order to improve yield in the manufacturing processes and to simplify the sealing effected by the capping member, two recording heads are usually mounted on one carriage. Further, the capping member is provided with cap units for individually sealing the respective recording heads and two suction pumps for applying negative pressure to the respective cap units. The two suction pumps are connected to a paper feed motor by way of a joint mechanism which is brought into or out of contact with a paper feed mechanism according to the position of the carriage.
Although such a configuration enables a reduction in load imposed on the motor at the time of actuation of the pump, it disadvantageously requires much time for maintenance of the recording head or a built-in mechanism provided in the pumps for selecting between the two pumps according to the direction of rotation, which in turn results in complication of the structure of the pumps or renders the pumps bulky.
In order to greatly improve the resolution of an image recorded on the recording sheet, the number of nozzle orifices formed on each recording head tends to be increased more and more, or the diameter of the nozzle orifices tends to be reduced further. In the configuration of the ink jet recording apparatus, in which the individual recording heads are alternately sucked by means of a single suction pump, a deficiency arises in the suction capability of the pump.
For example, air bubbles, which have entered the ink channel in association with replacement of an ink cartridge, go on to enter the recording head, thereby resulting in ink ejecting failures.
In order to prevent the ink ejecting failures, the air bubbles are discharged from the inside of the recording head (i.e., a replacement cleaning operation is performed) simultaneous with suction and discharge of ink from the recording head. In a case where the flow rate of ink is lower than a predetermined flow rate as a result of a deficiency arising in the suction capability of the pumps, air bubbles present in the recording head remain caught within a complicated flow channel within the recording head. The replacement cleaning operation may result in mere consumption of ink but never ends in elimination of the air bubbles. For this reason, a flow rate faster than the predetermined flow rate must be achieved in order to sufficiently discharge the ink, whose viscosity has been increased, and air bubbles from the inside of the recording head. To this end, the suction capability of the pump must be increased greatly.
This type of recording apparatus generally employs, as a suction pump, a tube pump which generates negative pressure by sequentially squeezing a tube arranged in a circular-arch pattern through use of a roller, for the purpose of implementing an inexpensive suction pump, ensuring the operation of the suction pump, and preventing ink stains.
A conceivable measure to improve the suction capability of such a tube pump is to increase the number of rotations of the pump, as well as to increase the radius of the tube arranged in the circular-arch pattern.
However, if the number of rotations of the pump is increased, the number of times the tube is squeezed by t
Hara Kazuhiko
Takahashi Nobuhito
Uchiyama Yukihiro
Hsieh Shih-Wen
Le N.
Seiko Epson Corporation
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