Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
1999-06-03
2003-10-14
Hsieh, Shih-wen (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S030000
Reexamination Certificate
active
06631972
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ink-jet recording apparatus for discharging ink from a recording head to a recording material to effect recording and to a control method of the apparatus.
2. Description of the Prior Art
A recording apparatus such as a printer, a copier, a facsimile or the like is constructed to record an image comprising a dot pattern according to image information on the recording material such as paper, cloth, plastic film and the like.
Recording apparatuses can be divided into an ink-jet type, a wire-dot type, a thermal type, a laser beam type and the like according to the recording method; of these, the ink-jet type (ink-jet recording apparatus) is constructed so that an ink (recording liquid) drop is discharged from a discharge port of the recording head to adhere to the recording material thereby achieving recording.
Recently, an increased number of recording apparatuses have been used, and high-speed recording, high resolution, high image quality, and low noise are required for these recording apparatuses. The ink-jet recording apparatus can be one of recording apparatuses which meet such requirements.
To achieve a high-quality printed image, recently various attempts are being made for outputting pictorial images using an ink-jet printer. One of the examples is a recording method which uses a reduced dot diameter of ink droplet. By reducing the dot diameter, a particulate state (coarse feeling due to ink droplets) in a high-contrast portion can be reduced.
However, if the dot diameter of all ink droplets is reduced, an increased number of dots to that extent must be applied, which increases the amount of data and the time required for printing.
For example,
FIGS. 29A and 29B
show cases of printing with densities of 360 dpi (dots/inch) and 720 dpi in an area of {fraction (1/360)} inch square. When printed with 360 dpi, recording is completed by only one dot in the area; however, when printed with 720 dpi, recording is not completed unless up to four dots are recorded in the area. It can be seen that even when printing in the same area, if the resolution is increased to two times and the dot diameter is reduced, four times the number of dots, that is, four times the amount of data, are required.
The dot diameter of an ink droplet on paper increases with increasing ink amount discharged from the discharge port of the print head. To increase the amount of ink droplet discharged from the discharge port, energy applied for ink discharge is increased, or for the case of a thermal ink-jet printer using an electrical-thermal conversion element (discharge heater), the area of the discharge heater is increased.
For example, when the area of the discharge heater per one nozzle (unless otherwise specifically noted, hereinafter used to collectively refer to the discharge port, a liquid passage communicating with the discharge port and a device to generate energy utilized for discharging) is enlarged, the size of a formed bubble is also increased by the function of thermal energy, the ink amount pushed out by the bubble is increased, and an ink droplet of large dot diameter can be formed. Hereinafter, this is called a large dot. On the contrary, when the area of the discharge heater per one nozzle is decreased, the size of the formed bubble is also decreased, and, as a result, the discharge ink amount is decreased, and an ink droplet of small dot diameter can be formed. Hereinafter, this is called a small dot.
Further, by appropriately determining the shape, size, disposition or number of discharge heaters so that a bubble covering a large area of the discharge heater is formed when printing a large dot, and a bubble covering a small area of the discharge heater is formed when printing a small dot, that is, by varying the area of bubble generation, it is possible to selectively print a large dot and a small dot even with a single nozzle.
As described above, a recording head is developed which is capable of selectively printing large and small dots by controlling application of energy (applied energy) provided for the discharge operation. By using this recording head, high image quality can be achieved with an ink-jet recording apparatus.
Still further, for the ink-jet recording apparatus, since an ink is discharged from the recording head, stabilization of ink discharge and stabilization of ink discharge amount are required in order to meet the above requirements. Stabilization of ink discharge is achieved by the following means.
Specifically, in the ink-jet recording apparatus, a cap for capping the discharge port is provided which is used to make suction recovery operation for eliminating or preventing discharge trouble by sucking the ink from the discharge port of the recording head.
Yet further, there is a case in which in association with the progress of discharge operation, ink splashed back from the printing medium or mist and the like generated during discharging accumulate in the vicinity of the discharge port, and the accumulated ink adheres to the discharge port resulting in discharge trouble such as discharge failure or altered discharge direction. To prevent this, a construction is employed in which ink on the surface is removed by wiping the surface (face) where the discharge port of the recording head is disposed with a wiping member such as urethane rubber or the like. Although the wiping performance of the wiping member depends on the material quality and mechanical setting conditions, to always maintain its performance, it is more preferable that the surface of the wiping member itself be clean. For this purpose, a cleaning mechanism is often provided which presses the wiping member against an absorber to absorb the ink removed by wiping.
In the ink-jet recording apparatus, in general, ink suction in the ink flow passage of the recording head and wiping of the face are performed to maintain good discharge performance of the recording head for the purpose of preventing occurrence of printing troubles due to discharge failure (an ink droplet is not discharged from the nozzle for discharge operation, resulting in white stripes on the printed matter) caused by a bubble generated or mixed in the ink flow passage or liquid passage of the recording head, or printing troubles due to “dot mis-alignment” (discharged ink is not ejected in the desired direction, resulting in white stripes on the printed matter) caused by wetting of the face of the recording head.
Wetting of the face of the recording head is also generated by the fact that the ink discharged from the discharge port is pulled from the discharge port by a surface tension of the ink and does not flow back to the liquid passage after ink discharge but appears on the face and stays there. When ink is discharged in the state in which ink remains on the periphery of the discharge port, the discharged ink is affected by the surface tension of the ink on the periphery of the discharge port, is not discharged in the predetermined direction, and appears as dot mis-alignment in the image on the printing material. Further, the wetting of the face become considerable with increasing ink discharge times.
Still further, a bubble in the ink flow passage or liquid passage of the recording head is formed while air dissolved in the ink repeats bubble generation and shrinkage due to the temperature of the recording head. When such a bubble is formed, a space not filled with ink is produced in the liquid passage which is to be filled with ink, and a discharge operation is not performed even if sufficient energy is applied, thus resulting in a printing trouble on the recording material. Yet further, such a bubble becomes liable to be formed with increasing ink discharge times.
For these reasons, it is strongly desirable to perform recovery operations such as suction and wiping when discharge times are increased; however, excessive suction tends to increase ink consumption. Further, the suction operation and wiping require interruption of the printing operati
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Hsieh Shih-wen
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