Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
1999-06-10
2002-09-17
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
C347S011000
Reexamination Certificate
active
06450603
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an ink jet recording apparatus which is capable of ejecting ink drops of different volumes through the same nozzle orifice, and more particularly to a method of driving an ink jet recording head of the ink jet recording apparatus.
The ink jet recording apparatus is composed of a recording head having linear arrays of nozzle orifices, a carriage mechanism for moving the recording head in the main scanning direction (a width direction of a recording paper), and a paper feeding mechanism for moving a recording paper in the subscanning direction (paper feeding direction).
The recording head includes pressure generating chambers communicated to the nozzle orifices, and pressure generating elements for varying ink pressures within the pressure generating chambers. In operation, a drive pulse is applied to each pressure generating element to vary an ink pressure in the associated pressure generating chamber, so that an ink drop is jetted from the related nozzle orifice.
The carriage mechanism moves the recording head in the main scanning direction. The recording head ejects ink drops through the nozzle orifices at times determined by dot pattern data, while moving in the main scanning direction. When the moving recording head reaches the terminal end of its moving range, the paper feeding mechanism moves a recording paper in the subscanning direction. Upon end of the recording paper movement, the carriage mechanism moves again the recording head in the main scanning direction. The recording head ejects ink drops while moving.
Repeating the above sequence of operations, the recording head records an image represented by dot pattern data on a recording paper.
The ink jet recording apparatus depicts an image on a recording paper by combinations of ejection and non-ejection of ink, viz., combinations of presence and absence of dots. For this reason, a half-tone method has been used in which one pixel is formed by a plurality of dots, for example, 4×4 or 8×8 dots. To print or visually recording an image at high quality on the recording paper by the half-tone method, it is essential to eject ink drops of extremely small volumes. Reduction of the volume of the ink drop creates another problem of reducing printing speed.
Achieving of the improvement of the print quality and increase of the printing speed is one of the important technical subjects currently imposed on engineers. There are some technical solutions, so far as we know, to this contradictory subject.
In the solution disclosed in, for example, Japanese Patent Publication No. 4-15735B and U.S. Pat. No. 5,285,215, a plurality of drive signal capable of generating fine ink drops are applied to the recording head. In turn, the recording head ejects a plurality of fine ink drops through the same nozzle orifice. In this case, the fine ink drops jetted are merged into a single large ink drop before those fine ink drops land on a recording paper.
The technical solution involves some problems to be solved, however. The number of fine ink drops that may be merged is limited. The result is that the volume of one ink drop, which results from the ink drop merging, may be increased with a limited ink volume and within a narrow range where the ink volume is variable. Further, control for merging fine ink drops into one large ink drop before they land on the recording paper is difficult.
A technical proposal is made in this connection. In the technique, a drive signal consisting of a succession of different drive pulses, which correspond to the volumes of fine ink drops to be jetted, is generated, and the drive pulses extracted from the drive signal are applied to the pressure generating element.
In the solution disclosed in the publications, mere connection of different drive pulses will create the following problems.
A first problem is that a drive period required for printing one dot is long. It is necessary to connect the number of drive pulses corresponding to the number of the different volumes of ink drops. The drive period is increased with increase of the number of drive pulses connected. The increase of the drive period leads to decrease of the printing speed.
A second problem is that the flying velocity of the ink drop depends on the volume of the ink drop. When comparing a large ink drop for forming a large dot with a medium ink drop for forming an medium dot, the flying velocity of the large ink drop is higher than that of the medium ink drop. Increase of the ink-volume difference leads to increase of the flying velocity difference. The flying velocity difference causes an incorrect landing position of the ink drop, resulting in degradation of the print quality.
SUMMARY OF THE INVENTION
The present invention is made to successfully solve the problems described above, and has an object to efficiently confine an increased number of drive pulses, which are capable of ejecting ink drops of different volumes, within a limited drive period.
Another object of the present invention is to lessen the flying velocity difference caused by the volume difference among the ink drops.
In order to achieve the above objects, according to a first aspect of the present invention, there is provided an ink jet recording apparatus comprising: a recording head including a pressure generating element provided in association with a pressure generating chamber communicating with a nozzle orifice, an ink drop is jetted from the nozzle orifice by applying a drive pulse to the pressure generating element; drive signal generating means for generating a drive signal; and drive pulse generating means for generating a drive pulse from the drive signal; wherein the drive signal generated by the drive signal generating means contains wave elements capable of activating the pressure generating element and a connection element incapable of activating the pressure generating chamber and for connecting connection ends of the wave elements having different voltage levels, and wherein the drive pulse generating means appropriately selects the wave elements in the drive signal and composes them into the drive pulse.
According to a second aspect of the. present invention, in the ink jet recording apparatus of the first aspect, the time period of the voltage-gradient portion of the connection element is not longer than that of the wave elements.
According to a third aspect of the present invention, in the ink jet recording apparatus of the first or second aspect, the wave elements include a plurality of ejection wave elements capable of driving the pressure generating element to eject an ink drop. The connection element interconnects the ejection wave elements.
According to a fourth aspect of the present invention, in the ink jet recording apparatus of the third aspect, the wave elements include a filling wave element capable of driving the pressure generating element to fill ink into the pressure generating chamber. The drive pulse generating means generates a plurality kinds of drive pulses at the time of selecting the ejection wave element and the filling wave element.
According to a fifth aspect of the present invention, in the ink jet recording apparatus of the first to fourth aspects, the wave elements include a plurality of ejection wave elements capable of driving the pressure generating element to eject ink drops at different timings. The drive pulse generating means generates a plurality of drive pulses such that an ink drop forming a small-volume dot is ejected earlier than an ink drop forming a large-volume dot.
According to a sixth aspect of the present invention, in the ink jet recording apparatus of the first to fourth aspects, the wave elements include a plurality of ejection wave elements capable of driving the pressure generating element to eject ink drops at different timings. The drive pulse generating means generates a small-dot drive pulse capable of ejecting a small-volume ink drop to form a small dot, a medium-dot drive pulse capable of ejecting a medium ink drop to form a medium-v
Barlow John
Dudding Alfred
Seiko Epson Corporation
Sughrue & Mion, PLLC
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