Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
1999-08-30
2001-10-30
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S044000, C347S047000
Reexamination Certificate
active
06309050
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an ink jet recording apparatus. More particularly, the invention relates to an ink jet recording apparatus having a deflection means for deflecting droplets of ink emitted through a nozzle.
BACKGROUND OF THE INVENTION
Personal computer printers and the like employ ink jet recording technology. Ink jet recording apparatus have several advantages, such as easy handling, superior print performance, and low cost. Because of these benefits, ink jet recording apparatus have now become widespread. There exist various types of ink jet recording apparatus and they are classified according to how ink droplet is emitted. For example, there is an ink jet recording apparatus of the thermal type in which thermal energy is utilized to create a bubble in ink, and a droplet of the ink is emitted by a pressure wave caused by the created bubble. There is another ink jet recording apparatus of the electrostatic type in which an ink droplet is sucked and emitted by electrostatic force. There is still another ink jet recording apparatus of the piezoelectric type in which an ink droplet is ejected by means of an oscillator such as a piezoelectric element. In addition to these ink jet recording types, Japanese Unexamined Patent Gazette No. H05-278212 further discloses an ink jet recording apparatus which is a combination of the piezoelectric type and the electrostatic type.
Whichever of the foregoing ink jet recording types is employed, ink droplets are emitted from many nozzles formed in an ink jet head in an ink jet recording apparatus. These emitted ink droplets land on a sheet of recording paper to form an ink dot. Then, by properly arranging many dots, printing of characters or images is performed on the recording paper sheet.
However, in a typical ink jet recording apparatus, the number of ink droplets each nozzle emits during one print cycle is limited to one. This means that dot density (i.e., the number of dots per unit area) depends upon nozzle density (i.e., the number of nozzles formed in an ink jet head per unit area). Therefore, in order to provide an improved dot density, the nozzle density must be improved.
However, with conventional ink jet head structures, it is difficult to provide improved nozzle densities for cost reasons. Accordingly, it has been considered that rapid improvement in dot density is difficult to achieve.
Further, another problem arises. That is to say, the landing positions of ink droplets emitted through each nozzle align in line in a scanning direction. This results in the occurrence of a so-called white stripe due to the deviation of landing positions in a direction normal to the scanning direction, and due to the variation in ink-droplet emission volume among nozzles. Such white striping causes the quality of printing of characters and images to deteriorate.
Bearing in mind the above-described problems with the prior art techniques, the present invention was made. Accordingly, an object of the invention is to provide improvement in the quality of printing of characters or images by heightening the dot density or by reducing the occurrence of white striping.
SUMMARY OF THE INVENTION
According to the present invention, the landing positions of droplets of ink emitted from nozzles are properly altered in a direction normal to a scanning direction.
More specifically, an ink jet recording apparatus in accordance with the present invention comprises (a) an ink jet head having a nozzle through which a droplet of ink is emitted, (b) a relative movement means for causing the ink jet head and a recording medium placed face to face with the nozzle to relatively move in a scanning direction, with a specified clearance maintained between the nozzle and the recording medium, (c) a facing electrode disposed face to face with the nozzle in such a way as to put the recording medium between the nozzle and the facing electrode, and (d) a voltage applying means for electrifying an ink droplet emitted from the nozzle and for applying a voltage between the nozzle and the facing electrode thereby to create an electric field, wherein the nozzle is formed in such a way as to emit an ink droplet in a direction nonparallel with a virtual plane formed by the scanning direction and the direction of the electric field, and wherein a landing position varying means is provided which is capable of freely varying the landing position of an ink droplet emitted from the nozzle in a direction normal to the scanning direction on the recording medium.
As a result of such arrangement, (i) the relative movement means relatively moves the ink jet head and the recording medium in a scanning direction, (ii) the ink jet head emits an ink droplet for each given print cycle, and (iii) characters, images, or the like are recorded on the recording medium. An ink droplet is emitted in a direction nonparallel with a virtual plane formed by the scanning direction and the direction of the created electric field. When the voltage applying means is actuated, the ink droplet is electrified, so that its flying direction is deflected by an electric field created between the nozzle and the facing electrode, and then the landing position of the ink droplet is altered in a direction normal to the scanning direction by the landing position varying means. Accordingly, it is possible to set the landing position of ink droplets which are emitted from the same nozzle at a plurality of landing points according to whether an ink droplet is charged or uncharged or by making a change in ink droplet charge amount. This makes it possible to heighten the dot density above the nozzle density as well as to suppress the occurrence of white striping.
An arrangement, as shown in, for example,
FIG. 6
, may be made, wherein the ink jet head has a nozzle row of a plurality of nozzles arranged in a direction normal to the scanning direction and the ink jet head is constructed such that each of the plurality of nozzles is capable of emitting two or more ink droplets during a print cycle of a given interval of time and wherein the landing position varying means is constructed such that the two or more ink droplets emitted from each of the plurality of nozzles during the print cycle land on different landing positions along a direction normal to the scanning direction on the recording medium.
As a result of such arrangement, during one print cycle two or more ink droplets are emitted from each of the nozzles of the ink jet head. Each ink droplet lands on different landing positions along a direction normal to a principal scanning direction on the recording medium, as a result of which the number of dots thus created exceeds the number of nozzles. Accordingly, the dot density is rapidly improved.
An arrangement, as shown in, for example,
FIG. 9
, may be made, wherein the landing position varying means is constructed such that the voltage applying means applies a plurality of voltages of different levels during one print cycle.
As described above, the voltage applying means applies, during one print cycle, a plurality of voltages of different levels. As a result of such voltage application, the landing point of each ink droplet is altered depending on the voltage level. To sum up, if a plurality of voltages of different levels are applied during one print cycle, this makes it possible to alter the landing point of each ink droplet according to the voltage level, which facilitates altering the landing points of ink droplets.
An arrangement, as shown in, for example,
FIG. 9
, may be made, in which voltages which are applied by the voltage applying means are set in such a way as to vary at a period of 1
of the print cycle, where the number n is a natural number equal to or greater than two.
Accordingly, the voltage applying means varies a voltage which is applied at a period of 1
of the print cycle, as a result of which the landing point of each ink droplet is varied at a period of 1
in synchronization with the print period.
In the way described above, if a voltage which is applied i
Fukano Akira
Ikeda Koji
Sogami Atsushi
Barlow John
Loper, Jr. Robert
Matsushita Electric - Industrial Co., Ltd.
Nixon & Peabody LLP
Robinson Eric J.
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