Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
1999-05-17
2001-06-19
Nguyen, Thinh (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S014000
Reexamination Certificate
active
06247788
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to an inkjet recording apparatus and method and, more particularly, to an inkjet recording apparatus and method for recording an image on a recording medium by an interlace printing method.
2. Description of the Related Art
Inkjet recording apparatuses are used in various image-forming apparatuses such as a printer, a facsimile machine or a copy machine. There are several types of inkjet recording apparatuses such as a serial scanning type inkjet recording apparatus or a line type inkjet recording apparatus.
The line type inkjet recording apparatus records an image by using a recording head having a length corresponding to the entire length of a main scanning area. That is, the recording head is provided with a plurality of nozzles arranged in an extending direction of the recording head which corresponds to a main scanning direction so that the nozzles cover the entire width of a recording medium such as a recording paper on which an image is formed. According to the line type inkjet recording apparatus, an image is recorded on the recording medium by projecting ink drops onto the recording medium by moving the recording medium in a direction perpendicular to the extending direction of the recording head.
The serial scanning type inkjet recording apparatus records an image by using a recording head having a plurality of nozzles arranged in a sub-scanning direction. An image is recorded on a recording medium such as a recording paper by projecting ink drops onto the recording medium by moving the recording head in a main scanning direction while the recording medium is stepwisely moved in a sub-scanning direction.
In the above-mentioned inkjet recording apparatuses, recording density (dot density) is determined by a pitch of the nozzles provided on the recording head. Accordingly, in order to achieve a high-density recording, the pitch of the nozzles must be decreased. However, there is a limit in the pitch size due to difficulty in formation of the nozzles with a small pitch. Thus, there is a limit in increasing the recording density.
As a conventional inkjet recording apparatus, Japanese Patent Publication No.3-56186 discloses an inkjet recording apparatus which uses an interlace printing method in which a main scanning is performed k times while a recording head moves a single pitch D of nozzles arranged on the recording head in a sub-scanning direction so as to record an image with a dot density smaller than the pitch D of the nozzles in the sub-scanning direction. Additionally, Japanese Patent No.2613205 discloses an inkjet recording apparatus which has a recording head provided with N nozzles and performs a main scanning operation and a sub-scanning operation with a dot pitch P alternately n times, and, thereafter, a sub-scanning is performed with a pitch corresponding to P{n(N−1)+1}.
Additionally, Japanese Laid-Open Patent Application No.7-242025 discloses an inkjet recording apparatus which eliminates a non-recordable area generated when an image is recorded by an interlace printing method such as that used in the inkjet recording apparatus disclosed in the above-mentioned Japanese Patent Publication No.3-56186.
Further, Japanese Laid-Open Patent Application No.5-155040 discloses an inkjet recording apparatus which generates an irregular thin-out pattern in a template buffer by utilizing a random numbers each time a recording operation corresponding to a single scanning is performed so that a lower half of data corresponding to a single scanning operation and an upper half of data corresponding to a subsequent scanning operation are thinned out in accordance with the thin-out pattern.
However, in the above-mentioned conventional inkjet recording apparatuses which use an interlace printing method in which a plurality of main-scanning operations are performed while the recording head travels a distance corresponding to a pitch of the nozzles, an unevenness in density of a recorded image is generated in an area between a part of the recorded image by a train of nozzles and a subsequent part of the recorded image since a travel of a recording head in a sub-scanning direction fluctuates due to variation in a thickness of a recording medium on which the image is recorded or an eccentricity of a roller for feeding the recording medium. The unevenness in image density is generally referred to as a band which is periodically appears in each area between series of scanning operations in a sub-scanning direction.
Additionally, in the inkjet recording apparatus using a template buffer, there is a problem in that a large memory is required since the buffer must store data corresponding to a whole scanning operation.
SUMMARY OF THE INVENTION
It is a general object of the present invention to provide an improved and useful inkjet recording apparatus and method in which the above-mentioned problems are eliminated.
A more specific object of the present invention is to provide an inkjet recording apparatus and method which reduces band-like unevenness in a recorded image which unevenness is generated in relation to an interlace printing method.
In order to achieve the above-mentioned objects, there is provided according to one aspect of the present invention an inkjet recording apparatus for recording a dot image on a recording medium by using an interlace recording method, the inkjet recording apparatus comprising:
a recording head having a plurality of nozzles arranged at a uniform interval D in a sub-scanning direction;
a moving mechanism for moving the recording medium in the sub-scanning direction; and
a control unit which controls a scanning operation so that k main scanning operations are performed within the interval D, where k is an integer equal to or greater than 2,
wherein a part of an area recorded by the nth main scanning operation is overlapped with a part of an area recorded by the (n+k)th main scanning operation, where n is an integer equal to or greater than 1; and
a part of dots included in the overlapping area is recorded by the nth main scanning operation so that the rest of the dots included in the overlapping area are complementarily recorded by the (n+k)th main scanning operation.
According to the above-mentioned invention, since the overlapping area is provided in a boundary between the area recorded by the nth main scanning operation and the area recorded by the (n+k)th main scanning operation, unevenness in the density of the dot image such as a white band is reduced in the boundary area.
In the above-mentioned inkjet recording apparatus, the control unit may include:
a memory storing a banding pattern table used for the complementary recording, the banding pattern table being defined by a matrix “R×C”, where R is a number of rows of the dots included in said overlapping area and C is a number of dots arranged in the main scanning direction; and
a determining unit determining whether each of the dots included in the overlapping area is to be recorded by the nth main scanning operation or the (n+k)th main scanning operation,
wherein a size of the banding pattern table is greater than “2×3” or “3×2”.
According to this invention, the overlapping area is complementarily recorded by both the nth main scanning operation and the (n+k)th main scanning operation in accordance with the banding pattern table having a size greater than “2×3” or “3×2”. Thus, a band-like unevenness in the density of the image in the boundary area can be easily diffused, which results in a high-quality image.
Additionally, there is provided according to another aspect of the present invention an inkjet recording apparatus for recording a dot image on a recording medium by using an interlace recording method, the inkjet recording apparatus comprising:
a recording head having a plurality of nozzles arranged at a uniform interval D in a sub-scanning direction;
a moving mechanism for moving the recording medium in the sub-scann
Cooper & Dunham LLP
Nguyen Thinh
Ricoh & Company, Ltd.
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