Complementary recording system using multi-scan

Details Complementary recording system using multi-scan Complementary recording system using multi-scan

2002-02-27

2003-01-28

Barlow, John (Department: 2853)

Incremental printing of symbolic information

Ink jet

Controller

Reexamination Certificate

active

06511146

ABSTRACT:

FIELD OF THE INVENTION AND RELATED ART
The present invention relates to an image forming apparatus, an image forming method and an image processing method for effecting recording on a recording material wherein a density non-uniformity attributable to variation of a recording property among a plurality of recording elements of a recording head. More particularly, it relates to an image forming apparatus, an image forming method and an image processing method wherein moire or the like attributable to error in a mounting position of the recording heads.
An ink jet recording apparatus is known in which a recording head provided with a plurality of ink ejection outlets, as an example of an apparatus using a recording head provided with a plurality of recording elements.
In such an apparatus, sizes and/or positions of the dots provided by the ink are not uniform due to variations in ejection outlet diameters of the ejection outlets and/or ejecting directions, and if this occurs, the printed image density. Particularly, in a recording device of a serial type in which the recording head is scanningly moved in a direction different from the direction of arrangement of the recording elements, for example, perpendicular thereto, the density non-uniformity attributable to the above-described variation in the ejection outlet diameters results in stripes in the printed image, with the result that quality of the image is deteriorated.
In order to correct such a density non-uniformity, it has been proposed that in the image formation using a recording head of an ink jet recording type, one pixel or pixels of a line corresponding to one scanning of a recording head, is printed by ink ejected from different ejection outlets on the basis of image data which have been processed for low gradation. This can be done by feeding the sheet through a distance smaller than the width of the recording head and completing one pixel by a plurality of scans for paths. Plurality of
FIG. 3
shows an arrangement of a conventional ink jet recording head The printer usable with this recording head forms an image by CMYK ink s (four colors). The recording head
601
is provided with two ink jet heads of each ink color, and a head
603
(rear head) disposed at an upper position in the Figure and a lower head
602
(front head) are disposed in a sub-scan direction with a distance of 2.5 bands (one band is a unit of a width measured in a direction of the nozzle array operated in one scan of the ink jet head).
FIG. 4
shows an overlaying state of printing using the head
602
and the rear head
603
in the printer using the recording head show in FIG.
3
. One sub-scan is carried out for one main-scanning. A distance of feeding in the sub-scan direction is one band, so that image is formed with deviation of half-band between the front head
602
and the rear head
603
. Here, the half-band
703
is constituted by the uproar one half of the front head
602
and the lower one half of the rear head
603
, and the half-band
704
is constituted by the lower one half of the front head
602
and the upper one half of the rear head
603
.
Referring to
FIG. 5
, the description will be made as to the process in which the image data of a multi-level type fed to the printer are binarized, and are converted to head driving data to eject the ink from the nozzle.
(1) The image data of the multi-level type transferred from a host computer is stored in an image data storing apparatus
801
. The data are fed out from here one by one band.
(2) A pallet conversion circuit
802
separates the image data to multi-level data of respective ink colors. The description will be made as to black ink Bk as a representative.
(3) A “gamma” conversion circuit
803
-K effects a “gamma” conversion to the multi-level data separated for each ink color.
(4) A non-uniformity correcting circuit
804
-K corrects the non-uniformity due to the variation in the properties of the nozzles, using a non-uniformity correction table (look-up table for conversion from multi-level data to multi-level data).
(5) A binarizing circuit
805
-K coverts the multi-level to binary data using an error diffusion method (ED).
(6) A SMS (sequential multi- scanning) circuit
806
-K determines which one of the front head
602
-K and the rear head
603
-K is to be used. The SMS circuit, when a certain raster scan is considered, allots the data to the front, rear, front, rear, namely, alternatingly from the left end dot, and they are outputted to the TMC (Timing Memory Controller) circuits
807
-K
1
,
807
-K
2
. By doing so, it does not occur that adjacent dots are printed by the same head, and the printing operation can be carried out at double speed the driving frequency of the head. The dot appearing first in each raster scan is printed by the rear head
603
-K in the case of an odd number raster scan and by the front head
602
-K in the case of an even number raster scan.
(7) In the TMC circuits
807
-K
1
,
807
-K
2
, the data for one band are outputted to each head
602
-K,
603
-K. A positional deviation in the main-scanning direction between the heads
807
-K
1
,
807
-K
2
is adjusted using lateral registration adjusting value, the output timing for one array is different depending on the lateral registration adjusting value.
(8) PHC (Printer/head connector) substrates
808
-K
1
,
808
-K
2
output the binary data in the nozzle array direction, corresponding to the nozzles which actually effect printing. A positional deviation in the nozzle array direction between heads
807
-K
1
,
807
-K
2
is adjusted by longitudinal registration adjusting value. The recording head in this example has 1344 nozzles and additional upper and lower 8 nozzles which are effective for printing, and therefore, the longitudinal registration adjusting value is in the range of −8-+8. When the longitudinal registration adjusting value is ±0, central 1344 nozzles are used, but when the longitudinal registration adjusting value is ±1-8, the actually used nozzles are deviated by 1-8 nozzles from the center. The data for 1344 nozzles are outputted corresponding to the nozzles to be actuated, using the longitudinal registration adjusting value.
(9) Finally, the binary data for each nozzle are converted to head driving data by a print control device (Head CPU)
809
to eject the ink for printing.
Referring to
FIG. 7
, there is shown the processes (5), (6) in more detail. The multi-level data after the color separation, the “gamma” conversion and the non-uniformity correcting process (
802
,
803
,
804
in
FIG. 5
) are subjected to error diffusion process (
FIG. 7B
) using an error diffusion matrix A (
FIG. 6A
) to effect binarization (FIG.
7
C). In
FIG. 6
, asterisk indicates the noting pixel. By SMS (
806
in FIG.
5
), the determination will be made as to whether the front head or the rear head is to be used. The data shown in
FIG. 7E
is fed to the front head, and the data shown in
FIG. 7F
are fed to the rear head.
According to the above-described method, an image in the predetermined region is formed by different nozzles of two heads, and therefore, the density non-uniformity or the like due to variation in the properties of nozzles can be reduced. In addition, the pitch of the interfaces is half-band so that bandings is less conspicuous.
In this manner, the density non-uniformity attributable to the properties peculiar to the ejection outlets of the ink jet head, can be diffused on the recording material, by which the density non-uniformity is reduced. This is called “multi-scan” or “multi-path”. Furthermore, a so-called sequential multi-scan (SMS) system has been proposed in which the ink ejection outlets are actuated in a predetermined order mainly to make use frequency of the ink ejection outlets uniform.
However, it has been found that there is a point to improve in use with large scale multi-color ink jet printing apparatus, for example, a textile printing apparatus in which the scanning range is as large as several meters, and in addition to the yellow color,

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