Printing – Layout or registration
Reexamination Certificate
1999-07-12
2001-07-10
Hilten, John S. (Department: 2854)
Printing
Layout or registration
C400S076000, C400S070000, C400S061000, C400S074000, C347S009000, C347S019000
Reexamination Certificate
active
06257143
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method for adjusting dot forming or depositing positions in dot matrix recording and a printing apparatus using the method. More particularly, the invention relates to a method for adjusting dot forming positions, which are applicable to printing registration in the case of bi-directionally printing by a forward and reverse scan of a print head or to printing registration in the case of printing by means of a plurality of print heads, and printing apparatus using the method.
2. Description of the Related Art
In recent years, office automation instruments such as the personal computer and the word processor, which is relatively cheap, are widely used, and an improvement in high-speed technique and an improvement in high image quality technique of various recording apparatuses for printing-out the information which are entered by the instruments are being developed rapidly. In recording apparatuses, a serial printer using a dot matrix recording (printing) method is a recording apparatus (a printing apparatus) which realizes printing with high speed or high image quality but with low cost. For such printers, which print at high speed, for example there is a bi-directional printing method, as well as which print in high image quality, for example, there is a multi scanning printing method.
(Bi-directional printing method)
To improve high-speed printing, in a printing head which has a plurality of printing elements (although it is also considered to increase the number of a printing elements and improve a scanning speed of the print head), bi-directional printing scans of the print head are performed.
Although, since there is usually the time required for paper-feeding and paper-discharging or the like, it does not become a simply proportional relation, in the bi-directional printing, a printing speed of approximately two times can be obtained as compared with the one-directional printing in the printing apparatus.
For example, when using the print head having 64 ejection openings arranged with 360 dpi (dots/inch) in printing density in a direction different from the printing scanning (main scanning) direction (for example, in a sub-scanning direction which is the feeding direction of the printing medium), a printing is performed on, a printing medium of A4 size set in the lengthwise direction, the printing can be completed by scanning approximately 60 times. The reason is that, in one-directional printing, each printing scanning is performed only at the time of the movement in the one direction from the predetermined scanning commencement position, and since non-printing scanning to the inverse direction for returning to the scanning commencement position from a scanning completion position is attended, reciprocation of approximately 60 times is required. On the other hand, printing is completed by reciprocating printing scanning of approximately 30 times in bi-directional printing, so that printing can be performed and since it becomes possible at a speed of approximately 2 times. As such, bi-directional printing can be considered to be an effective method for an improvement in a printing speed.
In order to register dot-forming positions (for example, for an ink jet printing apparatus, a deposition or landing position of ink) at a forward trip and a return trip together in such bi-directional printing, using a position detection means such as an encoder, based on the detecting position, printing timing is controlled. However, to form such a feedback controlled system causes an increase in the cost of the printing apparatus. As a result, it is difficult to realize this in a printing apparatus which is relatively cheap.
(Multi scanning printing method)
Secondly, a multi scanning printing method is explained as one example of an improvement in high image quality technique.
When printing is performed using a print head which has a plurality of printing elements, quality of the printed image depends on performance of a print head itself greatly. For example, in the case of the ink-jet print head, slight differences, which is generated in a print head manufacturing step, such as variations of a form of ink ejection openings and the elements for generating energy for ejecting ink such as an electro-thermal converting elements (ejection heaters), influence a direction and an amount of ejected ink, and result in an unevenness in density of the image which is formed finally thereby reducing the image quality.
Specific examples are described using
FIGS. 1A
to
1
C and
FIGS. 2A
to
2
C. Referring to
FIG. 1A
, a reference numeral
201
denotes a print head, and for simplicity, is constituted by eight nozzles
202
(herein, as far as not mentioned specifically, refer to the ejection opening, the liquid passage communicated with this opening and the element for generating an energy used for ink). A reference numeral
203
denotes the ink, for example, which is ejected as a drop from the nozzle
202
. It is ideal that the ink is ejected from each ejection opening in an approximately uniform amount of discharge and in a justified direction as shown in this drawings. When such discharge is performed, as shown in
FIG. 1B
, ink dots which are justified in size are deposited or landed on the printing medium and, as shown in
FIG. 1C
, the uniform images are produced with no unevenness in density as a whole can be obtained.
However, there are the variations in the nozzles in the print head
20
actually as is mentioned above, and when printing is performed as mentioned above, as shown in
FIG. 2A
, the variations are caused in size of the ink drops and in the ejecting direction of ink discharged from nozzles and the ink drops deposited or landed on a printing medium as shown in FIG.
2
B. In this drawing, part of the white paper there exists an area factor can not be served up to 100% periodically with respect to the horizontal scanning direction of the head, moreover, in contrast with this, the dots overlap each other more than required or white stripes as shown in the center of this drawing have been generated. A gathering of the landed dots in such condition forms the density distribution shown in
FIG. 2C
to the direction in which nozzles are arranged, and the result is that, so far as usually seen by eyes of a human, these objects are sensed as the unevenness in density.
Therefore, as a countermeasure of this unevenness in density, the following method has been devised. The method is described using
FIGS. 3A
to
3
C and
FIGS. 4A
to
4
C.
According to this method, in order that the printing with regard to the same region as shown in
FIGS. 1
to
1
C and
FIGS. 2A
to
2
C is made to be completed, the print head
201
is scanned 3 times as shown in FIG.
3
A and
FIGS. 4A
to
4
C. The region defining four pixels which is a half of eight pixels as a unit in the direction of length in the drawing has been completed by two passes. In this case, the 8 nozzles of the print head are divided into a group of 4 nozzles of upper half and 4 nozzles of lower half in the drawing and the dots which one nozzle forms by scanning of one time are the dots that the image data are thinned into approximately a half in accordance with the certain predetermined image data arrangement. Moreover, at the second scanning, the dots are embedded in the image data of the half of the remaining and the regions defined four pixels as the unit are completed progressively. Hereinafter, the printing method described above is referred to as a multi scanning printing method.
Using such printing method, even when the print head
201
which is equal to the print head
201
shown in
FIG. 2A
are used, the influence to the printed image by the variations of each nozzle is reduced by half, whereby the printed image becomes as shown in FIG.
3
B and no black stripe and white stripe as shown in
FIG. 2B
becomes easy to see. Therefore, the unevenness in density is fairly also mitigated as compared with the case of
FIG. 2C
as shown in FIG.
3
C.
W
Chikuma Toshiyuki
Iwasaki Osamu
Nishikori Hitoshi
Otsuka Naoji
Takahashi Kiichiro
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Hilten John S.
Nolan, Jr. Charles H.
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