Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
1999-04-05
2002-11-05
Nguyen, Thinh (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
Reexamination Certificate
active
06474767
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a calibration method of an optical sensor, as well as an adjustment method of dot printing positions using the calibration method and a printing apparatus. An adjustment of dot printing position is, for example, registration of dot printing positions where printing is performed in the bi-directions of a forward scan and a reverse scan and a printing registration between the heads where printing is performed using a plurality of print heads.
2. Description of the Related Art
The optical sensor which has a light-emitting portion and a light receiving section to irradiate with the light on a measuring object to detect the reflected light and to obtain some information concerning the object is applied to various apparatuses in various fields.
In a field of a printing technique, the sensor is used, for example, on the occasion of printing processing, in order to detect existence of the printing medium which is a printing object and the size (e.g. paper width) thereof. In addition, in order to perform a processing (so-called head shading) which corrects a drive condition of a printing element for obtaining a printing image without unevenness in density, it is sometimes used as a means which reads the unevenness in density which is developed on a predetermined test patterns. In addition, it is effective to use the optical sensor in a printing registration, and hereinafter, a processing of the registration for dot printing positions is described.
In recent years, the 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 developed rapidly. In recording apparatuses, a serial printer using a dot matrix recording (printing) method comes to attention as a recording apparatus (a printing apparatus) which realizes printing of a high speed or high image quality with the low cost. For such printers, as the technique which prints at high speed, for example there is a bi-directional printing method and as the technique which the prints in high image quality, for example, there is a multi scanning printing method. [Bi-directional printing method]
As the improvement in high-speed technique, in a printing head which has a plurality of printing elements, although it is also thought to plan an increase in the number of a printing elements and an improvement in a scanning speed of the print head, it is also an effective method to perform bi-directional printing scannings of the print head.
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 which the 64 pieces of ejection openings are 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 direction of the length, the printing can be completed by scanning of 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 the reciprocating printing scanning of approximately 30 times in bi-directional printing, so that printing can be performed and since it becomes possible on at the speed of approximately 2 times, whereby 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, it has been thought that since to form such a feedback controlled system causes an increase in the cost of the printing apparatus, it is difficult to realize this, in the printing apparatus which is relatively cheap.
(Multi Scanning Printing Method)
Secondly, a multi scanning printing method is explained as one example of the improvement in high image quality technique.
When printing is performed using the 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, the 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 the cause which makes the unevenness in density of the image which is formed finally to reduce 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 the eight pieces of 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, in summary). A reference numeral
203
denotes the ink, for example, which are ejected as a drop from the nozzle
202
. It is ideal that the ink is ejected from each ejection opening by the approximately uniform amount of discharge and in the 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 that there is no unevenness in density also 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 it is, 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 are deposit or landed on a printing medium as shown in FIG.
2
B. In this drawing, a part of the white paper that an area factor can not be served up to 100% periodically exists with respect to the horizontal scanning direction of the head, moreover, in contrast with this, the dots are overlapped 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
B.
According to this method, in order that the printing with regard to the same region as shown in FIG.
1
and
FIG. 2
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
Chikuma Toshiyuki
Iwasaki Osamu
Nishikori Hitoshi
Otsuka Naoji
Takahashi Kiichiro
Fitzpatrick ,Cella, Harper & Scinto
Mouttet Blain
Nguyen Thinh
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