Dot recording using plural sub-scan feed amounts

Details Dot recording using plural sub-scan feed amounts Dot recording using plural sub-scan feed amounts

1998-12-08

2001-10-09

Nguyen, Thinh (Department: 2861)

Incremental printing of symbolic information

Ink jet

Ejector mechanism

C347S016000

Reexamination Certificate

active

06299283

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a technique of recording dots on the surface of a printing medium with a dot recording head.
DISCUSSION OF THE BACKGROUND
Serial scan-type printers and drum scan-type printers are dot recording devices which record dots with a recording head while carrying out scans both in a main scanning direction and a sub-scanning direction. There is a technique called the “interlace scheme”, which is taught by U.S. Pat. No. 4,198,642 and Japanese Patent Laid-Open Gazette No. 53-2040, for improving the image quality of printers of this type, especially ink jet printers.
FIG. 22
is a diagram for explaining an example of the interlace scheme. In this specification, the following parameters are used to define a printing scheme.
N: Number of nozzles;
k: Nozzle pitch [dots];
s: Number of scan repeats;
D: Nozzle density [nozzles/inch];
L: Sub-scanning pitch [dots] or [inch];
w: Dot pitch [inch].
The number of nozzles N is the number of nozzles actually used to form dots. In the example of
FIG. 22
, N=3. The nozzle pitch k is the interval between the centers of the recording head nozzles expressed in units of the recorded image pitch (dot pitch w). In the example of
FIG. 22
, k=2. The number of scan repeats s is the number of main scans in which all dot positions on a main scanning line are serviced. In the example of
FIG. 22
, s=1, i.e., all dot positions on a main scanning line are serviced in a single main scan. When s is 2 or greater, the dots are formed intermittently in the main scanning direction. This will be explained in detail later. The nozzle density D (nozzle/inch) is the number of nozzles per inch in the nozzle array of the recording head. The sub-scanning pitch L (inch) is the distance moved in 1 sub-scan. The dot pitch w (inch) is the pitch of the dots in the recorded image. In general, it holds that w=1/(D·k), k=1/(D·w).
The circles containing two-digit numerals in
FIG. 22
indicate dot recording positions. As indicated in the legend, the numeral on the left in each circle indicates the nozzle number and the numeral on the right indicates the recording order (the number of the main scan in which it was recorded).
The interlace scheme shown in
FIG. 22
is characterized by the configuration of the nozzle array of the recording head and the sub-scanning method. Specifically, in the interlace scheme, the nozzle pitch k indicating the interval between the centers of adjacent nozzles is defined as an integer not smaller than 2, while the number of nozzles N and the nozzle pitch k are selected as integers which are relatively prime. Further, sub-scanning pitch L is set at a constant value given by N/(D·k).
The interlace scheme makes irregularities in nozzle pitch and ink jetting Feature to thin out over the recorded image. Because of this, it improves image quality by mitigating the effect of any irregularity that may be present in the nozzle pitch, the jetting Feature and the like.
The “overlap scheme”, also known as the “multi-scan scheme”, taught for example by Japanese Patent Laid-Open Gazette No. 3-207665 and Japanese Patent Publication Gazette No. 4-19030 is another technique used to improve image quality in color ink jet printers.
FIG. 23
is a diagram for explaining an example of the overlap scheme. In the overlap scheme, 8 nozzles are divided into 2 nozzle sets. The first nozzle set is made up of 4 nozzles having even nozzle numbers (left numeral in each circle) and the second nozzle set is made up of 4 nozzles having odd nozzle numbers. In each main scan, the nozzle sets are each intermittently driven to form dots in the main scanning direction once every (s) dots. Since s=2 in the example of
FIG. 23
, a dot is formed at every second dot position. The timing of the driving of the nozzle sets is controlled so that the each nozzle set forms dots at different positions from the other in the main scanning direction. In other words, as shown in
FIG. 23
, the recording positions of the nozzles of the first nozzle set (nozzles number
8
,
6
,
4
,
2
) and those of the nozzles of the second nozzle set (nozzles number
7
,
5
,
3
,
1
) are offset from each other by 1 dot in the main scanning direction. This kind of scanning is conducted multiple times with the nozzle driving times being offset between the nozzle sets during each main scan to form all dots on the main scanning lines.
In the overlap scheme, the nozzle pick k is set at an integer no less than 2, as in the interlace scheme. However, the number of nozzles N and the nozzle pitch k are not relatively prime, but the nozzle pitch k and the value N/s, which is obtained by dividing the number of nozzles N by the number of scan repeats s, are set at relatively prime integers instead.
In the overlap scheme, the dots of each main scanning line are not all recorded by the same nozzle but by multiple nozzles. Even when the nozzle features (pitch, jetting Feature etc.) are not completely uniform, therefore, enhanced image quality can be obtained because the features of the individual nozzles is prevented from affecting the entire main scanning line.
As described above, in the conventional interlace scheme, it is required that the number of nozzles N and the nozzle pitch k are set at relatively prime integers. In the overlap scheme, on the other hand, it is required that the quotient N/s, obtained by dividing the number of nozzles N by the number of scan repeats s, and the nozzle pitch k are set at relatively prime integers. The conventional techniques do not use all the nozzles disposed in the dot recording apparatus but use only part of the nozzles, in order to satisfy these requirements. In other words, the prior art techniques can not effectively utilize the nozzles disposed in the dot recording apparatus in some cases.
SUMMARY OF THE INVENTION
The present invention is made to solve the problem of the prior art, and an object of the present invention is to provide a dot recording apparatus and a method therefore that effectively utilize the nozzles disposed in the dot recording apparatus.
In order to solve at least part of the above problems, there is provided a dot recording apparatus for recording dots on a surface of a printing medium with a dot recording head. The dot recording apparatus comprises: a dot-forming element array arranged on the dot recording head to face the printing medium, the dot-forming element array comprising a plurality of dot-forming elements for forming a plurality of dots of an identical color at a substantially constant pitch in a sub-scanning direction; a main scan driving unit that drives at least one of the dot recording head and the printing medium to carry out main scan; a head driving unit that drives at least part of the plurality of dot-forming elements to form dots in the course of the main scan; a sub-scan driving unit that drives at least one of the dot recording head and the printing medium every time when the main scan is completed, thereby carrying out sub-scan; and a control unit that controls the above units.
The control unit controls the head driving unit such that the dot recording head is driven according to a condition that a number of effective dot-forming elements and an element pitch k are set at integers which are no less than 2 and which are not relatively prime, the number of effective dot-forming elements representing a net number of raster lines in a main scanning direction which can be recorded by one main scan, the element pitch k representing a pitch of the plurality of dot-forming elements expressed in unit of a number of dots. The control unit also controls the sub-scan driving unit such that a plurality of different values are used in combination for sub-scan feed amounts for a plurality of the sub-scan feeds, thereby enabling all raster lines included in an effective recording area of the printing medium to be recorded.
In the above dot recording apparatus, since the integers which are no less than 2 and wh

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