Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
1999-12-03
2001-10-16
Nguyen, Thinh (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
C347S016000
Reexamination Certificate
active
06302517
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a printing apparatus and a printing method using multiple nozzle groups applicable to, for example, an inkjet serial- or line-printer, particularly to a printing apparatus equipped with a print head having multiple dot forming element groups arrayed at different group spacing from the dot forming element pitch and to a printing method therefor.
2. Description of the Related Art
Conventional printing apparatuses include, for example, the serial printer, which prints characters one by one, and the line printer, which prints a line of characters at one time. The serial nonimpact inkjet printer, for instance, provides a printout corresponding to the print data by driving a print head formed with multiple nozzles in the main scanning direction while jetting ink drops from the nozzles and conveying a printing paper or other printing medium in the sub-scanning direction perpendicular to the main scanning direction. Since this conventional inkjet printer forms adjacent dot lines on the printing medium with ink drops jetted from the same nozzles, however, the effect of variance in nozzle characteristics and the like is conspicuous and the print quality low.
This problem is addressed by, for example, U.S. Pat. No. 4,198,642, which teaches interlace printing with constant pitch sub-scanning, i.e., a printing scheme in which the number of used nozzles n and he nozzle pitch k are set to be relatively prime and paper feed is effected at a constant sub-scan amount of n dot pitch. Two integers are relatively prime when they do not have common divisors other than 1.
FIG. 1
is a diagram for explaining conventional interlace printing. The print head
100
has N nozzles #
1
-#
9
arrayed in the sub-scanning direction at a prescribed nozzle pitch k·D (N=9 and k=4 in the illustrated example). Sub-scan feed of a printing paper is conducted at a constant feed amount L·D. In the example shown in
FIG. 1
, since all of the nozzles are used to jet ink drops, the number of nozzles N and the number of used nozzles n is the same. D denotes the printing resolution and is called the “dot pitch.” Regarding the various parameters defined as integer multiples of the dot pitch D (k·D, L·D etc.) in the following description, only their integer portions are sometimes used. For instance, k may be called the “nozzle pitch” and L the “feed amount.” When interlace printing is conducted, the nozzle pitch k and the sub-scan feed amount L (=n) are relatively prime. For example, if k=4 and the printing resolution in the sub-scanning direction is 360 dpi, the nozzle pitch k is 4 dots (4/360 inch). Similarly, the paper feed amount, i.e., the sub-scan feed amount L (=n) is 9 dots (9/360 inch).
As shown in
FIG. 1
, effecting a sub-scan of L dot pitch once every main scan of the print head
100
causes adjacent dot lines to be printed by different nozzles. For instance, the dot line formed by the first main scan pass of nozzle #
7
is followed by a dot line formed by nozzle #
5
, which is followed by a dot line formed by nozzle #
3
, which is followed by a dot line formed by nozzle #
1
. Interlace printing can therefore produce high-quality printed images since it spreads out the effect of nozzle characteristic variance.
In the conventional inkjet printer of the interlace printing type, it is taken for granted that a constant nozzle pitch k can be secured. Based on this assumption, the nozzle pitch k and the number of driven nozzles n are set to be relatively prime and paper feed is conducted at a constant pitch of n dots.
Demand for higher printing speeds in recent years has heightened the need to form print heads with larger numbers of nozzles. Consistent formation of many nozzles at a constant nozzle pitch is, however, difficult. Nozzle pitch is apt to change midway and defects are likely to occur in some of the nozzles. When the prescribed nozzle pitch cannot be obtained, the quality of interlace printing by the prior art is markedly degraded owing to overwriting and/or skipping of raster lines. Since the prescribed nozzle pitch has to be secured in print heads, increase of the nozzle number will lower the production yield and raise the production cost proportionally. The prior art thus does not take into account the recent need for the larger number of nozzles. Since the prior art printing technique requires a constant nozzle pitch for all the nozzles of the nozzle head, it cannot be applied without modification to a printing apparatus having a large number of nozzles for which a constant nozzle pitch is difficult to obtain.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to reproduce a high-quality printed image using a print head with a large number of dot forming elements. Another object of the present invention is to enable interlace printing even when the pitch of the dot forming elements changes midway.
In order to attain the above and other objects of the present invention, there is provided a printing apparatus that effects printing by forming dots in a print region on a printing medium. The printing apparatus comprises: a print head; a first scan driver which moves at least one of the print head and the printing medium in a first scanning direction; a second scan driver which moves at least one of the print head and the printing medium in a second scanning direction perpendicular to the first scanning direction; and a print head driver which drives the print head to form dots on the printing medium responsive to print image data. The print head includes N number (N being an integer not smaller than 4) of dot forming elements, where a minimum element pitch in the second scanning direction between a neighboring pair of the dot forming elements is k·D (k being an integer; D being a dot pitch corresponding to printing resolution) in the print head. The N number of dot forming elements is classified into M number of dot forming element groups each including N/M number of dot forming elements (M and N/M being integers not smaller than 2), and an ith (
i
being an integer between 1 and (M−1)) dot forming element group and an (i+1)th dot forming element group among the M number of dot forming element groups are offset in the second scanning direction by an inter-group pitch pg
i
·D (pg
i
being an integer different from k). The first and second scan drivers and the print head driver drive the print head and the printing medium so that the M number of dot forming element groups have identical patterns of dot-formable positions and the identical patterns of the M number of dot forming element groups are shifted from each other to make all dot positions in the print region to be dot-formable.
The term “dot forming element” here denotes a mechanism which forms dots on the printing medium, including for example an inkjet type actuator using a piezoelectric vibrator or heater to jet ink drops from apertures.
Since this printing apparatus can effect interlace printing at a feed amount of 2·D or greater using M number of dot forming element groups, it can produce high-quality printed images using a print head equipped with a large number of dot forming elements.
The second scan driver may convey at least one of the print head and the printing medium in the second scanning direction using a combination of different feed amounts. Alternatively, The second scan driver may convey at least one of the print head and the printing medium in the second scanning direction at a constant feed amount that is at least twice the dot pitch D.
According to an aspect of the present invention, each neighboring pair of the dot forming element groups are spaced apart by an interval in the second scanning direction, and the N/M number of dot forming elements of each dot forming element group are capable of forming NIM number of identical dots aligned substantially in a single row in the second scanning direction at the minimum element pitch k·D.
In a preferred embod
Nguyen Thinh
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Seiko Epson Corporation
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