Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
1999-03-25
2002-11-12
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
C347S015000, C347S041000
Reexamination Certificate
active
06478394
ABSTRACT:
This application is based on Japanese Patent Application No. 10-079443 filed Mar. 26, 1998 and Japanese Patent Application No. 11-69025 filed Mar. 15, 1999, the contents of which are incorporated hereinto by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a printing apparatus. More particularly, the invention relates to a printing apparatus which performs a plurality of scans, while relatively shifting a printing medium and a printing head for respectively predetermined amounts (multi-pass printing), to complete an image.
2. Description of the Related Art
A printing head of an ink-jet printer has a large number of nozzles aligned in a paper feeding direction. Performing a scanning operation (a primary scan), with an ink ejection while the printing head is driven to move in a direction (a primary scanning direction) different from a nozzle alignment direction, and a paper feeding operation (an auxiliary scan), for respectively predetermined amounts, repeatedly for a plurality of times, completes an image of one area. However, due to hitting position error to be caused by fluctuation of an ink ejection amount, fluctuation of a paper feeding amount, kink of the nozzles (error in forming positions) and so on, and due to ink absorption properties of a printing medium, a printed image can be formed accompanied with irregular color or stripes in a lateral direction.
As a solution for the problem set forth above, there has been known a multi-pass printing, such as two-pass printing or four-pass printing. In the four-pass printing, for example, the paper feeding amount is set at one fourth of a maximum width printed by one scan with the printing head, and one fourth of dots included within the scanning width are printed in each scan. Thus, four times scanning completes all of dots which included in one printing region of a longitudinal width corresponding to the paper feeding amount.
Connecting stripes formed, between printing regions, in the primary scanning direction and in the multi-pass printing employing with the thinned patterns, are so visually perceptible that image quality is to be degraded. In the multi-pass printing, connecting stripes in the primary scanning direction between printing regions formed by the thinned patterns becomes visually perceptible to degrade image quality. One reason for such connecting stripes is paper feeding error which constantly occurs. The feeding error in constant can be caused due to difference in thickness at paper ends, or due to error in a diameter of a paper feeding roller. An alternative reason to the paper feeding error of the connecting stripes may also be scattering of a nozzle pitch about a design value.
FIG. 1
shows a system configuration of a conventional printer.
In
FIG. 1
, a printer
10
is provided with interconnected components, an interface(I/F)
11
, a CPU
12
, a ROM
13
, a RAM
14
and a print control unit
15
, and performs printing in communication with a host computer(PC)
18
.
The ROM
13
has a control program storage area
13
a
and a printing mask storage area
13
b
, and preliminarily stores a control program of the printer
10
and several printing masks which the printer
10
uses. The CPU
12
operates according to the control program stored in the control program storage area
13
a
to generate the printing masks to be used in a current printing mode. The RAM
14
has a printing buffer
14
a
and a printing mask storage area
14
b
to store printing data and the printing masks to be used in the current printing mode. The print control unit
15
controls a printing head (see
FIG. 5A
) having thirty-two nozzles for ink ejection.
FIG. 2
shows a side elevation of an essential part of the conventional printer.
A paper feeding device
22
is to perform the paper feeding operation. Here, the paper feeding operation means transporting of a printing medium M in an arrow A direction (the auxiliary scan). A printing head
20
is to perform the scanning operation (the primary scan). The scanning operation represents an ink ejection while shifting the printing head
20
in arrow B and/or C direction. The printer
10
carries out the multi-pass printing on the printing medium M while performing the paper feeding operation and the scanning operation repeatedly. It should be noted that relatively moving, in the two directions, of the printing medium M and the printing head
20
can accomplish the primary scan and auxiliary scan both.
The printing head
20
has a plurality of nozzles (not shown) aligned in the paper feeding direction. The printing head
20
is a so-called ink-jet head, in which a heater (not shown) is provided in a liquid path of each nozzle for ink ejection for printing, which is achieved by film boiling of the ink, within the liquid path, caused by driving the heater to generate thermal energy, based upon image data.
A printing process by the printer
10
will be explained.
At first, the host computer
18
performs designation of a printing mode via an interface. The CPU
12
retrieves the printing mask to be used in the current printing from the ROM
13
according to the designated printing mode to extend the printing mask in the printing mask storage area
14
b
of the RAM
14
. The printer
10
receives the printing data to extend bitmap data in the printing buffer
14
a
.
Whenever a predetermined amount of the bitmap data is stored in the printing buffer
14
a
, the CPU
12
issues a printing instruction to the print control unit
15
. The print control unit
15
drives the heater with the designated bitmap and the extended printing mask in order to eject the ink to the printing medium.
FIG. 3
shows one example of the conventional printing mask for accomplishing four-pass printing with the printing head.
A printing mask
30
is of a size of 32 dots, corresponding to number of nozzle in the paper feeding direction, by 36 dots in the primary scanning direction. All dots of the printing mask can be applicable to the ink ejection with combined values of (A-x, B-x, C-x, D-x) (1<x<8). The dots are arranged in such a way that an image of an area on the printing medium is completed by scanning the same area respectively with each of area A, B, C, D. A printing ratio in each area A, B, C, D is set at 25%. Namely, for hatched dots, the ink ejection is effective.
Operation of the print control unit
15
employing with the printing mask set forth above will be explained with reference to
FIGS. 1 and 4
.
The print control unit
15
retrieves bitmap data
400
in a printing buffer
14
a
and a printing mask
42
in the printing mask storage area
14
b
in sequential order, and an AND operation of both is carried out. In the printing mask
42
, when the dot is once retrieved up to the final dot, the dot retrieving address returns to the beginning. On the basis of the AND operation result, the effectiveness of the data is determined in order to perform the ink ejection according to the effective data while scanning the printing medium M with the printing head
20
.
A completing process of the image by four-pass printing while repeating the paper feeding operation by a prescribed quantity corresponding to 8 nozzles, will be explained with reference to
FIGS. 5B
, and
6
A to
6
H.
FIG. 5B
shows an image printing result by the multi-pass printing while employing the printing head
20
, the nozzle construction of which is shown in FIG.
5
A.
FIGS. 6A
to
6
H show a forming process of the connection stripes by every scan.
The printer
10
performs the paper feeding for eight nozzles and the scanning repeatedly. Thus, four times of scan completes the image, in each of which scan one fourth of the printing data is used, respectively.
Here, it is assumed that the paper feeding operation of the printer
10
causes a paper feeding error in feeding amount in short of 1%.
Under these conditions, connecting stripes
51
of
FIG. 5B
are formed by a first scan scanning the upper region in the drawing to a fifth scan scanning the lower region in the drawing, th
Barlow John
Canon Kabushiki Kaisha
Dudding Alfred
Fitzpatrick ,Cella, Harper & Scinto
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