Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
1999-08-27
2002-04-23
Le, N. (Department: 2861)
Incremental printing of symbolic information
Ink jet
Controller
Reexamination Certificate
active
06375297
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a printer with a recording head capable of ejecting an ink drop, and more particularly to a called bi-directional printer capable of printing on a printing medium in both a forward scan and a reverse scan by the recording head.
In the printer with a recording head for ejecting an ink drop, there are proposed techniques to curb an elongation of a printing time, which results from the size increase of a printing medium and the definition increase of a print image. An example of the technique is a bi-directional printing technique in which the printer prints on a printing medium in both the scanning directions of a forward scan and a reverse scan, which are performed by the recording head.
In the printer using such a technique, i.e., the called bi-directional printer, when an ink drop is ejected at the same timing (same ejection positions) in both the forward scan and the reverse scan, printing positions in the forward and reverse scans are off-set from each other. As shown in
FIG. 19A
, an ink ejection direction is expressed by a composite vector of a vector Vm, Vm′ (moving velocity vector) representative of a moving velocity of the recording head 1003 and a vector Vj (ejecting velocity vector) representative of an ink ejecting velocity of an ink drop ejected from the recording head
1003
. Where the timing of ejecting an ink drop in the forward scan F is the same as that of ejecting an ink drop in the reverse scan R, the direction of ejecting an ink drop in the forward scan will be different from that in the reverse scan since a direction of the moving velocity Vm of the recording head in the forward scan is different from direction of the moving velocity Vm′ in the reverse scan. As a result, a printing position on the printing medium in the forward scan is different from that in the reverse scan (PO in the figure).
To cope with this, in design, an ink ejection position JP in the forward scan F is off-set from that JP′ in the reverse scan R so as to secure the coincidence of the printing positions in the forward scan and in the reverse scan at PP as shown in FIG.
19
B. Further, a function to print a test pattern, which is used for detecting a printing-position off-set between the forward scan and the reverse scan is incorporated into the printer. To correct the printing-position off-set, an operator prints out the test pattern. He adjusts elevation of the recording head
1003
and the platen
1002
while referring the print result of the test pattern, to thereby set up a proper distance from the ink ejecting surface of the recording head to the printing surface of the printing medium
1001
.
Precision improvement in the paper feeding/discharging mechanism of the recent printer enables the printer to print on various types of printing media. Where the bi-directional printer prints on various types of printing media, the apparatus will meet the medium thickness difference. When the medium thickness difference exists, the distance from the ink ejecting surface of the recording head to the printing surface of the printing medium inevitably changes. An influence of the distance change upon the printing-position off-set is not negligible.
Let us consider a case where identical images are formed on a normal paper sheet and a post card (
1010
in FIG.
19
B). In this case, the normal paper sheet has a thickness of about 0.1 mm thick and the post card has a thickness of about 0.2mm. One of the normal paper sheet and the post card (or a printing medium having a thickness value between those values of them) is used for a reference for correcting the printing-position off-set, and the distance from the ink ejecting surface of the recording head to the printing surface of the printing medium is adjusted to as to correct the off-set. Then, the printer prints on the other sheet (both the sheets when the printing medium of the medium thickness is used for the reference). In this case, an off-set of the printing position in the forward scan from the printing position in the reverse scan is not so distinguished.
Let us consider another case where identical images are printed on thick printing media of about 1.5 mm thick, such as label sheets and thick sheets, in addition to the normal paper sheets and the post cards. The normal paper sheet or the post card is used for a reference for correcting the printing-position off-set, and the distance from the ink ejecting surface of the recording head to the printing surface of the printing medium is adjusted to as to correct the off-set. In this case, a great printing-position off-set PO′ is created when the printer prints on those thick printing media (
1011
in FIG.
19
B).
The related bi-directional printer is not designed such that it can handle various types of printing media of different thickness values. To correct the printing-position off-set, the related printer takes the following tasks: every time a printing medium having a different thickness is set to the printer, a test pattern is printed on the printing medium set anew; and an operator adjusts a position of the platen and/or recording head on the basis of the print result of the test pattern to set up a proper distance from the ink ejecting surface of the recording head to the printing surface of the printing medium. Following those tasks, the printer prints on the printing medium. The execution of those tasks is complicated and troublesome, and imposes heavy on the operator.
A viscosity of ink varies with variation of temperature. A variation of the viscosity of ink results in a velocity of ejecting an ink drop from the recording head. Normally, the recording head per se has a temperature-dependency. Therefore, when temperature of the recording head varies, the ink ejecting velocity also varies. Thus, an ink ejection direction is expressed by a composite vector of the moving velocity vector of the recording head and the ejecting velocity vector of the ejecting ink drop. Therefore, when the ink ejecting velocity varies, the ink ejecting direction varies. This yields a printing-position off-set between the forward scan and the reverse scan.
Some of recent bi-directional printer are capable of printing on a printing medium of large size, e.g., A
0
. To print on a large size printing medium by use of the bi-directional printer, the printing is contiguously performed for a relatively long time. During the long printing operation, temperature of the recording head varies and an ink ejecting direction varies. Therefore, the following expedience is inevasible. Even if the ink-ejection timing is corrected so as to eliminate the printing-position off-set between the forward and reverse scans by the recording head before printing on the printing medium starts, a temperature variation of the recording head during the printing operation inevitably yields a printing-position off-set between the forward and reverse scans.
SUMMARY OF THE INVENTION
For the above background reasons, the present invention is made and has an object to lessen stress imposed upon the operator when bi-directional printing on various types of printing media are carried out. The invention has another object to obviate a printing-position off-set between the forward scan and the reverse scan, which arises from the temperature-dependency of the recording head and ink used.
In order to achieve the above object, according to a first aspect of the present invention, there is provided a printer capable of printing on a printing medium in both a forward scan and a reverse scan by a recording head for ejecting ink drops, comprising- interface means for acquiring control information containing at least information on a thickness of the printing medium; and timing correction means for correcting timings of ejecting ink drops toward the printing medium during at least one of the forward and reverse scans in accordance with the thickness information of the printing medium contained in the control information acquired by the interface means.
The interfac
Hayashi Toshihiro
Matsuzawa Yoshihiko
Feggins R.
Le N.
Seiko Epson Corporation
Sughrue & Mion, PLLC
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