Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
1998-12-16
2001-08-07
Banow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
Reexamination Certificate
active
06270196
ABSTRACT:
This application is based on application No. H9-352798 filed in Japan on Dec. 22, 1997, the content of which is hereby incorporated by reference.
FIELD OF THE INVENTION
The present invention relates to a tandem type of direct printing apparatus for use in a color copying machine and printer.
BACKGROUND OF THE INVENTION
U.S. Pat. No. 5,477,250 issued on Dec. 19, 1995 discloses a tandem type of direct printing apparatus. In the direct printing apparatus, four printing stations are disposed along a sheet moving direction. Each printing station comprises a toner carrier retaining toner on its outer periphery, a backing electrode opposed to the toner carrier and a printing head disposed between the toner carrier and the backing electrode, the printing head having a plurality of apertures and a plurality of electrodes surrounding each aperture. On the outer periphery of the toner carrier in each printing station are retained toner having different colors, for example, magenta, cyan, yellow and black. The backing electrode of each printing station is electrically connected to a power source, thereby between the toner carrier and the backing electrode is formed an electric field for attracting the toner on the toner carrier and propelling it toward the backing electrode through the apertures of the printing head. Between the printing head and the backing electrode in each printing station is formed a passage for a sheet.
When an ON voltage is applied to the electrode of the printing head in the printing station positioned at the most upstream side in the sheet moving direction, for example, the magenta printing station, the toner attracting force due to the electric field between the toner carrier and the backing electrode propels the toner on the toner carrier through the apertures toward the backing electrode and adheres it to the sheet. When an OFF voltage is applied to the electrode of the printing head, the toner attracting force does not affect the toner on the toner carrier, whereby the toner is never propelled. Thus, when ON and OFF voltage applied to the electrode of the printing head are controlled on the basis of a desired image signal, a magenta image corresponding to the image signal is printed on the sheet. In the same manner, by controlling the ON and OFF voltage applied to the electrode of the printing head in each of the downstream printing stations a different color of image is laid on the previously printed image to form a desired image.
In the aforementioned tandem type of direct printing apparatus, as the images formed by the printing stations are overlaid on each other, it is necessary that each aperture of printing head of one printing station corresponds to that of the other printing stations and that the corresponding apertures between the printing stations are aligned on a line parallel to the sheet moving direction. However, each printing station is installed separately from each other. Therefore, the corresponding apertures between the printing stations are shifted in a direction perpendicular to the sheet moving direction (hereinafter referred as a main scanning direction) due to the installation error of the printing head of each printing station. As the position shift of the apertures in the main scanning direction results in color deviation of the image, it is not possible to obtain a clear image.
For example, as shown in
FIG. 8
, in the case that an installation error of 50 &mgr;m exists between the first printing station
104
a
and the second printing station
104
b
which have six apertures
102
with a pitch of 42 &mgr;m, a position shift or a color deviation of 50 &mgr;m which is same as the installation error is caused between the first aperture
102
of the first printing station
104
a
and the first aperture
102
of the second printing station
104
b
. In order to eliminate such color deviation, after setting the printing head
106
of the second printing station
104
b
, the position of the printing head
106
can be adjusted with high precision so that the installation error become zero. However, as this adjusting work is very difficult, the accuracy obtained by the adjusting work is limited.
SUMMARY OF THE INVENTION
Accordingly, the present invention has been accomplished to solve the aforementioned disadvantages of the prior arts. An object of the present invention is to provide a tandem type of direct printing apparatus in which color deviation is minimized without position adjustment of the printing head.
In order to achieve the aforementioned object, according to the present invention, there is provided a tandem type direct printing apparatus comprising a plurality of printing stations for depositing printing particles on a print medium, the plurality of printing stations being positioned in a moving direction of the print medium, the printing station comprising:
a bearing member for bearing charged printing particles thereon;
a backing electrode opposed to the bearing member;
a power supply connected to the backing electrode for generating an electric field that attract the charged printing particles on the bearing member to propel the same toward said backing electrode;
a printing head disposed between the bearing member and the backing electrode, the printing head having a plurality of apertures through which the printing particles can propel and a plurality of electrodes disposed around the plurality of apertures;
a driver for applying the plurality of electrode with a voltage for allowing the printing particles to be propelled and a voltage for forbidding the printing particles to be propelled in response to an image signal; and
a controller for outputting the image signal to the driver;
wherein each of the plurality of apertures of the printing head in any one of the printing stations corresponds to the aperture of the printing head in another printing station so that the latter is closest to a line along the moving direction of the printing medium which pass through the center of the former.
In the tandem type direct printing apparatus of the present invention having such construction as described above, each of the plurality of apertures of the printing head in any one of the printing stations corresponds to the aperture of the printing head in another printing station so that the latter is closest to a line along the moving direction of the printing medium which pass through the center of the former, whereby no position adjusting work of each printing stations is necessary. a quantity of color deviation is reduced to at most half the pitch of the apertures.
Preferably, the number of the plurality of apertures of the printing head in each of the printing stations may be larger than an effective dots number to prevent lack of dot. In this case, the controller may output the image signal as a dummy to the driver so that the electrodes corresponding to the dots over the effective dots number are supplied with a voltage for forbidding the printing particles to be propelled. Moreover, the electrodes corresponding to the dots over the effective dots number may be supplied with a voltage for forbidding the printing particles to be propelled.
Preferably, the bearing member in each of the printing stations may bear the charged printing particles with different color thereon to perform color print.
REFERENCES:
patent: 5477250 (1995-12-01), Larson
patent: 5596356 (1997-01-01), Lee
patent: 5650809 (1997-07-01), Kitamura
Hiraguchi Hiroshi
Shibata Yoshifumi
Shimada Hirokatsu
Uno Koji
Yamaki Toshio
Banow John
Gordon Raquel Yvette
Minolta Co. , Ltd.
Morrison & Foerster / LLP
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