Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
1999-03-09
2001-07-24
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
Reexamination Certificate
active
06264308
ABSTRACT:
This application is based on application No. H10-61063 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 direct printing apparatus for use in a color or monochrome copying machine, printer, facsimile and composite thereof.
BACKGROUND OF THE INVENTION
U.S. Pat. No. 5,477,250 issued on Dec. 19, 1995 discloses a direct printing apparatus. In the direct printing apparatus, four printing stations are disposed along a sheet conveying 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. 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, 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, an image corresponding to the image signal is printed on the sheet.
In the aforementioned direct printing apparatus, a distance between the printing head and the toner carrier affects the flying distance of the toner. Thus, the distance between the printing head and the toner carrier necessitates an allowance of approximately 10 &mgr;m, thereby high accuracy is required. Conventionally, for example, in Japanese patent Laid-open publication 6-297753, as means for positioning the printing head and the toner carrier (developing roller) to ensure the accuracy of the position, there has been provided a spacer made of resin between the printing head and the developing roller such that the spacer comes into contact with the developing roller.
However, the aforementioned direct printing apparatus has the following disadvantage. Since the spacer comes into contact with the developing roller, the toner particles enter and accumulate in the contact portion therebetween. Thus, the heat due to the long time operation of the apparatus causes the accumulated toner particles to gradually deteriorate and melt to adhere to the surface of the spacer. Then, the adhered toner provide noise to the thin uniform layer of toner particles formed on the outer periphery of the developing roller and disturb the uniform layer, whereby noise appear on the printed image.
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 direct printing apparatus which is possible to form fine image without causing noise due to the adhesion of the toner to the spacer for long time operation.
In order to achieve the aforementioned object, according to the present invention, there is provided a direct printing apparatus which comprises a bearing member for bearing printing particles thereon, the printing particles being charged to a predetermined polarity, a backing electrode
44
opposed to the bearing member, and 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, whereby the printing particles are directly deposited on a print medium which is conveyed between the backing electrode and the printing head, wherein:
a positioning spacer is provided between the bearing member and the printing head so that the surface of the bearing member comes into contact with the spacer; and
at least a part of the spacer which comes into contact with the bearing member is made of a material which is apt to be worn by the printing particles.
Preferably, the part of the spacer which comes into contact with the bearing member may be made of such a material that maximum wearing depth per unit moving distance of the bearing member is more than 2.0×10
−3
&mgr;m/m.
In the direct printing apparatus of the present invention having such construction as described above, since the contact part of the spacer with the bearing member is made of such material that is apt to be worn by the printing particles, the spacer is worn away by the printing particles. Thus, the toner particles neither accumulate on the contact part nor adhere to the surface of the spacer.
Preferably, the bearing member may comprise an endless sleeve for bearing the printing particles thereon and a drive roller having outer diameter smaller than the inner diameter of the sleeve and being disposed in the sleeve.
REFERENCES:
patent: 5477250 (1995-12-01), Larson
patent: 6086186 (2000-07-01), Bergman et al.
patent: 6-297753 (1994-10-01), None
Barlow John
Gordon Raquel Yvette
Minolta Co. , Ltd.
Morrison & Foerster / LLP
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