Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
1998-12-16
2001-06-26
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
Reexamination Certificate
active
06250743
ABSTRACT:
This application is based on application No. H9-352795 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 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. 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 conveying 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, since the different color of the toner is retained on the toner carrier of each printing station, the electric charge quantity of the toner is different at each printing station, causing variance of the toner retaining force on the surface of the toner carrier. Moreover, the printing station at the most upstream side in the sheet conveying direction performs print on the sheet surface where the toner is not adhered yet, while the printing station at the downstream side performs print again on the toner adhered to the sheet surface by the upstream printing station. Thus, the laminated condition of the toner is different at each printing station, causing variance of the attracting force due to the electric field between the toner carrier and the backing electrode. The variance of both the toner retaining force and the attracting force also causes variance of characteristic that toner is detached from the toner carrier and propelled by the attracting force due to the electric field between the toner carrier and the backing electrode, i.e. transferability at each printing station, resulting in a disadvantage that desirable image is difficult to obtain.
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 having a high transferability in spite of variance of printing particle retaining force and attracting force at each printing station.
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 to form a layer of printing particles, the plurality of printing stations being positioned in a moving direction of the print medium, the printing station positioned downstream with respect to the moving direction of the print medium forming a layer of printing particles on the layer of printing particles formed by the printing station positioned upstream, 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; and
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;
wherein at least any one of the printing stations is different in intention of the electric field from another in accordance with a charge quantity of printing particles or the number of the layer of printing particles in the one of the printing stations.
In the tandem type direct printing apparatus of the present invention having such construction as described above, each printing stations is different in intention of the electric field in accordance with the charge quantity of printing particles or the number of the layer of printing particles. In the concrete, the intensity of the electric field in the printing station using a small charge quantity of printing particles is made small, while the intensity of the electric field in the printing station using a large charge quantity of printing particles is made large. Thus, even though there is a variance of printing particle retaining force due to the difference in charge quantity of the printing particles at each printing station, the transferability that the printing particles are detached from the carrying member and propelled is same at each printing station. Alternatively, the intensity of the electric field in the upstream printing station in which the print medium has a small number of the layer of printing particles is made small, while the intensity of the electric field in the printing station in which the print medium has a large number of the layer of printing particles is made large. Thus, the variance of the attracting force due to the difference in the number of the layer of printing particles disappears, thereby the transferability is same at each printing station.
As the intensity of the electric field at each printing station has parameters of the voltage applied to the backing electrode by the power supply and the distance between the backing electrode and the printing head, the intention of the electric field in each printing stations is preferably different from one another by changing such parameters.
Preferably, the printing medium may be a sheet which is conveyed through a pass formed between the backing electrode and the printing head. In this case, the sheet may be conveyed by an endless belt type of conveyance belt or an cylindrical type of conveyance drum.
Preferably, the printing medium may be an intermediate transfer member which is conveyed through a pass formed between the backing electrode and the printing head and the apparatus may further comprise a transfer roller which comes into pressure contact with the intermediate transfer roller to transfer the layer of printing particles form
Hiraguchi Hiroshi
Shibata Yoshifumi
Shimada Hirokatsu
Uno Koji
Yamaki Toshio
Barlow John
Gordon Raquel Yvette
Minolta Co. , Ltd.
Morrison & Foerster / LLP
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