Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
2002-06-06
2003-06-03
Gordon, Raquel Yvette (Department: 2853)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
Reexamination Certificate
active
06572219
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a print head for electrostatic printing of documents in accordance with the so called aperture matrix technique, which usually is called DCF-technique being an abbreviation of Digital Control Filter technique, which print head includes means for charging of tuner particles with a certain polarity, a tuner depositing matrix which is provided with a plurality of apertures, trough which the toner particles can pass, means for controlling the deposit of tuner particles to certain specific depositing positions, and means for feeding a document, which in to be printed under the aperture matrix.
PRIOR ART
During approximately the last 10 to 15 years work has proceeded to simplify the so-called laser printer technique. Characteristic of his technique is that a digitalized picture is applied on a rotating, light sensitive drum by means of digitalized light. Then different electrical levels on the drum surface will represent the picture, subsequently the picture is developed by electrically charged powder, and finally the picture is moved to the document by pressure transfer. Pressure and heat between a pair of rollers fix the digitalized picture now existing on the document.
The characterising feature of this printing technique is that a pulverised dry ink is used, which generally is called a toner and is fixed to the documents by a fuse-pressure process, whereby the document is provided with an excellent durability for a long time and resistance to external influence by mechanical wear and moisture etc.
The present simplifying proceedings is to eliminate the previous intermediate step of storing the picture on a drum, where it is developed and later moved to the document This involves unnecessary costs due to additional components and an increased risk for distorting the digital information on its way from the computer to the state, in which is fixed on a document.
The most recently developed laser printers provide a picture quality of 600 DPI (dots per inch) or better. To cover an A4 page with all possible dot positions 34 million positions are required at a resolution of 600×600 DPI. The problem is to find a technique by which it is possible to apply a powder dot in the shape of a small dot on the correct location on the document, when there are 34 million possibilities.
The most successful technique during the last few years is to use a so-called “Digital Controlled Filter” (DCF), henceforth called a matrix or an aperture matrix, comprising a row of small apertures in a thin foil. The apertures are opened or closed by application of an electrical voltage, which generates a field that attracts the electrically charged powder to pass or not to pass through the apertures. On one side of the foil the document is situated, upon which the particles land, and on the other side of the foil the charged powder is situated on a conveyor. In most applications this conveyor consists of a roller with a thin layer of electrically charged powder.
This technique was described for the first time in the U.S. Pat. No. 3,689,935 to Pressman and Casanova in Sep. 5, 1972. Several later patents disclose various improvements of the Pressman/Casanova patent, e.g. U.S. Pat. No. 4,491,855 (Fuji/Ando—Canon from 1985), U.S. Pat. No. 4,912,489 (Schmidlin—Xerox from 1990) and Swedish patent No. 8704883-1 (Ove Larsson—Array Printers from 1989). The various improvement methods disclosed in these patents relate to how the electrical field around each aperture is appplied to obtain a more efficient transfer of the powder through the apertures down to the document.
Problem
An aperture matrix may comprise a row of apertures covering the width of an A4 sheet, i.e. 210 mm or a row of 4960 apertures to create a 600 DPI print-out. The advantage with this type of aperture matrix is that printing can be done with continuous paper feed and with continuous fixing, and in other words a continuous printing process is obtained.
There are many problems connected with an aperture matrix being as wide as said 210 mm.
1. If every aperture is connected with a drive circuit for the application of a voltage on a round electrode, which is arranged around the aperture, this involves several thousands ring electrodes, connection lines and drive circuits, and with increasing number of apertures in the aperture matrix the probability increases for breakdown in any of these apertures, rings, connection lines or drive circuits.
2. If the control field for opening and closing the apertures in the aperture matrix is applied between ring electrode and powder feed surface there is an additional problem, for the distance between the aperture matrix and the powder feed must have the magnitude of 0.1 to 0.15 mm, since available drive circuits can stand a maximum of 300 to 350 volt. Therefore this distance is not allowed to vary more than 0.02-0.04 mm since the variation of the distance has an influence on the electrical filed, which in turn has an influence on the blackness of the printout. Since the aperture matrix is a thin foil it is very difficult to maintain a distance of 0.1 to 0.15 mm within the said tolerance between the aperture matrix an the powder feed surface over the entire width of an A4 sheet.
3. According to paragraph 2 drive circuits are required, which can stand at least 300 volts and preferably more, and such drive circuits in the form of integrated circuits are still too expensive, which creates a cost problem. The solution of the cost problem is to use lower voltage or fewer circuits.
4. A further problem is that there exists a certain percentage of powder, which not will be charged or charged to the opposite potential. This powder can not be controlled by electric control fields but will fly around without control or deposit on undesirable surfaces.
Common types of printing powder will be electrically charged with negative potential, when the powder particles rub against some other suitable material. This rubbing is usually created in two ways, either with a rotating magnetic field in case the powder is provided with magnetite and a rotating magnetic brush is created, which rub the particles against a roller. In case the powder lacks magnetite a rotating brush or a foam rubber roller, which rotates against a steel roller, rubs the powder particles against this steel roller. In booth cases the correct amount of powder is dosed on the rotating steel roller by means of a flexible rubber blade. This dosing, called doctoring, has a grinding influence on the powder, and the disintegration of powder particles causes creation of particles, which are booth incorrectly charged and uncharged.
The four main problems mentioned above are the reason for the fact that the technique mentioned above not yet has been any great commercial success, though it offers direct transfer of digital information from a computer to a document.
The Invention
Our proposal is to use an aperture matrix comprising en isolating foil with a completely covering, electrically conducting surface on one side of the foil (called the base side). On the other side of the foil there are a greater number of electrically conducting rings (called ring side), each of which is formed around an aperture through the aperture matrix. Each ring is connected to a voltage source through a separate line to a control transistor. The base side of the foil has a common potential, since it has a completely covering, electrically conducting surface.
According to the invention it is proposed that the electrically charged powder now is applied above the base side on the aperture matrix as a cloud of charged particles, which constantly are moving. This cloud is created in such a way, that toner which is situated in a toner container, is fed forwards by a feeding brush, which rotates clockwise (in the case shown in
FIG. 2
) with a low number of revolutions to correspond with the consumption of tuner in the printing process.
Tangential to the feeding brush is a flipping brush, which rotates anticlockwise with a higher number of revolutions
Digital Filter Printing AB
Gordon Raquel Yvette
Larson & Taylor PLC
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