Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
1998-03-06
2001-01-16
Brase, Sandra (Department: 2852)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
Reexamination Certificate
active
06174048
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to direct electrostatic printing methods in which charged toner particles are transported under control from a particle source in accordance with image information to form a toner image used in a copier, a printer, a plotter, a facsimile, or the like.
BACKGROUND TO THE INVENTION
According to a direct electrostatic printing method, such as that disclosed in U.S. Pat. No. 5,036,341, a background electric field is produced between a developer sleeve and a back electrode to enable the transport of charged toner particles therebetween. A printhead structure, such as an electrode matrix provided with a plurality of selectable apertures, is interposed in the background electric field and connected to a control unit which converts an image information into a pattern of electrostatic control fields which selectively open or close the apertures, thereby permitting or restricting the transport of toner particles from the developer sleeve. The modulated stream of toner particles allowed to pass through opened apertures impinges upon information carrier, such as paper, conveyed between the printhead structure and the back electrode, to form a visible image.
According to such a method, each single aperture is utilized to address a specific dot position of the image in a transverse direction, i.e. perpendicular to paper motion. Thus, the transversal print addressability is limited by the density of apertures through the printhead structure. For instance, a print addressability of 300 dpi requires a printhead structure having 300 apertures per inch in a transversal direction.
A new concept of direct electrostatic printing, hereinafter referred to as dot deflection control (DDC), was introduced in U.S. patent application Ser. No. 08/621,074 (now U.S. Pat. No. 5,847,733). According to the DDC method each single aperture is used to address several dot positions on an information carrier by controlling not only the transport of toner particles through the aperture, but also their transport trajectory toward a paper, and thereby the location of the obtained dot. The DDC method increases the print addressability without requiring a larger number of apertures in the printhead structure. This is achieved by providing the printhead structure with at least two sets of deflection electrodes connected to variable deflection voltages which, during each print cycle, sequentially modify the symmetry of the electrostatic control fields to deflect the modulated stream of toner particles in predetermined deflection directions.
For instance, a DDC method performing three deflection steps per print cycle, provides a print addressability of 600 dpi utilizing a printhead structure having 200 apertures per inch.
An improved DDC method, disclosed in U.S. patent application Ser. No. 08/759,481, (now U.S. Pat. No. 5,984,456) provides a simultaneous dot size and dot position control. This later method utilizes the deflection electrodes to influence the convergence of the modulated stream of toner particles thus controlling the dot size. According to the method, each aperture is surrounded by two deflection electrodes connected to a respective deflection voltage D
1
, D
2
, such that the electrical field generated by the control electrodes remains substantially symmetrical as long as both deflection voltages D
1
, D
2
have the same amplitude. The amplitudes of D
1
and D
2
are modulated to apply converging forces on the toner particles to obtain smaller dots. The dot position is simultaneously controlled by modulating the amplitude difference between D
1
and D
2
. Utilizing this improved method enables 60 &mgr;m dots to be obtained utilizing 160 &mgr;m apertures.
With or without DDC in direct electrostatic printing methods a plurality of apertures, each surrounded by a control electrode, are preferably arranged in parallel rows extending transversally across the print zone, i.e. at a right angle to the motion of the image receiving medium. As a pixel position on the image receiving medium passes beneath a corresponding aperture, the control electrode associated with this aperture is set on a print potential allowing the transport of toner particles through the aperture to form a toner dot at that pixel position. Accordingly, transverse image lines can be printed by simultaneously activating several apertures of the same aperture row.
However, it can be considered a drawback of current direct electrostatic printing methods that image lines or edges that are not parallel, i.e. not aligned to the dot grid, appear stepped. Particularly, image lines disposed at a slight angle to the row direction, being formed of a plurality of transverse line segments, appear unsharp. Therefore, there seems to still exist a need to improve the current direct electrostatic printing method.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method of and device for improving edge smoothness in direct electrostatic printing methods.
A further object of the present invention is to provide a method of direct electrostatic printing which increases the edge sharpness of an image recorded onto an information carrier.
Still a further object of the present invention is to provide a method of and a device for improving control over dot placement in direct electrostatic printing methods.
Yet a further object of the present invention is to provide a method of and a device for edge enhancement in direct electrostatic printing methods.
Another object of the present invention is to provide a method of and device for reducing or eliminating jaggedness in lines or contours not aligned with the aperture grid in direct electrostatic printing methods.
Still another object of the present invention is to provide a method of and a device for trajecting toner particles to predetermined positions in view of an image which is to be recorded.
Said objects are achieved according to the invention by providing a direct electrostatic printing device and method for printing an image to an information carrier with increased edge smoothness. By controlling the transport of toner particles, dots can, if needed, be adjusted from the exact alignment of a dot matrix to form smoother edges that are not aligned with the dot matrix. The control of toner particle transport can be effected by time displacement of the opening and closing of the apertures, and/or modification of the deflection voltages. A further improvement is the control of the deflection voltages for controlling the size of the dots, alone or in combination with one or both of the position modifications of the dots.
Said objects are also achieved according to the invention by an image printing device and method for printing an image onto an information carrier. The direct electrostatic printing device includes a pigment particle source, a voltage source, a printhead structure, a control unit, and an image receiving member. The pigment particle source provides pigment particles. The image receiving member and the printhead structure move relative to each other during printing. The image receiving member has a first face and a second face. The printhead structure is placed between the pigment particle source and the first face of the image receiving member. The voltage source is connected to the pigment particle source and the back electrode to thereby create an electrical field for transport of pigment particles from the pigment particle source toward the first face of the image receiving member. The printhead structure includes control electrodes connected to the control unit to thereby selectively open or close apertures through the printhead structure to permit or restrict the transport of pigment particles to thereby enable the formation of a pigment image on the first face of the image receiving member nominally aligned with a dot matrix. According to the invention the control unit controls the transport of pigment particles in such a way that edges of image features, not aligned with the dot matrix, of the image which is to be pri
Array Printers AB
Brase Sandra
Knobbe Martens Olson & Bear LLP
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