Electrophotography – Image formation – Development
Reexamination Certificate
1999-08-02
2001-01-30
Grimley, Arthur T. (Department: 2852)
Electrophotography
Image formation
Development
C399S292000, C399S293000
Reexamination Certificate
active
06181902
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for operating an electrographic printer or copier in which toner particles of different colors are deposited onto a toner image carrier by at least two developer units.
2. Description of the Related Art
When the developer units in an electrographic printer have to develop two charge images with different colors in succession, where the regions to be developed in the two charge images have the same potential, one of the two developer units must be selectively switched into a transfer mode in which toner particles are deposited on the toner image carrier. The other developer unit, or respectively, the other developer units must be in a resting state in which no toner particles are deposited on the toner image carrier. It must be guaranteed that a developer unit deposits toner particles onto the charge image only when the charge image is to be developed with toner particles of this developer unit. It is therefore necessary that the developer units with toner particle of a color that is not needed remain in the resting state when the charge image is moved past them. This is true regardless of whether the charge image has already been developed with toner particles or it will be developed with toner particles at a subsequent developer unit. The toner image carrier is a photoconductor, for example, from which the toner image is directly or indirectly transferred, via a transfer band, onto a final image carrier, such as paper.
A known solution according to a first embodiment in European Patent Document EP 0 691 586 A1 provides that the developer units are swivelled away from the toner image carrier in the resting state, in order to prevent a transfer of toner particles of the wrong color. This method is disadvantageous in that the developer units must be swivelled relatively far away in order to switch over from the transfer state to the resting state. Accordingly, in the changeover from the resting state into the transfer state, the developer units must be swivelled relatively far again back to the toner image carrier. The changeover thus cannot be executed arbitrarily rapidly. Besides, the motorized swivelling of the developer units is only possible with a plurality of additional mechanical components, which are subjected to heavy wear. Often, in addition to swivelling, other measures must be taken, such as an activation and deactivation of rotating components in the developer unit, in order to prevent a dusting or undesired spreading of the toner. This dust would lead to undesirable background formations on the toner image carrier and to contamination of the printer. The activation and deactivation of the rotating components further prolongs the time for the changeover. The European Patent Document EP 0 691 586 A1 also describes a second embodiment, in which a force field in the development gap is activated, or respectively, deactivated in order to switch on, or respectively, switch off the developer unit.
In a developer unit according to U.S. Pat. No. 5,270,782, in the off state of the developer unit, the toner particles on the developer roll are removed by means which are not further detailed.
The above described problems arise in electrographic, magnetographic and ionographic printers or copiers, among others, which fall under the heading of electrographic printers. The toner used is either a single-component or multi-component toner. Solid or liquid toners may be used.
According to German Patent Document DE 4113 777 A1, charge regions of equal potential can be developed with toner particles of different colors if an exposure unit is allocated to each developer unit. A developer unit does not develop if the allocated exposure unit is switched to dark. The above problems with respect to the activation and deactivation of the developer units do not arise. However, for this, a plurality of exposure units must be installed in the printer, which units require space and which entail expensive manufacturing technology.
SUMMARY OF THE INVENTION
It is an object of the invention to propose an additional, simple method for operating an electrographic printer or copier, which method permits a rapid activation and deactivation of the developing power of the developer units.
This object is achieved by a method for operating an electrographic printer or copier, in which toner particles of different colors are deposited on a toner image carrier by at least two developer units, one of the two developer units being selectively switched into a transfer state in which toner particles are deposited onto the toner image carrier, the other developer unit being in a resting state in which no toner particles are deposited onto the toner image carrier, a force field being applied to at least one segment of the transport path of the toner particles from a toner container to the toner image carrier in the transfer state of the developer unit, the force field effecting the transport of the toner particles in the direction of the toner image carrier, and the transport of the toner particles is interrupted at the segment by the altering of the force field in the resting state of the developer unit, the force field acting in the region of a toner particle stock contained in the toner container, and/or the force field acting in the region of a transfer gap of a transport mechanism which transports the toner particles to be applied, subsequent to removal from the toner container, to a development gap between the toner image carrier and a delivery element for delivering toner particles from the developer unit. Advantageous developments of the invention are provided by the force field being altered by reversing the polarity or by switching off an electrical supply voltage for the buildup of the force field. Further, an additional force field may be provided acting in the region of a development gap between the toner image carrier and a delivery element for delivering toner particles from the developer unit. In one embodiment, a toner image carrier onto which toner particles of different colors are deposited by at least two developer units, a control unit which selectively switches one of the two developer units into a transfer state in which toner particles are deposited onto the toner image carrier, the other developer unit is in a resting state in which no toner particles are deposited on the toner image carrier, and at least one field generator for each developer unit, whose force field acts on a segment of the transport path of the toner particles from the toner container to the toner image carrier, the control unit switches the force field in the transfer state such that the force field effects the transport of the toner particles in the direction of the toner image carrier, and the control unit switches the force field in the resting state such that the transport of the toner particles is interrupted at the segment, at least one of the developer units contains the following elements: a device for creating a mixture of air and toner particles in the toner container, which mixture behaves like a fluid, a corona means with a predetermined potential for the electrical charging of the toner particles, and a toner accepting surface, which is arranged opposite the corona device and onto which the charged toner particles settle under the influence of the force field, and/or at least one of the developer units contains a transport device for transporting the charged toner particles, the transport device transporting the charged toner particles, subsequent to removal from the toner container, in the direction of a delivery for delivering the toner particles from the developer unit, and a force field is arranged inside the transport device.
As a further development, the toner particles are transported using at least one rotating surface which rotates with a prescribed speed in the transfer state and in the resting state. The force field may be generated between opposed conductive surfaces or surface portions that have a po
Grimley Arthur T.
Oce Printing Systems GmbH
Schiff & Hardin & Waite
Tran Hoan
LandOfFree
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