Electrophotography – Control of electrophotography process – Control of developing
Reexamination Certificate
1999-08-09
2001-01-16
Grainger, Quana (Department: 2852)
Electrophotography
Control of electrophotography process
Control of developing
C399S272000
Reexamination Certificate
active
06175697
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to a method for the operation of an electrographic printer or copier, whereby a layer containing toner particles, referred to in brief as a toner layer, is deposited on a toner acceptance surface under the influence of a force field.
2. Description of Related Art
Such a method is implemented in the developer unit that is set forth in U.S. Pat. No. 4,777,106. Given this developer unit, the toner particles are electrically charged in a toner reservoir wherein a toner-air mixture is located and the toner particles are subsequently deposited on the toner acceptance surface that is grounded or provided with a potential, being deposited thereon as a toner layer under the influence of an electrical force field. Due to the rotation of a developer drum whose generated surface forms the toner acceptance surface, the deposited toner particles are conducted past a development gap between the developer drum and a toner image carrier. The toner image carrier carries a latent charge image onto which toner particles are selectively applied at the development gap, whereby a toner image arises. The toner image is then applied onto an ultimate image carrier, for example onto paper, from the toner image carrier with or without employment of an intermediate image carrier.
A developer unit having more than one toner acceptance surface is explained in European Patent EP 0 494 454 B 1. The second toner acceptance surface is the generated surface of a transfer drum on which the toner particles are applied directly from the reservoir. The toner particles are then deposited onto the surface of the developer drum at a transfer gap between the transfer drum and the developer drum.
What is disadvantageous about the known method is that a monitoring of the developing process and, in particle, of the amount of toner output by the developer unit is not possible. When the toner amount per surface on the toner acceptance surface or the charge of the toner particles during developing as well lies below or above a predetermined rated value or, respectively, rated range, then the error is not recognized until the finished print image. A reaction thus ensues relatively late. The disturbances in the print image are particularly noticeable given picture elements in the print image that are printed large-area.
In the known method, it is also not possible to exactly set the toner mass per surface section on the toner acceptance surface or the toner charge per surface section, to keep it constant during printing mode and to potentially adapt it to specific print jobs.
U.S. Pat. No. 5,212,522 discloses a method and an apparatus for controlling the mass-related toner charge q/m. The width of a gap between developer drum and a doctor for defining the thickness of the toner layer on the developer drum is employed as a manipulated variable. The gap width is modified with an additional adjustment mechanism. The rotational speed of the toner image carrier and the rotational speed of the developer drum are employed as an auxiliary manipulated variable.
Given a toner concentration monitoring mechanism according to German Patent Document DE 29 30 782 C2, a photo sensor is employed for acquiring the actual toner mass per unit of area on the developer drum. Dependent on the output signal of the photo sensor, the concentration of the toner in a two-component developer is slowly increased.
A developer unit is explained in PCT Patent Application WO, A, 95 10801. The developer unit contains a toner reception surface and an electrode. The toner mass per surface section is acquired with the assistance of a sensor unit. The strength of the charge field between the electrode and the toner reception surface (developer drum) is then set dependent on the output signal of the sensor unit in order to set the toner mass to a rated value.
European Patent Application EP A 0 520 144 explains a developer unit in which the mass relationship between toner and carrier particles is acquired with the assistance of a sensor. Dependent on the acquired mass relationship, printing process parameters such as the charge potential of the photoconductor, the bias potential of the developer unit, the illumination or the toner density are then controlled such an a control procedure that the influence of a modified mass relationship on the quality of the print image is compensated.
The Abstract of Japanese Patent Application JP, A, 0 4 238366 explains a method for the control of the toner concentration in a two-component toner. An optical sensor acquires the toner concentration. A motor for the delivery of toner is then controlled such in a control circuit dependent on the output signal of the sensor that a predetermined toner concentration is established. The optical density of a test mark that is located outside the image region is acquired in a second control circuit with the assistance of a sensor. Parameters of the printing process are then controlled such dependent on the output signal that a predetermined optical density derives.
Both dry toner as well as liquid toner are employed as toner. Given liquid toners, for example, mechanical devices with electrical auxiliary potential are employed for applying the toner. The toners that are employed can still be divided into a single-component and multi-component toner.
What are understood by the term electrographic printer are, in particular, electrophotographic printers, ionographic printers and magnetographic printers. It is also known to employ bands on which the toner layer is deposited instead of the developer drums.
SUMMARY OF THE INVENTION
An object of the invention is to provide a simple method for operating an electrographic printer or copier that enables developing with high quality.
This object is achieved by a method having the method steps of depositing a layer containing toner particles on a toner acceptance surface under the influence of a force field; acquiring the actual toner mass per surface section at at least one location of the layer; whereby the force field is modified in a first control circuit dependent on the deviation of the actual toner mass from a predetermined rated toner mass; and whereby the actual toner charge per surface section is acquired at at least one location of the layer, in that the charge of the toner particles of the layer is modified in a control circuit dependent on the deviation of the actual toner charge from a predetermined rated toner charge.
In a preferred embodiment, the rated toner charge lies above the value of the toner charge of the layer immediately after the application of the toner particles. The voltage in a development gap in which the toner particles are transferred from the toner acceptance surface onto a toner image carrier is taken into consideration in the prescription of the rated toner mass and/or of the rated toner charge.
The invention also provides a developer unit for an electrographic printer or copier, comprising a toner acceptance surface for the acceptance of a layer containing toner particles; a field generating means for generating a force field with which the toner particles are deposited on the toner acceptance surface; at least one sensor unit for acquiring the actual toner mass per surface section of the layer; a first control means that modifies the strength of the force field dependent on the deviation of the actual toner mass from a predetermined rated toner mass; and at least one sensor unit for acquiring the actual toner charge per surface section of the layer, characterized by at least one charging device arranged close to the toner acceptance surface for charging the toner particles on the toner acceptance surface; and by a second control means that modifies the charge behavior of the charging device dependent on the deviation of the actual toner charge from a predetermined rated toner charge. The developer unit is further characterized in that the charging device is a corotron or a scorotron that is preferably operated with a DC voltage s
Apel Reinhard
Kopp Walter
Schleusener Martin
Grainger Quana
Hill & Simpson
Oce Printing Systems GmbH
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