Electrophotography – Diagnostics – Consumable
Reexamination Certificate
2002-03-27
2004-03-16
Pendegrass, Joan (Department: 2852)
Electrophotography
Diagnostics
Consumable
C399S058000
Reexamination Certificate
active
06708007
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to an image forming apparatus such as an electrophotographic or electrostatic recording-type copier, printer or the like that adheres a developer to a potential image formed on an image carrying medium so as to turn the potential image into a visible image, and more particularly, to an image forming apparatus equipped with a developer control unit for adjusting the density of a two-part toner, and an image forming method thereof.
BACKGROUND OF THE INVENTION
Generally, in a developing apparatus equipped with an electrophotographic or electrostatic recording-type image forming apparatus, a two-part developer consisting of toner particles and carrier particles is used. Particularly with color image forming apparatuses that use electrophotography to form a full color or multi-color image, most of the developing apparatuses use a two-part developer.
FIG. 1
shows a schematic cross-sectional view of a conventional two-part developing apparatus. Numeral
10
denotes a developer container; numeral
2
denotes the developing sleeve. The developing sleeve
2
is an empty metallic sleeve, within which is contained a magnetic roller
3
that constitutes a magnetic field generating means. Two agitation devices that are screws A and B are arranged inside the developer container
10
. The A screw
5
is disposed substantially parallel to the developing sleeve
2
, with B screw
6
disposed on the opposite side of A screw
5
, away from the developing sleeve
2
.
FIG. 2
shows a plan view of a conventional developing apparatus. As shown in the diagram, the A screw
5
and the B screw
6
are disposed substantially parallel to each other in a latitudinal direction, with an inner wall
7
is disposed between the A screw
5
and the B screw
6
so as to prevent the developer from getting directly in between the two screws A and B. It will be noted that the inner wall
7
does not extend all the way to the longitudinal ends, so that the developer is able to travel between the two screws A and B. The two screws A and B are set to churn the developer in opposite directions. A gear not shown in the diagram connects the developing sleeve and the two screws A and B. When the developing sleeve
2
rotates, the developer circulates continuously within the container in the direction of the arrows.
As is commonly known, the toner density of a two-part developer, that is, the ratio of the weight of the toner particles to the total weight of the carrier particles and toner particles combined is an extremely important factor in stabilizing the image quality. The developer toner particles are consumed during development, so the toner density changes. As a result, it is necessary to use a toner density control unit (ATR) to detect the developer toner density accurately in a timely manner and to replenish the toner as the density changes in order to maintain the toner density at a uniform level and thereby to maintain the quality of the image.
In order to compensate for these changes in the density of the toner inside the developing apparatus as the developing process progresses, it is necessary to control the amount of toner supplied to the developing apparatus. Toward this end, a variety of systems have conventionally been used for the toner density detection apparatus and the density control apparatus.
For example, there are developer density control apparatuses that make use of the fact that the reflectance of light brought near to the developer holder (typically a developing sleeve is often used for this purpose, so hereinafter the developer holder is referred to as the “developing sleeve”), or a developer transport path of the developer container and directed onto transported developer located atop the developing sleeve or the developer inside the developer container differs according to the toner density to detect and control the toner density. Additionally, there are inductance detection-type developer density control apparatuses that use detection signals from an inductance head that detects a nominal magnetic permeability from the relative proportions of the magnetic carrier and the nonmagnetic toner sticking to the side walls of the developer container and converts the detected magnetic permeability into an electrical signal in order to detect the actual density of the toner inside the developer container, and to supply toner based on a comparison of the detected density with some reference value.
Additionally, there are systems in which a patch image density formed on an image retaining body (typically a photosensitive drum is often used for this purpose, so the image retaining body is hereinafter is referred to as a “photosensitive drum”) is acquired by a sensor that receives light directly or via reflection from a light source disposed opposite the surface of the photosensitive drum, the acquired patch image density is converted to a digital signal by an analog-digital converter and transmitted to a CPU, and the CPU then cuts off the supply of toner until the indicated reading returned to an initial preset value if the read density is higher than such initial preset value, as a result of which the toner density is maintained indirectly at a desired value.
However, there is a drawback to the system for detecting toner density from the reflectance of light directed onto either the transported developer located atop the developing sleeve or the developer inside the developer container, in that accurate toner density readings cannot be obtained if the toner dirties the detecting means.
Similarly, there is a drawback to the inductance detection-type ATR, in that the sensor detection signals change discontinuously due to changes in the apparent density of the developer due to fluctuations in the disposition and environment directly before the image forming apparatus stops operation and directly after the image forming apparatus recommences operation.
Similarly, there is a drawback to the system for controlling toner density indirectly from the patch image density, in that if the patch density measurements are taken too infrequently the intervening toner densities cannot be gauged accurately, whereas if the measurements are taken too frequently the print is interrupted and consequently the number of sheets of paper output cannot be accurately determined. Additionally, as the image forming apparatus is made compact, the space needed to form the patch image or provide the detecting means cannot be retained.
Accordingly, as a method that eliminates the above-described drawbacks, a toner supply system that utilizes a video count has been commercialized.
According to such a system, in order to maintain the toner density at a constant level inside the developer container as the density decreases through developing, the output levels of the digital image signals of each of the pixels are integrated to obtain a print ratio for the image, which is used to calculate the amount of toner to be consumed and thus to be supplied. In other words, from the signals input to a laser scanner or other such exposure device, the exposure output level for each of the pixels is integrated, converted to a video count factor and then transmitted to the CPU. The CPU converts the video count factor to a supply volume, transmits a toner supply signal to activate a toner supply unit, and supplies the required amount of toner to the interior of the developer container, thus maintaining the density of the toner inside the developer container at a constant level.
FIG. 3
is a flowchart of steps in the conventional process of video count-based toner supply, and
FIG. 4
is a corresponding timing chart thereto. The main power supply indicates the ON-OFF status of the main power supply for the image forming apparatus, and the print operation denotes the status of operations relating to the image output (S
806
). The developer unit rotation refers to the rotational state (S
807
) of the developing sleeve and agitation devices. The exposure device drive refers to a state (S
808
)
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