Electrophotography – Image formation – Development
Reexamination Certificate
2000-01-27
2001-02-20
Moses, Richard (Department: 2852)
Electrophotography
Image formation
Development
C399S359000
Reexamination Certificate
active
06192212
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to an image forming apparatus such as a copier, printer etc., for performing electrophotographic image formation, in particular, relating to an image forming apparatus having a toner recycling function of reusing the toner collected from the photoreceptor surface.
(2) Description of the Prior Art
In the image forming process using the electrophotographic technique effected in image forming apparatus such as copiers, printers and the like, a static latent image is formed on the photoreceptor surface by the photoconductive effect and developed into a visual image with a powder developer supplied from a developing device. This visual image supported on the photoreceptor is transferred to a recording medium. At that event, some part of the developer constituting the visual image on the photoreceptor surface will remain on the photoreceptor surface, failing to transfer to the recording medium. In general the photoreceptor surface is used repeatedly for image forming operations, so if the remaining developer is left as it is on the photoreceptor surface, this will cause degradation of the image quality for subsequent image forming operations. Therefore, the developer left on the photoreceptor surface after the transfer step is removed by means of a cleaning device and discarded.
If all the developer not having been used for image forming on the recording medium during the image forming operation is to be discarded, the developer is wasted, raising the running cost.
A conventional image forming apparatus using a dual-component developer consisting of a toner and a carrier has a so-called toner recycling function for collecting the toner which has been removed from the photoreceptor surface by a cleaning device, into the developing device, and reusing the toner thus removed from the photoreceptor surface for subsequent image forming, to thereby avoid waste of toner and realize a reduction in running cost.
Typically, as shown in
FIG. 1
, provided around and opposing a photoreceptor drum
51
are a primary charger
52
, a developing unit
54
, a transfer device
55
, a cleaning device
57
and a charge erasing device
58
, in this sequential order, and furthermore, a conveying device
59
for conveying toner from the cleaning device
57
to the developing unit
54
. Cleaning device
57
located between transfer device
55
and primary charger
52
with respect to the rotational direction of photoreceptor drum
51
includes a scraper member
57
a
such as a blade etc., abutting the surface of photoreceptor drum
51
and collects the toner remaining on photoreceptor drum
51
after passage of the opposing position of transfer device
55
and falling into cleaning device
57
. The toner collected in cleaning device
57
is conveyed to developing unit
54
by driving at an appropriate timing, a conveying device
59
constituted by, for example, a screw conveyer mechanism.
In order to maintain a constant density of the image formed on the recording medium in the image forming operation by the electrophotographic technique using a dual-component developer, a necessary and sufficient amount of toner for developing the static latent image needs to be stored in the developing unit. Therefore, a conventional image forming apparatus, for example, includes a toner concentration sensor such as a magnetic permeameter or the like which detects the amount of the toner stored in the developing unit based on the detection signal from the toner concentration sensor and replenishes the developing unit with the toner based on the detection result. Since only the toner among the developer is consumed during the image forming process while the stored amount of the carrier in the developing unit will be theoretically unchanged, variation in the ratio of the toner to the developer consisting of the magnetic component, i.e., the carrier and the non-magnetic toner will appear as the change in magnetic permeability of the developer. Accordingly, the amount of the toner stored in the developing unit can be obtained from the detection result of the permeability of the developer by the magnetic permeability sensor.
However, so-called recycled toner, which has been removed from the photoreceptor surface after the transfer step and collected into the developing unit contains foreign substances such as paper dust, talc etc. from the paper as the recording medium and this recycled toner is returned into the developing unit, so that the foreign substances mixed with the developer have an influence on the detection result of the toner concentration sensor. However, there has been no conventional image forming apparatus having a toner recycling function, which takes into consideration the variation of the detection result of the toner concentration sensor due to the foreign substances mixed with the developer in the developing unit. Thus, it has been impossible to detect an exact amount of the toner stored in the developing unit, which might cause surplus or deficiency of the amount of the toner replenishing the developing unit, making it impossible to maintain correct image density.
Further, the amount of foreign substances contained in the recycled toner will vary depending upon image forming conditions such as the number of image forming operations, the sizes of recording media as well as environmental conditions such as temperature, humidity etc. Therefore, it has been impossible to definitely determine the amount of foreign substances mixed in the developer based on the amount of the recycled toner collected into the developing unit, and it has not been easy to compensate the errors arising in the detection result of the toner concentration due to mixture of foreign substances in the developing unit. Hence, it has been difficult for an image forming apparatus having a toner recycling function to keep a correct image density.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an image forming apparatus which can constantly store an appropriate amount of toner in the developing unit and maintain proper image forming conditions such as image density etc., regardless of the amount of foreign substances mixed in with the developer, by predicting the amount of foreign substances mixed in the developing unit based on the image forming conditions and the environmental conditions and controlling the stored amount of the toner in the developing unit based on the prediction.
The present invention has been devised in order to the above object and is configured as follows:
In accordance with the first aspect of the present invention, an image forming apparatus for forming images by electrophotography using a dual-component developer consisting of a toner and a carrier wherein the toner remaining on the photoreceptor surface after completion of the transfer step is removed by the cleaning device, collected and returned to the developing portion as the recycled toner and reused together with the fresh toner for a subsequent developing step, includes a controller which predicts the characteristics of the recycled toner based on the image forming conditions and the environmental conditions for individual image forming operations and executes control of the storage state of the toner in the developing portion in accordance with the prediction.
In accordance with the second aspect of the present invention, the image forming apparatus having the above first feature is characterized in that the characteristics of the recycled toner predicted by the controller include the state of foreign substances mixed in the recycled toner.
In accordance with the third aspect of the present invention, the image forming apparatus having the above second feature is characterized in that the controller comprises:
a means for measuring the numbers of image forming operations for individual sizes of recording media used for image forming operations as the image forming conditions having influence on the emergent amount of paper dust; and
Kimura Takahiro
Kunihiro Hisashi
Nakakuma Akira
Moses Richard
Sharp Kabushiki Kaisha
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