Electrophotography – Image formation – Development
Reexamination Certificate
2002-01-30
2003-07-01
Brase, Sandra (Department: 2852)
Electrophotography
Image formation
Development
C399S035000, C399S259000
Reexamination Certificate
active
06587661
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus for a dry electrophotographic developing apparatus and the like, and in particular it elates to an image forming apparatus equipped with such a developing apparatus in which a toner and a carrier corresponding in amounts to their consumptions are replenished to a developer material supply path from a toner replenishment device and a carrier replenishment device thereby to maintain the mixing ratio by weight between the toner and the carrier constituting the developer material and the amount of the developer material held in the developer material supply path at constant levels, respectively, wherein a part of the developer material held in the developer material supply path is supplied to a photoreceptor through a developing roller while being stirred, so that a latent image formed on the photoreceptor is visualized by the toner contained in the developer material thus supplied, and at the same time, that part of the developer material to be held in the developer material supply path which exceeds a predetermined amount is discharged as a discharged developer material from a developer material discharge port and received in a discharged developer material receiving part.
2. Description of the Related Art
In a developing apparatus of an image forming apparatus applying an electrophotographic method, a method (trickle development) using a developer material composed of at least two components, a carrier and a toner, is mainstream. In the case of a developing apparatus using such a type of developer material, it is necessary to stir a carrier and a toner thereby to electrify the toner through stirring friction. However, a resin constituting the toner is fused to the carrier due to the heat of stirring friction, so that the carrier is gradually coated with the fused toner, finally reaching a state in which the carrier is contaminated by coatings. Thus, when the carrier comes to the state of contamination, it becomes impossible to sufficiently electrify the toner by the stirring friction, resulting in the formation of defective images. In order to avoid such defective images, conventionally, the entire amount of developer material has been replaced with a new one when the period of use of the developer material exceeds a prescribed period of time.
When the developer material is taken out of a container for such a replacement, there might arise a problem that the developer material is dispersed or scattered around to float in the surroundings and contaminate the surrounding environment. Accordingly, it is necessary to carry out the replacement of the developer material carefully, and hence replacing the entire developer material requires a lot of time. Thus, it has been proposed to replace the container storing the developer material on the whole in order to avoid such an annoying or troublesome replacement operation. However, by merely facilitating the replacement of the container without taking appropriate measures as to how to use the developer material, the amount of developer material to be wasted is not decreased at all. The developer material cannot be wasted or discarded as general garbage. Therefore, it is necessary to perform special processing on the developer material to be discarded. Thus, as the amount of wasted developer material increases, the cost of maintaining the developing apparatus increases, too.
As an invention with a possibility of solving the above-mentioned problem, there is a developing apparatus for an electrophotographic copier using a trickle development method as disclosed in Japanese Patent Publication No. 2-21591 (corresponding to U.S. Pat. No. 4,614,165). In this developing apparatus, a new carrier is replenished to the developing apparatus little by little in accordance with the replenishment of a toner, and a part of the surplus developer material is similarly discharged from the developing apparatus to a developer material collection tank little by little, whereby the developer material in the developing apparatus is continuously refreshed little by little. As a result, the deterioration speed of the electrification performance of the developer material used can be greatly slowed down, so that the usable life of the developer material can be extended to the same extent as the service life of the developing apparatus. In this developing apparatus, however, only the height of a weir installed in a discharge port is finally controlled so as to adjust the discharge of the deteriorated developer material, but the amount of the discharge is not fed back to the amount of supply of the developer material. Thus, it is impossible to perform the replenishment or discharge of the developer material at an amount corresponding to the amount of the discharge or replenishment thereof in an accurate manner. As a result, the amount of developer material in a development tank varies, making it impossible to carry out the precise control of keeping the concentration of the toner and the electrification performance of the developer material in the development tank in a good condition.
Thus, there have been made proposals for improved developing apparatuses such as, for example, those disclosed in Japanese Patent No. 2,986,001 (corresponding to U.S. Pat. No. 5,548,385) and in Japanese Patent No. 2,930,834 (corresponding to U.S. Pat. No. 5,592,270). In the developing apparatus disclosed in the Japanese Patent No. 2,986,001, a toner concentration sensor is arranged in a development tank, and a magnetic permeability sensor is arranged in a developer material collection tank. A control unit calculates the amount of developer material in the development tank from outputs of the toner concentration sensor and the magnetic permeability sensor, and performs control in such a manner that the amount of developer material in the development tank is made constant, thereby keeping the electrification performance thereof in a good condition. On the other hand, in the developing apparatus disclosed in Japanese Patent No. 2,930,834, a shutter, which can be opened and closed under the action of a solenoid, is arranged in a discharge port, and it is controlled to discharge a developer material at an amount corresponding to the amount of replenishment thereof. However, with the arrangements in the above examples as disclosed in Japanese Patent No. 2,986,001 and in Japanese Patent No. 2,930,834, the component parts employed are expensive and the control required thereof becomes complicated since the magnetic permeability sensor or the like is arranged in the developer material collection tank, or the shutter is arranged in the developer material discharge port, so that the sensor or shutter is controlled by a control circuit to keep the amount of developer material in the development tank at a constant level so as not to deteriorate the electrification performance of the developer material in the development tank. In addition, in cases where developing is performed in full color, it is necessary to install four sets of these elements in the developing apparatus, thus resulting in a substantial increase in the cost.
SUMMARY OF THE INVENTION
The present invention has been made to solve the above-mentioned problems, and has for its object to provide an image forming apparatus which is capable of keeping the weight ratio between a toner and a carrier in a developer material inside a development tank as well as the amount of the developer material at their prescribed constant values even with the use of simple component parts and easy control.
In order to solve the above-mentioned problems, the present invention resides in an image forming apparatus equipped with a developing apparatus in which a toner and a carrier constituting a developer material are replenished from a replenishment device to a developer material supply path, and in which an excess part of the amount of developer material to be held in the developer material supply path is discharged from a developer material
Shimmura Shoko
Watanabe Takeshi
Brase Sandra
Foley & Lardner
Kabushiki Kaisha Toshiba
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