Electrophotography – Control of electrophotography process – Control of developing
Reexamination Certificate
2000-05-10
2002-02-05
Lee, Susan S. Y. (Department: 2852)
Electrophotography
Control of electrophotography process
Control of developing
C399S043000, C399S044000, C399S058000, C399S059000, C399S149000, C399S175000
Reexamination Certificate
active
06345162
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus such as a copying machine, a printer, a recording image display device or a facsimile machine in which an electrostatic latent image formed on an image bearing member is developed to form a visible image by using the electrophotographic system, the electrostatic recording system or the like.
In particular, the present invention relates to an image forming apparatus including a charging device which abuts against an image bearing member, a magnetic brush portion of a magnetic brush charging member having a magnetic brush portion formed by magnetically binding charge magnetic carrier particles, and applies a charge bias to the magnetic brush charging member to charge the image bearing member, an image information writing device that forms an electrostatic latent image on the charged image bearing member, a developing device that visualizes the electrostatic latent image as a toner image by using a two-component developer consisting of toner particles and developing magnetic carrier particles, and a transferring device which transfers the toner image onto a transfer material, in which the developing device serves as cleaning means that collects the toner remaining on the image bearing member after the toner image has been transferred onto the transfer material by the transferring member.
2. Related Background Art
(A) Developing Device
In general, in a developing device (developing machine) equipped in an image forming apparatus of the electrophotographic system or the electrostatic recording system, there is used a two-component developer mainly containing toner particles and magnetic developing carrier particles (hereinafter referred to as “developing carriers”). In particular, in most of color image forming apparatuses that form a full-color or multi-color image by the electrophotographic system, the two-component developer is employed from the viewpoint of the color tone etc. of an image.
As well known, the toner density of the two-component developer (that is, the ratio of the toner weight to the total weight of the developing carrier particles and the toner particles) is extremely important in stabilization of the image quality. The toner particles in the developer are consumed during a developing process, and the toner density of the developer is varied. For that reason, it is necessary that the toner density of the developer is accurately detected by using a developer density control device (ATR), a toner is replenished in accordance with a change in the density of toner, the density of toner is always controlled to a constant value (T/D ratio control) and the quality of image is maintained.
In order to correct the above change in the developer density within a developer container of the developing device which is caused by developing, that is, in order to control the quantity of toner which is replenished to the developer, devices for detecting and controlling the toner density of the developer within the developer container have been variously proposed and put into practical use.
For example, the following devices have been employed:
(a) a developer density control device disposed in the vicinity of a developer bearing member (called “developer sleeve” in the following description, since there are generally many cases in which a developer sleeve is used) or a developer carrying path in the developer container, for detecting and controlling the density of toner by utilizing the fact that a reflectance of a light applied to a developer carried onto the developer sleeve, or a developer within the developer container differs depending on the density of toner;
(b) a developer density control device of the inductance detecting system designed such that an inductance head (sensor) for detecting an apparent permeability caused by the mixture ratio of magnetic developing carriers and non-magnetic toner particles to convert it into an electric signal, is located on a side wall of the developing device, the actual toner density of the developer within the developer container is detected according to a detected signal from the inductance head, and the toner is replenished according to a comparison of the actual toner density with a reference value; and
(c) a developer density control device of the system in which a patch image density formed on an image bearing member (called “photosensitive drum” in the following description, since there are generally many cases in which a photosensitive drum is used) is read by using a light source and a patch sensor for receiving a reflected light from a surface thereof, located opposite to the surface of the photosensitive drum, converted into a digital signal by an analog-to-digital convertor, and thereafter is transmitted to a CPU. In the CPU, the patch image density thus converted into the digital signal is compared with an initial set value, and if the density is higher than the initial set value, the replenishment of the toner is then suspended until the density is returned to the initial set value. On the other hand, if the density is lower than the initial set value, the toner is forcedly replenished until the density is returned to the initial set value, as a result of which the density of toner is indirectly maintained to a desired value.
However, the system described in the above item (a) in which the density of toner is detected according to the reflectance of a light applied to a developer carried onto the developer sleeve or a developer within the developer container, suffers from the following problem. That is, if the detecting means is stained by scattered toner or the like, the density of toner cannot be accurately detected. Also, the system described in the above item (c) in which the density of toner is indirectly controlled according to the patch image density suffers from a problem in that a space where a patch image is formed or a space where the detecting means is located cannot be ensured with a downsized copying machine or image forming apparatus.
On the contrary, the inductance detecting system described in the above item (b) is regarded as the optimum toner density detecting system in the copying machine or image forming apparatus which is low in the cost and small in space, because the system is not affected by the above described problem of the spaces and problem of the stain due to the scattered toner in addition that the cost of a sensor unit is low.
The above developer density control device of the inductance detecting system (inductance detecting system ATR) controls the density of toner according to the following manner. That is, control is made such that the replenishment of toner starts if it is detected that the apparent permeability of the developer is large, since it means that the ratio of the developing carrier to the developer within a constant volume becomes high and the density of toner becomes lower. On the contrary, the replenishment of toner is suspended if it is detected that the apparent permeability of the developer is small, since it means that the ratio of the developing carrier to the developer within the constant volume becomes lower and the density of toner becomes higher.
(B) Magnetic Brush Charging Device
In general, a corona photosensitive member has been employed as charging means for an image bearing member such as an electrophotographic photosensitive member or an electrostatic recording dielectric equipped in the image forming apparatus of the electrophotographic system or the electrostatic recording system.
In recent years, because of having merits of low ozone, low electric power, etc., a contact charging device has been put into practical use, that is, a device of the system in which a charging member to which a voltage is applied is abutted against a member to be charged to allow the member to be charged. In particular, a device of the roller charging system using an electrically conductive roller as the charging member has been preferably employed from the viewpoint o
Hibino Masaru
Kobayashi Yoshiaki
Ozawa Ichiro
Shida Masanori
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