Electrophotography – Diagnostics – Consumable
Reexamination Certificate
2001-05-30
2002-12-31
Ngo, Hoang (Department: 2852)
Electrophotography
Diagnostics
Consumable
C399S062000, C399S175000, C399S058000, C399S059000
Reexamination Certificate
active
06501916
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus using an electrophotographic system or an electrostatic recording system and, more particularly, to an image forming apparatus such as a copying machine, printer, or a facsimile machine.
2. Related Background Art
Conventionally, a two-component developer having toner and carrier particles as main components are used in developing devices provided in image forming apparatuses using an electrophotographic system or an electrostatic recording system. It is preferred from the viewpoint of image hues or tones that a two-component developer should be used, in particular, in a color image forming apparatus for forming a full-color or multicolor image by an electrophotographic system. As is well known, the density of toner (i.e., the proportion of the weight of toner particles to the total weight of carrier and toner particles) of a two-component developer is a particularly important factor in stabilizing image quality. Toner particles in a developer are consumed during development to change the toner density in a developing device (developing container) and there is, therefore, a need to perform toner density control for maintaining the toner density in a suitable range to ensure the desired image quality. For this control, a toner density controller (automatic toner replenisher (ATR)) is used which accurately detects at suitable intervals the density of the developer (toner) provided in the developing device and supplies toner according to a change in the toner density.
Various methods have been proposed and put to practical use as a method for detecting the toner density in a developing device and a method for controlling the developer density for the purpose of correcting a change in toner density due to consumption during development, i.e., for controlling the amount of toner supplied to a developing device.
For example, a method (1) is known which uses a toner density controller having a detection means arranged close to a development sleeve ordinarily used as a developer bearing member or a developer transport path in a developing container to detect an amount of a developer on the development sleeve or light reflected by a developer in the developing container when the developer is irradiated with light. The toner density controller detects and controls the toner density by utilizing a phenomenon in which the intensity of reflected light changes depending on the toner density.
A method (2) is also known which uses an inductance detection type of toner density controller having an inductance head provided on, for example, a side wall portion of a developing container as an inductance sensor for detecting the apparent permeability according to the mixture ratio of a magnetic carrier and a nonmagnetic toner and for converting the apparent permeability into an electrical signal. The actual toner density in the developer in the developing container is detected through the detection signal from the inductance head and is compared with a reference value, and toner is supplied according to the result of this comparison.
Further, a method (3) is known in which the density of a patch image formed on a cylindrical electrophotographic photosensitive member, i.e., a photosensitive drum, ordinarily used as an image bearing member is detected by using a light source provided at such a position opposite to the surface of the photosensitive drum and a sensor for receiving light reflected from the surface. A signal representing the patch image density is converted into a digital signal. by an analog-to-digital converter, and the digital signal is supplied to a central processing unit (CPU) and compared with an initial set value by the CPU. If the density is higher than the initial set value, supply of toner is stopped until the density becomes equal to the initial set value. If the density is lower than the initial set value, forced toner supply is continued until the density becomes equal to the initial set value. The toner density is thus controlled indirectly to be maintained at the desired value.
Methods in which the density of toner is detected from the reflectivity of a developer transported onto a development sleeve or contained in a developing container while the developer is being irradiated with light, as in the above-described method (1), entail a problem that accumulation of a contaminant, e.g., scattered toner on the detection means reduces the accuracy with which the toner density is detected. Methods in which the toner density is indirectly controlled through the density of a patch image, as in the above-described method (3), entails a problem that the difficulty in securing the space for formation of the patch image and the space for placement of the detection means is increased with the reduction in size of image forming apparatuses designed as copying machines or the like.
In contrast, inductance detection methods, typified by the above-described method (2), are considered to be most effective in realizing an image forming apparatus designed as a space-saving type manufactured at a low cost, because the sensor unit is low priced and because they are free from the problem of contamination of a detection means due to scattering of toner and the space problem described above with respect to the methods (1) and (3).
The inductance detection type of toner density controller (inductance detection type of ATR) controls the toner density on the basis of a control method such that, when it is determined as a detection result that the apparent permeability of the developer is large, supply of toner is started because the detection result signifies that the toner density has become lower while the proportion of the volume occupied by carrier particles in a certain volume of the developer has been increased, and that, when the apparent permeability is reduced, supply of toner is stopped because the detection result signifies the toner density has become higher while the proportion of the volume occupied by carrier particles in the certain volume of the developer has been reduced.
On the other hand, corona chargers have generally been used as charging means (charging device) for charging an image bearing member such as an electrophotographic photosensitive member or an electrostatic recording dielectric member in electrophotographic type or electrostatic recording type of image forming apparatuses. In recent years, however, contact-type charging devices, i.e., charging devices based on a method of charging a member to be charged with electricity (hereinafter referred to as a “charged member”) by bringing a charging member, to which a voltage is applied, into contact with the charged member, have been put to practical use because of their advantage of limiting generation of ozone and power consumption. In particular, charging devices of a roller charging type having a charging roller as a charging member are preferred by considering charging stability and are being advantageously used.
In the charging system using the roller charging type of charging device, however, the electrical resistances of the charging roller and the image bearing member change under the influence of environmental changes since charging is performed by discharge from the charging member to the charged member, resulting in variation in the surface potential of the image bearing member.
A charging method which reduces the influence of environmental changes, e.g., the one described in Japanese Patent Application Laid-Open No. 7-5748, which is a counterpart of U.S. Pat. No. 5,606,401, has recently been proposed in which a photosensitive member having a charge injection, layer formed in its surface and a conductive powder (SnO
2
or the like) for a trap level dispersed in the charge injection layer is charged in a contact charging manner through an electroconductive contact-type charging member (a charging fur brush, a charging electromagnetic brush, a charging roller, or the like) to which a voltage is appli
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