Electrophotography – Image formation – Charging
Reexamination Certificate
1999-12-21
2001-01-09
Moses, Richard (Department: 2852)
Electrophotography
Image formation
Charging
C399S174000, C399S115000, C361S225000
Reexamination Certificate
active
06173142
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus using an electrophotographic process, particularly, relates to an image forming apparatus having a mechanism for satisfactorily maintaining a function of a roller-shaped charging brush.
2. Description of the Related Art
There have been known, as a conventional image forming apparatus, an apparatus using an electrophotographic process such as a copy machine, a facsimile, an electrophotographic apparatus or an electrostatic printer. In general, the image forming apparatus is provided with a process cartridge which has a photoreceptor drum and a developed device for allowing toner to be adsorbed onto an electrostatic latent image formed on a surface of the photoreceptor drum so as to develop the image. The process cartridge has a toner housing chamber and a developing chamber which are adjacent to each other. A connecting opening which connects the toner housing chamber and the developing chamber is formed in a separation board between the toner housing chamber and the developing chamber, and a toner mixer for feeding toner from the connecting opening to the side of the developing chamber is provided in the toner housing chamber.
In the process cartridge of the convention image forming apparatus, a non-contact type corona charger which utilizes corona discharge has been used as a charger for charging a body to be charged such as a photoreceptor drum prior to form an electrostatic latent image thereon. The corona charger is effective as means for uniformly charging the body to be charged, but at the same time it has a disadvantage that the discharge causes generation of ozone.
There has been known a contact type charger which can suppress the generation of ozone. Since the contact type charger, particularly, a rotating charger shaped like a roller can charge the surface of the photoreceptor more uniformly than a fixed charger, this rotating charger is utilized in a lot of apparatuses.
In recent years, since a particle diameter of toner becomes smaller according to the heightening of resolution of electrophotography and lifetime becomes longer according to the lowering of the cost of a process cartridge, it is important to maintain uniform charging for a long period. Since the contact type charger always contacts with the surface of the photoreceptor, it is easily influenced by toner or paper powder which remains on the surface of the photoreceptor, shavings of the photoreceptor or the like after development, and thus various measures are taken in order to execute the uniform charging for a long period.
In an apparatus disclosed in Japanese Patent Application Laid Open No. 8 254877, a rotating brush charger is oscillated in a direction of a rotating shaft and simultaneously brush pile is brought into contact with a photoreceptor, and an extended length of the brush pile from a brush charger main body is made to be uniform so that a cleaning effect for the surface of the photoreceptor is heightened.
In an apparatus disclosed in Japanese Patent Application Laid-Open No. 6-137207, a cleaning member for removing dirt is moved in an axial direction as the need arises so that a brush charger is cleaned.
In a apparatus disclosed in Japanese Patent Application Laid-Open No. 4-366863, a shaft-type thin dirt removing member having electrical conductivity is held in a state that it digs into a brush of a rotating brush charger by a constant amount, and toner particles, which were removing mechanically from the brush charger by the dirt removing member, are adsorbed on an electrode to which a voltage whose polarity is opposite to that of the toner particles was applied.
In an apparatus disclosed in Japanese Patent Application Laid-Open No. 7-072774, after a voltage, which is higher than the main body of a photoreceptor, is applied to a brush, an electrophotographic printer is aged so that dirt on the brush is transferred onto the surface of the photoreceptor so as to be cleaned.
In an apparatus disclosed in Japanese Patent Application Laid-Open No. 10-221932, a voltage whose polarity is opposite to that of a voltage applied the time of forming an image is applied to a brush when an image is not formed so that cleaning is executed.
In an apparatus disclosed in Japanese Patent Application Laid-Open No. 7-306571, a voltage, whose polarity is the same as charging polarity of toner and whose absolute value is small, is applied to a brush of a brush charger when an image is not formed so that dirt on the brush is adsorbed on the surface of a photoreceptor and is cleaned.
Incidentally, electrically conductive brush fiber which is used in a brush charger is made of fine and soft fiber because such fiber does not damage a photoreceptor. Since a contact type brush charger is always contact-pressed against a photoreceptor, if it is influenced by environment or the like, peculiarity such as raising or laying of the brush occurs easily on a boundary between a portion where the brush fiber is pressed and a portion where the brush fiber is not pressed, and such peculiarity is hardly eliminated. At this time, since the brush or the brush type charger contacts uniformly with the surface of the photoreceptor, defective charging is caused, and thus there is a possibility that a defective image is formed with a period of one rotation.
In addition, in a roller-shaped charging brush, dirt such as residual toner, paper powder and photoreceptor shavings is apt to be gradually accumulated towards an inner portion of a brush in the process that the lifetime of a process cartridge ends. Recently, a slanted filling type brush roller, whose brush pile previously is laid in a direction opposite to rotation of the brush roller in order to be proof against peculiarity such as the raising to some degree, is frequently used. In such a slanted filling type brush roller, dirt is strongly apt to be accumulated on the inner part of the brush, and the accumulated dirt cannot be removed sufficiently only by electrical cleaning, and thus there arises a great problem about the extension of the lifetime.
Japanese Patent Application Laid-Open No. 8-254877 discloses a cleaning method which eliminates the above problem. In this cleaning method, dirt which was accumulated on an inner portion of the slanted filling brush is cleaned by oscillation, but a sufficient effect for eliminating the dirt from the inner portion of the brush cannot be expected.
Moreover, Japanese Patent Application Laid-Open No. 7-072774, Japanese Patent Application Laid-Open No. 10-221932 and Japanese Patent Application Laid-Open No. 7 306571 disclose respectively apparatuses for electrically cleaning dirt accumulated on an inner portion of a slanted filling brush, but in these examples cannot produce a sufficient effect.
Japanese Patent Application Laid-Open No. 8-137207 and Japanese Patent Application Laid-Open No. 4-366863 discloses respectively apparatuses having an eliminating member, but in these apparatuses the eliminating member might damage the brush roller and this possibly causes a defective image.
Further, Japanese Patent Application Laid-Open No. 7-104562 discloses a brush roller having a cleaning grid for electrically cleaning dirt accumulated on a slanted filling brush, but cannot produce a sufficient effect.
SUMMARY OF THE INVENTION
The inventor found that it is difficult to correct the peculiarity of a brush and remove dirt of an inner portion of the brush by means of non-uniformly set length of the brush pile or a dirt removing member which digs into a roller-shaped charging brush by a constant amount.
It is an object of the present invention to provide an image forming apparatus which is capable of reducing peculiarity of a roller-shaped charging brush such as raising and laying of brush and of efficiently eliminating dirt accumulated on an inner portion of, particularly, a slanted filling type brush, and of always maintaining a state that a photoreceptor is charged by the roller-shaped charging brush satisfactorily.
In order to overco
Moses Richard
NEC Corporation
Ostrolenk Faber Gerb & Soffen, LLP
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