Electrophotography – Control of electrophotography process – Control of charging
Reexamination Certificate
2003-04-18
2004-10-19
Tran, Hoan (Department: 2852)
Electrophotography
Control of electrophotography process
Control of charging
C399S149000, C399S150000
Reexamination Certificate
active
06807384
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus of, for example, a copier, a printer or a facsimile apparatus or the like.
2. Description of the Related Art
In a related art, a transferring system image forming apparatus of a copier, a printer, a facsimile or the like using a transferring type electrophotography system is constituted by a photosensitive member which is an image bearing member generally of a rotary drum type, a charging apparatus for charging the photosensitive member uniformly at predetermined polarity and potential (charging step), an exposing apparatus as information writing means for forming an electrostatic latent image to the charged photosensitive member (exposing step), a developing apparatus for visualizing the electrostatic latent image formed on the photosensitive member by a toner which is a developer (exposing step), a transferring apparatus for transferring the toner image from a face of the photosensitive member to a transferring material of paper or the like (transferring step), a cleaning apparatus for cleaning the face of the photosensitive member by removing the toner remaining on the photosensitive member after the transferring step although an amount thereof is small (cleaning step), and a fixing apparatus for fixing the toner image on the transferring material (fixing step) and the photosensitive member is repeatedly applied with an electrophotography process (charging, exposing, developing, transferring, cleaning) to form an image.
Inside of the cleaning apparatus is provided with a waste toner collecting container for containing the toner remaining on the photosensitive member removed from the face of the photosensitive member by the cleaning apparatus. Therefore, it is necessary to make the container large-sized to constitute an apparatus having long service life, which is disadvantageous in view of small-sized formation of the apparatus.
Hence, there is an image forming apparatus of a cleanerless system abolishing the cleaning apparatus having the waste toner collecting container and removing and collecting the remaining transferring toner on the photosensitive member after the transferring step from above the photosensitive member by “developing and cleaning” in a developing apparatus.
The developing and cleaning is a method of disposing of the remaining transferring toner on the photosensitive member after transferring by charging the photosensitive member at a developing step at a succeeding step and thereafter, that is, successively, exposing the photosensitive member to form an electrostatic latent image, and collecting the remaining transferring toner present on a portion of the face of the photosensitive member (non-image portion) which is not to be developed by the toner by fog removing bias (a fog removing potential difference Vback which is a potential difference between direct current voltage applied to the developing apparatus and surface potential of the photosensitive member) in a procedure of the developing step of the electrostatic latent image.
According to the method, the remaining transferring toner is collected by the developing apparatus and reused in developing the electrostatic latent image at the succeeding step and thereafter and therefore, the waste toner can be eliminated and trouble of maintenance can be reduced and is advantageous in small-sized formation of the image forming apparatus by eliminating the waste toner container.
Meanwhile, in recent years, the charging means is switched to a corona charger, particularly, a roller charging system using a charging roller as a contact charging member is preferably used in view of stability of charging. According to the roller charging, a conductive elastic roller (charging roller) is brought into press contact with a charged body and the charged body is charged by applying voltage thereto.
With regard to the charging system, as disclosed in JP-A-63-149669, an AC charging system for applying voltage constituted by superposing an AC component having peak to peak voltage of 2×Vth or higher to DC voltage in correspondence with desired surface potential Vd of the charged body to a contact charging member has been proposed and reduced into practice. By the effect of smoothing potential by AC, charging can be made uniform more than a DC charging system and potential of the charged body is substantially converged to Vd which is a center of peaks of AC voltage.
According to the image forming apparatus of a cleanerless system for removing and collecting the remaining transferring toner on the photosensitive member after the transferring step by developing and cleaning in the developing apparatus, in the case of using the contact charging apparatus as the apparatus of charging the photosensitive member, when the remaining transferring toner on the photosensitive member passes a charging portion which is a contact nip portion of the photosensitive member and the contact charging apparatus, particularly a toner in the remaining transferring toner in which charge polarity is inverted to a polarity reverse to normal polarity is adhered to the contact charge apparatus and the contact charge apparatus is contaminated with the toner more than allowable to cause a charge failure.
The cause is derived from the fact the toner as the developer is mixed with a toner in which the charge polarity is inherently inverted to a polarity reverse to the normal polarity, or even a toner having the normal polarity of the charge polarity in which the charge polarity is inverted by being influenced by transferring bias or exfoliation discharge or removed of electricity and having a small charge amount, although an amount thereof is small.
That is, the remaining transferring toner is mixed with the toner having the normal polarity of the charge polarity, the inverted toner having reverse polarity and the toner having the small charge amount and the inverted toner or the toner having the small charge amount is liable to adhere to the contact charge apparatus when passing the charging portion which is the contact nip portion of the photosensitive member and the contact charge apparatus.
Further, in order to remove and collect the remaining transferring toner on the photosensitive member by developing and cleaning of the developing apparatus, it is necessary that the charge polarity of the remaining transferring toner on the photosensitive member carried to the developing portion by passing the charging portion is the normal polarity and the charge amount is the charge amount of the toner capable of developing the electrostatic latent image of the photosensitive member by the developing apparatus. The inverted toner or the toner having the impertinent charge amount cannot be removed and collected from the photosensitive member to the developing apparatus to cause a failed image.
Hence, in JP-A-2001-215798, the applicant has proposed an image forming apparatus provided with uniform remaining transferring toner forming means (first charge providing means) downstream from a transferring portion and provided with a developer charge amount controlling means) (second charge providing means) upstream from charging means for charging the photosensitive member further downstream therefrom.
According to the image forming apparatus, the uniform remaining transferring forming means is means for eliminating a pattern of a remaining toner image in a shape of a pattern on an image bearing member carried from the transferring portion to the developer charge amount controlling means by dispersing to distribute the remaining toner pattern at a face of the image bearing member. Specifically, the pattern of the image of the remaining developer is scratched to destroy or disturbed by abrading the face of the image bearing member by an abrading member to disperse to distribute the developer on the face of the image bearing member.
By providing the image uniform remaining transferring toner forming means, a total normal polarity charging processing is
Adachi Motoki
Kinoshita Masahide
Ojima Masaki
Okubo Kazuhiro
Uyama Masao
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