Electrophotography – Control of electrophotography process – Having temperature or humidity detection
Reexamination Certificate
2002-09-04
2004-06-01
Chen, Sophia S. (Department: 2852)
Electrophotography
Control of electrophotography process
Having temperature or humidity detection
C399S071000, C399S129000, C399S150000, C399S343000
Reexamination Certificate
active
06744994
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART
The present invention relates to an image forming apparatus equipped with a developer charging member for charging the developer remaining on an image bearing member, and is suitable for a cleaner-less image forming apparatus, that is, an image forming apparatus which does not have a dedicated cleaner. In particular, it relates to a cleaner-less image forming apparatus, in which the developer (toner) remaining on an image bearing member after the image transfer process is removed (recovered) from the image bearing member by the developing apparatus so that the recovered developer can be reused.
Heretofore, an electrophotographic image forming apparatus of a transfer type, such as a copying machine a printer, a facsimile, etc., comprises: a photoconductive member as an image bearing member which usually is in the form of a drum; a charging apparatus (charging process) for uniformly charging the photoconductive drum to predetermined polarity and potential level; an exposing apparatus (exposing process) as an information writing means for forming an electrostatic latent image on the charged photoconductive member; a developing apparatus (developing process) for visualizing the electrostatic latent image formed on the photoconductive member with the use of toner as developer; a transferring apparatus (transferring process) for transferring the toner image from the surface of the photoconductive drum onto transfer medium, for example, a piece of paper; a cleaning apparatus (cleaning process) for cleaning the surface of the photoconductive drum by removing the toner remaining, by a certain amount, on the surface of the photoconductive drum; a fixing apparatus (fixing process) for fixing the toner image on the transfer medium; and so forth. The photoconductive member is repeatedly subjected to an electrophotographic processes (charging, exposing, developing, transferring, and cleaning processes) to form images.
The toner remaining on the photoconductive drum after the transferring process is removed from the surface of the photoconductive drum by the cleaning apparatus, and collected as waste toner in the cleaning apparatus. From the standpoint of environmental preservation, effective utilization of natural resources, and so on, it is desired that waste toner such as the above described one is not generated.
Thus, there has been developed an image forming apparatus in which the untransferred residual toner, or the so-called waste toner collected in the cleaning apparatus, is returned to the developing apparatus to be reused.
There has also been developed a cleaner-less image forming apparatus which does not have a dedicated cleaning apparatus, and in which the untransferred residual toner, or the toner remaining on the photoconductive drum after the transferring process, is removed from the photoconductive drum by the developing apparatus to be reused, at the same time as an electrostatic latent image on the photoconductive drum is developed by the developing apparatus (developing/cleaning process).
The elimination of the dedicated cleaning system makes it possible to reduce image forming apparatus size and simplify an Image forming apparatus. Further, the lack of a dedicated cleaning member means that there is no rubbing of the surface of the photoconductive drum by the cleaning member, lengthening the service life of the photoconductive drum. In other words, the elimination of the dedicated cleaning system offers substantial merits.
The developing/cleaning process is a process in which the toner remaining on the photoconductive drum after the image transfer is recovered by the developing apparatus during the following developing process. More specifically, after the image transfer, the area of the photoconductive drum, from which the toner image has been transferred, is charged, and then, is exposed to form an electrostatic latent image thereon. Then, the untransferred residual toner on the portions of the peripheral surface of the photoconductive member (non-image portions), to which toner is not to be adhered, is recovered into the developing apparatus, by the fog prevention bias (difference Vback in potential level between DC voltage applied to developing apparatus, and the surface potential level of photoconductive drum. According to this method, the untransferred residual toner is recovered into the developing apparatus and is reused for developing electrostatic latent image in the following image formation cycles. In other words, no toner is wasted.
Therefore, a user does not need to be bothered by the waste toner.
Further, having no dedicated cleaner is advantageous from the standpoint of image forming apparatus size reduction. Since the untransferred residual toner on the photoconductive drum is recovered by the developing apparatus, it is desired that a reversal developing method, that is, a developing method in which the polarity to which the photoconductive drum is charged is the same as the normal polarity to which toner is charged, is employed.
However, if a cleaner-less image forming apparatus such as the above described one which recovers (removes) the transfer residual toner remaining on the photoconductive drum after image transfer, and reuse it, is such an image forming apparatus that employs a contact charging apparatus which charges the surface of the photoconductive member by making contact with the photoconductive member, the toner particles in the untransferred residual toner, the polarity of which have been made opposite to the normal polarity to which the toner becomes charged, adhere to the contact charging apparatus while the transfer residual toner on the photoconductive member passes the charging station, that is, the contact nip between the photoconductive member and contact charging apparatus, contaminating the contact charging apparatus beyond the tolerable range. As a result, the photoconductive member is unsatisfactorily charged.
More specifically, normally, the toner as developer contains a certain amount of toner particles, the polarity of which is opposite to the normal toner polarity, although the amount is relatively small. Further, some of the toner particles with the normal polarity are reversed in polarity, or reduced in the amount of charge, by the transfer bias, the electrical discharge from the recording medium separation, etc.
Thus, the untransferred residual toner contains the toner particles with the normal polarity, toner particles with the reverse polarity, and toner particles with a smaller amount of electrical charge Among these three types of toner particles, the toner particles with the reverse polarity and the toner particles with reduced electrical charge are likely to adhere to the contact charging apparatus while they are moving through the charging station, or the contact nip between the photoconductive drum and contact charging apparatus.
Further, in order to remove and recover the untransferred residual toner on the photoconductive drum (in order to clean the photoconductive drum) by the developing apparatus at the same time as a latent image on the photoconductive drum is developed by the developing apparatus, it is necessary that the toner particles in the untransferred residual toner on the photoconductive drum, which are being carried to the developing station through the charging station, are normal in polarity (for example, negative), and also that the amount of electrical charge they are holding is proper for them to be used by the developing apparatus to satisfactorily develop the electrostatic latent image on the photoconductive drum. The toner particles with the reverse polarity (for example, positive polarity) and the toner particles improper in the amount of electrical charge cannot be removed and recovered from the photoconductive drum by the developing apparatus, effecting unsatisfactory images.
An image defect traceable to the failed recovery of the positively charged toner particles by the developing apparatus is called a positive ghost, which is a problem peculiar t
Adachi Motoki
Watanabe Yasunari
Yoshikawa Tadanobu
Canon Kabushiki Kaisha
Chen Sophia S.
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