Electrophotography – Image formation – Development
Reexamination Certificate
1999-09-07
2001-01-09
Chen, Sophia S. (Department: 2852)
Electrophotography
Image formation
Development
C399S043000, C399S149000, C399S174000, C430S110100
Reexamination Certificate
active
06173144
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART
The present invention relates to an image forming apparatus such as a copying machine or a printer which employs an electrophotographic system, an electrostatic recording system, or the like.
In the past, a corona type charging apparatus (corona discharging device) has been used as a charging apparatus for charging an image bearing member, for example, an electrophotographic photosensitive member, an electrostatically recordable dielectric member, or the like, in an image forming apparatus, for example, an electrophotographic image forming apparatus, an electrostatic recording apparatus, or the like, to predetermined polarity and potential level.
A corona discharging apparatus is a noncontact type charging apparatus. It comprises an ion discharging electrode constituted of, for example, a piece of wire or the like, and an electrode in the form of a shield which surrounds the ion discharging electrode. The shield electrode is provided with an ion discharging opening directed toward the surface of an object to be charged, but, not in contact with the object. In operation, high voltage is applied to the ion discharging electrode and the shield electrode to generate discharge current (corona shower) to which the surface of the object is exposed to be charged to predetermined polarity and potential level.
In recent years, however, a substantial number of contact type charging apparatuses have been proposed, and some of them have been put to practical use as a charging apparatus for charging an object such as an image bearing member or the like because of their advantages over a corona type charging apparatus. For example, they are smaller in the amount of ozone production and power consumption.
A contact type charging apparatus includes an electrically conductive charging member in the form of, for example, a roller (charge roller), a fur brush, a magnetic brush, or a blade, which is placed in contact with a member to be charged, for example, an image bearing member or the like. In operation, charge bias, or electrical voltage with a predetermined potential level, is applied to the contact charging member (contact type charging member, contact type charging device, or the like, which hereinafter will be referred to as a contact type charging member), which is placed in contact with a member to be charged, for example, an image bearing member or the like, so that the peripheral surface of the object to be charged is charged to predetermined polarity and electrical potential.
The charging mechanism (charging principle) in a contact type charging apparatus comprises a mixture of two charging mechanism: (1) a mechanism based on electrical discharge, and (2) a mechanism based on direct injection of electrical charge. Thus, the characteristics of a contact type charging apparatus vary depending on which of the two mechanisms is dominant.
(1) Charging Mechanism based on Electrical Discharge
This is a charging mechanism which charges the peripheral surface of an object to be charged, with the use of the electrical discharge which occurs across a microscopic gap between a contact type charging member and the object to be charged.
In a charging system based on electrical discharge, there is a threshold voltage value above which electrical discharge occurs between a contact type charging member and an object to be charged. Thus, in order for an object to be charged to a predetermined potential level, voltage, the potential level of which is greater than the predetermined voltage level, must be applied to a contact type charging member. In addition, an electrical discharge based charging system inherently produces by-products, the amount of which, however, may be extremely small compared to those produced by a corona based charging device. Therefore, even if a contact type charging system is employed, it is impossible to completely avoid the problems caused by active ions such as ozone.
(2) Mechanism Based on Electrical Charge Injection
This is a charging system which directly injects electrical charge into an object from a contact type charging member so that the peripheral surface of the object is electrically charged. It is called the direct charging system or the injection charging system. It also it called the charging injection charging system.
More specifically, a contact type charging member, the electrical resistance of which is in a medium range, is placed in contact with the peripheral surface of an object to be charged, to charge the object without triggering the electrical discharge. In other words, this charging mechanism is a charging mechanism which directly injects electrical charge into the peripheral surface of an object to be charged. In principle, it does not rely on electrical discharge. Therefore, even if the potential level of the voltage applied to a contact type charging member is less than a threshold voltage level, the object to be charged can be charged to a potential level substantially equal to the potential level of the applied voltage. Since this direct injection charging system does not involve ion generation, it does not suffer from the ill effects associated with the by-products of electrical discharge.
However, since a contact type charging system is a system based on charging injection, its performance is greatly affected by the state of contact between a contact type charging member and an object to be charged. Thus, it is very important that a contact type charging member is high in density, that there is provided a sufficient amount of difference in surface velocity between the charging member and the object to be charged, and that the contact type charging member makes contact with the object to be charged, with a sufficiently high frequency.
A) Charging by Roller
Among various contact type charging apparatuses, those which employ a roller based charging system, in other words, those which employ an electrically conductive roller (charge roller) as a contact type charging member, are widely used, because of their safety in a charging operation.
In the case of a charging roller, the charging mechanism based on electrical discharge (1) is the dominant charging mechanism.
A charge roller is formed of rubber or foamed material which is electrically conductive, or the electrical resistance of which is in the medium range. Sometimes, different materials are layered in order to obtain a predetermined characteristic.
A charge roller is provided with elasticity so that a predetermined state of contact can be kept between the charge roller and an object to be charged (hereinafter, photosensitive member). Therefore, a charger roller has a large frictional resistance on its peripheral surface. Generally, it is enabled to follow the rotation of a photosensitive member, or is driven at a speed slightly different from that of the photosensitive member. Thus, when a charge roller is used to directly inject electrical charge into a photosensitive member, it cannot be avoided that the charge roller is deteriorated in its absolute performance and/or the state of contact between itself and the photosensitive member by the contaminants adhered to the charge roller and/or the photosensitive member. As a result, the photosensitive member is nonuniformly charged, in spite of the fact that a charge roller is a contact type charging member. In other words, in the case of a conventional charging roller, the charging mechanism based on electrical discharge is dominant in charging the photosensitive member.
FIG. 6
is a graph which shows the efficiencies of various contact type charging members. The abscissa represents the potential level of the bias applied to a contact type charging member, and the ordinate represents the correspondent potential level of a photosensitive member.
The characteristic of a conventional charge roller is depicted by line A. In other words, the charging of the photosensitive drum begins when the potential level of the voltage applied to the charge roller passes the threshold value of approximately −500 V. T
Chigono Yasunori
Hirabayashi Jun
Ishiyama Harumi
Shinohara Seiichi
Canon Kabushiki Kaisha
Chen Sophia S.
Fitzpatrick ,Cella, Harper & Scinto
LandOfFree
Image forming apparatus which supplies image bearing member... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Image forming apparatus which supplies image bearing member..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Image forming apparatus which supplies image bearing member... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2451044