Electrophotography – Control of electrophotography process – Control of developing
Reexamination Certificate
1999-09-20
2001-08-21
Royer, William J. (Department: 2852)
Electrophotography
Control of electrophotography process
Control of developing
C399S284000, C399S285000
Reexamination Certificate
active
06278849
ABSTRACT:
This application is based on application No. H10-266541 filed in Japan on Sep. 21, 1998, the content of which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
The present invention relates to a developing apparatus for use in a copying machine, a printer and so on.
In a conventional developing apparatus, developer is carried on a developing sleeve applied with a predetermined developing bias voltage and conveyed to a developing region, where the developer serves to develop an electrostatic latent image formed on an electrostatic latent image carrier. In order to triboelectrically charge the toner and to regulate a quantity of the toner, a developer regulating member is provided to come into contact with the developing sleeve.
In the case that non-magnetic toner is used as the developer, there has been a disadvantage that the toner is difficult to enter between the developing sleeve and the toner regulating member because of its poor fluidity, whereby a uniform toner layer can not be formed on the developing roller.
In order to eliminate the above disadvantage, Japanese patent publication 5-19145 proposes a developing apparatus in which an alternating voltage is applied to the developer regulating member to form an alternating electric field between the developing sleeve and the toner regulating member. In this developing apparatus, the alternating electric field causes micro-oscillation of the toner regulating member, allowing the non-magnetic toner of poor fluidity to smoothly enter between the developing sleeve and the toner regulating member, whereby a uniform toner layer can be formed on the developing roller.
Further, the conventional developing apparatus does not have sufficient compliance with a high density and high area-rate of image. Therefore, a toner consuming portion of an image print pattern is printed with a smaller quantity of toner than a toner non-consuming portion due to insufficient compliance when the toner consuming portion reaches a developing region, causing a ghost (negative-memory). If there is a solid image or the like before a half-tone image, the toner quantity is reduced, whereby dots can not be reproduced, resulting in an unclear image and bad tone reproduction.
To this end, in the conventional developing apparatus in which an alternating voltage is applied to the developer regulating member, it will be considered that not only the toner is sufficiently oscillated to be triboelectrically charged by enlarging the peak voltage of the alternating voltage or by making the frequency of the alternating voltage high, but also the toner is made movable to the developer carrying member by enlarging the potential difference between the direct current component of the developing bias applied to the developer carrying member and the direct current component of the blade bias applied to the toner regulating blade. However, both the developer carrying member and the developer regulating blade are made of conductive material and opposed to each other, which causes a leak at a potential difference of about 500V in accordance with the Pachen's law, resulting in image noise.
In order to reduce the maximum potential difference including the alternating component between the developing bias and the blade bias below 500v, the peak voltage difference is enlarged to activate the toner oscillation, the direct voltage difference would be made small. On the contrary, if movement of the toner to the developer carrying member is emphasized, the peak voltage difference would be made small. This means that the conventional developing apparatus is not enough to reduce the maximum potential difference between the developing bias and the blade bias below 500v. For example, even if the potential difference is reduced to 500V by using only a direct current component, the toner would not be oscillated and triboelectrically charged, resulting in no effect. Even if the potential difference of the direct component is reduced to 250V an alternating component having an amplitude of 500v is applied, enough effect would not be obtained.
In addition, a variation in toner fluidity due to deterioration of the toner caused by long-term printing or a variation in environment causes a variation in conveying quantity and charge property of the toner, which causes a problem that stability of tone reproduction could not be maintained until the end of apparatus life.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a developing apparatus that prevents deterioration of image quality due to leakage, holding cost-up and oscillation sound to a minimum, decreasing the difference of developing property on the developer carrying member between developer consuming time and developer non-consuming time, enhancing compliance with a high density of image and a high printing area rate of image, decreasing ghost of image, attempting stabilization of tone reproduction and uniformalization of halftone, and realizing high image quality.
In order to solve the aforementioned problems, the present invention provides a developing apparatus for developing an electrostatic latent image formed on an image carrying member with developer, the developing device comprising:
a developer carrying member for carrying developer and conveying it to a developing region;
a conductive contact member positioned to come into contact with the developer carrying member at the upstream side of the developing region with respect to the developer conveying direction; and
a voltage applying member for applying the developer carrying member with a predetermined direct voltage as a developing voltage, applying the contact member with a direct voltage which has the same polarity as the developing voltage and an absolute value larger than the developing voltage, and applying between the developer carrying member and the contact member with an alternating voltage;
wherein a ratio t
1
/t
2
of a time t
1
for applying a voltage of absolute value larger than that of a center voltage of the alternating voltage to a time t
2
for applying a voltage of absolute value smaller than that of the center voltage of the alternating voltage satisfies a relation of t
1
/t
2
>1.
The contact member may be a developer regulating member for regulating a quantity of developer on the developer carrying member. Instead of making the developer regulating member the contact member, the contact member may be positioned at the upstream side of the developer regulating member with respect to the developer conveying direction.
According to the present invention having the above construction, the voltage applying time at the high voltage side of the alternating voltage applied between the developer carrying member and the contact member is longer than that at low voltage side, whereby the developer fully moves from the developer regulating member to the developer carrying member. Thus, the conveyance of the developer to the developer carrying member at the toner consuming time is enhanced, enabling stabilized developing properties whether the developer is consumed or not. As a result, it is possible to enhance compliance with a high density of image and a high printing area rate of image, decrease ghost of image, attempt stabilization of tone reproduction and uniformalization of halftone, and realize high image quality.
Preferably, the developing apparatus of the present invention may further comprise a controller for controlling the direct voltage applied to the contact member to regulate an image density. Thus, in spite of long-term printing or variation in environment, the developing property can be stabilized by controlling the direct voltage applied to the contact member.
Alternatively, the developing apparatus of the present invention may further comprise a controller for controlling the ratio t
1
/t
2
of the alternating voltage to regulate an image density. Thus, in spite of long-term printing or variation in environment, the developing property can be also stabilized by controlling the ratio t
1
/t
Burns Doane , Swecker, Mathis LLP
Minolta Co. , Ltd.
Royer William J.
LandOfFree
Developing apparatus for developing an electrostatic latent... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Developing apparatus for developing an electrostatic latent..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Developing apparatus for developing an electrostatic latent... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2540905