Electrophotography – Image formation – Development
Reexamination Certificate
2000-02-11
2001-04-17
Grimley, Arthur T. (Department: 2852)
Electrophotography
Image formation
Development
C399S053000
Reexamination Certificate
active
06219513
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a developing device for supplying a developing agent to an electrostatic latent image formed on an image carrier and developing the image.
Conventionally, there is known a developing device of the two-component development type, in which a carrier and a toner that is mixed in a given ratio are agitated, charged, and supplied to an electrostatic latent image that is formed on the outer peripheral surface of a photoconductor drum for use as an image carrier, and the electrostatic latent image is developed with the charged toner.
The developing device of this type comprises a magnet roller having a plurality of magnetic poles arranged along its outer peripheral surface and a nonmagnetic cylindrical developing sleeve that is located around the magnet roller with a given gap. The magnet roller is fixedly provided in a predetermined position adjacent to the photoconductor drum so that its main pole faces the photoconductor drum. The developing sleeve is located for rotation in a position at a given distance from the outer peripheral surface of the photoconductor drum with a given developing gap between them.
A developing agent is held on the outer peripheral surface of the developing sleeve by means of a magnetic field that is generated by the magnet roller, whereupon a magnetic brush based on the developing agent is formed on the outer peripheral surface. The magnetic brush formed in this manner is trimmed to a given length by means of a doctor blade that is opposed to the outer peripheral surface of the developing sleeve, and is transported to the developing gap opposite the outer peripheral surface of the photoconductor drum as the developing sleeve rotates. The toner of the magnetic brush is supplied to the electrostatic latent image by means of a developing bias that is applied between the developing sleeve and the photoconductor drum, whereupon the electrostatic latent image is visualized.
In the conventional developing device of the two-component development type described above, however, a magnetic force (development inhibiting force) that settles a threshold value for development gradually changes in the developing gap where the developing sleeve faces the photoconductor drum, and the density of the magnetic brush that is formed on the developing sleeve according to the distribution of the magnetic poles of the magnet roller is subject to unevenness. Accordingly, the conventional developing device has a problem involving a phenomenon (hereinafter referred to as “tailing”) such that the toner floating on the lower-stream side of the developing gap is attracted to the outer peripheral surface of the photoconductor drum in a magnetic trough (low-magnetism portion) between the main pole of the magnet roller and the magnetic pole that is situated directly on the lower-stream side of the main pole.
BRIEF SUMMARY OF THE INVENTION
This invention has been contrived in consideration of these circumstances, and its object is to provide a developing device capable of vibrating a developing agent with high frequency in a developing region opposite an image carrier and realizing development with a relatively high resolution without causing tailing.
In order to achieve the above object, a developing device of this invention serves to supply a developing agent, formed of a mixture of a toner and a carrier, to an electrostatic latent image, formed on an outer peripheral surface of an image carrier, and visualize the electrostatic latent image with the toner, and comprises a developing sleeve opposed to the outer peripheral surface of the image carrier and capable of rotating with the developing agent held on an outer peripheral surface thereof, thereby transporting the developing agent to the electrostatic latent image, a magnet roller located for rotation in the developing sleeve and having a plurality of magnetic poles for generating a given magnetic force on the outer peripheral surface of the developing sleeve, arranged in the rotating direction thereof, and developing bias applying means for applying a given developing bias between the image carrier and the developing sleeve to supply the toner in the developing agent held on the outer peripheral surface of the developing sleeve to the electrostatic latent image formed on the outer peripheral surface of the image carrier, wherein A>280 is fulfilled where A is given by:
A=|Rs×&ohgr;m−Rd×&ohgr;d|×P×Vs×T/Vp,
where Rs (mm) is the radius of the developing sleeve, &ohgr;m (rpm) is the rotational frequency of the magnet roller, Rd (mm) is the radius of the image carrier, &ohgr;d (rpm) is the rotational frequency of the image carrier, P is the number of magnetic poles of the magnet roller, Vs (mm/sec) is the peripheral speed of the outer peripheral surface of the developing sleeve, T is a magnetic flux density on the outer peripheral surface of the developing sleeve, and Vp (mm/sec) is the peripheral speed of the outer peripheral surface of the image carrier.
Further, a developing device of this invention serves to supply a developing agent, prepared by mixing a magnetic toner and a magnetic carrier in a given ratio, to an electrostatic latent image, formed on an outer peripheral surface of a substantially cylindrical image carrier rotating in a given direction, and visualize the electrostatic latent image with the magnetic toner, and comprises a substantially cylindrical developing sleeve extending substantially parallel to the image carrier, having an outer peripheral surface opposed to the outer peripheral surface of the image carrier with a given developing gap therefrom and rotatable in the same direction as the outer peripheral surface of the image carrier in a region for the developing gap, and capable of transporting the developing agent held on the outer peripheral surface thereof to the developing gap, a magnet roller located coaxially in the developing sleeve with a given gap therefrom, having a plurality of magnetic poles of different polarities for generating a given magnetic force on the outer peripheral surface of the developing sleeve, arranged alternately in the rotating direction thereof, and rotatable reversely to the developing sleeve, and developing bias applying means for applying a given developing bias between the image carrier and the developing sleeve to supply the magnetic toner in the developing agent held on the outer peripheral surface of the developing sleeve to the electrostatic latent image formed on the outer peripheral surface of the image carrier in the region for the developing gap, wherein A>280 is fulfilled where A is given by:
A=|Rs×&ohgr;m−Rd×&ohgr;d|×P×Vs×T/Vp,
where Rs (mm) is the radius of the developing sleeve, &ohgr;m (rpm) is the rotational frequency of the magnet roller, Rd (mm) is the radius of the image carrier, &ohgr;d (rpm) is the rotational frequency of the image carrier, P is the number of magnetic poles of the magnet roller, Vs (mm/sec) is the peripheral speed of the outer peripheral surface of the developing sleeve, T is a magnetic flux density on the outer peripheral surface of the developing sleeve, and Vp (mm/sec) is the peripheral speed of the outer peripheral surface of the image carrier.
According to the invention described above, moreover, the magnetic toner in the developing agent held on the outer peripheral surface of the developing sleeve, along with the magnetic carrier, is rolled on the outer peripheral surface of the developing sleeve to be charged by the agency of the magnetic force of the magnet roller rotating reversely to the developing sleeve, and is supplied to the electrostatic latent image by means of the developing bias given by the bias voltage applying means.
Further, a developing method of this invention is a developing method for holding a developing agent, formed of a mixture of a toner and a carrier, on an outer peripheral surface of a developing sleeve opposed to an outer peripheral surf
Foley & Lardner
Grimley Arthur T.
Ngo Hoang
Toshiba Tec Kabushiki Kaisha
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