Electrophotography – Internal machine environment – Forced air circulation
Reexamination Certificate
2002-03-11
2003-09-16
Pendegrass, Joan (Department: 2852)
Electrophotography
Internal machine environment
Forced air circulation
C399S098000
Reexamination Certificate
active
06621995
ABSTRACT:
FIELD
This invention generally relates to image-forming machines having a development station. More particularly, this invention relates to image-forming machines having systems to remove or control airborne toner and carrier from a development station.
BACKGROUND
Image-forming machines usually transfer images onto paper or other medium using an electrophotographic process. An image-forming machine typically has a photoconductor, one or more chargers, an exposure machine, a development station, a fuser station, and a cleaning station. The image-forming machine also may have a logic control unit (LCU) or other microprocessor, a graphic user interface, and other components.
The photoconductor is selectively charged and optically exposed to form an electrostatic latent image on the surface. The development station deposits toner onto the photoconductor surface. The toner is charged, thus adhering to the photoconductor surface in areas corresponding to the electrostatic latent image. The toner image is transferred onto a sheet of paper or other medium. In the fuser station, the sheet is heated causing the toner to fix or adhere to the paper or other medium. The photoconductor is refreshed, cleaned to remove residual toner and charge, and then is ready to make another image. The sheet exits the image-forming equipment.
At the development station, toner is attracted to the photoconductor under the influence of an electric field in a development region between the development station and the photoconductor. The development station stores and mixes a developer, which may be mono-component or bi-component. A mono-component developer comprises toner. A bi-component developer comprises a mixture of toner and a carrier. Toner is the marking material in an image-forming machine and usually comprises a polymer, a pigment, and a charging agent. Carrier is a transport medium and usually comprises magnetic particles, which are typically made of iron or an ironbased material.
The mixing of a mono-component developer tribo-electrically charges the toner. The electrostatic-charged toner is transported to the development region. The electric field in the development region lifts the toner slightly from the development station toward the photoconductor for attachment onto the surface of the photoconductor.
The mixing of a bi-component developer tribo-electrically charges the toner and carrier. The electrostatic-charged toner adheres to the opposite electrostatic-charged carrier. The carrier transports the toner to the development region. The electric field in the development region releases the toner from the carrier for attachment onto the on the surface of the photoconductor.
In the development region, the toner turns the electrostatic latent image on the photoconductor into a visible image. Portions of the photoconductor surface having the electrostatic latent image attract the toner. Portions on the photoconductor surface not having the electrostatic latent image repulse the toner.
The unused toner from a mono-component or bi-component developer usually returns to the development station for mixing with additional toner and reuse in the image-forming process. However, “dusting” occurs often in which the development station emits airborne toner or airborne toner and carrier into the image forming machine. Airborne toner and carrier represent a loss of material and can adversely affect other subsystems. The migration of airborne toner and carrier throughout the image-forming machine may cause machine errors and image quality artifacts. The airborne toner may accumulate and form “toner stacks” on various components within the image-forming machine. The toner stacks often fall onto portions of the electrophotographic process such as the development roller prior to the development region, the photoconductor, or the sheet or other medium prior to the fusing operation. The toner from the toner stack may cause a comet-shaped smudge or other artifact on the sheet. The toner and carrier also may retain an electrostatic charge and thereby are attracted to components such as the chargers. The build-up of toner on a charger often causes a charger fault or arcing.
Dusting also may adversely affect the development operation in image-forming machines having multiple development stations such as a black-pigment development station and a color-pigment development station. Dusting from each development station may adversely affect the development process in the other development stations. If similarly charged, the airborne toner from one development station may adhere to the photoconductor in place of the toner from another development station. The blending of toner from different development stations also adversely affects the toner properties and subsequently the image quality. If oppositely charged, the airborne toner may blend with the toner from the other development station and may then be attracted to the non-image areas producing a background or fog in the image.
Some image-forming machines implement one or more approaches to remove or otherwise control the airborne toner and carrier. A vacuum pump, fan, or other air movement device may be used to remove and filter the airborne toner from the air within the image-forming machine. Smaller vacuum pumps may be used to remove toner stacks or other build-up of toner in the image-forming machine. Some image-forming machines have a vacuum or electrostatic tube with several openings for applying a vacuum or an electrostatic charge along the trailing edge of the development station. These trailing edge openings collect airborne toner and carrier exiting along the trailing edge. In other approaches, the development region may be physically enclosed. The image-forming machine may have a membrane between the development station and photoconductor at the lead edge of the development station. This lead edge membrane may interfere with the surface of the photoconductor and the electrostatic latent image. The lead edge membrane may need to be removed when the image-forming machine has multiple development stations because the lead edge membrane in a subsequent development station interfere with the toner deposited by a previous development station.
SUMMARY
This invention provides a dusting control system for a development station in an image-forming machine. The dusting control system generates a flow barrier adjacent to a development region for the development station.
In one aspect, an image-forming machine has a photoconductor operatively connected to one or more chargers, an exposure machine, and a development station. The chargers electrostatically charge the photoconductor. The exposure machine forms an electrostatic image on the photoconductor. The development station applies toner on the photoconductor within a development region. The development station has a dusting control system that generates a flow barrier adjacent to the development region.
In another aspect, an image-forming machine has a photoconductor operatively connected to a development station. The development station has a dusting control system and a leading edge. The development station applies toner on the photoconductor. The dusting control system generates a flow barrier adjacent to rig at least a portion of the leading edge.
In a further aspect, a development station for an image-forming machine has a dusting control system that spans at least a portion of a leading edge. The dusting control system generates a flow barrier adjacent to a development region.
REFERENCES:
patent: 3685485 (1972-08-01), Kutsuwada et al.
patent: 3-127087 (1991-05-01), None
patent: 11-327295 (1999-11-01), None
JP11327295A—Machine translation from Japanese Patent Office website, Nov. 1999.
Allen Richard G.
Rejewski Robert S.
Heidelberger Druckmaschinen AG
Pendegrass Joan
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