Developer roll having magnetic zones of varying axial length for a dual component development electrophotographic image forming device

A developer unit for a dual component development electrophotographic image forming device, comprising:

• a housing having a reservoir for storing a developer mix that includes toner and magnetic carrier beads;
• and
• a developer roll mounted on the housing, the developer roll includes a stationary core and a cylindrical sleeve positioned around the core, the core includes at least one permanent magnet forming a magnetized portion of the core that includes a plurality of circumferentially spaced magnetic poles, the plurality of magnetic poles includes a release pole, the sleeve is rotatable relative to the core about an axis of rotation in an operative rotational direction, the core includes a pair of axial ends relative to the axis of rotation, an outer circumferential surface of the sleeve is positioned to transport developer mix magnetically attracted from the reservoir to the outer surface of the sleeve by the magnetized portion of the core in the operative rotational direction, the release pole is positioned to magnetically attract developer mix to the outer circumferential surface of the sleeve to transport developer mix on the outer circumferential surface of the sleeve in the operative rotational direction to a release point where the developer mix releases from the outer circumferential surface of the sleeve back into the reservoir,
• wherein an axial length of the magnetized portion of the core decreases at both axial ends of the core as the magnetized portion of the core approaches the release point in the operative rotational direction,
• further comprising a shunt positioned at each axial end of the core, each shunt is composed of a magnetically permeable metal that redirects a magnetic field of the at least one permanent magnet at a respective axial end of the core, each shunt is positioned outside of a circumference of the sleeve and in close proximity to the outer circumferential surface of the sleeve from the release pole to the release point, an inner axial end of each shunt is positioned axially in line with a respective outermost axial end of the magnetized portion of the core or axially between the respective outermost axial end of the magnetized portion of the core and a respective axial end of the magnetized portion of the core immediately prior to the release point.

A developer roll for transporting a developer mix that includes magnetic carrier beads and toner in a dual component development electrophotographic image forming device, comprising:

• a core including at least one permanent magnet forming a magnetized portion of the core that includes a plurality of circumferentially spaced magnetic poles generating a magnetic field, the plurality of magnetic poles includes a release pole;
• and
• a cylindrical sleeve positioned around the core, the sleeve is rotatable relative to the core about an axis of rotation in an operative rotational direction, the core includes a pair of axial ends relative to the axis of rotation,
• wherein the release pole is positioned to magnetically attract developer mix to an outer circumferential surface of the sleeve to transport the developer mix on the outer circumferential surface of the sleeve in the operative rotational direction when the sleeve rotates relative to the core to a release point where a magnitude of a total magnetic field strength of the magnetic field falls below 15 mT at the outer circumferential surface of the sleeve,
• wherein an axial length of the magnetized portion of the core decreases at both axial ends of the core as the magnetized portion of the core approaches the release point in the operative rotational direction,
• wherein the axial length of the magnetized portion of the core decreases at both axial ends of the core beginning downstream from a transport pole of the plurality of magnetic poles that immediately precedes the release pole in the operative rotational direction.

A developer roll for transporting a developer mix that includes magnetic carrier beads and toner in a dual component development electrophotographic image forming device, comprising:

• a core including at least one permanent magnet forming a magnetized portion of the core that includes a plurality of circumferentially spaced magnetic poles generating a magnetic field, the plurality of magnetic poles includes a release pole;
• and
• a cylindrical sleeve positioned around the core, the sleeve is rotatable relative to the core about an axis of rotation in an operative rotational direction, the core includes a pair of axial ends relative to the axis of rotation,
• wherein the release pole is positioned to magnetically attract developer mix to an outer circumferential surface of the sleeve to transport the developer mix on the outer circumferential surface of the sleeve in the operative rotational direction when the sleeve rotates relative to the core to a release point where the magnetic field is insufficient to retain developer mix against the outer circumferential surface of the sleeve,
• wherein an axial length of the magnetized portion of the core decreases at both axial ends of the core as the magnetized portion of the core approaches the release point in the operative rotational direction,
• wherein the axial length of the magnetized portion of the core decreases at both axial ends of the core beginning downstream from a transport pole of the plurality of magnetic poles that immediately precedes the release pole in the operative rotational direction.

A developer unit for a dual component development electrophotographic image forming device, comprising:

• a housing having a reservoir for storing a developer mix that includes toner and magnetic carrier beads;
• and
• a developer roll mounted on the housing, the developer roll includes a stationary core and a cylindrical sleeve positioned around the core, the core includes at least one permanent magnet forming a magnetized portion of the core that includes a plurality of circumferentially spaced magnetic poles, the plurality of magnetic poles includes a release pole, the sleeve is rotatable relative to the core about an axis of rotation in an operative rotational direction, the core includes a pair of axial ends relative to the axis of rotation, an outer circumferential surface of the sleeve is positioned to transport developer mix magnetically attracted from the reservoir to the outer surface of the sleeve by the magnetized portion of the core in the operative rotational direction, the release pole is positioned to magnetically attract developer mix to the outer circumferential surface of the sleeve to transport developer mix on the outer circumferential surface of the sleeve in the operative rotational direction to a release point where the developer mix releases from the outer circumferential surface of the sleeve back into the reservoir,
• wherein an axial length of the magnetized portion of the core decreases at both axial ends of the core as the magnetized portion of the core approaches the release point in the operative rotational direction,
• wherein the axial length of the magnetized portion of the core decreases at both axial ends of the core beginning downstream from a transport pole of the plurality of magnetic poles that immediately precedes the release pole in the operative rotational direction.

A developer unit for a dual component development electrophotographic image forming device, comprising:

• a housing having a reservoir for storing a developer mix that includes toner and magnetic carrier beads;
• and
• a developer roll mounted on the housing, the developer roll includes a stationary core and a cylindrical sleeve positioned around the core, the core includes at least one permanent magnet forming a magnetized portion of the core that includes a plurality of circumferentially spaced magnetic poles, the plurality of magnetic poles includes a release pole, the sleeve is rotatable relative to the core about an axis of rotation in an operative rotational direction, the core includes a pair of axial ends relative to the axis of rotation, an outer circumferential surface of the sleeve is positioned to transport developer mix magnetically attracted from the reservoir to the outer surface of the sleeve by the magnetized portion of the core in the operative rotational direction, the release pole is positioned to magnetically attract developer mix to the outer circumferential surface of the sleeve to transport developer mix on the outer circumferential surface of the sleeve in the operative rotational direction to a release point where the developer mix releases from the outer circumferential surface of the sleeve back into the reservoir,
• wherein an axial length of the magnetized portion of the core decreases at both axial ends of the core as the magnetized portion of the core approaches the release point in the operative rotational direction,
• wherein axial ends of the magnetized portion of the core immediately prior to the release point are axially inset from axial ends of the magnetized portion of the core at the release pole.

A developer unit for a dual component development electrophotographic image forming device, comprising:

• a housing having a reservoir for storing a developer mix that includes toner and magnetic carrier beads;
• and
• a developer roll mounted on the housing, the developer roll includes a stationary core and a cylindrical sleeve positioned around the core, the core includes at least one permanent magnet forming a magnetized portion of the core that includes a plurality of circumferentially spaced magnetic poles, the plurality of magnetic poles includes a release pole, the sleeve is rotatable relative to the core about an axis of rotation in an operative rotational direction, the core includes a pair of axial ends relative to the axis of rotation, an outer circumferential surface of the sleeve is positioned to transport developer mix magnetically attracted from the reservoir to the outer surface of the sleeve by the magnetized portion of the core in the operative rotational direction, the release pole is positioned to magnetically attract developer mix to the outer circumferential surface of the sleeve to transport developer mix on the outer circumferential surface of the sleeve in the operative rotational direction to a release point where the developer mix releases from the outer circumferential surface of the sleeve back into the reservoir,
• wherein an axial length of the magnetized portion of the core decreases at both axial ends of the core as the magnetized portion of the core approaches the release point in the operative rotational direction,
• wherein the axial length of the magnetized portion of the core decreases at both axial ends of the core by a constant axial distance per degree as the magnetized portion of the core approaches the release point in the operative rotational direction.

A developer roll for transporting a developer mix that includes magnetic carrier beads and toner in a dual component development electrophotographic image forming device, comprising:

• a core including at least one permanent magnet forming a magnetized portion of the core that includes a plurality of circumferentially spaced magnetic poles generating a magnetic field, the plurality of magnetic poles includes a release pole;
• and
• a cylindrical sleeve positioned around the core, the sleeve is rotatable relative to the core about an axis of rotation in an operative rotational direction, the core includes a pair of axial ends relative to the axis of rotation,
• wherein the release pole is positioned to magnetically attract developer mix to an outer circumferential surface of the sleeve to transport the developer mix on the outer circumferential surface of the sleeve in the operative rotational direction when the sleeve rotates relative to the core to a release point where a magnitude of a total magnetic field strength of the magnetic field falls below 15 mT at the outer circumferential surface of the sleeve,
• wherein an axial length of the magnetized portion of the core decreases at both axial ends of the core as the magnetized portion of the core approaches the release point in the operative rotational direction,
• wherein the axial length of the magnetized portion of the core decreases at both axial ends of the core by a constant axial distance per degree as the magnetized portion of the core approaches the release point in the operative rotational direction.

A developer roll for transporting a developer mix that includes magnetic carrier beads and toner in a dual component development electrophotographic image forming device, comprising:

• a core including at least one permanent magnet forming a magnetized portion of the core that includes a plurality of circumferentially spaced magnetic poles generating a magnetic field, the plurality of magnetic poles includes a release pole;
• and
• a cylindrical sleeve positioned around the core, the sleeve is rotatable relative to the core about an axis of rotation in an operative rotational direction, the core includes a pair of axial ends relative to the axis of rotation,
• wherein the release pole is positioned to magnetically attract developer mix to an outer circumferential surface of the sleeve to transport the developer mix on the outer circumferential surface of the sleeve in the operative rotational direction when the sleeve rotates relative to the core to a release point where the magnetic field is insufficient to retain developer mix against the outer circumferential surface of the sleeve,
• wherein an axial length of the magnetized portion of the core decreases at both axial ends of the core as the magnetized portion of the core approaches the release point in the operative rotational direction,
• wherein the axial length of the magnetized portion of the core decreases at both axial ends of the core by a constant axial distance per degree as the magnetized portion of the core approaches the release point in the operative rotational direction.