End sealing and magnetic field truncation of a magnetic roll of a dual electrophotographic image forming device

摘要

A developer unit according to one example embodiment includes a housing having a reservoir for storing a developer mix that includes toner and magnetic carrier beads. A magnetic roll includes a stationary core and a sleeve positioned around the core that is rotatable relative to the core. The stationary core includes at least one permanent magnet having circumferentially spaced magnetic poles. An upper and a lower magnetically permeable metal shunt are positioned at each axial end of the magnetic roll. Each upper shunt and each lower shunt is positioned axially outboard of the core and in close proximity to the outer surface of the sleeve. A combination of the upper shunt and the lower shunt at each axial end of the magnetic roll surrounds greater than 180 degrees of the outer surface of the sleeve.

主权项

1. 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; a magnetic roll including a stationary core and a sleeve positioned around the core that is rotatable relative to the core about an axis of rotation, the stationary core includes at least one permanent magnet having a plurality of circumferentially spaced magnetic poles, an outer surface of the sleeve is positioned to carry developer mix attracted to the outer surface of the sleeve by the at least one permanent magnet from the reservoir through an exposed portion of the magnetic roll and back to the reservoir, in the exposed portion of the magnetic roll the magnetic roll is exposed from the reservoir to permit transfer of toner from the outer surface of the sleeve to a photoconductive drum; and an upper shunt and a lower shunt positioned at each axial end of the magnetic roll, each upper and lower 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 magnetic roll, each upper shunt and each lower shunt is positioned axially outboard of the core and in close proximity to the outer surface of the sleeve, each upper shunt is positioned along an upper circumferential portion of the outer surface of the sleeve and each lower shunt is positioned along a lower circumferential portion of the outer surface of the sleeve, wherein a combination of the upper shunt and the lower shunt at each axial end of the magnetic roll surrounds greater than 180 degrees of the outer surface of the sleeve.