Scavengeless development apparatus including an electroded donor roll

Abstract

An electroded donor roll development unit including an electroded donor roll assembly for mounting partially within a mixing chamber of a housing of the development unit for forming a development nip with an image bearing member, and for moving charged toner particles from the mixing chamber to the development nip. The electroded donor roll assembly includes a donor roll having a dielectric layer, and axially extending electrodes formed in the surface of the dielectric layer. The donor roll assembly also includes a bias voltage source for biasing the electrodes and a tri-contact commutator or assembly mounted on the donor roll and connected to the bias voltage source for commutating a bias voltage to the electrodes while significantly reducing and eliminating risk of sporadic electrical arcing during bias commutation. The tri-contact commutator assembly includes a disc forming a circular flange at one end of the donor roll, a series of commutator contact pads connected to the electrodes on the donor roll and having relatively large fanned out spacings between adjacent contact pads. Importantly, the tri-contact commutator assembly includes a plurality of commutating members, connected to the bias voltage source for commutating a bias voltage to the commutator contact pads. The plurality of commutating members include first and second high resistivity members that are spaced from each other circumferentially relative to the circular flange, and a low resistivity, third member spaced from the high resistivity first and second members in a radial direction relative to the circular flange, so as to enable effective commutation of the bias voltage without significant risk of sporadic electrical arcing.