System for reducing background developer deposition in an electrostatic copier

Claim 2

Apparatus for inhibiting the development of background areas of residual electrical potential in a latent electrostatic image including in combination, a member having a photoconductive first surface portion adapted to receive said latent electrostatic image and a conductive second surface portion, a developer unit adapted to apply developer to a surface, means for moving said surface portions relative to and adjacently past said developer unit, a biasing electrode associated with said developer unit, means for applying a potential to said biasing electrode and means for applying said potential to said second surface portion in the course of its movement adjacent to said developer unit.

Claim 3

An apparatus as in claim 1 in which said member is a rotating drum the surface of which is formed with said photoconductive first surface portion and said conductive second surface portion, and insulating means for insulating said photoconductive first surface portion from said conductive second surface portion.

Claim 4

Apparatus as in claim 1 in which said developer unit comprises means for holding a supply of developer, means for applying said developer from said supply to said latent image and means mounting said biasing electrode in said unit.

Claim 5

Apparatus as in claim 2 including a pair of electrical contacts connected in parallel with said biasing electrode and disposed adjacent the leadiNg and trailing edges of said developer unit to contact said conductive second surface portion of said drum.

Claim 6

Apparatus as in claim 4 including a surface-charge-sensing detector disposed adjacent said rotating drum to measure the residual background potential of a charged and exposed area of said photoconductive surface portion and voltage control means responsive to output of said detector for controlling the voltage applied by said voltage source to said biasing electrode and said conductive surface portion as its periphery engages one of said electrical contacts during its transit through the developing unit.

Claim 7

Apparatus as in claim 5 in which said surface-charge-detector measures the absolute value of said background potential and in which said voltage control means adjusts the voltage applied to said electrode and to said conductive second surface portion to the value of said measured potential.

Claim 8

Apparatus as in claim 1 including a corona charging unit positioned adjacent to said member, and a first electrical contact connected in parallel with said biasing electrode and positioned adjacent to the leading edge of said charging unit to contact said second surface portion as it moves thereby.

Claim 9

Apparatus as in claim 7 including second and third electrical contacts connected in parallel with said biasing electrode and positioned respectively adjacent to the leading and trailing edges of said developer unit to contact said second surface portion as it moves thereby.

Claim 10

Electrostatic copying apparatus including in combination, a member having a photoconductive surface portion and a conductive surface portion, a charger adapted to apply a charge to a surface moving adjacent thereby, an optical exposure unit adapted to project an image onto said charged surface to produce a latent electrostatic image thereon, a developer unit adapted to apply developer to said surface to develop the latent electrostatic image, an electrode associated with said developer unit, means for applying a potential to said electrode, means for driving said member successively to move said surface portions past said charger and said exposure unit and said developer unit, and means for applying said potential to said conductive surface portion in the course of its movement past said developer unit.

Claim 11

Electrostatic copying apparatus including in combination, a member having a photoconductive surface portion and a conductive surface portion, a charger adapted to apply a charge to a surface moving adjacent thereby, an optical exposure unit adapted to project an image onto said charged surface to produce a latent electrostatic image thereon, a developer unit adapted to apply developer to said surface to develop the latent electrostatic image, an electrode associated with said developer unit, means for applying a potential to said electrode, means for driving said member successively to move said surface portions past said charger and said exposure unit and said developer unit, and means for applying said potential to said conductive surface portion in the course of its movement past said developer unit.

Claim 12

Apparatus as in claim 9 in which an organic photoconductor provides said photoconductive surface portion, said organic photoconductor retaining a residual background potential after exposure, and in which said potential applied to said electrode substantially equals said background potential.