Device for controlling potential of latent image for use in electrophotographic apparatus

In an apparatus for electophotography of the kind comprising:

• a photosensitive element on a movable drum and including an electrode layer, a photoconductive layer and a transparent insulating layer, these layers being integrally provided in the order described;
• a first corona discharging means for applying first charges of one polarity to said insulating layer of said photosensitive element under the condition that an interface between said photoconductive and insulating layers is substantially filled with trapped charge carriers which have flowed through said photoconductive layer;
• a second corona discharging means for applying second charges of a polarity opposite to said one polarity and simultaneously projecting a light image to said element;
• and means for projecting a substantially uniform light to said element;
• the recited means thereby completing formation of an electrostatic latent image on said insulating layer;
• and means for developing said latent image by use of a developing agent;
• the improvement comprising:
• further uniform light projecting means operative just before said second corona discharging means to release some of said charge carriers from the trapped condition, such that the released charge carriers can flow to said electrode layer during the application of said second charge to said insulating layer to control the potential of said latent image, said further uniform light projecting means including a lamp for emitting light to said photoconductive layer of said element and control means for controlling the quantity of the light reaching said photoconductive layer, thereby causing the flow of an appropriate amount of said released charge carriers to said electrode layer of said element to control the surface potential of said insulating layer of said element to a desired value.

In an apparatus for electrophotography of the kind comprising:

• a photosensitive element on a movable drum and including an electrode layer, a photoconductive layer and a transparent insulating layer, these layers being integrally provided in the order described;
• a first corona discharging means for applying first charges of one polarity to said insulating layer of said photosensitive element under the condition that an interface between said photoconductive and insulating layers is substantially filled with trapped charge carriers which have flowed through said photoconductive layer;
• a second corona discharging means for applying second charges of a polarity opposite to said one polarity and simultaneously projecting a light image to said element;
• and means for projecting a substantially uniform light to said element;
• the recited means thereby completing formation of an electrostatic latent image on said insulating layer;
• and means for developing said latent image by use of a developing agent;
• the improvement comprising:
• further uniform light projecting means operative from the insulating layer side of said photosensitive element and just before said second corona discharging means to release some of said charge carriers from the trapped condition, such that the released charge carriers can flow to said electrode layer during the application of said second charge to said insulating layer to control the potential of said latent image.